The Art of Refractive Surgery 9388257871, 9789388257879

Table of contents :
Contents
1. Evolution of Corneal Refractive Surgery
2. Classification of Refractive Surgeries
3. Preoperative Evaluation and 3. Investigations for Refractive Surgery
4. Decision-making in Refractive Surgery
5. Surface Ablation Procedures
6. Laser in Situ Keratomileusis Surgery
7. Small Incision Lenticular Extraction
8. Comparison amongst Corneal 8. Refractive Surgery
9. Enhancements after Refractive Surgery
10. Phakic Intraocular Lens
11. Refractive Lens Exchange
12. Hyperopic Refractive Surgery
13. Corneal Incision Surgery
14. Presbyopia Correction
15. Bioptics
Appendix: Patient Information and Consent
Index

Citation preview

The Art of Refractive Surgery Sudarshan Khokhar, MD(AIIMS), FRCS(Ed) Professor and Head of Unit Cataract and Refractive Services Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Chirakshi Dhull MD(AIIMS), DNB, FICO Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Yogita Gupta MD(AIIMS), DNB, FICO Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India

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Contents Videos........................................................................................................................................................................................................ vii Preface ....................................................................................................................................................................................................... ix Acknowledgment ................................................................................................................................................................................... xi Contributors............................................................................................................................................................................................xiii 1.

Evolution of Refractive Surgery...............................................................................................................................................1 Yogita Gupta, Chirakshi Dhull, and Sudarshan Khokhar

2.

Classification of Refractive Surgeries.....................................................................................................................................9 Yogita Gupta, Chirakshi Dhull, and Sudarshan Khokhar

3.

Preoperative Evaluation and Investigations for Refractive Surgery......................................................................... 13 Yogita Gupta, Deeksha Rani, Chirakshi Dhull, and Sudarshan Khokhar

4.

Decision-making in Refractive Surgery..............................................................................................................................35 Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

5.

Surface Ablation Procedures..................................................................................................................................................55 Yogita Gupta, Karthikeyan Mahalingam, Chirakshi Dhull, and Sudarshan Khokhar

6.

Laser in Situ Keratomileusis Surgery..................................................................................................................................73 Yogita Gupta, Chirakshi Dhull, Bhavika Bansal, and Sudarshan Khokhar

7.

Small Incision Lenticular Extraction...................................................................................................................................95 Chirakshi Dhull, Deeksha Rani, Yogita Gupta, and Sudarshan Khokhar

8.

Comparison amongst Corneal Refractive Surgery........................................................................................................127 Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

9.

Enhancements after Refractive Surgery...........................................................................................................................135 Yogita Gupta, Monikha T., Chirakshi Dhull, and Sudarshan Khokhar

10.

Phakic Intraocular Lens.........................................................................................................................................................157 Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

11.

Refractive Lens Exchange.....................................................................................................................................................171 Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

12.

Hyperopic Refractive Surgery.............................................................................................................................................185 Yogita Gupta, Chirakshi Dhull and Sudarshan Khokhar

13.

Corneal Incision Surgery.......................................................................................................................................................195 Abhidnya Surve, Chirakshi Dhull, Yogita Gupta and Sudarshan Khokhar

v

14.

Presbyopia Correction............................................................................................................................................................207 Pulak Agarwal, Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

15. Bioptics.......................................................................................................................................................................................219 Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar



Appendix: Patient Information and Consent..................................................................................................................225

Index............................................................................................................................................................................................235

vi

Videos Video 1: Surface ablation The surgical technique of surface ablation is shown in video 1. An excimer laser is used for epithelial debridement followed by ablation of tissue for refractive correction using excimer laser. A bandage contact lens is placed at the end. https://www.thieme.de/de/q.htm?p=opn/cs/20/2/11181877-81af8706 Video 2: LASIK Surgical technique of femtosecond laser in situ keratomileusis (LASIK) is shown in video 2. In the video, the flap is created using a femtosecond laser. The flap is lifted carefully, followed by stromal ablation for refractive correction using an excimer laser. The flap is replaced at its original position. https://www.thieme.de/de/q.htm?p=opn/cs/20/2/11181878-4ec126b2 Video 3: SMILE In small incision lenticule extraction (SMILE), a femtosecond laser is used for the creation of a lenticule for refraction correction. After the application of a suction cone, the femtosecond laser is fired. The first pass is the posterior cut or lenticule cut followed by the side cut, cap cut, and side incision cut. The lenticule is dissected and removed manually. https://www.thieme.de/de/q.htm?p=opn/cs/20/2/11181879-0f9a1f67 Video 4: Toric–ICL In implantable contact lens (ICL) implantation, the loading of the lens is just as important as the surgery. The video shows the stepwise loading of ICL. This is followed by marking the cornea, creation of corneal wound, implantation of ICL, and viscoaspiration. At the end of the surgery, intraoperative anterior segment optical coherence tomography (ASOCT) can be used to check the lens vault. https://www.thieme.de/de/q.htm?p=opn/cs/20/2/11181880-651e589e Video 5: Refractive lens exchange (RLE) It involves the usual steps of cataract surgery. An adequate-sized capsulorhexis is required. Since the lens is clear with minimal nuclear sclerosis, the video shows the use of irrigation, aspiration of nucleus, and cortex removal. Good cortical cleanup and polish is recommended followed by implantation of intraocular lens (IOL) in a bag as shown in the video. https://www.thieme.de/de/q.htm?p=opn/cs/20/2/11181881-6b6ff895

vii

Preface Refractive surgery is a continuously evolving field of science. With an increasing incidence of refractive errors, especially in the southeast Asian subcontinent, the demand for refractive surgery is on the rise. The indications for surgery may vary from cosmetic and professional to rehabilitative. Patients having very high refractive errors are virtually blind without their glasses and also, the vision is not very clear due to aberrations. This book Art of Refractive Surgery is written with the intent to simplify the planning and surgical aspect of refractive surgery. It is directed at residents or fellows in training as well as specialists in the field. Our book meticulously explains the preoperative investigations and planning required for decision-making in refractive surgery. It includes the recent advances in the field of refractive surgery, including SMILE surgery, topography-guided LASIK, Presbyond, etc. It guides the readers about using these procedures as well as combining various refractive procedures (Bioptics). Management of difficult situations is dealt in separate chapters, such as hyperopia and presbyopia. The book provides comprehensive information regarding management of refractive surgery by including various case scenarios with their preoperative parameters and investigation employed in planning the surgery. Most refractive books include either corneal refractive surgery or lens-based surgery. This is a comprehensive textbook that includes the various practical aspects of refractive surgery. It includes in-depth discussion of—surface ablation, LASIK, and SMILE surgery. In addition, we have compared corneal surgery and retreatment in a separate chapter. The book also contains videos with voice over, showing standard surgical techniques for surface ablation, LASIK, SMILE, phakic IOL, and RLE. These videos will help readers in learning the surgical steps with ease. This book is a result of years of experience in refractive surgery while keeping a watch at the internationally accepted norms pertaining to it. This field is especially challenging as suboptimal outcomes are unacceptable to the young, healthy adults undergoing surgery for cosmesis and/or quality of life. Good outcomes emerge from meticulous preoperative workup, smart decision-making, and skillful surgical management. We hope that this textbook educates ophthalmologists in the successful management of refractive errors.

“Only the educated are free”—Epictetus Sudarshan Khokhar, MD(AIIMS), FRCS(Ed) Chirakshi Dhull, MD(AIIMS), DNB, FICO Yogita Gupta, MD(AIIMS), DNB, FICO

ix

Acknowledgment A book of this scope is a product of efforts well beyond the editors and authors, and our’s is no exception. First and foremost, we would like to thank the Almighty for providing us with the strength and perseverance to compile this work and also an opportunity to learn, work and treat in the “Mecca” of ophthalmology in India. We are extremely thankful to our institution for providing an environment amenable to academics and research. We are also grateful to our families for their endless patience, love, and support through the course of this challenging task. We are thankful to the residents, optometrists and staff involved in the day-to-day functioning of the refractive clinic and refractive OT services. We would like to especially thank Mrs Anita Sharma for her assistance in providing corneal imaging and maintaining patient records in the refractive clinic. We also sincerely acknowledge the contribution of the entire publication team at Thieme publications. Finally, we must remember and thank all our patients who placed their faith in us, made it to all the scheduled visits despite the odds, and smiled at the end of each visit.

Sudarshan Khokhar, MD(AIIMS), FRCS(Ed) Chirakshi Dhull, MD(AIIMS), DNB, FICO Yogita Gupta, MD(AIIMS), DNB, FICO

xi

Contributors Editors Sudarshan Khokhar, MD(AIIMS), FRCS(Ed) Professor and Head of Unit Cataract and Refractive Services Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Chirakshi Dhull MD(AIIMS), DNB, FICO Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Yogita Gupta MD(AIIMS), DNB, FICO Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India

Contributors Abhidnya Surve, MD Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Bhavika Bansal, MBBS Postgraduate Student Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India

Karthikeyan Mahalingam, MD Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Monikha T., MBBS Postgraduate Student Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Parmanand Kumar, MD Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Prabhav Puri, MBBS Postgraduate Student Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Priyanka Prasad, MBBS Postgraduate Student Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India Pulak Agarwal, MD Senior Resident Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India

Deeksha Rani, MBBS Postgraduate Student Dr. Rajendra Prasad (RP) Centre for Ophthalmic Sciences All India Institute of Medical Sciences (AIIMS) New Delhi, India

xiii

Chapter 1 Evolution of Refractive Surgery

Early Work in Refractive Surgery...................................................2 History of Radial Keratotomy and Keratomileusis....................2 Evolution of Lasers and Development of Modern Laser-Assisted In Situ Keratomileusis ..........................................3 Classification of Mechanical Microkeratomes............................3 Evolution of Femtosecond Lasers: Laser Microkeratomes.......................................................................4 Laser Physics.........................................................................................5 Timeline: Refractive Surgery Through the Years.......................7

1. Evolution of Corneal Refractive Surgery Yogita Gupta, Chirakshi Dhull, and Sudarshan Khokhar

Early Work in Refractive Surgery Refractive surgery refers to surgical alteration of the eye to correct refractive errors. The earliest treatise on refractive

History of Radial Keratotomy and Keratomileusis Furthering Sato’s work, S.N. Fyodorov from Russia, along

errors was written in 1864 by Frans Donders, who discour-

with F.S. Yenaleyev, described the technique of radial

aged refractive surgery in his textbook On the Anomalies of

keratotomy (RK)3 (Fig. 1.1a) in 1960 (anterior corneal

Accommodation and Refraction of the Eye. Among the works

incisions) and described a nomogram after careful analysis

on refractive surgery, Hermann Boerhaave2 was the first

of the effect of variation in the size of the optical zone on

to describe clear lensectomy for treating myopia in 1764.

myopic correction. Their work quickly spread in the former

The astigmatic keratotomy was first described by Dutch

Soviet Union. He introduced his technique in the United

ophthalmologist Herman Snellen, who illustrated curved

States by first performing it at the Kresge Eye Institute,

corneal incisions along the steepest corneal meridian to

Detroit. Bores, Myers, and Cowden performed the first RKs

treat astigmatism. Hjalmar Schiötz, a Norwegian physician,

in the US. The three-year results of RK were published as

performed limbal relaxing incision to partially correct a

‘Prospective Evaluation of Radial Keratotomy (PERK) Study’4

post cataract surgery astigmatism of ~20 diopters in 1885.

in 1987, which found that 65% of patients achieved spectacle

In 1896, a Dutch ophthalmologist, Lendert Jan Lans, stud-

independence. However, RK faced criticism from practi-

ied the effect of corneal incisions in a case series to treat

tioners worldwide due to resulting glare, halos, fluctuating

Later, in 1930, Japanese ophthalmologist

vision, irregular astigmatism, hyperopic drift, and corneal

Tsutomu Sato attempted corneal incisions (on anterior

weakening. Visual outcomes were largely unpredictable

and posterior corneal surface) to correct myopia in mili-

with RK. Also, the large epithelial plugs caused scattering

tary pilots having irregular astigmatism. However, corneal

of light postoperatively, causing starbursts-like visual phe-

decompensation and endothelium damage was noted.

nomenon (Fig. 1.1b).

1

3

astigmatism.

4

a

b

Fig. 1.1  (a) It involves making incisions radially on the anterior surface of cornea; (b) Artist image of starbursts that are optical phenomena commonly seen by patients post RK.

Evolution of Corneal Refractive Surgery

3

The first well-developed refractive surgery, called

physicist performed this treatment on blind human eyes in

Keratomileusis, was developed by José Ignacio Barraquer

1985 and developed the technique of photorefractive kera-

in the Barraquer ophthalmologic clinic (Bogota, Colombia)

tectomy (PRK). Trokel’s colleague, Marguerite McDonald

in 1949. He is revered as the ‘Father of Modern Refractive

performed the same on live human eyes in 1988. Following

Surgery’ and developed the first true lamellar surgery. His

that, in 1989, Dr Lucio Buratto performed this ablation using

technique led to the development of the modern laser-

laser on the stromal surface after using microkeratome to

assisted in-situ keratomileusis (LASIK) as we understand

create a corneal flap. The first patent for the technique of

it today.

cutting and raising a corneal flap, excimer laser ablation, fol-

Keratomileusis (Greek: keratos = cornea, mileusi = carving) was first used by Barraquer for spherical ametropia and involved manual dissection of almost half of the corneal thickness. He later developed his first manual microkeratome to obtain a precise cut of cornea. Due to problems

lowed by replacing the flap (LASIK surgery) was granted to an Iranian ophthalmologist Dr Gholam Ali Peyman, who is also known as “Inventor of LASIK” in 1989. The term LASIK was coined by University of Crete and Vardinoyannion Eye in 1991.

with handling a thin corneal lamella, he invented a tech-

Summit, Schwind, and VISX technologies developed the

nique to freeze the corneal lamella with cryolathe to fixate

first excimer laser systems for medical use. The advent of

and manage it. Later, Krumeich and Swinger, while working

excimer lasers increased the predictability of in-situ ker-

with Barraquer, developed a no-freeze technique to cut the

atomileusis surgery. Dr Ioannis G Pallikaris, a Greek ophthal-

cornea that caused less damage to the keratocytes. The three

mologist popularized the creation of nasal corneal hinge,

developed the BKS 1000 (Barraquer-Krumeivh-Swinger)

that is, leaving a small amount of cornea while performing

microkeratome non-freeze technique in the early 1980s.

lamellar cut to create a hinge nasally. In 1991, Brint and Slade

In the late 1980s, Ruiz published an ‘in situ’ keratomileusis

performed the first excimer laser keratomileusis, that is,

technique involving two, consecutive in situ corneal cuts,

the first modern LASIK surgery. In 1996, Buratto described

varying in depth and size, using various microkeratomes,

the Down-Up technique of in-situ keratomileusis, which

applanation lenses, and applanation plates.

involved a superior hinge creation that was more physiological than other hinge positions in terms of blinking.

Evolution of Lasers and Development of Modern Laser-Assisted In Situ Keratomileusis

Classification of Mechanical Microkeratomes

Refractive surgeons were unsatisfied with the unpredict-

Improvements in microkeratomes took place parallel to

ability of performing corneal surgery with diamond or steel

the development of keratomileusis. However, many factors

knives. Search was on worldwide for a precise technique of

were identified as influencing the flap thickness while creat-

corneal surgery. Taboada et al studied the effect of the kryp-

ing flaps with mechanical microkeratomes, such as suction

ton fluoride (KF) excimer laser pulses on cornea in 1981.

5

pressure, speed of cut, reuse of blades, and abnormal kerato-

Excimer (excited dimer) gases have unstable molecules that

metry (Table 1.1). The Hansatome microkeratome (Bausch

emit photons of ultraviolet light as they decay. Dr. Stephen

& Lomb) made the Down-Up technique easy to perform.

L. Trokel (associate professor of ophthalmology at Columbia University) and Rangaswamy Srinivasan (a scientist at IBM) first proposed the use of excimer laser [argon fluoride (ArF) laser of 193 nm] for ablating corneal tissue to flatten or steepen corneal curvature without damage to the

Table 1.1  Complications related to mircokeratomes due to abnormal keratometry K value

Possible complication in flap creation

Flap size recommendation

ArF for corneal reshaping after mechanical removal of cor-

> 47 D

Buttonhole

Smaller diameter and thicker

neal epithelium. Theo Seiler, a German ophthalmologist and

≤ 41 D

Free cap

Larger diameter and thicker

surrounding tissues. Dr Trokel and Dr John Marshall used 6

4

Chapter 1

It minimized the chances of buttonholing, free cut, and incomplete cuts. Mechanical microkeratomes were first used by Barraquer

Evolution of Femtosecond Lasers: Laser Microkeratomes

for creating corneal flaps. Corneal flaps have three basic parts

The femtosecond laser was subsequently introduced to

(Figs. 1.2 and 1.3): a peripheral part (the microkeratome,

create a more precise and smoother corneal cut. It enabled

suction ring with applanation plate, microkeratome cutting

the creation of even thinner flaps as compared to microker-

head working at various depths, and motorized drive unit),

atomes. Today, its use has been extended to arcuate kera-

central unit (the main power supply), and connections/

totomies to treat astigmatism, to create corneal incisions for

accessories. The cutting head has a block (with applanation

femto-assisted cataract surgery, and for lamellar keratoplas-

plate) and an oscillating blade.

ties as well.

Advancements have continued in the development of mechanical keratomes of different types (Table 1.2).

The femtosecond laser was first introduced by Kurtz et al in 1998. United States Food and Drug Administration

Drive unit

Central unit

Connection to suction tube

Different microkeratome heads

Peripheral unit

Connecting suction tube

Microkeratome head Suction ring

Fig. 1.2  A mechanical microkeratome (Zyoptix XP, Bausch & Lomb) includes central unit, peripheral unit, and connections/accessories. (Image courtesy: Sr Sudha & Sr Vibha, Dr R.P. Centre LASIK OT, AIIMS.)

Fig. 1.3  Parts of peripheral unit of a mechanical microkeratome.

Table 1.2  Classification of mechanical microkeratomes on the basis of head propulsion, head translation, and reusability Head propulsion

Head translation

Reusability

Automated, e.g., M2 (Moria), Hansatome Excellus (Bausch & Lomb), ZYOPTIX XP (Bausch & Lomb) (Fig. 1.2), MK-2000 (Nidek)

Linear, e.g., MK-2000 (Nidek), Amadeus II (AMO)

Single use, e.g., M2SU (M2 single use, Moria), CBSU (CB single use, Moria)

Manual, e.g., Carriazo–Barraquer (CB, Moria)

Arciform, e.g., M2 and CB (Moria), Hansatome (Bausch & Lomb)

Reusable, e.g., LSK-One (Moria)

Pendular, e.g., Carriazo-Pendular (Schwind)

Evolution of Corneal Refractive Surgery (US-FDA) approved its use for ophthalmology through the IntraLase system in 2000. With subsequent generations of

5

Laser Physics

the IntraLase system delivering higher energy pulses, flap

The femtosecond lasers deliver ultrashort energy pulses with

creation became faster (the fifth-generation system has

duration as short as 10–15 seconds, wavelengths in the infra-

a frequency of 150 kHz and creates a flap in 10 seconds).

red range (~1056 nm), and high powers (up to 1020 w/cm2),

In 2007, VisuMax was approved by US-FDA for LASIK (the

with low energy pulses. Femtosecond pulses are created

current model has 500 kHz frequency and delivers pulses

through Nd:glass (amplification glass matrix mixed with

of ~150 μJ).

neodymium), emitting pulses at 1056 nm. A pulse ampli-

Sekundo et al introduced the technique of femto­second refractive lenticule extraction (FLEx), that is, fashioning a

fication system placed distal to the pulse generator amplifies these emitted low-energy pulses. Three galvanometers

flap as well as lenticule using femtosecond laser, followed

perform three-dimensional scanning of the laser and an

by extraction of lenticule and reposition of flap, which was

aspheric converging lens focuses the laser beam on the

a major breakthrough in refractive surgery. Creation of full-

desired corneal depth at a frequency of ~15 kHz. Flap crea-

thickness flap was replaced by the creation of an incision

tion uses a pulse energy of 1.5–2 µJ.

to remove the fashioned lenticule. This led to the evolution of small incision lenticule extraction (SMILE) in 2011. The VisuMax system was approved by US-FDA for SMILE in September 2016, and for LASIK in 2007.

In the corneal stroma, femtosecond pulses cause disruption of molecules (photodisruption) by causing atomic ionization. Several photons are absorbed by single electrons of a given atom and leads to release of free electrons that

In 1991, J.T. Lin (a Chinese physicist) was granted patent

are highly energetic. Free electrons transfer their energy

for flying spot laser for customized LASIK. An eye-tracking

to the surrounding medium and cause vaporization of the

device during LASIK to ensure better centration was granted

target tissue, leading to the formation of small but precise

to Dr S. Lai (Chinese physicist) in 1993.

cavitation bubbles (Fig. 1.4). This juxtaposing of very small

Spot separation

Spot size

Pulse parameter: High energy (µJ), Low frequency (kHz)

Fig. 1.4  Creation of cavitation bubbles by firing of high-frequency ultrashort femtosecond pulses on the target tissue (photodisruption).

6

Chapter 1

impacts ~2–3 µm in diameter leads to a regular lamellar

would exceed that of chemical bonds of living tissue, caus-

dissection of the target tissue, with little or no collateral

ing the target tissue compounds to dissociate and vaporize

damage. The impacts are delivered in raster mode (con-

(Fig. 1.5), causing the cornea to achieve a specific profile

secutive lines of impact) after placement of an applanation

desired by the refractive surgeon.

glass lens on the cornea to ensure creation of a parallel cut.

Types of excimer laser beam delivery systems are:

The excimer lasers used in refractive surgery, however,

••Broad-beam emission.

utilize the photoablation principle. These are ultraviolet

••Scanning slit delivery.

radiations with very high photonic energies. Their energy

••Flying spot laser emission.

Photoablation Excimer beam

Photon energy (6.4 eV) 0.25 µm

Binding energy (3.5 eV) Photoablation

Fig. 1.5  Mechanism of excimer laser for ablation.

1949

1981

Russian ophthalmologist Svyatoslov N. Fyodorov, invented radial keratotomy (RK) procedure to treat myopia–manual corneal incisions

1974

Excimer laser technology introduced by Srinivasan (at IBM), who found argonfluo-rine (ArF) excimer laser could be used to precisely ablate fine layers of living tissue with little to no damage to the surrounding area

1988

In collaboration with Dr. Srinivasan, Stephen Trokel, performed the first excimer laser photorefractive keratectomy (PRK) on cornea of cadaveric eyes

1983

1989

1995

2002

Following its introduction with PRK in 1999, wavefront-guided analysis for LASIK was approved for wavefront - customized correction

2000

The FDA approved the first bladeless femtosecondassisted LASIK system, made by IntraLase

Dr. Fred Kremer received FDA approval for the first excimer laser system for LASIK.

1998

The US-FDA approved the first excimer laser system for PRK by Summit Technology

Greek ophthalmologist Ioannis Pallikaris, described the technique we now call LASIK using microkeratome. Around same time, in New Orleans, Gholam Peyman, got a patent for a similarly described procedure

Marguerite McDonald of Louisiana State University, performed the first PRK procedure on living human subject

Fig. 1.6  Timeline showing the evolution of refractive surgery.

Lendeer Jans Lans, an ophthalmology teacher in Holland, published theoretical work on the potential for cutting the cornea to correct astigmatism. Two years later, he described thermokeratoplasty (electrocauterization to corneal stroma to reshape cornea) in 19751,2

1896

The “father of refractive surgery” ophthalmologist Jose Ignacio Barraquer, introduced keratomileusis and keratophakia. He also developed his first microkeratome

Timeline: Refractive Surgery Through the Years (Fig. 1.6)

2016

US-FDA approves SMILE

2011

SMILE launched internationally

Evolution of Corneal Refractive Surgery 7

8

Chapter 1

References 1. Donders FC. On the Anomalies of Accommodation and Refraction of the Eye [translated by William D. Moore, M.D.]. London: New Sydenham Society; 1864 2. Boerhaave H. Praelectiones publicae de morbis oculorum. Gottingae: apud a. von den Hoeck; 1764 3. Thornton SP. Background of incisional refractive surgery. In: Wu HK, Thompson VM, et al, eds. Refractive Surgery. New York: Thieme Medical Publishers; 1999: 127–134

4. Waring GO III, Lynn MJ, Culbertson W, et al. Threeyear results of the Prospective Evaluation of Radial Keratotomy (PERK) Study. Ophthalmology 1987;94(10):1339–1354 5. Taboada J, Mikesell GW Jr, Reed RD. Response of the corneal epithelium to KrF excimer laser pulses. Health Phys 1981;40(5):677–683 6. Trokel SL, Srinivasan R, Braren B. Excimer laser surgery of the cornea. Am J Ophthalmol 1983;96(6):710–715

Chapter 2 Classification of Refractive Surgeries

The Goal of Refractive Surgery..................................................... 10 Classification of Refractive Surgeries......................................... 10 Terminology Commonly Used in Refractive Surgery............ 12

2. Classification of Refractive Surgeries Yogita Gupta, Chirakshi Dhull, and Sudarshan Khokhar

The Goal of Refractive Surgery

Classification of Refractive Surgeries

Surgeries that are aimed at reducing the dependency of an

Refractive surgeries can be broadly categorized as: (1)

individual on spectacles or contact lenses for their daily

corneal, (2) lens based, (3) combined (Table 2.1). Corneal

routine activities are called refractive surgeries. Refractive

procedures can be incisional techniques, excimer laser abla-

surgeries have tremendously evolved recently, with sev-

tion, non-laser lamellar, collagen shrinkage, and corneal col-

eral advancements taking place in the last few decades.

lagen crosslinking procedures. Intraocular surgeries can be

More often than not, a refractive surgeon deals with eyes

implantation of phakic intraocular lenses (pIOLs) or refrac-

of normal individuals and not diseased eyes of “patients”.

tive lens exchange (cataract surgery followed by implanta-

Majority of these individuals have 20/20 vision with glasses

tion of monofocal, multifocal, accommodative, or toric IOLs).

or contact lenses. A refractive surgeon has to choose the best

The corneal and intraocular procedures can be combined to

option from all available options of refractive techniques,

deal with high refractive errors. This is called bioptics if two

keeping in mind the risk–benefit ratio, patient suitability,

procedures are combined and trioptics if three procedures

affordability, and advantages and disadvantages of various

are combined.

procedures. The appropriate refractive procedure would be one that closely matches the individual’s needs.

Classification of Refractive Surgeries

11

Table 2.1  Classification of refractive surgeries Procedure type

Refractive conditions treated

Subtypes

Abbreviations

Photorefractive keratectomy

PRK

Laser subepithelial keratomileusis

LASEK

Epipolis laser in situ keratomileusis

Epi-LASIK

Laser assisted in situ keratomileusis

LASIK

Femtosecond laser in situ keratomileusis

Femto-LASIK

Small incision lenticule extraction

SMILE

Myopia

Femtosecond lenticule extraction

FLEx

Myopia

Radial keratotomy

RK

Astigmatism

Arcuate keratotomy

AK

Astigmatism

Limbal relaxing incisions

LRI

Astigmatism

Corneal-based surgeries Laser techniques (a) Surface treatment

(b) Lamellar treatment (c) Refractive lenticule extraction (ReLEx) Incisional

Nonlaser lamellar

Collagen shrinkage procedure

Myopia, hyperopia, astigmatism

Ruiz procedure

Astigmatism

Epikeratophakia, epikeratoplasty

Myopia, hyperopia, astigmatism

Intrastromal corneal ring segments

ICRS

Myopia, keratoconus

Epipolis laser in situ keratomileusis

Epi-LASIK

Myopia, hyperopia, astigmatism

Laser thermokeratoplasty

LTK

Hyperopia, astigmatism

Conductive keratoplasty

CK

Hyperopia, astigmatism

CXL

Keratoconus

Corneal collagen crosslinking Lens-based surgeries Phakic IOLs

Angle-supported

Myopia

Iris-supported

Myopia

Sulcus-supported (posterior chamber implantation), e.g., implantable Collamer lens (ICL)

ICL

Myopia, hyperopia

CLE

Myopia, hyperopia, presbyopia

Multifocal/accommodative intraocular lens (IOL)

RLE

Myopia, hyperopia, presbyopia

Toric IOLs

RLE

Myopia, hyperopia, astigmatism

Femtosecond Laser Assisted Cataract Surgery

FLACS

Myopia, hyperopia, astigmatism

Clear lens extraction Refractive lens exchange

Combined surgeries Bioptics

Myopia, hyperopia, astigmatism, presbyopia

Trioptics

Myopia, hyperopia, astigmatism, presbyopia

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Chapter 2

Table 2.2  Abbreviations commonly used in refractive surgery Abbreviations

Expansion

BCVA

Best corrected visual acuity; also, called CDVA (corrected distance visual acuity)

D

Diopter

LogMAR

Base-10 Logarithm of the minimum angle of resolution

RGP

Rigid gas permeable lenses

RSBT

Residual stromal bed thickness

PTA

Percentage tissue ablation

UCVA

Uncorrected visual acuity; also known as UDVA (uncorrected distance visual acuity)

RMS

Root mean square

SIM K

Simulated K; corneal power simulation measurements

KC

Keratoconus

I-S value

Inferior-superior value; dioptric asymmetry in between superior and inferior corneal halves

DLK

Diffuse lamellar keratitis

ASA

Advanced surface ablation

CCT

Central corneal thickness

HOA

Higher order aberrations

LOA

Lower order aberrations

WFO

Wavefront-optimized

WTW

White-to-white; refers to the corneal diameter in milllimeters

ACD

Anterior chamber depth; refers to the depth of the anterior chamber in millimeters

PMT

Post mydriatic test; refers to the refractive error tested in noncycloplegic conditions

OD

Oculus dextrus

OS

Oculus sinister

Box 2.1  Outcomes commonly evaluated to quantify success in refractive surgeries Uncorrected visual acuity1 Stereoacuity2,3 Residual refractive error Patient satisfaction Contrast sensitivity Complication rate, e.g., dry eyes, ectasia incidence

Terminology Commonly Used in Refractive Surgery Refractive surgeons often deal with the terms discussed in Table 2.2. The commonly used indicators of success in refractive surgery are listed in Box 2.1.

References 1. Bamashmus MA, Hubaish K, Alawad M, Alakhlee H. Functional outcome and patient satisfaction after laser in situ keratomileusis for correction of myopia and myopic astigmatism. Middle East Afr J Ophthalmol 2015;22(1):108–114 10.4103/0974-9233.148359 2. Khokhar S, Gupta S, Gogia V, Tewari R, Agarwal T. Changes in stereoacuity following implantable Collamer lens implantation in patients with myopia. Indian J Ophthalmol 2015;63(10):788–790 10.4103/03014738.171510 3. Kirwan C, O’keefe M. Stereopsis in refractive surgery. Am J Ophthalmol 2006;142(2):218–222

Chapter 3 Preoperative Evaluation and Investigations for Refractive Surgery Introduction....................................................................................... 14 Patient History.................................................................................. 14 Patient Examination........................................................................ 15 Conclusion.......................................................................................... 32

Preoperative Evaluation and 3. Investigations for Refractive Surgery Yogita Gupta, Deeksha Rani, Chirakshi Dhull, and Sudarshan Khokhar

Introduction A thorough and complete patient evaluation is an integral component of refractive surgery practice. An experienced surgeon should be able to decide whom to exclude for refractive surgery. In this chapter, we shall be dealing with all the important parts of preoperative refractive surgery evaluation (Box 3.1).

Patient History The first and foremost part of the workup should focus on knowing the patient’s needs and expectations. The indication for surgery should be recorded, whether cosmetic or professional. While speaking to the patient, the refractive surgeon should try to estimate the level of motivation the patient has for undergoing suitable refractive surgery and what their goals of surgery are. Patients who are too demanding and who have unrealistic expectations, such as hoping for 6/6 uncorrected visual acuity even when best corrected visual acuity (BCVA) is worse than 6/6 not attributable to just existing refractive error, are not ideal candidates for refractive surgeries. Patient satisfaction largely depends upon their expectations. Moreover, the surgeon should also stress the need for regular follow-ups. In myopes, the surgeon should clarify to the patient that refractive surgery is not “treating” the

Box 3.1  Important points in refractive surgery workup History Age of patient Social history: Professional vision requirements Medical history: Diseases such as diabetes, autoimmune disorders; systemic drugs Ocular history: Ocular drugs, trauma; contact lens use; previous keratitis; previous surgery Pregnancy/lactation (if reproductive-aged female) Patient expectations Ocular examination Uncorrected visual acuity Best corrected visual acuity: Distance, near Manifest and cycloplegic refraction, power of glasses Slit-lamp examination, external examination, ocular motility, pupillary examination (reaction and size) Tear film assessment: Schirmer’s test, tear break-up time, tear osmolarity, pH Corneal sensations Corneal pachymetry Corneal topography Tonometry–noncontact/applanation Stereopsis Axial length: Noncontact/ultrasonic Dilated fundus examination: Direct and indirect ophthalmoscopy Specular microscopy Contrast sensitivity Color vision Glare acuity Ocular dominance test Wavefront analysis: iTrace Confocal microscopy Monovision tolerance test (for presbyopia)

myopia and that dilated fundus evaluation at periodic intervals is a must in future follow-ups. Glaucoma and cataract evaluation at regular intervals will be required for those implanted with phakic intraocular lenses (pIOLs).

help in subsequent patient counseling. Working distance will differ for individuals in different professions and must be documented. Certain jobs, e.g., army and police, do not

Patient history must include identification of the patient’s

recruit individuals with past intraocular surgeries. Certain

profession and their vision requirements. This will also

activities like playing tennis, golf, driving, and airplane

Preoperative Evaluation and Investigations for Refractive Surgery piloting require good bilateral distant visual acuity. Certain activities like reading books, watchmaking, craftwork, and using computers need good bilateral near visual acuity. It is the surgeon’s duty to provide a balanced education about the type of refractive surgery the patient needs and if monovision is necessary. A surface procedure may be more suitable than lamellar procedure for persons in contact sports, such as football, baseball, and martial arts, due to a possible risk of flap dislocation following ocular trauma in those who have had a lamellar procedure such as LASIK.1,2 A thorough medical history should be taken to rule out

15

Patient Examination Visual Acuity and Refraction Distance visual acuity (at 6 m or 20 ft) and near visual acuity (at 36 cm or 14 in) (Fig. 3.1) should be tested in unaided state as well as with glasses. The current prescription of glasses should be checked with a lensometer (Fig. 3.2). Contrast sensitivity must be tested in all subjects (Fig. 3.3). A manifest and cycloplegic refraction must be performed to determine the exact amount of refractive error that is to

any systemic disease that may potentially affect refractive surgery outcomes by affecting wound-healing, e.g., diabetes and autoimmune diseases. Diseases like rheumatoid arthritis, systemic lupus erythematosus, and Sjogren’s syndrome are considered as contraindications to corneal refractive surgery because there is unpredictable wound-healing and potential risk for corneal melting. Risk of infections after refractive surgery increases in immunocompromised states such as HIV infections. Ocular history should rule out past history of viral keratitis or ocular herpes3 that may get reactivated; those oper-

Box 3.2  Contraindications to corneal laser refractive surgery7 1. Unstable refractive error 2. Diseases of the eye affecting visual axis, e.g., cataract, corneal ectasias/opacity, retinal pathology 3. Uncontrolled glaucoma 4. Diseases of ocular surface: Dry eyes, atopy, etc. 5. Uncontrolled autoimmune disease 6. Insufficient residual corneal thickness 7. Unrealistic patient expectations 8. Pregnancy and lactation

ated for strabismus that can recur after refractive surgery. The stability of refraction must be ensured for the last one year. The patient should be asked about previous use of contact lenses. Contact lenses must be removed prior to the preop examination for a minimum of 7–14 days for soft contact lenses and 3 weeks for rigid gas permeable lenses due to change in corneal curvature with the use of contact lenses (corneal warpage). History of significant dry eye symptoms, amblyopia, strabismus, eye infections, incomplete closure of eyes, and frequency of change in glasses must be elicited. History of intake of drugs that may affect refractive outcomes should be taken. Some drugs affect wound healing, e.g., systemic steroids, immunomodulator drugs, hormone replacement therapy, and antihistaminics. Certain retinoids (e.g., isotretinoin used for acne), antihistaminics, antidepressants, antirheumatic agents, sedatives, and opioids may increase the concern of dry eyes after refractive surgery.4–6 Pregnant and lactating females are absolute contraindications for refractive surgery (Box 3.2). 7

Fig. 3.1  Early Treatment Diabetic Retinopathy Study (ETDRS) chart for measuring distance visual acuity.

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Chapter 3

Fig. 3.3  Contrast sensitivity testing chart (Vector Vision, Greenville, OH).

Fig. 3.2  Lensometer to check power of glasses. be corrected. Refractive errors may be classified as: low to moderate ( 18 µm (for posterior) and > 12 µm (for anterior) in 9 mm BFS and if > 12 µm (for posterior) and > 8 µm (for anterior) in 8 mm BFS (9mm BFS is more sensitive due to larger area covered, but less specific) b. Using best fit toric ellipsoid (BFTE): The highest plus value in central 5 mm is checked. > 12 µm on anterior map and > 15 µm on posterior map raise suspicion for Keratoconus. c. Difference of anterior and posterior elevations > 5 µm: KC Suspect d. Any central island or skewed hourglass figure or tongue-like extension: KC Suspect 6. Pachymetric map a. Thinnest pachymetry (TP) location - paracentral corneal thinning, inferior thinning, global thinning: abnormal maps b. Y-coordinate of distance of AP and TP > 500 µm: KC suspect c. Difference between superior and inferior corneal thickness > 30 µm (in 4 mm zone) 7. Corneal asymmetry between the eyes. Score ≥ 4: abnormal.35 This score is based on differences in mean anterior and posterior keratometry, thinnest pachymetry, front and back elevation at thinnest point 8. The Pentacam’s BAD display: a. If these show abnormal anterior and posterior difference maps at the thinnest point: Keratoconus is suspected b. Corneal thickness spatial profile (CTSP): Gives information of change of corneal pachymetry from the thinnest point as we go peripherally. The curve shown in red line should not fall/slope down below the normal reference curve before 6 mm point. c. D value is derived from a series of parameters based on normative data. D values > 1.6: Keratoconus suspect (yellow color range); ≥ 2.6: Keratoconus (red color range) d. Pachymetry progression index (PI) refers to increase of corneal thickness from TP along each hemimeridian matched to reference population baseline statistics). Average pachymetry progression < 1.2: normal, ≥ 1.2: Keratoconus suspect 9. Other parameters read in Pentacam: a. Corneal volume b. Anterior chamber angle, > 30 degree: normal c. Anterior chamber depth (ACD) > 2.8 mm: normal d. Pupil diameter (For planning refractive surgery, pupil diameter should be less than optical zone by atleast 0.5mm) e. Corneal diameter

28

Chapter 3

Reference spherical wavefront

Aberrated wavefront Image plane

ƒ2

ƒ1

Wave aberration W (χ,γ) Exit pupil

Fig. 3.18  Wave aberration.

Wavefront aberrations can be further classified based on their Zernike notation as: ••Lower order aberrations (LOA): Zero, first, and second order—myopia, hyperopia, and regular astigmatism. ••Higher-order aberrations (HOA): Third order and above—spherical and chromatic aberrations, coma, and trefoil.

iTrace Aberrometer Aberrometers using various principles such as HartmannShack, Tscherning, Ray Tracing, and automatic retinoscopy have been developed to quantify these ocular aberrations. The iTrace System (Tracey Technologies) (Fig. 3.19) is a unique design with combined Placido corneal topography,

Fig. 3.19  iTrace aberrometer.

pupillography, autorefractometer, and an aberrometer based on the principle of ray tracing.51

Concept of Ray Tracing A sequential series of infrared beams of 785 nm wavelength is projected into the entrance pupil parallel to the eye’s line

respect to a position of reference, thus ultimately affecting the visual outcome. When analyzing iTrace data, we come across the following types of graphs:

of sight. Each of these points represents the entrance of

••Total wavefront graph and higher-order aberrations

parallel light rays into the eye, which become refracted by

graph. These are color coded graphs based on the loca-

the eye’s optical power and eventually focuses on the retina.

tion of the wavefront in front or back of the reference

The local aberrations at the beam’s entry point on the cornea

plane.

or the lens cause a shift in the location on the retina with

••Root mean square values.

Preoperative Evaluation and Investigations for Refractive Surgery ••Total refractive and higher-order aberrations graph. ••Point spread function total and HOA maps. ••Snellen letter total and HOA. ••Zernike polynomials. ••Aberrations of internal optics analysis.

Optical Aberrations after Refractive Surgery

29

Another method for corneal biomechanics is: Ocular Response Analyzer (ORA) corneal biomechanic index (CBI).

Implications in Refractive Surgery Both small incision lenticule extraction and femtosecond laser-assisted LASIK can cause biomechanical changes in the cornea. However, changes in the cornea’s viscoelastic prop-

••Though there is a correction of astigmatism and defo-

erties were less after lenticule extraction than after LASIK.53

cus post-refractive surgery, there is an increase in

Both microincision lenticule extraction and small inci-

higher-order corneal aberrations that correlate well with a decrease in contrast sensitivity. ••Refinement of ablation algorithms and a better understanding of the corneal biomechanical changes are needed to avoid induction of higher order aberrations.

sion lenticule extraction procedures significantly altered the biomechanical characteristics of the cornea.54,55 The smaller 2 mm incision was associated with less reduction in ORA parameters during the early postoperative period.

••Prior precision planning and counseling are essential to avoid postoperative disappointments in visual quality.

Corneal Biomechanics Corneal biomechanics is measured by an ocular response analyzer in terms of corneal hysteresis and corneal resistance factor.52 Although corneal hysteresis can differentiate normal cornea from those with keratoconus, there is a significant overlap. So, it is not the primary method for screening.

Corvis ST Corvis ST is a noncontact tonometer that also provides data of corneal biomechanical properties. The cornea is applanated with an air puff and a Scheimpflug camera is used to capture 4,330 images per second (Fig. 3.20). The velocity of corneal deformation at the first and second applanations and the maximum depth of corneal deformation due to the air jet are recorded by this camera. Intraocular pressure is measured by taking into account the biomechanical properties of the cornea. Central corneal thickness obtained by this device showed good accuracy and repeatability when compared with standard ultrasound pachymetry. Fig. 3.21 and Fig. 3.22 depict biomechanical assessment of a normal and post-LASIK subject, respectively.

Fig. 3.20  Corvis ST.

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Chapter 3

Fig. 3.21  Corvis ST map of a subject showing normal corneal biomechanics with corneal biomechanic index (CBI) in the normal range.

Fig. 3.22  Corvis ST map of a postoperative case after LASIK surgery, with increased CBI and D value.

Preoperative Evaluation and Investigations for Refractive Surgery

31

White-to-white Diameter

diameter, and in such cases, digital calipers used manually

Corneal diameter can be measured with the following

The sizing of phakic IOL, deciding the applanation cone

devices:

size, and deciding the Lasik flap diameter require WTW

••Orbscan: It gives the best estimate of corneal diameter with its slit scanning working principle. ••Digital calipers (Fig. 3.23) can be used to measure White-to-white Diameter (WTW). ••Others: IOL master (Fig. 3.24) and Pentacam. In patients with pigmentation at the limbus, optical devices may erroneously measure the wrong corneal

will be the best method to give an accurate measurement.

measurement.

Corneal Endothelial Cell Count Specular microscopy (Fig. 3.25) should be documented in all cases, especially in those undergoing intraocular procedures such as implantation of Implantable Collamer Lens (ICL). Fig. 3.26 shows specular microscopy capture of a normal subject.

Calculation of Residual Stromal Bed Thickness (RSBT) and Percentage Tissue Ablation Ablation Depth The corneal tissue ablation depth (AD) is calculated by the

Fig. 3.23  Digital calipers.

Fig. 3.24  Intraocular lens (IOL) master can be used to measure white-to-white diameter (WTW).

Munnerlyn formula.56,57 The Munnerlyn formula states

Fig. 3.25  Specular microscope to capture endothelial cell count (SP-1P, Topcon).

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Chapter 3

Randleman Ectasia Risk Score The Ectasia Risk Score System was designed by Randleman et al based on an evidence-based review of large case series of LASIK ectasia cases.59 It is used to identify high-risk subjects for refractive surgery.

Score ••0–2 points = low risk. ••3 points = moderate risk. ••4 points = high risk. The following point system is used59:

Fig. 3.26  Capture of specular microscopy of a subject showing normal cell density (CD), coefficient of variation (CV), percentage of hexagonality (HEX) with normal central corneal thickness (CCT).

••Abnormal topography, RSB –14 D: each 4 points. ••Inferior steepening pattern or skewed radial axis in topography, RSB between 240 to 259 microns, age between 18 to 21 years, corneal thickness between

that the depth of the ablation (P, in micrometers) per diopter of refractive change is equal to the square of the diameter

451 to 480 microns, MRSE between –12 to –14 D: each 3 points.

of the optical ablation zone (OZ, in millimeters), divided by

••RSB between 260 and 279 microns, age between 22

three. Transition zone (TZ) is the area between the treated

to 25 years, corneal thickness between 481 to 510

ablation zone and the untreated periphery.

microns and MRSE between –10 to –12 D: each 2

AD = D × (OZ)2 /3 where AD = Ablation depth (in microns) D = diopters of myopia OZ = optical zone (in millimeters)

points. ••Asymmetric bow tie pattern in topography, RSB between 280 to 290 microns, age between 26 to 29 years, MRSE between –8 to –10 D: each 1 point. ••Normal pattern or symmetric bow tie, RSB more than

Currently, most surgeons use an optical zone of 6.5 mm

300 microns, age more than 30 years, corneal thick-

to 7 mm, with a blend well beyond optical zone to reduce

ness more than 510 microns, MRSE less than -8 D:

spherical aberration.

each 0 point.

Percentage of Tissue Ablated Percentage of Tissue Ablated (PTA) is an index to detect those at risk of corneal ectasia after refractive surgery.58 PTA = (FT + AD) / CCT where AD = Ablation depth (in microns) FT = flap thickness (in millimeters) CCT = preoperative central corneal thickness (in millimeters) PTA greater than 40% at the time of LASIK is significantly associated with risk of ectasia in eyes with normal corneal topography.58

Conclusion A complete and detailed patient evaluation is the key to a successful refractive surgery. The surgeon needs to have a comprehensive approach to getting the subject investigated preoperatively.

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33. Hashemi H, Mehravaran S. Day to day clinically relevant corneal elevation, thickness, and curvature parameters using the Orbscan II scanning slit topographer and the Pentacam Scheimpflug imaging device. Middle East Afr J Ophthalmol 2010;17(1):44–55

46. Han SB, Liu Y-C, Noriega KM, Mehta JS. Applications of anterior segment optical coherence tomography in cornea and ocular surface diseases. J Ophthalmol 2016;2016:4971572

34. Hashemi H, Mehravaran S. Corneal changes after laser refractive surgery for myopia: comparison of Orbscan II and Pentacam findings. J Cataract Refract Surg 2007;33(5):841–847 35. Reinstein DZ, Couch DG, Archer T. Direct residual stromal thickness measurement for assessing suit­ ability for LASIK enhancement by Artemis 3D very highfrequency digital ultrasound arc scanning. J Cataract Refract Surg 2006;32(11):1884–1888 36. Reinstein DZ, Silverman RH, Raevsky T, et al. Arcscanning very high-frequency digital ultrasound for 3D pachymetric mapping of the corneal epithelium and stroma in laser in situ keratomileusis. J Refract Surg 2000;16(4):414–430 37. Klijn S, Reus NJ, Sicam VA.Evaluation of keratometry with a novel Color-LED corneal topographer. J Refract Surg. 2015 Apr;31(4):249-56 38. Kanellopoulos AJ, Asimellis G. Color light-emitting diode reflection topography: validation of keratometric repeatability in a large sample of wide cylindrical-range corneas. Clinical Ophthalmology. 2015;9:245-252 39. Barsam A. Technology for keratoconus screening. Cataract & Refractive Surgery Today Europe 2012;3: 26–27 40. Melki SA, Azar DT. LASIK complications: etiology, management, and prevention. Surv Ophthalmol. 2001; 46:95–116. 41. Rabinowitz YS, Rasheed K. KISA% index: a quantitative videokeratography algorithm embodying minimal keratometric criteria for diagnosing keratoconus. J Cataract Refract Surg. 1999;25 (10:1327–1335. 42. Konstantopoulos A, Hossain P, Anderson DF. Recent advances in ophthalmic anterior segment imaging: a new era for ophthalmic diagnosis? Br J Ophthalmol 2007;91(4):551–557 43. Ramos JLB, Li Y, Huang D. Clinical and research applications of anterior segment optical coherence tomography: a review. Clin Exp Ophthalmol 2009; 37(1):81–89 44. Wang J, Abou Shousha M, Perez VL, et al. Ultra-highresolution optical coherence tomography for imaging the anterior segment of the eye. Ophthalmic Surg Lasers Imaging 2011;42(Suppl):S15–S27 45. Li Y, Netto MV, Shekhar R, Krueger RR, Huang D. A longitudinal study of LASIK flap and stromal thickness

47. Tay E, Li X, Chan C, Tan DT, Mehta JS. Refractive lenticule extraction flap and stromal bed morphology assessment with anterior segment optical coherence tomography. J Cataract Refract Surg 2012;38(9):1544–1551 48. Shetty R, Malhotra C, D’Souza S, Wadia K. WaveLight FS200 vs Hansatome LASIK: intraoperative determina­ tion of flap characteristics and predictability by handheld bioptigen spectral domain ophthalmic imaging system. J Refract Surg 2012; 28(11, Suppl)S815–S820 49. Pallikaris IG, Kymionis GD, Astyrakakis NI. Corneal ecta­ sia induced by laser in situ keratomileusis. J Cataract Refract Surg 2001;27(11):1796–1802 50. Marcos S. Aberrometry: basic science and clinical appli­ cations. Bull Soc Belge Ophtalmol 2006; (302):197–213 51. Unterhorst HA, Rubin A. Ocular aberrations and wavefront aberrometry: A review. Afr Vision Eye Health. 2015;74(1) 52. Lau W, Pye D. A clinical description of Ocular Response Analyzer measurements. Invest Ophthalmol Vis Sci 2011;52(6):2911–2916 53. Wang D, Liu M, Chen Y, et al. Differences in the corneal biomechanical changes after SMILE and LASIK. J Refract Surg 2014;30(10):702–707 54. Wu Z, Wang Y, Zhang J, et al. Comparison of corneal biomechanics after microincision lenticule extraction and small incision lenticule extraction. Br J Ophthalmol 2017;101(5):650–654 55. Hirasawa K, Matsuura M, Murata H, et al. Association between corneal biomechanical properties with Ocular Response Analyzer and also CorvisST tonometry, and glaucomatous visual field severity. Transl Vis Sci Technol 2017;6(3):18 https://www.ncbi.nlm.nih.gov/ pmc/articles/PMC5472364/ [Internet] 56. Munnerlyn CR, Koons SJ, Marshall J. Photorefractive keratectomy: a technique for laser refractive surgery. J Cataract Refract Surg 1988;14(1):46–52 57. Chang AW, Tsang AC, Contreras JE, et al. Corneal tissue ablation depth and the Munnerlyn formula. J Cataract Refract Surg 2003;29(6):1204–1210 58. Santhiago MR, Smadja D, Gomes BF, et al. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal pre­operative topography. Am J Ophthalmol 2014;158(1):87–95.e1 59. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology 2008;115(1):37–50

Chapter 4 Decision-making in Refractive Surgery

Introduction....................................................................................... 36 Suitable Candidate........................................................................... 36 Making a Decision............................................................................ 36 Case-based Approach...................................................................... 39

4. Decision-making in Refractive Surgery Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

Introduction

includes discussing the procedure and likely outcomes to

Planning and decision-making for a refractive patient is one

list to aid in patient selection.1,2 Indications and contraindi-

of the most important aspects of refractive surgery. Since

cations vary based on the procedure of choice and have been

refractive surgery is performed in healthy individuals with

described in detail in respective chapters.

avoid expectation mismatch. Tables 4.1 and 4.2 provide a

refractive error, tolerance of suboptimal outcomes is very low. The success depends eventually on patient satisfaction. Hence, a complete understanding of principles and procedures pertaining to the planning of refractive surgery is necessary.

Suitable Candidate Selecting a suitable candidate for refractive surgery is a prerequisite. A detailed history should be taken from each patient and complete ocular examination and investigations should be performed. This has been discussed in detail in the previous chapter. An important aspect of patient selection Table 4.1  Candidate suitability requirements1,2 Suitable candidate ▪▪Age > 18 years ▪▪Stable refractive error (change < 0.5 D in the past 1 year) ▪▪No contraindications ▪▪Expectations explained

Making a Decision Decision for refractive surgery requires taking into account complex factors including preoperative parameter and patient’s needs and expectations. This can be simplified by following a stepwise approach for decision-making. This approach can reduce the chances of error in planning and postoperative suboptimal outcomes. Before planning a surgery, an approved range of correction for specific procedures should be kept in mind. Table 4.3 mentions the range for correction of refractive error with common procedures. Details of preoperative planning and investigations have been given in the previous chapter in detail. A few important terminologies and cutoffs to be remembered are listed in Table 4.4.3–5 A detailed, stepwise approach is shown in Fig. 4.1. This approach is a practical method taking into account the preoperative investigation and range of refractive error to be corrected. In the next section, we will

Table 4.2  Absolute and relative contraindications for refractive surgery Absolute contraindications

Relative contraindications

Systemic contraindications ▪▪Pregnancy ▪▪Systemic collagen vascular disease ▪▪Uncontrolled Diabetes mellitus Ocular contraindications ▪▪Keratoconus (for corneal ablative surgery) ▪▪Dry eye—severe (for corneal ablative surgery) ▪▪Uncontrolled glaucoma ▪▪Visually significant cataract [except refractive lens exchange (RLE)] ▪▪Shallow anterior chamber [for Phakic intraocular lens (IOL)]

Systemic contraindications ▪▪Diabetes mellitus—controlled Ocular contraindications ▪▪Dry eye—mild ▪▪Glaucoma—controlled, minimal nerve damage ▪▪Herpetic infection history (corneal surgery) ▪▪Epithelial basement membrane degeneration [no laserassisted in situ keratomileusis (LASIK), but can have photorefractive keratectomy (PRK)] ▪▪Endothelial dystrophy (for phakic IOL/RLE)

Decision-making in Refractive Surgery

37

Table 4.3  FDA-approved range for correction of refractive error Type of procedure

Procedure

Approved range for correction

Cornea-based procedure

LASIK

–10 DS to +4 DS Up to 4 DC (approval varies for different machines)

PRK/surface ablation

–12 DS to +4 DS Up to 4 DC (approval varies for different machines)

Small incision lenticule extraction (SMILE)

–10 DS Up to 3 DC Not approved for hyperopia

Phakic IOL

Myopia –3 DS to –20 DS Hyperopia +3 DS to +10 DS Up to 6 DC

Lens-based procedure

Surface ablation More suitable for thin cornea, low refractive error, epithelial abnormalities

Patient for refractive surgery

LASIK Suitable for most cases Yes

Age> 18 year stable refraction no ocular or systemic contraindication

Yes Detailed History Examination, Pachymetry, Corneal Topography, ABC and specular count (for intra-ocular surgery)

No

Corneal refractive surgery

Wait and watch

CCT>470 micron RSBT>250 micron PTA 300 microns < 250 microns contraindicated

Percentage tissue ablation (PTA) = (flap thickness + tissue ablation)/corneal thickness

< 40% is recommended

Postoperative keratometry (post K) = preoperative Km –0.8 × Refractive error for myopia Or = Preoperative Km +1 × Refractive error for hypermetropia

Range of 34 to 48 D is recommended

Endothelial anterior chamber depth (endo ACD)

> 2.8 mm (Myopia) > 3.0 mm (Hyperopia)

Specular count

> 2,500 cell/mm3 recommended

Lens-based Surgery: Phakic IOL

discuss a case-based approach in a few scenarios, which will help the readers in a better understanding of the decisionmaking process.

References 1. American Academy of Ophthalmology Refractive Management/Intervention Panel. Preferred Practice Pattern Guidelines. Refractive Errors & Refractive Surgery PPP. San Francisco, CA: American Academy of Ophthalmology; 2017

2. Dimitri T. Azar. Refractive Surgery. 2nd ed. Elsevier Inc China; 2007 3. Chang AW, Tsang AC, Contreras JE, et al. Corneal tissue ablation depth and the Munnerlyn formula. J Cataract Refract Surg 2003;29(6):1204–1210 4. Santhiago MR, Smadja D, Gomes BF, et al. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol 2014;158(1):87–95.e1 5. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology 2008;115(1):37–50

Decision-making in Refractive Surgery

39

Case-based Approach Case 1

Table 4.5  Patient parameters in Case 1

A 23-year-old healthy male wanted removal of glasses for

Parameter

OD

OS

occupational purposes. No systemic or ocular abnormality

Uncorrected visual acuity (UCVA)

6/60

6/60

was noted following a detailed workup. Table 4.5 shows

Best-corrected visual acuity (BCVA)

6/6

6/6

patient parameters. Fig 4.2 a, b show normal preoperative

Post cycloplegic refraction, post mydriatic test (PMT)

–3 DS/-0.5 DC @80

–3.25 DS

Keratometry mean (Km), in Dioptres

43.8

44.1

corneal topography.

Decision-making ••Patient was suitable for corneal refractive surgery. ••Patient was explained about all options and that a similar visual outcome can be expected in different corneal procedures. ••Patient chose SMILE surgery due to dry eye concerns. ••Postop: UCVA OD 6/6 OS 6/6 (1 day, 1 month, 1 year); postoperative corneal topography is shown in Fig. 4.3a, b.

Thinnest pachymetry, μm

516

507

Pupillary diameter (PD), mm

2.5

2.99

Posterior elevation (PE)

+6

+11

D value

0.59

1.0

RSBT, μm

361

358

PTA

30%

29.33%

Postoperative Km, D

41.2

41.5

40

Chapter 4

Fig. 4.2  (a) Pentacam 4 map refractive view showing corneal topography of OD for Case 1. Note normal topography. (b) Pentacam 4 map refractive view showing corneal topography of OS for Case 1. Note normal topography.

a

b

Decision-making in Refractive Surgery

41

Fig. 4.3  (a) Case 1: Pentacam at 1 year follow up, OD showing flat cornea and no change in posterior elevation map. (b) Case 1: Pentacam at 1 year follow up, OS showing flat cornea and no change in posterior elevation map.

a

b

42

Chapter 4

Case 2

Table 4.6  Patient parameters in Case 2

A 22-year-old male wanted removal of spectacles. He had

Parameter

OD

OS

stable refraction for 2 years. A detailed ocular examina-

UCVA

5/60

4/60

tion revealed no abnormality. Corneal topography was

BCVA

6/6

6/6

assessed using Pentacam HR. No abormality was detected

Post cycloplegic refraction, PMT –4.25 DS/ –1.5 DC @60

–3.75 DS/ –1.25 DC @75

Km, D

43.1

42.9

Thinnest pachymetry, μm

549

538

PD, mm

3

3.1

PE

+7

+9

D value

1.1

1.3

Calculated RSBT, μm

355

356

PTA

35.3%

33.8%

Postoperative Km, D

41.2

41.5

(Fig. 4.4a, b). The purpose of the removal of spectacles for the patient was cosmesis. Patient parameters are listed in Table 4.6.

Decision-making ••Suitable for corneal refractive surgery (LASIK, Surface ablation, SMILE). ••SMILE: Latest approval till 3 DC. Concerns related to optimal correction in significant cylinders. ••LASIK: Gives wow effect, first day. ••Surface ablation with higher refractive error may result in regression over time, more haze. ••Discussed with patient; patient chose LASIK. ••Postop: UCVA OD 6/6 OS 6/6 (1 day, 1 month, 1 year).

Decision-making in Refractive Surgery

43

Fig. 4.4  (a) Pentacam 4 map refractive view showing corneal topography of OD for Case 2. Note the normal topography. (b) Pentacam 4 map refractive view showing corneal topography of OS for Case 2. Note the normal topography.

a

b

44

Chapter 4

Case 3 A 25-year-old female patient wanted removal of spectacles. No abnormality was detected on ocular examination. Patient parameters are listed in Table 4.7. Fig. 4.5a, b shows preoperative Anterior segment optical coherence tomography (AS0CT) for anterior segment.

Table 4.7  Patient parameters in Case 3 Parameter UCVA BCVA Post-cycloplegic refraction, PMT

OD 2/60 6/6 –15 DS

Thinnest pachymetry, μm PE White to White (WTW), mm Endo ACD, mm Specular count, cells/mm2

495 +6 11.8 3.5 3,209

a

b Fig. 4.5   (a, b) Case 3: Preoperative ASOCT of OD and OS respectively with endo ACD > 3.0 mm.

OS 2/60 6/6 –14 DS/ –0.5 DC @180 494 +5 11.8 3.5 3,190

Decision-making in Refractive Surgery

Decision-making ••Not suitable for corneal refractive surgery. ••Patient was planned for both eyes implantable collamer lens (ICL).

45

••Since left eye had only -0.5Dcyl, ICL was planned instead of Toric ICL. For cylinder > 1D, toric ICL is more suitable. ••Postoperative UCVA of 6/6 achieved in both eyes. Vaulting in OD and OS at 6 months post-surgery is shown in Fig. 4.6a, b respectively.

a

b Fig. 4.6   (a, b) Case 3: Post­operative ASOCT of OD and OS showing healthy vault OD 453 u and OS 452 u (normal range 250–750 u)

46

Chapter 4

Case 4

Table 4.8  Patient parameters in Case 4

A 29-year-old male had been using glasses for the past 15

Parameter

OD

OS

years, and no change in glasses was noted in the last 6–7

UCVA

6/24

6/24

years. He had no associated ocular or systemic abnormality.

BCVA

6/6

6/6

Patient parameters are listed in Table 4.8. Fig. 4.7a, b shows

PMT post cycloplegic refraction

+4DS

+4DS

preoperative Pentacam for corneal topography.

K1, D

43.4

43.4

K2, D

43.9

43.7

Decision-making ••Two options: Corneal refractive surgery and lensbased surgery (Phakic IOL). ••Corneal refractive surgery: There is no absolute contraindication for the surgery, but postoperative Km is > 47 D, which is not recommended. There are greater chances of regression if LASIK/surface ablation is performed. ••Phakic IOL: The patient was explained the procedure; need for peripheral iridotomy (PI) was also explained. At present, central K- aquaport is not available in hyperopic ICL, hence there is a requirement for PI. ••Hyperopic ICL was planned for the patient.

Axis, degrees

93.1

91.5

K max, D

45.8

44.1

Thinnest pachymetry, μm

529

527

PD, mm

3.51

2.9

PE

+8

+9

D value

0.65

0.89

WTW, mm

12.5

12.4

Endo ACD, mm

3.01

3.03

Calculated RSBT, μm

369

367

Calculated Post Km, D

498

48.1

PTA

30.2%

30.3%

Specular count, cells/mm2

2882

3171

Decision-making in Refractive Surgery

a

b Fig. 4.7   (a, b) Case 4: Corneal topography maps for OD and OS respectively. Note the normal topography in both eyes with normal anterior and posterior float.

47

48

Chapter 4 an option, although problem haloes and glare may be

Case 5

there.

A 24-year-old female had been using spectacles since child-

••Patient opted for no refractive surgery: instead

hood. The last change in glasses was observed 2 years back.

decided to continue use of contact lens and spectacles.

No ocular or systemic comorbidity was noted. She had no associated abnormality. Patient parameters are listed in Table 4.9. Fig. 4.8a, b shows preoperative Pentacam for cor-

Table 4.9  Patient parameters in Case 5 Parameter

OD

OS

UCVA

6/60

6/60

BCVA

6/12

6/12

PMT post cycloplegic refraction

+9DS/+2.25 DC @130

+8DS/+2 DC @30

••Corneal refractive surgery is not suitable in this case.

K1, D

38.1

38.7

Refractive error is high and will cause percentage

K2, D

40.7

40.5

tissue alteration >40% (cut-off). Postoperatively cor-

Axis, degrees

153.4

26.3

neal steepness would be >50 D, increasing higher-

K max, D

41

40.9

order aberrations (HOA), dry eye, and increased

Thinnest pachymetry, μm

564

558

chances of regression.

PD, mm

3.46

4.63

PE

+20

+19

patient. Anterior chamber depth is 0.35 microns.2

the central corneal symmetry, without attempting to correct

Wavefront-optimized (WO) LASIK induces less HOAs as

other spherical, or regular astigmatic optical defects. Degree

compared with conventional LASIK. It particularly reduces

of ablation with the maximum depth of tissue loss is less

the spherical aberrations by creating a more prolate ablation

than 50 mm.4 TCAT is performed by linking the Topolyzer

profile, but with no effect on other HOAs.

with the WaveLight Allegretto Wave Excimer Laser System

3

Laser in Situ Keratomileusis Surgery

81

(WaveLight Laser Technologie AG), using data from eight

femtosecond laser, or both, and may force the surgeon to

topographic points, and the optical zone diameter is kept in

abort LASIK.8 These may occur due to old or worn out blade,

the range 5.5 to 6.5 mm.

defects in blade, poor suction, loss of suction, poor applanation, poor corneal lubrication, preexisting corneal pathology, poor metal blade quality, or uneven progression of micro-

Complications of LASIK and their Management

keratome.8 Thin corneas and corneas with steep curvature are at risk. Most of these cases would be best managed by

Complications of LASIK can be classified according to level of involvement6 or according to time of occurence7 (Box 6.1).

resurgery at a later date and by avoiding flap lift and stromal ablation.8

The common complications will be discussed in the follow-

••Thin flap: Its incidence in LASIK surgeries is 0.3 to

ing text:

0.75%. It has been seen to occur when keratome cut,

Flap Related Intraoperative Complications

above 12 µm). It is recognized by a shiny appearance of

Thin, irregular, or buttonhole flap are significant complica-

a poor-quality blade, poor suction or loss of suction,

tions of LASIK that can occur with use of microkeratomes,

irregular, steep cornea, repeated placement of suction

that is, above thick Bowman’s layer (approximately the stromal surface. Risk factors for thin flaps include

Box 6.1  Complications of LASIK Intraoperative

Early postoperative

Late Postoperative

Interface debris

Flap striae

Overcorrection

Epithelial defect

DLK

Undercorrection

Buttonholing or thin, irregular flap

GAPP syndrome

Optical aberrations (residual/induced)

Incomplete flap

Sterile infiltrates

Central islands

Free cap

Dislodged flap

Flap displacement

Flap striae

Infections

Corneal perforation8

Epithelial defects

Epithelial implantation and ingrowth

Vertical gas breakthrough

PISK

Glaucoma

Decentered ablation

CTK

Corneal ectasia

Bleeding during LASIK

Heme in LASIK tunnel

Regression

Difficult docking, e.g., deep seated, enophthalmic eyes, prominent brow/nose

Halos and glare Dry eyes and ocular surface problems Infectious keratitis Loss of contrast sensitivity Loss of BCVA Ptosis Corneal dysesthesia Others: retinal complications, etc.

Abbreviations: CTK, central toxic keratopathy; DLK, diffuse lamellar keratitis; GAPP, good acuity plus photosensitivity; LASIK, laser-assisted in situ keratomileusis; PISK, pressure-induced stromal keratopathy.

82

Chapter 6 rings leading to edema, or uncontrolled blinking by

••Flap subluxation: Incidence: Up to 2%. It may occur

the patient.

due to patient squeezing eyes during removal of drape

Treatment: Replace the flap immediately and defer

or speculum and/or due to eye rubbing.

the procedure till flap heals smoothly and patient

Prevention: Counsel patient to avoid rubbing their

can be taken up for surgery after 3 months; then, dif-

eyes in the immediate postoperative period. A careful

ferent depth plate should be used or ablation can be

slit examination should be done before the patient is

attempted.

sent home. Treatment: Flap is relifted and undersurface cleared

••Buttonhole flap: Its incidence ranges from nearly

off debris by irrigation with BSS syringe with cannula.

0.2 to 0.56%. It is seen to occur when microkeratome

Flap is repositioned.

travels more superficial and enters Bowman’s complex, and partial or full thickness exit from epithelium

••Corneal perforation: Occurs due to improper setting

occurs. It is identified as a “doughnut” shaped flap.

of thickness plate, failure to install it, and high IOP

Main risk factors are a steep cornea (> 46 D) and lack of

during procedure, which can result in expulsion of

synchronization between translational and oscillatory

intraocular contents including lens and vitreous. Can

microkeratome blade movement.

occur due to wrong depth calculation and excessive

Treatment: Flap is repositioned and the procedure

drying of the stromal bed. Cornea with ecstatic disor-

is aborted. A deeper flap may be planned to cut 3

ders are at higher risk.

months later.

Treatment: Suction should be turned off immediately and procedure should be aborted. If small, it

••Incomplete flap: Incidence—0.3 to 1.2%; It occurs when microkeratome blade stops before reaching the

can be managed by soft contact lens, patching of eye,

desired hinge location. This can occur due to microker-

and topical antibiotics; if large, repair by suturing and

atome jamming, leading to suction loss, electrical, or

reconstruction of anterior chamber is warranted.

mechanical failure. Treatment: If hinge is at the periphery, one can proceed with ablation. If hinge is in midperiphery, manual dissection could be considered. In case hinge

Femtosecond Laser-related Complications Intraoperative Problems

lies in center, it is best to postpone the procedure after

1. Suction loss: Loss of suction may occur during flap

repositioning the flap.

creation. Risk factors are improper application of

••Free cap: Incidence: 0.7 to 5.9%; free cap refers to a

suction ring, flat cornea, narrow palpebral fissure,

flap lacking hinge. Often the cause is a shallow engage-

deep set eyes, and patient movement.8 It is identified

ment of the microkeratome on the corneal surface.8

as a peripheral meniscus (Fig. 6.10).

Risk factors include flat corneas [< 41 D], decentered



Management: Laser should be discontinued as soon

suction placement, or decreased intraocular pressure

as suction loss is identified. Suction loss may rarely

(IOP) while creating a flap.

occur with microkeratomes and is managed by repo-

Treatment: Free cap should be preserved in antides-

sition of flap and a surface ablation after corneal heal-

iccation chamber with epithelial side down. Stromal

ing. Suction loss in femtosecond laser is managed by

ablation is carried as usual. Then, the flap is replaced

replacing suction ring, redocking of the applanation

on the corneal surface. Bandage contact lens (BCL)

cone, and restarting laser firing at the same depth. If

may be used to improve reepithelialization. If flap is

repeat docking also fails, it is best to perform a sur-

lost, a cap from donor corneal is taken out and sutured

face ablation with mitomycin C three months later. 2. Difficulty in flap lifting, flap tear: Flaps created by

to host cornea. Making corneal marks preoperatively (asymmetri-

femtosecond laser are many a times difficult to be

cal liner marks or rings) helps in the correct orienta-

lifted when compared with those created by micro-

tion in case a free flap occurs.

keratomes.9 Raster pattern of femtosecond laser

8

Laser in Situ Keratomileusis Surgery

Fig. 6.10 Suction loss during LASIK procedure. Abbreviation: LASIK, laser-assisted in situ keratomileusis.

83

Fig. 6.11  Difficult flap separation. Note how two instru­ ments are being used to lift the flap.

may leave few microadhesions between the flap and underlying stroma. These should then be removed by use of blunt instruments (Fig. 6.11) to lift the flap from the stromal bed; however, flap tears may also occur while doing so. If flap tear is peripheral, the procedure may be continued. If it lies in the visual axis, it is best to abort the procedure and reschedule a phototherapeutic keratectomy (PTK) or photorefractive keratectomy (PRK) after the wound heals. 3. Opaque bubble layer (OBL): It is a well-known complication of femto-LASIK. It may temporarily preclude pupillary tracking during the excimer laser portion of femtosecond LASIK procedure. Opaque bubble layer (OBL) (Fig. 6.12) occurs along the lamellar dissection plane during the femtosecond-assisted

Fig. 6.12  Opaque bubble layer during femto-LASIK. Abbreviation: LASIK, laser-assisted in situ keratomileusis.

flap creation, and occurs due to temporary stromal infiltration of compressed air which is generated

in cases with OBL. LASIK may be continued if OBL is

by the intracorneal femtosecond laser action that

peripheral and away from the visual axis (Fig. 6.13).

cannot be escaped. Shah and Melki postulated that

4. Vertical gas breakthrough: Vertical gas break-

in cases with high-laser energy (excessive bubbles

through (VGBT) (Fig. 6.14a–c) is a complication that

are formed) or very low-laser energy (causing inade-

occurs during femtosecond laser flap creation due to

quate pocket for release of bubbles), the microplasma

subepithelial escape of gas bubbles from the plane

bubbles may escape into corneal stroma and push

of dissection, which was first reported by Srinivasan

the collagen fibrils and cause OBL.10 Flap lifts may be

S et al in a case where femtosecond laser was used

more difficult if OBL occurs late in the intraoperative

to create 100 µm flap.11 The cause is not well-known

period. Laser settings may be changed to proceed

as yet and causes like thin flap or focal Bowman’s

84

Chapter 6 membrane breaks have been postulated as possible mechanisms.11 Fig. 6.14a shows an intraoperative image, showing occurrence of VGBT during a 100 µm flap creation, wherein a short canal was also noted. Another case is discussed in Fig. 6.15a–c, where LASIK had to be aborted; however, LASIK can be completed in a few cases. (Postoperative outcomes were unaffected in this case and a vision of 6/6 was noted on the first day [Fig. 6.15b]). 5. Epithelial defect (Fig. 6.16): Incidence is 1 to 5%. It may occur due to microkeratome passage across pressurized cornea, trauma by suction ring, minor

Fig. 6.13  LASIK may be continued if OBL is peripheral and not involving the visual axis. Abbreviations: LASIK, laser-assisted in situ keratomileusis, OBL, opaque bubble layer.

a

c

trauma induced by forceps or spatula, and overuse of topical anesthetic drops. Treatment: BCL, intensive lubricants, and occasionally punctual occlusion.

b

Fig. 6.14  Cases of VGBT where LASIK had to be aborted. (a) A case with early vertical gas breakthrough, without any flap creation; (b) another similar case though with flap creation; (c) postoperative image of the same case. Abbreviations: LASIK, laser-assisted in situ keratomileusis, VGBT, vertical gas breakthrough.

Laser in Situ Keratomileusis Surgery

a

c

85

b

Fig. 6.15  (a) Another case of VGBT, where flap was also created successfully, with adjacent OBL. (b) Immediate postoperative image of same case showing incomplete flap creation in the area of gas breakthrough. (c) Anterior segment OCT scan of the same case on postoperative day 3, showing that no dissection was performed in the area of VGBT. Abbreviations: OBL, opaque bubble layer; OCT, optical coherence tomography; VGBT, vertical gas breakthrough.

6. Anterior chamber bubbles: Presence of gas bubbles in the anterior chamber (AC) has incidence of nearly 0.1 to 0.2%. It may occur in cases where femtodissection is close to limbus.8 The passage used by the cavitation bubbles has been postulated to be through trabecular meshwork via Schlemm’s canal.12,13 AC bubbles may interfere with pupil registry and eye tracking (Fig. 6.17). Bubbles are mostly seen to spontaneously resolve within few hours after surgery. Very rarely, bubbles have been seen in interface also (Fig. 6.18). 7. Subconjunctival hemorrhages: A subconjunctival hemorrhage (Fig. 6.19) is leakage of blood from tiny

Fig. 6.16  Epithelial defect noted intraoperatively in a LASIK case. Abbreviation: LASIK, laser-assisted in situ keratomileusis.

blood vessels located underneath the thin, clear membrane (conjunctiva) that lies atop the white of the eye (sclera).

86

Chapter 6

Fig. 6.17  AC bubbles seen after flap lifting, causing interference in the eye tracking. Abbreviation: AC, anterior chamber.

Fig. 6.18 Few bubbles seen at LASIK interface. Abbreviation: LASIK, laser-assisted in situ keratomileusis.

Fig. 6.19  Subconjunctival hemorrhage in a case of LASIK where redocking was performed noted at 3 days after surgery. Abbreviation: LASIK, laser-assisted in situ keratomileusis.

Fig. 6.20  Tunnel bleed noted on postoperative Day 1 of a LASIK case. Abbreviation: LASIK, laser-assisted in situ keratomileusis.

These can occur during docking with multiple

Bleeding at the flap edge may occur in cases with

applications of suction ring, as seen in cases of suc-

pannus and peripheral corneal neovascularization

tion loss or decentration of applanation cone.10 It is

(e.g., in chronic contact lens users). Cellulose sponges

also seen more commonly in cases done with laser

are recommended to be used in such cases.

systems that build suction on the conjunctiva and

Intraoperative bleeding is more common in eyes

scleral surface, instead of that on the corneal sur-

with large diameter flaps, leading to interface haze

face.14 Subconjunctival hemorrhages have been seen

which, in turn, may lead to postoperative sterile inter-

to resolve within a maximum of 2 weeks, without

face keratitis and decreased contrast sensitivity.15

affecting the visual outcomes. Ocular surface should

Occasionally, bleed may be noted in the LASIK

be treated by lubricants. Proper patient counseling is

tunnel (Fig. 6.20).

required to avoid unnecessary anxiety. Slow and con-

8. Interface debris: Possible interface debris are metal

trolled suction build can prevent this complication.10

fragments/pieces from blade shattering during

Laser in Situ Keratomileusis Surgery dissection, oil material from the microkeratome, powder from gloves, air bubbles, sponge fibers, meibomian secretions, lint fibers, etc. Treatment: Debris can be visualized at the interface many a time (15–20) after surgery on the slit lamp (Fig. 6.21); if significant amount is present, flap needs to be relifted and debris has to irrigated. 9. Decentered

flap,

folded

flap:

A

decentered

87

Postoperative Problems 1. Flap dislodgment: Incidence is 1.1 to 2.0%. Flap dislodgement in postoperative period is an emergency, and should be repositioned as soon as possible to prevent development of fixed folds, infection, epithelial ingrowth, and loss of best-corrected visual acuity (BCVA). A peripheral gutter seen in the cornea may be a clue to flap slippage in the postoperative

(Fig. 6.22) or folded flap (Fig. 6.23) may be noted

period (Fig. 6.24). Delay in intervention may worsen

during or after irrigation of the interface. If observed

the visual prognosis in this condition. If occurring on

early, LASIK flap may be refloated with irrigation

the first postoperative day after the procedure, for

using BSS to center the LASIK flap.

example, due to eye rubbing or infrequent blinking,

Fig. 6.21  Foreign body (lint fiber) in LASIK interface. Abbreviation: LASIK, laser-assisted in situ keratomileusis.

Fig. 6.22  Decentered flap.

Wide peripheral gutter

Fig. 6.23  Folded LASIK flap. Abbreviation: LASIK, laserassisted in situ keratomileusis.

Fig. 6.24  Widened peripheral gutter in postoperative period is a sign of flap dislocation.

Chapter 6

88

immediate management is required. It is more com-

retroillumination of slit lamp (Fig. 6.25). Often,

monly observed in large diameter and thin flaps.

these occur due to flap dislocation and can cause



reduction of vision. On slit lamp, one may find

Treatment: Flap should be reflected and interface

a widened gutter, suggesting a slippage of flap

examined for cell debris.

in the postoperative period. A cause may not be

Scraping of the interface before repositioning the

identifiable many a time. There is full thickness

flaps. Flap should be repositioned carefully, as improper

flap tenting (due to contracture of stromal col-

placement can lead to astigmatism; in case of com-

lagen at the area where reepithelialization has

plete displacement, suturing is advised.

taken place, Fig. 6.26) involved in these cases.



Apply contact lens to prevent further displacement.

b. Microstriae: These are not visible on retroillumi-

2. Flap striae or folds: Its incidence is approximately

nation and can be detected by uneven pooling of

1.1 to 3.5% in LASIK surgeries. Risk factors for flap

tear film when seen on cobalt filter examination

striae include excessive irrigation under flap, thin

after staining the ocular surface with fluorescein

flaps (≤ 100 µm), deep ablations with flap bed

strips. These indicate fine wrinkles at the level of

mismatch, and flap desiccations. Anterior segment

Bowman’s membrane. They may be left untreated

optical coherence tomography (AS-OCT) imaging is

if optically not significant. Surface treatment by



lubricants should be advised.

a useful ocular investigation to image the flap folds.

Prevention: Flap should be hydrated completely

These are of two types: a. Macrostriae: Appear as multiple, parallel straight

before its placement. Adequate time (30 seconds to

lines (wind-swept sand appearance) seen best on

5 minutes) should be allowed for the flap to adhere

8

while repositioning the flap.

Ensure minimal peripheral gutter at the flap mar-

gins, as this ensures proper positioning of the flap. Treatment: Prompt treatment should be performed, ideally within the first 24 hours after surgery. To treat striae, flap should be lifted, floated with BSS, and gently repositioned. The epithelium at the gutter should be removed before lifting the flap to avoid the development of epithelium ingrowth. Epithelial debridement, followed by placement of BCL, can be attempted in cases of macrostriae to avoid fixed folds.

Fig. 6.25  Macrostriae seen after LASIK are viewed best on retro-illumination of a slit lamp microscope.

Prophylactic steroid and antibiotics drops should

be initiated as these corneas are at high risk of developing infective keratitis and diffuse lamellar

Epithelium

Normal cornea

Stroma

Acute striae

Fig. 6.26  Schematic diagram showing development of macrostriae.

Chronic striae

Laser in Situ Keratomileusis Surgery

89

keratitis (DLK). Few surgeons prefer PTK for treating

particles.8,17,19,20 Identification of DLK in early stages

macrostriae. This option should be timely discussed

prevents scarring and thus improves the visual out-

with the patient.

comes. Its management and prognosis depend upon

3. Flap edema: Postoperative inflammation may cause

the staging of DLK21 as discussed below:

edematous LASIK flap in the postoperative period. An

a. Stage 1 DLK: White, granular cells are seen in

infection must always be ruled out as the cause of

the periphery of the LASIK flap with clear visual

edema. AS-OCT is very useful in serial follow-up of a

axis.8,21 This is the most common presentation of

patient with flap edema. Topical steroids, antibiotics,

DLK on postoperative day 1.

and lubricants should be continued to reduce postoperative inflammation.

b. Stage 2 DLK: The white, granular cells are seen in the center of the flap, now involving even the

4. DLK: It is an inflammatory response in corneal stro-

visual axis. This is frequently seen on postopera-

mal tissue (Fig. 6.27), which later involves the LASIK

tive day 2 to 3. There is movement of inflammatory

interface. It is usually seen in the early postopera-

cells along the path of least resistance, making it

tive period with an incidence of 0.2 to 3.2%. Diffuse

appearance of “shifting sands.”

infiltrate is seen confined to the flap without signs

c. Stage 3 DLK: Clumping of cells is seen along the

of microbial keratitis. It begins at the periphery with

central visual axis. The aggregation of cells can

minimal or no AC reaction.

also be confirmed by confocal microscopy. A



It was first reported by Smith and Maloney, occur-

ring in 13 eyes in 1997 to 98 as a condition occur-

decline of visual acuity and a haze appreciated by the patient is usually reported in stage 3 DLK.

ring in the first few days after surgery with granular,

d. Stage 4 DLK: It is very rarely seen in DLK and it

white, diffuse, culture-negative lamellar keratitis.16

is characterized by permanent scarring, stromal

Other cases were reported with terminologies such

melting, and steep fall in visual acuity.8 There

as “Sands of the Sahara,” “shifting sands,” “non-

is release of collagenases by the inflammatory

specific diffuse intralamellar keratitis,” “post LASIK

cells, which causes volume loss in corneal stroma

interface keratitis.”17, 18

(especially paracentral) and leads to fluid accu-



The cause of DLK is still not very clear. It has been

proposed that DLK is a hypersensitivity reaction to

mulation and bullae formation.8 A hyperopic shift is reported due to paracentral tissue loss.

bacterial cell proteins that accumulate on autoclaved

Management: The stages 1 and 2 show a self-

instruments or oil, wax, metallic, and other foreign

limited course and usually resolve in 7– to 10 days.8 Aggressive topical steroid drops are the mainstay of treatment of DLK (prednisolone acetate 1% administered every hour). Patient is followed up after 24 or 48 hours after initiation of aggressive steroid therapy to monitor response. Lifting of the flap and gentle irrigation of the stromal bed and the undersurface of the cap is considered in stage 3 DLK along with aggressive steroid therapy, while lifting of the flap is avoided in stages 1 and 2.8 However, in stage 4 DLK where permanent scarring has started to take place, lifting flap will add to the stromal loss and cause more damage to the flap and bed because of the presence of collagenases in stage 4 DLK. Besides, a differential diagnosis of infective keratitis should

Fig. 6.27  Diffuse lamellar keratitis at postop day 1, showing “sands of Sahara” appearance.

always be kept in mind and ruled out appropriately by sending microbial cultures from the LASIK flap.

90

Chapter 6

5. Pressure-induced

stromal

keratitis:

Pressure-



Risk factors include:

induced stromal keratitis (PISK) is usually seen in ste-

a. Rocha KM et al reported that ultra-thin LASIK

roid responder population in the early postoperative

flaps (≤ 90 µm) have been associated with more

period, where IOP rises acutely and fluid seeps in the

postoperative haze.25 b. Younger age25: Often, no treatment may be pos-

interface and into the corneal stroma. High-index of suspicion is required to diagnose this complication. If

sible. A short course of steroids may be tried.

steroids are discontinued in time, loss of BCVA may

9. Dry eyes: Incidence is 60 to 70%—The probable causes

be avoided and IOP may be controlled adequately.

of tear film abnormalities after refractive surgeries

Antiglaucoma medications should be initiated to

like LASIK and PRK include:

lower the IOP.

••corneal denervation in the ablation zone (AZ).

6. Steroid-induced glaucoma after LASIK: Steroid-

••damage to the epithelium while operating. ••toxicity from topical eye drops (to drugs/

induced glaucoma is a late complication (usually

preservatives).

occurring after first two weeks) that may occur after

••cytokines and inflammatory mediators released

an uneventful LASIK. It may occur following a routine postoperative regimen or following aggressive

after surgery.

steroid therapy given for DLK, especially in steroid

••poor blink rate.

responder population. Early identification is imper-

••altered corneal contour.

22

••poor quality thin lipid layer.

ative to prevent permanent glaucomatous optic neuropathy and avoid serious visual loss.23 Moreover, intraocular pressure may be recorded falsely low, due to intrastromal and interface fluid and thin cornea postLASIK.23 Management includes stopping steroids and starting antiglaucoma medications. Surgery may be required in very few cases. IOP and topographic changes should be closely monitored in each follow-up while tracking patients of steroidinduced glaucoma. 7. Central toxic keratopathy: It refers to central stromal haze developing soon after LASIK (in first two weeks) due to noninflammatory process. It is a self-limiting condition and may resolve within 18 months. Unlike DLK, CTK is more central in location to start with, and it may cause stromal scarring if persisting for a long time. It is seen more in cases with stromal thinning and/or loss of flap tissue.8 8. Interface haze: It has been reported to have less incidence after LASIK than after surface ablations.6,8 The pathogenesis behind the interface haze has

••alterations in tear evaporation rate and osmolarity.

Diffuse punctate staining of the LASIK flap (Fig. 6.28) is the usually seen clinical sign. Preservative-free lubricants, steroids, temporary collagen plugs, and silicone punctual plugs, may be required to manage postLASIK dry eyes. Refractory cases may require platelet rich plasma (PRP) eye drops.

10. Good Acuity Plus Photosensitivity Syndrome or Transient Light Photosensitivity Syndrome (TLPS): The Good Acuity Plus Photosensitivity (GAPP) syndrome is a transient complication occurring due to use of femtosecond laser. This condition is characterized by good visual acuity but extreme sensitivity to light, with reported incidence of 1.1%.8 Its onset is usually seen 6 to 8 weeks after LASIK and it is often seen to occur bilaterally.8 11. Post LASIK keratitis: Infection after LASIK (Fig. 6.29) is rare but a vision-threatening complication and may develop despite the prophylactic broad-spectrum antibiotics like fluoroquinolones routinely prescribed after LASIK. Its incidence varies from 0.02

been found to be stromal keratocyte activation,

to 1.5%26,27 and has been declining with time due to

Stromal keratocyte activa-

better sterilization practices, use of femtosecond

tion is less in LASIK as compared to surface ablation.

laser that has reduced complications like persistent

Damage to epithelial basement membrane also leads

epithelial defect, and better understanding of anti-

to more keratocyte activation and more haze.

microbial agents. A higher risk of infection is noted

which leads to fibrosis.

24

Laser in Situ Keratomileusis Surgery

Fig. 6.28  Dry eye after LASIK. Abbreviation: LASIK, laserassisted in situ keratomileusis.

91

Fig. 6.29  PostLASIK keratitis. Abbreviation: LASIK, laserassisted in situ keratomileusis.

in cases where postoperative bandage contact lens is

procedures, enhancement surgery33 after LASIK,

used.26 Common organisms causing postLASIK kerati-

microkeratome-assisted flap creation, thin flaps,

tis are Staphylococcus epidermidis, Streptococcus viri-

buttonholing of flap, free cap, etc.

dans, Streptococcus pyogenes, Streptococcus viridans,

If detected early, epithelial ingrowth is seen as

and Staphylococcus aureus.28 Prompt management of

faint gray line, extending less than 2 mm from the

keratitis with topical and systemic antibiotics, early

flap edge which is best detected by direct focal tan-

flap lifting, scrapings, culture, and irrigation with anti-

gential slit lamp illumination. Epithelium advancing

biotics should be done to prevent severe visual loss.27

toward visual axis and decreasing vision may trigger

Uncommon organisms such as atypical mycobacteria

flap melting and can cause irregular astigmatism,

species, fungi, Nocardia, and Acanthamoeba, should also be considered as possible etiological agents.29

Late Postoperative Complications 1. Rainbow Glare: Krueger et al30 first reported this as a new optical effect which was noted with IntraLASIK surgery. Patients report this problem as seeing “rainbow around lights,” appreciated more prominently in a dark environment.31 A higher incidence

halos, blurring of vision, and foreign body sensation.

Probst classification has been described for epithelial ingrowth34: ••Stage 1: Thin ingrowth within 2 mm from flap edge and with no flap changes. ••Stage 2: Thicker ingrowth, at least, 2 mm from flap edge; adjacent flap may show folds. ••Stage 3: Advanced stage of ingrowth > 2 mm from the flap edge; corneal flap margins rolled with

is noted with IntraLase as compared with other laser systems.31, 32 These cases are observed over time and managed conservatively. 2. Epithelial ingrowth: It refers to a growth of island of epithelial cells in the flap–stomal bed interface. These cells may migrate to the visual axis and cause

flap edge melting or erosions.

Treatment: Flap is lifted and stromal bed and flap

undersurface are irrigated and scraped. 3. PostLASIK corneal ectasia and corneal apical scarring (Fig. 6.30): Occurs in preexisting corneal pathol-

visual obscuring. Although mostly asymptomatic,

ogy (keratoconus or forme fruste keratoconus), and

later stages pose a risk of flap melt.

weakening of the residual corneal stromal bed, lead-



Incidence is 1 mm compared with paracentral flattened area. Associated with decreased visual acuity, monocular diplopia, ghost images, and decreased contrast sensitivity. 7. Optical aberrations: Prevalent in some cases even after treatment with smaller AZs; after attempted higher spherical and cylindrical correction, it is exacerbated in dim light.

Fig. 6.30  A case of central corneal scarring due to postLASIK ectasia. Abbreviation: LASIK, laser-assisted in situ keratomileusis

Conclusion The advent of femtosecond lasers has revolutionized the outcomes of refractive surgeries. Although femtosecond



Ectasia leads to permanent weakening of anterior

cornea lamellae.

Histopathology shows intermellar and interfibril-

lar biomechanical slippage. 4. Vitreoretinal complications like retinal detachment, choroidal detachment, and vitreous hemorrhage may be seen late after surgery. 5. Residual refractive error: Incidence: undercorrection and regression: 5 to 51%; Overcorrection is 7%: a. Undercorrection is defined as mean spherical equivalent (MSE) ≥ –1.0 D in the first postoperative week.35 b. Regression is defined as a 0.25 D or greater myopic shift occurring between follow-up visits. c. Overcorrection occurs due to substantial stromal dehydration which develops before laser treatment is initiated, because more stromal tissue is ablated per pulse. It is more common in old people because cornea ablates more rapidly.

Undercorrection occurs more commonly at higher

degree of ametropia because of decreasing predictability and more severity of regression. Treatment: Overcorrection: Noncontact thermokeratoplasty using Ho:YAG laser and hyperopic LASIK are suggested treatment modalities for overcorrected myopic LASIK. Undercorrection: The undercorrections are generally treated between 6 weeks and 3 months after

lasers offer the advantage of precise, regular, and reproducible flap creation in a short time, they also have specific complications, for example, DLK, OBL, PISK, TLSS, VGBT, and rainbow glare, due to intense inflammatory reaction to the delivered laser energy on the corneal surface. Newer models of femtosecond lasers are continuously being developed to eliminate these complications.

References 1. Munnerlyn CR, Koons SJ, Marshall J. Photorefractive keratectomy: a technique for laser refractive surgery. J Cataract Refract Surg 1988;14(1):46–52 2. Stonecipher KG, Kezirian GM. Wavefront-optimized versus wavefront-guided LASIK for myopic astigmatism with the ALLEGRETTO WAVE: three-month results of a prospective FDA trial. J Refract Surg 2008;24(4):S424– S430 3. El Awady HE, Ghanem AA, Saleh SM. Wavefrontoptimized ablation versus topography-guided custom­ ized ablation in myopic LASIK: comparative study of higher order aberrations. Ophthalmic Surg Lasers Imaging 2011;42(4):314–320 4. Alió JL, Belda JI, Osman AA, Shalaby AM. Topographyguided laser in situ keratomileusis (TOPOLINK) to correct irregular astigmatism after previous refractive surgery. J Refract Surg 2003;19(5):516–527 5. Stulting RD, Fant BS, Bond W, et al; T-CAT Study Group. Results of topography-guided laser in situ kerato­ mileusis custom ablation treatment with a refractive excimer laser. J Cataract Refract Surg 2016;42(1):11–18 6. Gulani AC. LASIK complications. Ophthalmology 1999; 106(8):1457–1458

Laser in Situ Keratomileusis Surgery 7. Gimbel HV, Penno EE, van Westenbrugge JA, Ferensowicz M, Furlong MT. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology 1998;105(10):1839–1847, discussion 1847–1848 8. Alio JL, Azar DT, eds. Management of Complications in Refractive Surgery, https://doi.org/10.1007/978-3-31960561-6_8. Springer International Publishing AG; 2018 9. Salomão MQ, Wilson SE. Femtosecond laser in laser in situ keratomileusis. J Cataract Refract Surg 2010;36(6): 1024–1032 10. Shah DN, Melki S. Complications of femtosecondassisted laser in-situ keratomileusis flaps. Semin Ophthalmol 2014;29(5-6):363–375 11. Srinivasan S, Herzig S. Sub-epithelial gas breakthrough during femtosecond laser flap creation for LASIK. Br J Ophthalmol 2007;91(10):1373 12. Rush SW, Cofoid P, Rush RB. Incidence and outcomes of anterior chamber gas bubble during femtosecond flap creation for laser-assisted in situ keratomileusis. J Ophthalmol 2015;2015:542127 13. Lifshitz T, Levy J, Klemperer I, Levinger S. Anterior chamber gas bubbles after corneal flap creation with a femtosecond laser. J Cataract Refract Surg 2005;31(11): 2227–2229 14. Ang M, Mehta JS, Rosman M, et al. Visual outcomes comparison of 2 femtosecond laser platforms for laser in situ keratomileusis. J Cataract Refract Surg 2013;39(11): 1647–1652 15. Vajpayee RB, Balasubramanya R, Rani A, Sharma N, Titiyal JS, Pandey RM. Visual performance after interface haemorrhage during laser in situ keratomileusis. Br J Ophthalmol 2003;87(6):717–719 16. Smith RJ, Maloney RK. Diffuse lamellar keratitis. A new syndrome in lamellar refractive surgery. Ophthalmology 1998;105(9):1721–1726 17. Kaufman SC, Maitchouk DY, Chiou AG, Beuerman RW. Interface inflammation after laser in situ keratomileusis. Sands of the Sahara syndrome. J Cataract Refract Surg 1998;24(12):1589–1593

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21. Linebarger EJ, Hardten DR, Lindstrom RL. Diffuse lamellar kera-titis: recognition and management, chapter 33. In: Buratto L, Brint SF, eds. Custom LASIK Surgical Techniques and Complications. Thorofare, NJ: Slack, Inc.; 2003:745–50 22. Wordinger RJ, Clark AF. Effects of glucocorticoids on the trabecular meshwork: towards a better understanding of glaucoma. Prog Retin Eye Res 1999;18(5):629–667 23. Steroid-induced glaucoma after laser in situ keratomileusis associated with interface fluid. NCBI [Internet]. Available at: https://www.ncbi.nlm.nih.gov/ pubmed/11927421. Accessed December 19, 2019 24. Wound healing after keratorefractive surgery: review of biological and optical considerations. NCBI [Internet]. Available at: https://www.ncbi.nlm.nih.gov/ pubmed/23038040. Accessed December 19, 2019 25. Thresholds for interface haze formation after thin-flap femtosecond laser in situ keratomileusis for myopia. NCBI [Internet]. Available at: https://www.ncbi.nlm. nih.gov/pubmed/19327748. Accessed December 19, 2019 26. Infections after refractive surgery. NCBI [Internet]. Available at: https://www.ncbi.nlm.nih.gov/ pubmed/27138638. Accessed December 19, 2019 27. Llovet F, de Rojas V, Interlandi E, et al. Infectious keratitis in 204 586 LASIK procedures. Ophthalmology 2010;117(2):232–8.e1, 4 28. PubMed entry [Internet]. Available at: http://www.ncbi. nlm.nih.gov/pubmed/20006909. Accessed December 19, 2019 29. Garg P, Chaurasia S, Vaddavalli PK, Muralidhar R, Mittal V, Gopinathan U. Microbial keratitis after LASIK. J Refract Surg 2010;26(3):209–216 30. Krueger RR, Thornton IL, Xu M, Bor Z, van den Berg TJ. Rainbow glare as an optical side effect of IntraLASIK. Ophthalmology 2008;115(7):1187–1195.e1 31. Bamba S, Rocha KM, Ramos-Esteban JC, Krueger RR. Incidence of rainbow glare after laser in situ keratomileusis flap creation with a 60 kHz femtosecond laser. J Cataract Refract Surg 2009;35(6):1082–1086

18. Kaufman SC. Post-LASIK interface keratitis, Sands of the Sahara syndrome, and microkeratome blades. (letter) J Cataract Refract Surg 1999;25(5):603–604

32. Gatinel D, Saad A, Guilbert E, Rouger H. Unilateral rainbow glare after uncomplicated femto-LASIK using the FS-200 femtosecond laser. J Refract Surg 2013;29(7): 498–501

19. Peters NT, Iskander NG, Anderson PEE, Woods DE, Mo RA, Gimbel HV. Diffuse lamellar keratitis: isolation of endotoxin and demonstration of the in ammatory potential in a rabbit model. J Cataract Refract Surg 2001;27:917–923

33. Kamburoğlu G, Ertan A. Epithelial ingrowth after femtosecond laser-assisted in situ keratomileusis. Cornea 2008;27(10):1122–1125 34. Machat JJ, Slate S, Probst SE. The art of LASIK. 2nd ed. Thorofare, NJ: SLACK; 1999:427–33

20. Yuhan KR, Nguyen L, Wachler BS. Role of instrument cleaning and maintenance in the development of diffuse lamellar keratitis. Ophthalmology 2002;109(2):400– 403, discussion 403–404

35. Chayet AS, Assil KK, Montes M, Espinosa-Lagana M Castellanos A, Tsioulias G. Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia. Ophthalmology 1998;105:1194-99.

Chapter 7 Small Incision Lenticular Extraction

Principle and Procedure................................................................. 96 Introduction....................................................................................... 96 Principle.............................................................................................. 96 Precursors to SMILE......................................................................... 96 SMILE Procedure............................................................................... 98 Conclusion........................................................................................105 Complications of SMILE Surgery............................................... 106 Introduction.....................................................................................106 Complications..................................................................................106 Conclusion........................................................................................113 Case-based Approach....................................................................116

7. Small Incision Lenticular Extraction Chirakshi Dhull, Deeksha Rani, Yogita Gupta, and Sudarshan Khokhar

7.1 Principle and Procedure Introduction

vapor) that displaces the surrounding tissue. Contiguous

Refractive lenticule extraction (trademarked name ReLEx)

of a cleavage plane, and a cut of any geometry can be created

using the VisuMax femtosecond system (both Carl Zeiss

within the cornea.5,6 Femtosecond laser is thus used to create

Meditec AG) was developed as a single-laser procedure

lenticules within the cornea, which can then be dissected by

where an excimer laser is not required for lenticule creation

various maneuvers to achieve the desired refractive-error

or removal.

1–3

Initially, a flap was created similar to laser-

application of a series of laser pulses leads to the formation

correction.

assisted in situ keratomileusis (LASIK) using a femtosecond laser, with additional lenticule cut to create a stromal lenticule.1 Later, instead of flap, a small incision was made for removal of lenticule to avoid flap-related complications Small Incision Lenticule Extraction (SMILE) surgery.4

Principle SMILE uses femtosecond laser in refractive-error correction by extraction of a thin lenticule from cornea. The femtosecond is a solid-state Nd: YAG photodisruptive laser that has a wavelength of 1053 nm (near-infrared range). Laser power is defined as the energy delivered per unit time. Hence, decreasing the pulse threshold to femtosecond (10-15) level increases the power delivered per unit time and decreases fluence (damage threshold of tissue). This is the advantage of femtosecond lasers over nanosecond lasers.

Photodisruption

Precursors to SMILE In 1996, picosecond lasers were used to generate intrastromal lenticules. Lenticule was removed manually after lifting the flap, thereby avoiding the need for an excimer laser. (2) Refractive Lenticule Extraction (ReLEx) was first described by Sekundo et al 2008 as an alternative to femtosecond LASIK. Two types of techniques have been described for femtosecond assisted lenticule extraction: ReLEx FLEx and ReLex SMILE (Fig. 7.1a, b). In ReLEx FLEx, femtosecond laser disrupts tissue centripetally first to create the posterior cut of lenticule. This is then followed by side cuts and centrifugal creation of anterior surface of the lenticule. Side cut is then created circumferentially with the spared area of the hinge. The flap is lifted and lenticule is extracted manually using forceps. The flap is then repositioned.1,3,7

Femtosecond laser-firing causes the generation of a high-

In ReLEx SMILE, the creation of the posterior cut of the

intensity electric field, leading to the formation of a mixture

lenticule, side cut and cap cut is followed by side cut crea-

of free electrons and ions, known as the plasma state. The

tion.5,6 Lenticule is dissected using dissector through the side

plasma expands with supersonic velocity and the vaporized

cut and then removed. A flap is not created, and hence, it is

tissue forms a cavitation bubble (constituting of CO2 and H2O

devoid of flap-related complications.

Small Incision Lenticular Extraction

1

2

3

a 1 SMILE incision (2–2.5 mm)

2

3

Incision

b Fig. 7.1  (a) ReLEx FLEx, and (b) ReLex SMILE

4

97

98

Chapter 7

SMILE Procedure

coupled to the patient’s cornea and suction is initiated after

Machine and Laser Settings

the eye and ensures alignment of the eye with the laser-exit

VisuMax femtosecond LASER system (Carl Zeiss Meditec,

laser unit to the exit aperture.

Jena, Germany) is currently the only platform approved to use femtosecond laser for the creation of intrastromal refractive lenticule (Fig. 7.2).

Functional Components of the Machine The machine consists of a computer unit, laser arm, vacuum system, microscope, patient support system, and a foot switch. The illumination system used is of three types: diffuse, slit, and infrared. A treatment pack is used as an interface between the patient and the machine. This patient interface consists of a single-use disposable contact lens with attached tubing. The treatment is available in three different sizes depending upon the white-to-white measurement of the patient.

Computer Unit There is an inbuilt graphic user interface. Patient details and

pressing the central button on the joystick. This stabilizes aperture. The laser arm directs the laser radiation from the

Microscope A modified Zeiss OPMi pico operating microscope with LED illumination is used. It consists of an eyepiece, a magnification changer, an interpupillary distance changer, and a fine focus adjustment. The microscope is moved between the treatment position for docking and laser delivery and the observation position for lenticular extraction and dissection.

Illumination System In the observation system, the patient’s eye is illuminated by the light below the microscope. In the treatment position, the eye is illuminated by LED lights focusing on the circumference of the contact lens of the patient interface.

Slit Illumination System

detailed parameters of treatment and planning are entered

There is a knurled knob on the microscope. On rotating this

into the system. There are two output screens—one shows

knob, diffuse illumination is turned off and slit illumina-

the treatment planning and live monitoring of the ongoing

tion is turned on. The size of the slit is 0.5 mm × 12 mm.

treatment, the other displays the progress of the treatment.

It allows on-table assessment of the interface at the end of

Laser Arm and Vacuum System Adequate vacuum creation is necessary for the application of the laser. The glass contact lens of the patient interface is

the surgery.

Infrared Illumination It aids in centering the contact lens during docking.

Patient Support System There are three positions: The starting position (when the patient lies down on the system), the treatment position (when the laser is delivered), and the observation position (lenticule dissection and extraction is done). The bed can be adjusted to these positions using an analog joystick. The patient should be lying down comfortably on the system with head resting on a comfortable headrest.

Treatment Pack It provides an interface between the patient’s eye and laser

Fig. 7.2  VisuMax femtosecond system (Carl Zeiss Meditec AG).

delivery system. It consists of a glass contact lens attached to a tubing, filter, and a vacuum connection. Carl Zeiss VisuMax

Small Incision Lenticular Extraction

99

laser system uses a curved applanation surface to cause

Though usually kept at 15 microns, it can be increased to 25

docking, and hence, causes laser delivery for flap creation.

to 30 microns in cases with low spherical refractive errors

In vivo studies using real-time intraocular pressure (IOP)

where thinner lenticules are expected.

cannulation have shown that lower pressures are generated with curved applanation systems such as the VisuMax compared to flat applanation systems used for LASIK flap creation.8,9 The suction pressure generated by the VisuMax laser system is ~35 mm Hg.10 The treatment pack is available in three different sizes: small, medium, and large. Appropriate size is chosen according to the white-to-white corneal diameter of the patient.

Total Lenticule Thickness It is the sum of minimum lenticule thickness and amount of tissue that will be removed as per the amount of refractive error (calculated using Munnerlyn Formula).

Cap Parameters (Fig. 7.3b) Cap Thickness Usually kept at 120 microns, it can vary from 100 microns to 160 microns depending upon the refractive error.10

Laser Parameters The VisuMax laser system has an inbuilt application for FLEx, flap circle, keratoplasty, intracorneal ring segment incisions, and ReLEx SMILE. Appropriate entry of flap and lenticule parameters is necessary for effective and successful treat-

Cap Diameter It is 0.5–1 mm oversized from the optic zone diameter. It depends on treatment pack size, cap thickness, radius of corneal curvature, and side cut angle.10

ment. We study the parameters under two headings: lentic-

Cap Side Cut

ule parameters and flap parameters.

It is usually placed between 90° and 180° depending upon the surgeon’s ease. The incision width may vary from 2 mm

Lenticule Parameters (Fig. 7.3a)

to 5 mm. Side cut angle, size, and location can be seen on the treatment console (Fig. 7.4).

Optical Zone The optical zone is defined as the part of the corneal ablation area that receives the treatment that is designed to produce the full intended refractive correction.

11

The size

of the optical zone should be larger than the mesopic pupil

Steps of Surgery Patient Selection and Patient Counseling

size. Complaints of blur, glare, and halos have been reported

The FDA has approved SMILE surgery for myopia of up to

with small optical zones, especially when the scotopic pupil

–10 D and astigmatism of –0.75 to –3 D, with stable refraction

dilates beyond the surgical optical zone. It is usually set at

for the last 1 year. As of now, SMILE has not been approved

6 or 6.5 mm (range 5–8 mm) for an average-sized cornea

by the FDA for the treatment of hyperopia. It should be

of 10–12 mm. A larger optical zone leads to greater tissue

avoided in patients with ectatic disorders of cornea such as

ablation and hence lesser residual stromal thickness. The

keratoconus and pellucid marginal degeneration.

eye cannot be treated if the residual stromal thickness is less than 250 microns.

Transition Zone It depends on manifest refraction, being 0 mm for purely spherical errors and 0.10 mm for cylindrical errors.

Patients should be counseled about the procedure. Topical anesthetic 0.5% proparacaine is instilled into the eyes. The patient is explained that he/she has to fix on the green light and that he/she will feel some pressure once the docking is complete. Then the machine says ‘suction on’. After that, the patient has to stay still and not follow or search for the

Lenticule Diameter

green light. A proper preoperative counseling can reduce the

It is the sum of the optical zone and transition zone.

incidence of suction loss.12

Minimum Thickness of Lenticule

Patient Positioning

It refers to the thickness of the peripheral edge of the len-

The bed is positioned perpendicular so that the patient can

ticule and is equal to the height of the lenticule side cut.

lie down on it comfortably with the head resting on the

100 Chapter 7

a

b Fig. 7.3  (a) Lenticule data parameters for sample patient. (b) Cap and small incision parameters for sample patient.

Small Incision Lenticular Extraction 101 headrest. The bed is then pushed back to the treatment position. The eye is cleaned and draped, and a speculum is inserted to keep the lids apart. A wet Merocel sponge is used to moisten the surface of the cornea and clean any lipids or dirt or cotton fibers, as the presence of these can lead to the formation of black spots, thereby leading to inefficient laser delivery.

Docking The joystick is moved to position the patient’s head directly under the VisuMax laser delivery system. After selecting the patient and choosing settings in the machine (Figs. 7.5, 7.6, 7.7), the patient’s head is then moved up so that the contact

Fig. 7.4  Small incision size and position shown in relation to the lenticule and cap side cut.

Fig. 7.5  Graphic representation of lenticule parameters.

lens of the treatment pack acurvates the corneal surface. Suction is then turned on. Centration can be confirmed

102 Chapter 7

Fig. 7.6  Energy and laser parameters in expert mode in SMILE surgery.

Fig. 7.7  After completion of parameter check, system suggests intiation of treatment steps.

Small Incision Lenticular Extraction 103 using infrared light. The curved applanating surface of the

The total duration of femtosecond laser delivery is ~30–35

contact lens causes soft docking, causing a suction pressure

seconds and is independent of the magnitude of refractive

of ~35 mm Hg. It raises intraocular pressure to ~30–80 mm

error. At the end of this procedure, the suction is automati-

Hg, which allows intraocular blood circulation and vision of

cally stopped and the patient support system is moved to an

the patient to be maintained during the procedure. Manual

observation position using the joystick.

7

compression with cyclotorsion can be done in cases with significant astigmatism.13

Lenticule Dissection and Extraction

Femtosecond Laser Application

The hooked end of the lamellar dissector is used to open the

The parameters for cap and lenticule are entered in the

using the hooked end of the lamellar dissector to create an

machine settings and the laser is started.

anterior pocket. The dissectioned plane is then opened up

Four cleavage planes are created in the following sequence (Fig. 7.8): 1. Lenticule cut: The posterior surface of lenticule is cut in an outside-to-inside centripetal pattern. First, the posterior cut is made with the femtosecond laser. This will allow the creation of more anterior cleavage plane. 2. Lenticule side cut: A circumferential vertical cut is made, the thickness of which is equal to the minimum lenticule thickness. 3. Cap cut: A cap cut is created from center to periphery (centrifugal pattern) by an ‘inside out’ pattern of laser delivery. The cap size is 0.5 to 1 mm larger than the lenticule diameter. 4. Cap side cut: A cap side cut provides passage for the introduction of the instrument for lenticule dissec-

cap side cut. First, the anterior dissection plane is delineated

using the lamellar dissector. This is followed by dissection of the posterior dissection plane. The anterior dissection plane is always dissected first for smooth lenticule extraction. This is because an inadvertent posterior dissection of the lenticule cut will lead to adhesions between the anterior lenticule surface and the cap, leading to difficulty in lenticular extraction. The lenticule edge is then identified and the lenticule is extracted through the cap side cut using a lamellar dissector. The lenticule is then examined for its completeness. If complete, the interface is irrigated with a balanced salt solution, and a Merocel sponge is used to uniformly spread the cap. Stepwise surgical treatment is shown in Fig. 7.9. Various signs have been described to identify the dissection plane.

White Ring Sign

tion and extraction. The usual length is 2–5 mm and

A white ring is seen due to light reflection from the lentic-

the angle is 110 degrees.

ule side cut. The presence of the instrument anterior to this white ring indicates the anterior plane of dissection, while the instrument posterior to this white ring is indicative of dissection in the posterior dissection plane.14,15

Shimmer Sign The shimmer sign occurs due to the reflection of light across the edge of lamellar dissector and is seen in cases where posterior dissection is done inadvertently before anterior plane dissection.16

Meniscus Sign The double ring sign is observed at the beginning after the creation of a cap cut and a lenticule side cut, where the inner ring corresponds to the lenticule cut and the outer ring to

Fig. 7.8  Graphic representation of lenticule parameters.

the cap cut. The cap side cut is opened in its entire length.

104 Chapter 7

a

b

c

d

e

f

g

h

Fig. 7.9 Stepwise SMILE surgery. (a) Docking of eye while maintaining centration; (b) Posterior lenticule cut out-to-in; (c) After peripheral vertical cut, anterior cap cut is made in-to-out; (d) Side cuts are made; (e) Anterior and posterior cuts are identified and separated; (f) Lenticule is dissected; (g) Lenticule is extracted from the incision and checked for completeness; (h) After completion of surgery.

The anterior lamellar channel is created on the left-most

Various techniques of lenticule dissection have been

part of the cap side cut and the posterior lamellar channel

described by Jacob et al, Zhao et al, Kim et al, and Hamid

is created in the rightmost part of the cap side cut. During

et al.

the creation of the posterior lamellar channel, the lenticule

Jacob et al advised anterior lamellar dissection followed

is pushed away from the surgeon to create a gap between

by central posterior lamellar dissection, leaving a thin

the inner ring and the lenticule edge. This gap was observed

peripheral rim undissected. The lenticule side cut and the

as a meniscus sign. This technique prevents lenticule

thin peripheral dissection rim are dissected in a sequen-

misdissection.17

tial segmental manner. The lenticule is dissected in short,

Small Incision Lenticular Extraction 105 circumferential strokes to ensure a smooth, complete len-

The intrastromal pocket is then washed with a balanced

ticule dissection. This technique is especially described for

salt solution. Then antibiotic drops are instilled and the

thin lenticules.

speculum is removed. Postoperatively, topical antibiotics,

18

Zhao et al described a continuous curvilinear lenticulorhexis technique in which lenticule is extracted continuously in a circumferential manner without causing lamellar separation. However, this technique may lead to ripping of lenticule and retained lenticule in cases of thin lenticules. It is contraindicated in cases with opaque bubble layer formation.19 Kim et al introduced a Chung’s swing technique in which posterior lenticule dissection is followed by the identification of the lenticule edge by swinging the spatula tip at the left end of the incision and separating the lenticule into a fan shape. The lenticule is grasped with McPherson forceps and pushed toward the center of the cornea and pulled to remove the lenticule in a clockwise direction.20 Hamed et al described push-up and push-down tech-

steroids, and lubricants are prescribed.

Outcomes The safety, efficacy, predictability, and long-term stability of the procedure have been examined in various studies. The efficacy of SMILE in achieving >20/20 vision ranges from 62 to 92% and >20/40 vision from 95 to 100%.3,4,6,22–25 Visual recovery time may be associated with a learning curve.10 Satisfactory visual quality with lower higher-order aberrations and spherical aberrations, minimal haze, and good corneal clarity is achieved in most cases. A comparison with other corneal refractive procedures is discussed in detail in chapter 8.

niques with a special instrument with Y-shaped tip.21 In the push-up technique, the Y-shaped instrument is inserted into the cap side cut to push up the lenticule edge to facilitate

Conclusion

visualization. In the push-down technique, the instrument

SMILE provides a reliable and predictable alternative to

is engaged at the cut edge and the lenticule is pushed down

excimer-based refractive surgery, including LASIK and sur-

to create an anterior dissection plane. This technique is also

face ablation. The surgery has a learning curve, and a stepwise

helpful to break anterior lenticular adhesions.

approach to learning can aid in achieving optimal outcomes.

21

106 Chapter 7

7.2 Complications of SMILE Surgery Introduction

Complications

Small Incision Lenticule Extraction (SMILE) is a commonly

Complications in SMILE surgery are of two kinds (Table 7.1):

used modality for the treatment of myopia without corneal

1. Intraoperative complications.

flap production. Performed since 2011, this surgery involves

2. Postoperative complications.

removing the corneal stroma lenticule from a minimized incision.3,4 Various studies have shown that there is lesser impairment of the biomechanical effects and a greater pres-

Intraoperative Complications

ervation of corneal nerves when a patient is treated with

SMILE is associated with its own unique set of intraop-

SMILE instead of LASIK. This can reduce the incidence of

erative complications, which generally reduce with surgeon

dry eyes.

experience.32 Here are the description, cause, prevention,

26–29

On the one hand, elimination of the corneal flap is associated with no flap-related complications and greater biomechanical stability.26 On the other, it is more surgically challenging than LASIK, and difficulties encountered during the procedure may result in suboptimal visual and anatomical outcomes.30,31 Complications associated with SMILE surgery may be due to preoperative, intraoperative, or postoperative factors.

Preoperative Risk Factors Preoperative risk factors for postoperative corneal ectasia

and management of these complications (Table 7.2).

Suction Loss Suction loss remains a challenging situation in SMILE surgery.32–35 0.2–2.1%.

Incidence

33,35–38

of

suction

loss

ranges

from

Suction pressure is significantly lower

with the VisuMax platform for SMILE compared to microkerat­omes or other platforms used for LASIK surgery.

Table 7.1  Complications of SMILE surgery Intraoperative

Suction loss 0.2–2.1% Opaque bubble layer 0–51%

could be improper preoperative planning. Caution needs to

Black spots 11–14%

be applied in preoperative planning. High-risk patients with

Epithelial defect 2–41%

the following characteristics should be excluded: ••Myopia > –10 D.

Incorrect tissue plane identification/difficult extraction 1.9–9%

••Astigmatism >3 D (FDA approval is up to 3 D).

Cap tear & incision/side cut tears 0.3–16%

••Thin pachymetry   34) and residual stromal bed thickness (RSBT)

PE

+8

+6

(> 250). Hence, safety is reduced.

D value

0.35

0.56

Specular count, cells/mm2

3430

3068

vide better biomechanical strength, but there are high

WTW, mm

11.8

11.7

chances of corneal haze and suboptimal outcome.

••Surface ablation can preserve addition tissue and pro-

Endo ACD, mm

2.97

2.76

••Phakic intracular lens (implantable collamer lens (ICL)

Calculated RSBT, μm

380

324

cannot be performed since endo anterior chamber

Calculated Post K, D

40.2

35.8

depth (ACD) < 2.8 mm.

PTA, in %

33.9%

42%

Small Incision Lenticular Extraction 125

a

b Fig. 7.26 (a, b) OD and OS corneal topography, showing normal cornea.

126 Chapter 7

a

b Fig. 7.27  (a, b) One year postoperative corneal topo­graphy maps of Case 1 for OD and OS respectively. Note cornea has become flatter OS>>OD in the center but there is no significant change in posterior corneal curvature.

Chapter 8 Comparison amongst Corneal Refractive Surgery Introduction.....................................................................................128 Surgical Technique.........................................................................128 Outcomes Following Corneal Refractive Surgery................. 130 Conclusion........................................................................................132

Comparison amongst Corneal 8. Refractive Surgery Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

Introduction

is ablated from the exposed bed under the lifted flap using

Laser in situ keratomileusis (LASIK) has been the most com-

curve are less as compared with SMILE.

monly performed corneal refractive surgery in the past decade. It has been proved as a safe and predictable technique for correction of myopia.1 Although safe, flap-related complications and postoperative dry eye form major problems with this surgery.2,3 Surface ablation has become popular in the recent years as an alternative to LASIK surgery. Studies have shown

an excimer laser (193 nm). Surgical difficulty and learning Surface ablation involves removal of epithelium by excimer laser, alcohol, or manual debridement with brush (Fig. 8.1b). This is followed by corneal ablation similar to LASIK procedure. Bandage contact lens (BCL) is put at the end to facilitate epithelial regrowth. It is fairly easy to perform and has a short learning curve. SMILE is a new procedure which uses only femtosecond

improved safety and biomechanical strength with this

laser. It involves the creation of an intrastromal lenticule

surgery, especially in patients with thin corneas and high

between two photo disruption planes. The first step is

This can be attributed to thicker residual stromal

docking with precise centration and then suction is initi-

bed compared with cap or flap-based surgery. In surface

ated. Patient cooperation is of utmost importance. Then, a

ablation, after removing the corneal epithelium, an excimer

posterior lenticule is cut, followed by vertical edge incision;

laser is used to ablate the corneal stroma. Surface ablation

then, the cap cut and finally one or two side cuts. We use

does not create a flap and hence there are no potential flap-

two side cuts, where the second side cut is used as rescue

related complications.

and is opened only in case of adhesions or difficult dissec-

myopia.

4–6

Small incision lenticule extraction (SMILE) is a newer modality for treatment of myopia and myopic astigmatism without corneal flap production since 2011.7 The corneal stroma lenticule is removed from a small incision; this reduces the complications of corneal flap and dry eye.7,8 It has been shown in various studies that there is less impairment of the biomechanical effects and more corneal nerves are preserved when treated with SMILE compared with LASIK, which can reduce the incidence of dry eye.9–11

tion. The anterior and the posterior layer are dissected and mechanically removed through a small corneal incision tunnel. It is surgically challenging and there is a significant learning curve.

Treatment Approval and Customization LASIK and surface ablation are approved for myopia, hyperopia, and astigmatism, while SMILE is approved for only myopia and myopic astigmatism12 (Table 8.1). Values for LASIK/photorefractive keratectomy (PRK) vary according to

Surgical Technique

the machine for excimer treatment. LASIK/surface ablation

LASIK procedure is performed in two steps. The flap is cre-

sion correction can be used and where wavefront and/or

ated (typically 100–120 mm of cornea) by either a micro-

topographic data can be incorporated in the pattern of tissue

keratome or a femtosecond laser (1056 nm) (Fig. 8.1a). The

ablation. There is an eye tracker to take into account eye

second part is the refractive correction; the stromal tissue

movements.13,14 These are not available with SMILE surgery.

may be customized where pupil centroid shift and cyclotor-

Comparison amongst Corneal Refractive Surgery 129

a

b

Smile incision (2-2.5 mm)

Incision

c Fig. 8.1  Surgical steps of corneal refractive surgery. (a) Microkeratome assisted LASIK; (b) Surface ablation; (c) SMILE. Abbreviation: LASIK, Laser assisted in-situ keratomileusis; SMILE, Small incision lenticule extraction.

130 Chapter 8

Table 8.1  FDA approval for corneal refractive surgery: approximate summary; values vary according to the machine for excimer laser Refractive error

LASIK

Surface ablation (PRK/LASEK/Epi LASIK)

SMILE

Myopia

Up to − 10 D

Up to − 12 Diopter

Up to −10 Diopter

Hyperopia

Up to + 4 Diopter

Up to + 4 Diopter

Not approved

Astigmatism

Up to 4 Diopter

Up to 4 Diopter

−0.75 to −3 Diopter

Intraoperative Difficulty and Complications

Corneal Aberrations

LASIK and surface ablation have the potential benefit of vast

Surface ablation and LASIK have shown similar higher order

surgical and research experience. The surgical technique is

aberrations (HOA) in most studies.20,21 It has been observed

easy and possesses high-reproducibility. Major complica-

that HOA and spherical aberrations are greater in FS-LASIK

tions in LASIK are flap-related, while surface ablation dif-

than in SMILE surgery. No statistically significant difference

ficulties concern corneal haze, which can be overcome by SMILE. SMILE comes with its own set of complications. It has a learning curve. Difficulty in lenticule dissection, incorrect tissue planes, and suction loss are major challenges. If suction loss occurs during lenticule cut after 10 percent of cut, it has to be converted to femtosecond (FS)-LASIK. At any other time, procedure can be continued with set guidelines.

has been seen in either the horizontal coma or the vertical coma between the two groups in most studies.15,23–25 The reason for this is not clear. There is no transition zone for the SMILE procedure which may help reduce spherical aberration. Another possible explanation is that in SMILE, the lenticule is created with femtosecond laser scanning at two depths of the stroma, which may avoid the ablation efficiency reduction in the periphery and therefore induce less increase in corneal asphericity, whereas for an excimer

Outcomes Following Corneal Refractive Surgery

laser, the ablation efficiency reduction in the periphery of cornea would increase corneal asphericity even when the exact Munnerlyn ablation profile is used. Epithelial remodeling may also play a role.

Visual Outcome Most studies have demonstrated no significant difference between LASIK and SMILE uncorrected visual acuity (UCVA) of 20/20 or better in low to moderate myopia.11,15–17 Although faster visual recovery is noted with LASIK, postoperative mean refractive spherical equivalent and postoperative refraction within ± 1.0 D of the target refraction have been found similar between the two procedures.

11,15–17

Surface

ablation has been shown to have relatively inferior visual outcome as compared with LASIK in high-refractive error due to corneal haze.

18,19

In cases of low to moderate myopia,

both procedures have similar visual outcomes in most studies.20,21 Application of mitomycin C in PRK helps in

Contrast Sensitivity The contrast sensitivity usually recovers to the preoperative level later in the SMILE group than that in FS-LASIK. It has also been shown that contrast sensitivity was better in the SMILE group than in FS-LASIK, particularly at higher spatial frequencies.11,15,26 The decrease in contrast sensitivity is usually associated with increase in HOAs. In surface ablation, contrast sensitivity is affected almost similar to LASIK patients and mean score is lower than SMILE.27,28

Biomechanical Properties

reducing corneal haze and improving visual outcomes, espe-

Corneal refractive surgery involves removal or ablation of

cially in high myopia.

corneal stoma which invariably reduces the tensile strength

22

Comparison amongst Corneal Refractive Surgery 131 of cornea.29,30 Alteration of biomechanical properties of cornea may increase risk of development of postsurgery

Other Factors

ectasia. Postsurgery ectasia has been reported following all

SMILE offers reduced dependence on environmental factors

three procedures, although they may affect corneal biome-

that may influence excimer stromal ablation, such as laser

chanics differently.

fluence variability and stromal hydration. Moreover, there

In SMILE, anterior cornea undergoes less transverse separation, since side cut is 2 to 2.5 mm (35–45°) in most cases, while in LASIK, there is flap formation which cuts cornea by almost 360° (Fig. 8.1). This reduces the strength of the flap in LASIK significantly, while in SMILE cap, it does not completely separate from the cornea, providing strength to the

is probably reduced possibility for operating room airborne foreign-body interface contamination. However, temperature and humidity are to be controlled for LASIK, surface ablation, and SMILE machine for optimal functioning. Patient comfort during and immediately after surgery is much better in SMILE (SMILE > LASIK > Surface ablation).

residual tissue theoretically. Anterior one-third of the cornea is significantly stronger than the posterior two-third cornea. Preservation of an identical amount of anterior stroma will provide double the strength of posterior cornea of similar depth. In SMILE, since the anterior stroma is preserved and the tissue is removed from more posterior stromal layers than in LASIK, anterior stroma continues to provide strength to the cornea after surgery.29,30,31 According to a meta-analysis performed by Guo et al,32 using corneal hysteresis (CH) and corneal resistance factor (CRF) value, measured with ocular response analyzer (ORA) for corneal biomechanical strength, strength was preserved

Conclusion Corneal refractive procedures have performed well in studies in measures of safety, efficacy, and predictability for myopia correction. SMILE, a relatively newer and evolving procedure, has been so far employed for the correction of myopia and/or myopic astigmatism. All have their own advantages and disadvantages as summarized in Table 8.2. Proper patient selection and counseling can help in optimal use of these entities.

significantly better after SMILE than either FS-LASIK or LASIK.32 The difference was greater after postoperative 12 months, suggesting better wound healing after SMILE. The CH/CRF value was greater after PRK/LASIK compared

SMILE INCISION

LASIK FLAP

with SMILE, although the difference did not reach a significant mark in the meta-analysis.32

Dry Eyes

LIMBUS

SMILE is associated with lower induction of dry eye15,17,26,33 as very few corneal nerves are cut as compared with LASIK and surface ablation, where an almost 360-degree cut is made (Fig. 8.2).

Fig. 8.2  Incision in SMILE versus LASIK. Abbreviations: LASIK, laser-assisted in-situ keratomileusis; SMILE, small incision lenticule extraction.

132 Chapter 8

Table 8.2  Comparison amongst corneal refractive surgery Surface ablation

LASIK

SMILE

Advantages

Greater biomechanical strength, more tissue preserved No flap-based complications No suction, no IOP rise during procedure Treatment of hyperopia is possible Wavefront- and topographyguided treatment available Easy to perform

Faster visual recovery, wow factor Greater range of refractive correction, especially astigmatic correction Treatment of hyperopia is possible Wavefront- and topography-guided treatment available Tried and tested over years Relatively surgical ease as compared with SMILE

Reduced dry eye No flap-based complications Better patient comfort May have lesser tensile strength reduction, so may reduce incidence of ectasia Lower HOA and spherical aberration Better contrast sensitivity Lower dependence on environmental factors

Disadvantages

Corneal haze Longer recovery period Greater patient discomfort till epithelial healing May give suboptimal outcomes in high-refractive error

Flap-based complications More dry eyes More IOP built at the time of suction More HOA, spherical aberration; can be reduced with topographyguided or Custom-Q LASIK Lesser biomechanical strength

Longer learning curve Requires high-degree of patient cooperation Difficult dissection, retained lenticule, and suction loss may cause suboptimal outcome Treatment for hyperopia not yet approved No eye tracker, custom or topographyguided treatment not possible

Abbreviations: IOP, intraocular pressure; HOA, higher order aberrations; SMILE, small incision lenticule extraction.

References 1. Vryghem JC, Devogelaere T, Stodulka P. Efficacy, safety, and flap dimensions of a new femtosecond laser for laser in situ keratomileusis. J Cataract Refract Surg 2010;36(3):442–448 2. Golas L, Manche EE. Dry eye after laser in situ keratomileusis with femtosecond laser and mechanical keratome. J Cataract Refract Surg 2011;37(8):1476– 1480 3. dos Santos AM, Torricelli AA, Marino GK, et al. Femtosecond laser-assisted LASIK flap complications. J Refract Surg 2016;32(1):52–59 4. Munnerlyn CR, Koons SJ, Marshall J. Photorefractive keratectomy: a technique for laser refractive surgery. J Cataract Refract Surg 1988;14(1):46–52 5. Vestergaard AH. Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy and a prospective study of refractive lenticule extraction. Acta Ophthalmol 2014;92 Thesis 2:1–21 6. Sánchez P, Moutsouris K, Pandolfi A. Biomechanical and optical behavior of human corneas before and after photorefractive keratectomy. J Cataract Refract Surg 2014;40(6):905–917 7. Sekundo W, Kunert KS, Blum M. Small incision corneal refractive surgery using the small incision lenticule

extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study. Br J Ophthalmol 2011;95(3): 335–339 8. Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: All-in-one femtosecond laser refractive surgery. J Cataract Refract Surg 2011;37(1): 127–137 9. Wei S, Wang Y. Comparison of corneal sensitivity between FS-LASIK and femtosecond lenticule extraction (ReLEx flex) or small-incision lenticule extraction (ReLEx smile) for myopic eyes. Graefes Arch Clin Exp Ophthalmol 2013;251(6):1645–1654 10. Wu D, Wang Y, Zhang L, Wei S, Tang X. Corneal biomechanical effects: small-incision lenticule extrac­ tion versus femtosecond laser-assisted laser in situ keratomileusis. J Cataract Refract Surg 2014;40(6): 954–962 11. Liu M, Chen Y, Wang D, et al. Clinical outcomes after SMILE and femtosecond laser-assisted LASIK for myopia and myopic astigmatism: a prospective randomized comparative study. Cornea 2016;35(2):210–216 12. Food and Drug Administration, USA. Available at: https://www.fda.gov/medical-devices. Accessed December 19, 2019 13. Amigó A, Bonaque-González S, Guerras-Valera E. Control of induced spherical aberration in moderate

Comparison amongst Corneal Refractive Surgery 133 hyperopic LASIK by customizing corneal asphericity. J Refract Surg 2015;31(12):802–806

on corneal wavefront aberration in the treatment of myopia. Res Adv Ophtalmol 2013;33(7):651–655

14. Goyal JL, Garg A, Arora R, Jain P, Goel Y. Comparative evaluation of higher-order aberrations and corneal asphericity between wavefront-guided and aspheric LASIK for myopia. J Refract Surg 2014;30(11):777–784

24. Li K, Wang YL, Zhang CW, Wu J, Huang HY. Comparison of SMILE surgery and femotosecond laser LASIK for myopia. Chin J Ophthalmol Vis Sci 2014;16(8):478–482

15. Lin F, Xu Y, Yang Y. Comparison of the visual results after SMILE and femtosecond laser-assisted LASIK for myopia. J Refract Surg 2014;30(4):248–254

25. Ye M, Liao R, Liu C. Comparison of higher-order aberrations changes in anterior corneal surface after four refractive surgeries in myopia. Acta Universitatis Medicinalis Anhui 2007; 8(3): 177–180

16. Chan TC, Ng AL, Cheng GP, et al. Vector analysis of astigmatic correction after small-incision lenticule extraction and femtosecond-assisted LASIK for low to moderate myopic astigmatism. Br J Ophthalmol 2015

26. Ganesh S, Gupta R. Comparison of visual and refractive outcomes following femtosecond laser-assisted lasik with smile in patients with myopia or myopic astig­ matism. J Refract Surg 2014;30(9):590–596

17. Denoyer A, Landman E, Trinh L, Faure JF, Auclin F, Baudouin C. Dry eye disease after refractive surgery: comparative outcomes of small incision lenticule extraction versus LASIK. Ophthalmology 2015;122(4): 669–676

27. Ganesh S, Brar S, Patel U. Comparison of ReLEx SMILE and PRK in terms of visual and refractive outcomes for the correction of low myopia. Int Ophthalmol 2017;27:1–8

18. Alió JL, Ortiz D, Muftuoglu O, Garcia MJ. Ten years after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for moderate to high myopia (control-matched study). Br J Ophthalmol 2009;93(10):1313–1318 19. Rosman M, Alió JL, Ortiz D, Perez-Santonja JJ. Comparison of LASIK and photorefractive keratectomy for myopia from –10.00 to –18.00 diopters 10 years after surgery. J Refract Surg 2010;26(3):168–176 20. Hatch BB, Moshirfar M, Ollerton AJ, Sikder S, Mifflin MD. A prospective, contralateral comparison of photo­ refractive keratectomy (PRK) versus thin-flap LASIK: assessment of visual function. Clin Ophthalmol 2011;5:451–457 21. Slade SG, Durrie DS, Binder PS. A prospective, contralateral eye study comparing thin-flap LASIK (sub-Bowman keratomileusis) with photorefractive keratectomy. Ophthalmology 2009;116(6):1075–1082 22. Fazel F, Roshani L, Rezaei L. Two-step versus single application of mitomycin-C in photorefractive kerat­ ectomy for high myopia. J Ophthalmic Vis Res 2012; 7(1):17–23 23. Hu YK, Li WJ, Gao XW, Dong J, Guo YL. Effects of femtosecond laser small incision lenticule extraction

28. Hashemi H, Ghaffari R, Miraftab M, Asgari S. Femtosecond laser-assisted LASIK versus PRK for high myopia: comparison of 18-month visual acuity and quality. Int Ophthalmol 2017;37(4):995–1001 29. Peyman M, Tai LY, Khaw KW, Ng CM, Win MM, Subrayan V. Accutome PachPen handheld ultrasonic pachymeter: intraobserver repeatability and interobserver repro­ ducibility by personnel of different training grades. Int Ophthalmol 2015;35(5):651–655 30. Søndergaard AP, Ivarsen A, Hjortdal J. Corneal resistance to shear force after UVA-riboflavin cross-linking. Invest Ophthalmol Vis Sci 2013;54(7):5059–5069 31. Sinha Roy A, Dupps WJ Jr, Roberts CJ. Comparison of biomechanical effects of small-incision lenticule extraction and laser in situ keratomileusis: finiteelement analysis. J Cataract Refract Surg 2014;40(6): 971–980 32. Guo H, Hosseini-Moghaddam SM, Hodge W. Corneal biomechanical properties after SMILE versus FLEX, LASIK, LASEK, or PRK: a systematic review and metaanalysis. BMC Ophthalmol 2019;19(1):167 33. Li M, Zhao J, Shen Y, et al. Comparison of dry eye and corneal sensitivity between small incision lenticule extraction and femtosecond LASIK for myopia. PLoS One 2013;8(10):e77797

Chapter 9 Enhancements after Refractive Surgery

Residual Refractive Error: Overview and Causes................. 136 Indications and Considerations for Refractive Surgery Enhancement..................................................................136 Retreatment after Phakic Intraocular Lens Insertion......... 137 Retreatment in Surface Ablation Procedures........................ 137 Retreatment in LASIK....................................................................138 Retreatment in Small-incision Lenticule Extraction .......... 138 Conclusion........................................................................................140 Case-based Approach....................................................................144

9. Enhancements after Refractive Surgery Yogita Gupta, Monikha T., Chirakshi Dhull, and Sudarshan Khokhar

Residual Refractive Error: Overview and Causes

(LASIK)/photorefractive keratectomy (PRK) include high initial correction,2 astigmatism (≥1 D), and hyperopic corrections.3 Retreatment rates are generally not influenced

Refractive surgery to correct refractive error is performed

by age, corneal characteristics, or environmental factors.3

on otherwise healthy individuals. However, despite the

Hersh et al reported higher retreatment rates after LASIK

best efforts, a refractive surgeon may face such dissatisfied

in cases with higher initial corrections and older age, and

patients in their clinic who do not achieve the desired level

also reported that manual lifting of LASIK flap can be done

of uncorrected visual acuity (UCVA). Although refractive sur-

up to 3 years after LASIK.2 Regression of the initial surgery

geries are now well-established methods to treat refractive

effect has been postulated to occur due to compensatory

errors, retreatment may be necessary in cases of overcor-

epithelial hyperplasia (CEH).4 Early postoperative regres-

rection or undercorrection to improve patient satisfaction.1

sion has been noted to stabilize between 3 to 6 months

Preoperative counseling is important to make sure that the

after LASIK.4

patient has no unrealistic expectations. An informed consent should be taken after counseling the patient about potential risks and benefits and the possibility of a residual refractive error and possibly a need for enhancement procedures. Retreatment rates in laser refractive surgery range from

A recent paper entitled “Symptoms and Satisfaction of Patients in the Patient-Reported Outcomes with LASIK (PROWL) Studies” was conducted to examine the visual symptoms and patient satisfaction post LASIK surgery. The PROWL-1 study was a single-center study in military

in various studies. Researchers have identified a

population, while PROWL-2 was a multicenter study in the

few causes of residual refractive error (Table 9.1). Risk factors

general population. They found that 1-4% of participants

for retreatment after laser-assisted in situ keratomileusis

had dissatisfaction with vision.5 These studies found that at

5–10.5%

2,3

3 months after LASIK, 99% of patients in PROWL-1 and 96% Table 9.1  Causes of post–corneal refractive surgery residual error I. Early

Incorrect data entry

in PROWL-2 had binocular UCVA of 20/20 or better.5 The different causes of residual refractive error have been listed in Table 9.1.

Under or overcorrection Decentered ablation Inadequate laser fluence Inexperienced surgeon II. Late

Indications and Considerations for Refractive Surgery Enhancement

Regression of refractive error after use of excimer laser due to CEH

If satisfactory UCVA is not achieved, the refractive surgeon

Unstable refractive error (e.g., progression of axial myopia)

the patient’s needs and expectations are realistic. Extreme

should consider the option of enhancement, provided that

Lenticular myopia

caution should be taken while planning a retreatment and

Fluctuation of refractive error due to pregnancy or lactation (in reproductive-aged females) or endocrine disorders

ments taken after surgery, with a detailed workup to rule

each case should be planned based on the new measureout any contraindication for a repeat refractive surgery.

Enhancements after Refractive Surgery 137 The following considerations should be kept in mind

against the benefits. Unless the patient would greatly bene­ fit from surgery, one should be cautious before planning a

before planning any enhancement procedure: 1. The patient and surgeon must have realistic

repeat surgery. Best-corrected visual acuity (BCVA) should be reassessed carefully, ruling out all possible causes of

expectations. 2. The residual refractive error must be stable, as

diminution of vision. An informed consent must be taken for

documented by stable refraction on repeat measure-

refractive surgery enhancement. A few patients with mild

ments, for at least 3 months.6

refractive error may still be satisfied and be able to manage

3. Sufficient residual stromal bed thickness (RSBT) should be present if further laser ablation is planned on the cornea with/without flap lift. The RSBT may be calculated based on central corneal thickness readings, for which anterior segment optical coherence tomography (ASOCT) may be reliable. Following parameters should be met if the surgeon is planning 7

any LASIK procedure:

their daily tasks despite the refractive error. A refractive surgeon may choose from the various available options for a repeat refractive surgery: either a procedure to lift the original flap or surface ablation (with or without use of mitomycin-C) or ablation on the undersurface of flap stroma.1,9,12–14 These can be wavefront-guided or nonguided ablations.15 Cutting out a new flap can often result in the intersection of surgical planes in corneal stroma

a. RSBT ≥ 250 µm. b. Percentage tissue ablation (PTA) < 40%. c. Posterior corneal elevation < 40 µm.

8

4. There should be no contraindication for a repeat refractive surgery as basic elements will remain the same as those while planning primary surgery. Corneal topography and pachymetry should be repeated again before the secondary procedure. 5. Data entered and all patient records must have been reviewed for correctness before planning enhancements. 6. All other causes of residual refractive error should be ruled out carefully. These include post-Lasik ectasia, keratoconus, progression of axial myopia, presence of lenticular myopia, lenticular opacities, surgically induced astigmatism (SIA), induced irregular astigmatism, and accommodation (that may lead to error in measurement of refractive error if not performed under cycloplegic effect). The indications for an enhancement after refractive surgery9–11 include: 1. Amount of residual refractive error is ±0.5 to 0.75 D

and displacement of stromal tissue, causing loss of BCVA and irregular astigmatism.6 In case a flap-lifting procedure is planned, the risk of epithelium ingrowth must be considered and epithelium should be preserved carefully.

Retreatment after Phakic Intraocular Lens Insertion Unsatisfactory results due to residual refractive error after an implantable Collamer lens (ICL) implantation must prompt the surgeon to look for other causes of poor outcomes, including the following: 1. Discrepancy in the ICL sizing (calculated from a nomogram based on white-to-white diameter and anterior chamber depth). 2. Axis of alignment, in case of toric ICL. 3. Surgically induced astigmatism (SIA). 4. Incorrect data entry. 5. Incorrect label on lens or implantation of wrong lens. Further discussion on retreatment options after ICL will be discussed in Chapter 10.

or more or if regression is ±0.5 D or more, which is stable (change of no more than 0.5 D) for a minimum of 3 months, and 2. Patient dissatisfaction.

Retreatment in Surface Ablation Procedures

Besides, if a patient’s activities of daily living are affected

Retreatment after photorefractive keratectomy (PRK) has

by the postoperative residual refractive error, a retreat-

been reported as a safe and effective technique to treat

ment should be considered. With any enhancement surgery,

regression or undercorrections.16 Gartry DS et al17 recom-

there exists a risk of complications, which must be weighed

mended a deliberate overcorrection (by 50%) to reduce

138 Chapter 9 chances of further regression in cases showing regression

PRK may be unacceptable for some patients. The risk of these

after PRK to up to –3.5 D. They recommended great caution

complications should be discussed with patients in detail.

for post-PRK cases with regression beyond –3.5 D of myopia and significant anterior haze due to risk of further regression and haze.17

Retreatment in Small-incision Lenticule Extraction

Retreatment in LASIK

Retreatment rates after small incision lenticule extraction

Retreatment rates after LASIK have been reported to be rang-

While planning an enhancement after SMILE, complete

ing from 4 to 28%.2,18–21 The available options for enhance-

examination of the existing incisions is recommended using

ment after LASIK are:

anterior segment OCT imaging.

(SMILE) have been reported to be ~4% by Reinstein et al.22

1. Re-lifting the original flap and retreating with excimer laser.

VisuMax® Circle Treatment (Fig. 9.1) (Carl Zeiss, Meditec, Jena, Germany)

2. Surface ablation techniques. 3. Repeat LASIK (secondary LASIK). These options are also useful in cases of LASIKs aborted due to intraoperative complications. Laser-assisted in Situ Keratomileusis retreatment surgery has been reported to have had good outcomes, with UCVA of 20/20 or better in 59% and 20/40 or better in 92% of eyes.

18

A retrospective

study compared the lifting of the flap and recutting of the flap for LASIK enhancement. The authors reported that recutting of LASIK flaps should be avoided— unless other alternative options are unavailable—because of the risk of significant loss of BCVA.

13

However, Durrie et al

21

reported

no loss of BCVA after lifting of flap for LASIK retreatment. Hersh et al2 concluded that lifting of LASIK flap can be considered safe up to 3 years after primary LASIK surgery using the manual technique. While planning a repeat LASIK, the

The VisuMax® Circle Treatment has been designed to help refractive surgeons convert SMILE cap into a LASIK flap by application of femtosecond laser incisions. The following retreatment options have been described after SMILE: 1. VisuMax® Circle, followed by excimer ablation (S+C).23 2. Secondary SMILE surgery anterior to the initial surgery (S+SE).23 3. Surface ablation to treat the residual error (S+P).23 Irregular astigmatism after SMILE can be treated with topography-guided PRK.24 Riau et al23 studied the in vivo tissue responses in rabbit eyes after various SMILE

surgeon should plan the depth, thickness, and diameter of the new flap, considering the parameters of initial surgery.

1

Anterior segment optical coherence tomography (OCT) is

2

useful to locate the depth of initial incisions. Possible complications of lifting the flap include difficulty

3

4

in flap-lifting, epithelial ingrowth, flap striae, diffuse lamellar keratitis, flap-related complications, infections, and postLASIK ectasia. Retreatment by PRK eliminates flap-related complications and reduces the risk of post-LASIK ectasia. The PRK is a suitable retreatment option for thin corneas. However, it may have to be combined with the use of mitomycin-C to reduce postoperative stromal haze. It may be done after epithelial removal with 20% alcohol, or mechanical scraping, or with phototherapeutic keratectomy (PTK). Postoperative pain and visual acuity fluctuation after

Fig. 9.1  Schematic diagram of VisuMax® Circle enhance­ ment (Carl Zeiss, Meditec, Jena, Germany) showing creation of (1) flap side cut and (2) lamellar ring or cap extension (3) initial cap cut; (4) initial SMILE incision with VisuMax® circle enhancement after SMILE surgery. Additionally, a junction cut connects 2 and 3 in a few circle patterns.

Enhancements after Refractive Surgery 139 retreatment strategies reported that S+C induced more cor-

Orientation mark refers to the cap and incision parameters

neal haze and corneal edema, S+P was simple technique that

used in initial SMILE surgery (Fig 9.2) and are explained

maintained corneal integrity, while S+SE offered the advan-

below:

tage of minimal inflammation and cell death, though it carried a risk of difficult lenticular extraction in thin lenticules. VisuMax Circle has the following procedure: ®

1. Using VisuMax®, a junction cut (J) (Fig. 9.1) is created to connect new incisions to the existing one. 2. A lamellar ring-shaped extension (L) is made from the existing cap cut. 3. A side cut is created which has the same parameters as that of a standard LASIK flap. 4. Incisions are carefully dissected manually.

••Diameter = initial SMILE cap diameter in mm ••Depth = initial SMILE cap thickness in mm ••Position = initial SMILE incision position in degrees ••Angle = angle of initial SMILE incision There are four modes in Circle treatment planning (Fig. 9.3) based on the location of the new junction cut and lamellar ring. These have been studied experimentally in rabbit eyes.25 Pattern A (side cut only) creates only a perpendicular circular side cut to join the existing SMILE cap cut (can be used in large diameter caps).25 However, pat-

5. Flap is lifted to perform a standard LASIK procedure.

terns B, C, and D would design a lamellar ring cut posterior,

The corneal keratometric and pachymetric parameters

anterior, and at the same depth, respectively, to the existing

are entered using the VisuMax application (Fig. 9.2). The

cap incision, along with a junction cut that would join this

new incisions are designed such that the new hinge of the

lamellar ring to the existing cap cut.23,25 All these incisions

flap should not be at the position of the initial incision.

should lie outside the optical zone, i.e., within the clearance

®

Fig. 9.2  Patient eye parameters, treat­ ment pack size, and orientation mark entered using VisuMax® application.

140 Chapter 9

Fig. 9.3 VisuMax® Circle enhancement option plan­ ning application: choosing Circle pattern, selecting lamellar ring and flap side cut parameters and junction cut parameters (for B, C, and D patterns only).

Table 9.2  Lamellar and side cut parameters recommended for VisuMax® Circle enhancement Parameter

Description

Range

Lamellar Outer diameter and side cut

▪▪Refers to the outer diameter of the lamellar ring in mm ▪▪Would be the same as posterior diameter of side cut

5 mm to 9.7 mm

Depth

▪▪Depth of lamellar ring and side cut ▪▪Same as cap thickness

80 to 240 µm

Side cut angle

▪▪Same as for LASIK flap

45° to 135°

Hinge position

▪▪Same as for LASIK flap ▪▪Should not be the same as that of initial SMILE incision

0° to 359° (usually kept superior, i.e., 90°)

Hinge width/angle

Same as for LASIK flap

30° to 330°

Diameter

Diameter of junction cut Same as inner diameter of lamellar ring

4 to 9.6 mm (recommended as diameter of initial optical zone, i.e., 6 to 6.5 mm)

Upper depth

Depth of the anterior end of the junction cut

60 to 240 µm (Recommended: 10 µm less than the initial cap thickness)

Lower depth

Depth of the posterior end of junction cut

80 to 260 µm (Recommended: 10 µm more than the initial cap thickness

Junction

zone. Pattern D (a lamellar ring adjacent to the cap cut) has

steps as those for SMILE and flap creation in the VisuMax®

been studied to provide the best results.25 Parameters for the

laser system.

lamellar ring, side cut, and junction cuts are entered sub-

Complications of Circle treatment include suction loss,

sequently (Table 9.2). Treatment is reviewed on the video

difficult dissection, corneal tears and difficulty in lifting flap.

screen. The rest of the treatment procedure involves similar

Proper documentation (Fig. 9.4) must be done.

Enhancements after Refractive Surgery 141

Fig. 9.4  Documentation of surgical para­meters used for VisuMax® Circle treatment for a patient, done 3 months post-SMILE surgery.

142 Chapter 9

Conclusion The selection of refractive surgery option for enhancement after initial surgery is a major challenge for a refractive surgeon. If at all any intervention is planned, factors like surgical difficulty level, reported postoperative visual outcomes, possible complications, and patient preferences must be kept in mind to arrive at a suitable decision. The option of wavefront-guided enhancements is also becoming popular with many refractive surgeons and may hold good prospects in the future.

References 1. Schallhorn SC, Venter JA, Hannan SJ, Hettinger KA, Teenan D. Flap lift and photorefractive keratectomy enhancements after primary laser in situ keratomileusis using a wavefront-guided ablation profile: Refractive and visual outcomes. J Cataract Refract Surg 2015; 41(11):2501–2512 2. Hersh PS, Fry KL, Bishop DS. Incidence and associations of retreatment after LASIK. Ophthalmology 2003; 110(4):748–754 3. Randleman JB, White AJ Jr, Lynn MJ, Hu MH, Stulting RD. Incidence, outcomes, and risk factors for retreatment after wavefront-optimized ablations with PRK and LASIK. J Refract Surg 2009;25(3):273–276 4. Chayet AS, Assil KK, Montes M, Espinosa-Lagana M, Castellanos A, Tsioulias G. Regression and its mechan­ isms after laser in situ keratomileusis in moderate and high myopia. Ophthalmology 1998;105(7):1194–1199 5. Eydelman M, Hilmantel G, Tarver ME, et al. Symptoms and Satisfaction of Patients in the Patient-Reported Outcomes With Laser In Situ Keratomileusis (PROWL) Studies. JAMA Ophthalmol 2017;135(1):13–22 6. American Academy of Ophthalmology Refractive Management/Intervention Panel. Preferred Practice Pattern Guidelines. Refractive Errors & Refractive Surgery PPP. San Francisco, CA: American Academy of Ophthalmology; 2017. [Internet]. Available from: https://www.aaojournal.org/article/S01616420(17)33028-2/pdf 7. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology 2008;115(1):37–50 8. Rao SN, Raviv T, Majmudar PA, Epstein RJ. Role of Orbscan II in screening keratoconus suspects before refractive corneal surgery. Ophthalmology 2002;109(9):1642– 1646

9. Parikh NB. Management of residual refractive error after laser in situ keratomileusis and photorefractive kerat­ ectomy. Curr Opin Ophthalmol 2014;25(4):275–280 10. Broderick KM, Sia RK, Ryan DS, et al. Wavefrontoptimized surface retreatments of refractive error following previous laser refractive surgery: a retro­ spective study. Eye Vis (Lond) 2016;3:3 https://www. ncbi.nlm.nih.gov/pmc/articles/PMC4750286/ [Internet] 11. Brahma A, McGhee CN, Craig JP, et al. Safety and predictability of laser in situ keratomileusis enhance­ ment by flap reelevation in high myopia. J Cataract Refract Surg 2001;27(4):593–603 12. Domniz Y, Comaish IF, Lawless MA, Rogers CM, Sutton GL. Recutting the cornea versus lifting the flap: comparison of two enhancement techniques following laser in situ keratomileusis. J Refract Surg 2001;17(5):505–510 13. Rubinfeld RS, Hardten DR, Donnenfeld ED, et al. To lift or recut: changing trends in LASIK enhancement. J Cataract Refract Surg 2003;29(12):2306–2317 14. Maldonado MJ. Undersurface ablation of the flap for laser in situ keratomileusis retreatment. Ophthalmology 2002;109(8):1453–1464 15. PubMed entry [Internet]. [cited 2019 Sep 17]. Available from: http://www.ncbi.nlm.nih.gov/pubmed/26703501 16. Montard M, Fau JL, Perone JM. [Retreatment after PRK for low and medium myopia. Results and study of con­ trast sensitivity]. J Fr Ophtalmol 2000;23(4):333–339 17. Gartry DS, Larkin DF, Hill AR, Ficker LA, Steele AD. Retreatment for significant regression after excimer laser photorefractive keratectomy. A prospective, randomized, masked trial. Ophthalmology 1998;105(1): 131–141 18. Netto MV, Wilson SE. Flap lift for LASIK retreatment in eyes with myopia. Ophthalmology 2004;111(7):1362– 1367 19. Febbraro JL, Buzard KA, Friedlander MH. Reoperations after myopic laser in situ keratomileusis. J Cataract Refract Surg 2000;26(1):41–48 20. Alió JL, Muftuoglu O, Ortiz D, et al. Ten-year follow-up of laser in situ keratomileusis for high myopia. Am J Ophthalmol 2008;145(1):55–64 21. Durrie DS, Aziz AA. Lift-flap retreatment after laser in situ keratomileusis. J Refract Surg 1999;15(2):150–153 22. Reinstein DZ, Carp GI, Archer TJ, Gobbe M. Outcomes of small incision lenticule extraction (SMILE) in low myopia. J Refract Surg 2014;30(12):812–818 23. Riau AK, Liu Y-C, Lim CHL, et al. Retreatment strategies following small incision lenticule extraction (SMILE): in vivo tissue responses. PLoS One 2017;12(7):e0180941

Enhancements after Refractive Surgery 143 24. Ivarsen A, Hjortdal JØ. Topography-guided photo­ refractive keratectomy for irregular astigmatism after small incision lenticule extraction. J Refract Surg 2014;30(6):429–432

25. Riau AK, Ang HP, Lwin NC, Chaurasia SS, Tan DT, Mehta JS. Comparison of four different VisuMax circle patterns for flap creation after small incision lenticule extraction. J Refract Surg 2013;29(4):236–244

144 Chapter 9

Case-based Approach Case 1

a residual error of –0.25 DS/–0.25 DC × 150°, with BCVA of

A 23-year-old male presented to us with a history of using

eyes and the patient counseled to wait for stabilization of

spectacles for the last 8 years, with a power of –9.5 DS OU,

residual refractive error.

OU 6/9. Ocular surface treatment was given for both the

stable for the past 2 years. He wanted to undergo refractive surgery to get rid of his glasses. Preoperative parameters were as given in Table 9.3 and Fig. 9.5a, b. Both eye SMILE surgery was performed for him (Figs. 9.6 and 9.7). Settings for SMILE cap were: 100 µm thickness and 7.3 mm diameter, with SMILE lenticule of 6.3 mm diameter with 0.1 mm transition zone.

At 3 months post-SMILE, left eye had UCVA 6/9 and the right eye was noted to have UCVA 6/12, BCVA 6/9 and a residual error of OD –1 DS was noted with parameters as shown in Fig. 9.8 and Table 9.4. The patient was keen on right eye enhancement surgery. A surface ablation was planned for him in OD (Fig. 9.9). A final postop of OU 6/9 was achieved in this patient after OD PRK (Table 9.5).

At 1 week post-SMILE, UCVA of OD 6/12 was noted with a residual error of –0.75 DS/–1.75 DC × 50° and OS 6/9 with

Table 9.3  Preoperative parameters of Case 1 with OU –9.5 D of myopia, in which SMILE surgery was planned in both the eyes

Table 9.4  Parameters at 3 months of OD after 3 months of SMILE surgery Parameter

OD

Parameter

OD

OS

UCVA

6/12p

UCVA

2/60

2/60

BCVA

6/9

BCVA

6/9

6/9

PMT post cycloplegic refraction

–1 DS

PMT post cycloplegic refraction

–9.50 DS

–9.50 DS

K1, D

39.0

K1, D

44.6

44.6

K2, D

39.8

K2, D

44.9

45.1

Steep axis, degrees

100.5

Steep axis, degrees

121.8

33.9

K max, D

46.1

K max, D

45.3

45.4

Thinnest pachymetry, μm

467

Thinnest pachymetry, μm

576

587

Posterior elevation, μm

+8

Pupil diameter, mm

2.80

3.14

D value

4.60

Posterior elevation, μm

+8

7

D value

0.88

0.43

White to white (WTW) diameter, mm

11.7

11.6

Anterior chamber depth (ACD), mm

3.96

3.77

Table 9.5  Final postop visual acuity of Case 1 after OD PRK Parameter

OD

UCVA 1 day post PRK

6/9

UCVA 3 months post PRK

6/9 6/9 6/9

Calculated RSBT, μm

336

333

UCVA 6 months post PRK

Specular count, cells/mm2

2880

2448

UCVA 1 year post PRK

Enhancements after Refractive Surgery 145

a

b Fig. 9.5  (a, b) Preoperative topography map of Case 1 (a) OD; (b) OS.

146 Chapter 9

Fig. 9.6  SMILE surgery of Case 1: intraoperative parameters used.

Fig. 9.7  SMILE surgery settings used for Case 1.

Enhancements after Refractive Surgery 147

Fig. 9.8  Postop topographic map of Case 1, three months after SMILE surgery of right eye.

148 Chapter 9

Fig. 9.9  PRK surgery for Case 1, done for enhancement to treat residual –1 D myopia OD after SMILE surgery.

Enhancements after Refractive Surgery 149

Case 2

Table 9.6  Preoperative parameters for Case 2

A 25-year-old female who wanted to get rid of her glasses

Parameter

OD

OS

presented to us. All refractive investigations were performed

UCVA

3/60

3/60

(Table 9.6) and the patient was found to be fit to undergo

BCVA

6/6

6/6

both-eyes LASIK surgery. Intraoperatively, OD LASIK was

PMT post cycloplegic refraction

–6 DS/ –0.75 DC @30

–7.25 DS/ –0.5 DC @70

K1, D

43.7

43.7

K2, D

44.6

44.7

Steep axis, degrees

114.1

73.3

K max, D

45.1

45.0

Thinnest pachymetry, μm

557

558

Pupil diameter

3.95

3.28

Posterior elevation, μm

+8

7

D value

0.70

1.04

WTW, mm

12

11.9

ACD, mm

3.91

3.92

Calculated RSBT, μm

307

293

PTA, %

36.804%

39.202%

Specular count, cells/mm2

3497

3279

uneventful, while OS LASIK, a vertical gas breakthrough (a known complication of femto-LASIK) was noted (Fig. 9.10) and the procedure was aborted. Enhancement surgery was planned. LASIK flap thickness for repeat surgery was different (140 µm versus 100 µm) from that kept for the first surgery (Figs. 9.11 and 9.12). A good BCVA of OU 6/6 was achieved at 6 months after surgery (Fig 9.13).

Fig. 9.10  While performing OS LASIK surgery of Case 2, intraoperatively vertical gas breakthrough was noted and surgery was aborted.

150 Chapter 9

Fig. 9.11  Parameters used for OS Re-LASIK surgery in Case 2, successfully performed three months after primary surgery. A different flap diameter and a different flap size can be created to avoid dissection in the plane of flap creation used in the first surgery.

Enhancements after Refractive Surgery 151

Fig. 9.12  Parameters used for repeat LASIK surgery in Case 2.

152 Chapter 9

Enhancements after Refractive Surgery 153

Healed LASIK incision

Fig. 9.13  Postoperative clinical photograph taken at 3 months after re-LASIK surgery. A UCVA of 6/6 was achieved in the treated eye.

154 Chapter 9

Case 3

surgery was then planned. VisuMax® Circle treatment was

A 27-year-old male with a myopia of OU –3.5 DS presented

the already created lenticule was extracted (Fig. 9.16a–d)

to us and wanted to get rid of his glasses. All refractive inves-

and flap reposited. A good BCVA of OU 6/6 was achieved at

tigations were performed (Table 9.7) and the patient was

3, 6 and 12 months after surgery (Fig. 9.17).

used to create a flap side-cut only (pattern A) (Fig. 9.15) and

found to be fit to undergo both-eyes SMILE surgery. During SMILE surgery for the right eye, suction loss was noted after the step of cap cut creation (Fig. 9.14). A SMILE enhancement

Fig. 9.14  Suction loss during SMILE surgery OD noted after the creation of a cap cut.

Table 9.7  Preoperative parameters for Case 3. SMILE surgery was planned Parameter

OD

OS

UCVA

6/60

6/60

BCVA

6/6p

6/6P

PMT post cycloplegic refraction

–3.50 DS

–3.50 DS

K1, D

45.3

45

K2, D

46.1

45.6

Steep axis, degrees

78.8

104.5

K max, D

46.1

46.3

Thinnest pachymetry, μm

563

559

Pupil diameter

2.94

2.92

Posterior elevation, μm

+6

+8

D value

0.49

0.87

WTW, mm

11.6

11.5

ACD, mm

3.83

3.73

Calculated RSBT, μm

393

389

27.087%

18.389%

3238

3282

PTA, % Specular count, cells/mm

2

Enhancements after Refractive Surgery 155

Fig. 9.15 VisuMax® Circle treatment parameters used for Case 3.

156 Chapter 9

a

b

c

d

Fig. 9.16  (a–d) VisuMax® Circle treatment was used for Case 3 (pattern A, side cut only) to convert SMILE to flap surgery.

Fig. 9.17  A good visual outcome was noted at 6 months after surgery, with an unaided visual acuity of 6/6 in the treated eye.

Chapter 10 Phakic Intraocular Lens

Introduction.....................................................................................158 History...............................................................................................158 Types of Phakic IOL........................................................................159 Patient Selection.............................................................................161 Sizing of Implantable Collamer Lens........................................ 161 Surgical Technique of Implantable Collamer Lens/Toric ICL................................................................162 Outcomes..........................................................................................163 Complications..................................................................................164 Conclusion........................................................................................164 Case-based Approach....................................................................167

10. Phakic Intraocular Lens Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

Introduction

surgery may result in improvement of best corrected visual acuity in patients with very high refractive error.

Corneal refractive surgery has been accepted widely over the past 20 years for the correction of myopia, hyperopia, and astigmatism in adults with stable refraction.1,2 It has rapidly evolved into laser-based procedures using excimer or femtosecond laser. Although it can be used to treat a variety of refractive errors, there is a limitation regarding the range of myopia and astigmatism it can correct refractive error based on corneal thickness and range of hyperopia based on thickness as well as postoperative keratometry.1–3 Lens-based surgery is recommended in cases where cornea-based procedures cannot be performed or may give suboptimal outcome.4 Phakic intraocular lens (pIOL) and refractive lens exchange (RLE) are included in lens-based procedures.4–6 RLE has two major disadvantages compared to pIOL: loss of accommodation and a greater risk of retinal detachment.7 Hence, pIOLs are the first-line lens-based procedure in such patients.

Understanding Surgically induced Magnification in Refractive Surgery In myopia, there is magnification of image/ visual acuity chart when refractive correction is performed at corneal plane instead of spectacle plane. Since corneal refractive surgery corrects refractive error in corneal plane and phakic IOL correct it closer to the nodal point; there is a magnification of image which can be expected.8

History Anterior Chamber pIOL Strampelli performed the first pIOL implantation in 1953, with minus-power anterior chamber pIOL (AC pIOL).10 Subsequently, Barraquer published the encouraging result of a large sample of pIOL implantation in 1959.11 Apple et al reported multiple complications related to pIOLs such as chronic endothelial cell loss, iris atrophy, pupillary block, peripheral anterior synechiae, and uveitis glaucoma hyphema syndrome (UGH).12 Currently used AC pIOLs include Kelman Duet and Acrysof IOL (foldable).

Iris-fixated Anterior Chamber IOL Iris claw or “lobster claw” IOL was designed and first introduced in 1978 by Worst. It was a single-piece poly (methyl methacrylate) (PMMA) IOL, which was enclaved to the midperipheral iris. Although initially it was used in cataract surgery or secondary IOL implantation, Fechner and Worst used this IOL for correction of myopia in 1978.13 The risk of endothelial cell loss is seen with this pIOL as well. Currently used iris-claw pIOLs include rigid Artisan (Ophtec BV) or Verisyse (Abbott Medical Optics, Inc.) and foldable Artiflex (Ophtec BV).

In a logMAR chart, the increase in magnification between lines is a factor of 1.2589. Log of 1.2589 is equal to 0.1 log unit, which means with each line there is 0.1 log unit change

Posterior Chamber pIOL

of acuity. This means for each 25 % magnification induced by

In 1986, Fyodorov developed a “collar-button” or “mush-

surgery, there should be one-line increase in visual acuity

room” posterior chamber phakic IOL (PC pIOL).14 This was

of the patient.9 With this principle, corneal or lens-based

a silicone pIOL with an optic of 3.2 mm, with a concave

Phakic Intraocular Lens 159 anterior surface and an overall diameter of 8.0 mm. This was

separated in case of change in power or problem with sizing

soon abandoned due to complications such as endothelial

respectively.

touch, decentration, pupillary block, and cataract formation.15 The implantable Collamer lens (ICL) (Staar Surgical Co.) and the phakic refractive lens (PRL) (Carl Zeiss Meditec) are the two currently available PC pIOLs.

Acrysof AC pIOL It is a hydrophobic acrylic angle-fixated AC pIOL (Fig. 10.1b). Details are given in Table 10.1. An anterior chamber depth (ACD) ≥ 2.7 mm is required for this IOL.

Types of Phakic IOL

Artisan/Verisyse pIOL

Types of various phakic IOLs are given in Table 10.1. In this chapter, implantable Collamer Lens (ICL) will be discussed in-depth as it is the most widely used pIOL. It is considered one of the safest pIOLs. Other pIOLs may also be used by some surgeons or in some circumstances. We will briefly discuss them.

It is an iris-claw single-piece rigid PMMA pIOL (Fig. 10.2a). The material used is Perspex CQ-UV. Details about sizing and available power are given in Table 10.1. The haptics of the IOL are fixed to midperipheral iris stroma, with a concave surface towards the iris with a vault of 0.87 mm. This is done to maintain adequate distance from the anterior capsule of the lens to provide aqueous clearance. The recommended

Kelman Duet AC pIOL

ACD is ≥ 2.7 mm. Another advantage is the sizing of the IOL is fixed (8.5 mm) and there is no need to plan sizing

It is a tripod PMMA haptic and silicon optic IOL (Fig. 10.1a).

per patient as needed in angle or sulcus-fixated IOL. It has

First, the haptics are inserted in the eye manually. Optic is

shown good and predictable visual outcomes in studies.16,17

then injected using the injecting system and fixated using

It was approved by the FDA in 2006. The major complication

Sinskey hooks. The optic and the haptics can be exchanged

is endothelial cell loss noted between 3 and 7 years.17

Table 10.1  Types of phakic IOLs Type Anterior chamber pIOL

Subtype (trade name)

Material

Available power (Dioptres)

Optic size (mm)

Overall size (mm)

FDA approval

Kelman Duet

Silicone optic, PMMA haptic

–8 to –20

5.5

12.5 to 13.5

No

Acrysof

Hydrophobic acrylic

–6 to –16.5

6

12.5 to 14

No

PMMA

Myopia –3 to –15.5 (6 mm optic) –3 to –23.5 (5 mm optic); Hyperopia +1 to +12 (5 mm optic); Astigmatism +12 to –23.5 spherical (5 mm optic) with toricity of +1 to +7

5/6

8.5

Yes

Veriflex/ Artiflex

Polysiloxane optic, PMMA haptics

Myopia –2 to –14.5 Astigmatism –1 to –13.5 spherical with toricity of –1 to –5

6

8.5

No

ICL

Collamer

Myopia –3 to –23; Hyperopia +3 to +22; Astigmatism +1 to +6

4.65 to 5.5

11.5, 12.1, 12.6, 13.2, 13.7

Yes

PRL

Silicone

Myopia –3 to –20; Hyperopia +3 to +15

4.5 to 5.5

10.8, 11.3, 10.6

No

Iris-fixated pIOL Verisyse/ Artisan

Posterior chamber pIOL

160 Chapter 10

Side-up indicator

Fig. 10.1  Anterior chamber Phakic IOL (AC pIOL) (a) Kelman Duet AC pIOL; (b) Acrysof AC pIOL Acrys of Cachet.

6.0 mm Optic

Bridge

a

Four-point fixation haptics

b

Fig. 10.2  Iris fixated pIOL (a) Artisan Iris-claw pIOL; (b) Artiflex Iris-claw pIOL.

a

b

The artiflex phakic lens (Ophtec) is the only IOL that does not rotate.

Artiflex/Veriflex pIOL

Implantable Collamer Lens

It is a foldable hydrophobic polysiloxane iris-claw pIOL18

Implantable Collamer lens (ICL) is the most commonly used

(Fig. 10.2b). Details about sizing and available power are

pIOL, with significantly fewer complications. It is made of

given in Table 10.1.

a unique material that is known as Collamer (0.2% collagen

Phakic Intraocular Lens 161 and 60% hydroxyethyl methacrylate copolymer). This is a biocompatible material and helps in the deposition of a layer

Patient Selection

of fibronectin on the IOL surface. This layer inhibits aque-

Inclusion and exclusion criteria are given in Table 10.2.

ous protein binding and the IOL is virtually invisible to the

These can be used while planning of patients suitable for

immune system.

pIOL surgery. Details of this are given in the chapter 4 on

19

The older model’s version 2 (V2) and V3 had a higher incidence of cataract formation.20 The V4 model improved on this by providing an additional 0.13 to 0.21 mm anterior vault.18 This allows free change of fluids and nutrients to lens and helps in reducing cataract formation. But this was not sufficient, hence peripheral laser iridotomy (PI) is recommended. In myopic eyes, Shimuzu et al21 introduced a central KS-AquaPORT of 350 μm. This model is called V4c. This promotes natural aqueous outflow in the anterior chamber and eliminated the need for PI. This has no visual implication. But in hyperopia, this is not possible as the IOL is thickest in the center. For hyperopia, the V4 model is used with a PI. Sizing of ICL, surgical technique and complications are discussed in detail later in this chapter.

Phakic Refractive Lens

decision-making in refractive surgery.

Sizing of Implantable Collamer Lens Before understanding sizing, we need to understand that ICL is placed in the sulcus while maintaining an adequate distance from the anterior surface of the crystalline lens. At the same time, if the distance is too much, it is likely to cause shallow AC and peripheral angle closure. Keeping these two in mind, the vaulting of ICL is recommended in the range of 250 to 750 μm. If vault < 250 μm, it increases the chances of cataract formation. If vault > 50 μm, it may cause secondary glaucoma. Vaulting can be measured with ASOCT postoperatively. An intraoperative anterior segment optical coherence tomography (ASOCT) gives an estimate at the time. Table 10.3 provides the FDA guidelines used for the sizing of ICL. Fig. 10.3 shows available sizes for myopia and hyperopia.

It is an ultrathin silicone lens whose base diameter matches that of the anterior curvature of the crystalline lens (10 mm). This property is utilized where the IOL stays afloat in the aqueous over the clear lens. Details of sizing and refrac-

Hyperopia 11.5 12.1 12.6 13.2 13.7

tive correction are provided in Table 10.1. Although, this IOL

Myopia

appeared promising in the beginning, complications such as IOL decentration and dislocation, including dislocation in the vitreous cavity, warrant caution before use.22,23

Fig. 10.3  Illustration showing sizes of ICL available for myopia and hyperopia.

Table 10.2  Inclusion and exclusion criteria for phakic IOLs Inclusion criteria

Exclusion criteria

▪▪Stable refraction for at least 1 year ▪▪Age > 21 years (as per FDA approval for ICL) ▪▪Higher refractive error not correctable with corneal refractive surgery/patient unsuitable for corneal refractive surgery ▪▪Corneal endothelial cell count (cECC) > 2,300 cells/mm2 ▪▪Mesopic pupil size < 6.0 mm ▪▪Normal iridocorneal angle (≥ 30°)

▪▪Recurrent or chronic uveitis ▪▪Any form of clinically and visually significant cataract ▪▪IOP > 21 mm Hg or glaucoma ▪▪Abnormal retinal condition including high risk of retinal detachment, macular disorder

162 Chapter 10

Table 10.3  Recommended vision ICL size based on whiteto-white (WTW) and ACD

Calculation of power in ICL is done using Oslen Formula for pIOL.24 This uses spectacles power at 12 mm vertex distance, keratometry, and adjusted ultrasound central ACD.

White to white (mm)

ACD (mm)

Recommended ICL length

–6 D.43 RLE can induce acute posterior vitreous detachment and result in retinal traction or breaks. Alio et al43 found greater risk of RD in patients < 50 years old compared with > 50 years old and with eyes with longer AL. In addition, peripheral retinal degenerations, intraoperative rupture of the posterior capsule, and Nd:YAG capsulotomy for PCO were found to be risk factors. RLE should be avoided in high myopic eyes with extensive peripheral lattice degenerations or subclinical RD, fellow eye history of RD, family history of RD, patients with no posterior vitreous detachment, or myopic choroidal neovascularization (CNV) in the same or fellow eye. Apart from RD, there is a greater risk of cystoid macular edema in high myopia in the first few weeks following surgery. Posterior capsular opacification is a long-term complication following lens extraction. There is an increased risk of RD with YAG capsulotomy in high myopia. PCO risk can be reduced by meticulous surgical technique, central circular capsulorhexis covering IOL, square-edge haptic IOL, and good cortical cleanup. Endophthalmitis, although rare, is a

Conclusion RLE provides refractive surgery options to patients where corneal refractive surgery or phakic IOLs are unsuitable or contraindicated. Patient counseling and patient education is of paramount importance. Decision should be taken after considering the likely risk-to-benefit ratio.

References 1. Bjerke K. Die operative Beseitigung der durchsichti­ gen Linse wegen hochgradiger Myopie. Zeitschr Augenheilkd. 1902;8:136–175 2. Fukala V. Zur Geschichte der Heilung hochgradiger Myopie durch Linsenentfernung. Wien Med Presse. 1898;39:214–2 3. Fischer. Biographisches Lexikon der hervorragenden A¨ rzteder letzten fu¨ nfzig Jare. Berlin and Vienna, Urban & Schwarzenberg; 1932:466 4. Fukala V. Mehrja¨ hrige Beobachtungen an wegen hoherMyopie extrahierten Augen. Bericht Ophthalmol Gesellsch Heidelberg. 1893;23:191–209 5. Pieh S, Lackner B, Hanselmayer G, et al. Halo size under distance and near conditions in refractive multifocal intraocular lenses. Br J Ophthalmol 2001;85(7):816– 821 6. Hayashi K, Hayashi H, Nakao F, Hayashi F. Capsular capture of silicone intraocular lenses. J Cataract Refract Surg 1996;22(Suppl 2):1267–1271 7. Masket S, Sarayba M, Ignacio T, Fram N. Femtosecond laser-assisted cataract incisions: architectural stability and reproducibility. J Cataract Refract Surg 2010;36(6): 1048–1049 8. Stonecipher K, Ignacio TS, Stonecipher M. Advances in refractive surgery: microkeratome and femtosecond laser flap creation in relation to safety, efficacy, predictability, and biomechanical stability. Curr Opin Ophthalmol 2006;17(4):368–372 9. Nagy ZZ, Filkorn T, Takács AI, et al. Anterior segment OCT imaging after femtosecond laser cataract surgery. J Refract Surg 2013;29(2):110–112 10. American Academy of Ophthalmology. Preferred Practice Pattern Guidelines. In Cataract in the Adult Eye. San Francisco, CA: American Academy of Ophthalmology; 2011

178 Chapter 11 11. Zuberbuhler B, Seyedian M, Tuft S. Phacoemulsification in eyes with extreme axial myopia. J Cataract Refract Surg 2009;35(2):335–340 12. Wu W, Dawson DG, Sugar A, et al. Cataract surgery in patients with nanophthalmos: results and compli­ cations. J Cataract Refract Surg 2004;30(3):584–590 13. Byrne SF, Green RL. Ultrasound of the eye and orbit. 2nd edn. St Louis, MO: Mosby; 2002 14. Singh OS, Simmons RJ, Brockhurst RJ, Trempe CL. Nanophthalmos: a perspective on identification and therapy. Ophthalmology 1982;89(9):1006–1012 15. Kimbrough RL, Trempe CS, Brockhurst RJ, Simmons RJ. Angle-closure glaucoma in nanophthalmos. Am J Ophthalmol 1979;88(3 Pt 2):572–579 16. Day AC, MacLaren RE, Bunce C, Stevens JD, Foster PJ. Outcomes of phacoemulsification and intraocular lens implantation in microphthalmos and nanophthalmos. J Cataract Refract Surg 2013;39(1):87–96

27. Güell JL, Rodriguez-Arenas AF, Gris O, Malecaze F, Velasco F. Phacoemulsification of the crystalline lens and implantation of an intraocular lens for the correction of moderate and high myopia: four-year follow-up. J Cataract Refract Surg 2003;29(1):34–38 28. Arne JL. Phakic intraocular lens implantation versus clear lens extraction in highly myopic eyes of 30- to 50-year-old patients. J Cataract Refract Surg 2004; 30(10):2092–2096 29. Horgan N, Condon PI, Beatty S. Refractive lens exchange in high myopia: long term follow up. Br J Ophthalmol 2005;89(6):670–672 30. Emarah AM, El-Helw MA, Yassin HM. Comparison of clear lens extraction and collamer lens implantation in high myopia. Clin Ophthalmol 2010;4:447–454 31. Siganos DS, Pallikaris IG. Clear lensectomy and intraocular lens implantation for hyperopia from +7 to +14 diopters. J Refract Surg 1998;14(2):105–113

17. Olsen T. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 1992;18(2):125–129

32. Fink AM, Gore C, Rosen ES. Refractive lensectomy for hyperopia. Ophthalmology 2000;107(8):1540–1548

18. Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg 1993;19(6):700–712

33. Alfonso JF, Fernández-Vega L, Baamonde B, MadridCosta D, Montés-Micó R. Refractive lens exchange with spherical diffractive intraocular lens implantation after hyperopic laser in situ keratomileusis. J Cataract Refract Surg 2009;35(10):1744–1750

19. Hoffer KJ. Clinical results using the Holladay 2 intraocular lens power formula. J Cataract Refract Surg 2000;26(8):1233–1237 20. Speicher L. Intra-ocular lens calculation status after corneal refractive surgery. Curr Opin Ophthalmol 2001;12(1):17–29 21. Alió JL, Grzybowski A, El Aswad A, Romaniuk D. Refractive lens exchange. Surv Ophthalmol 2014;59(6): 579–598

34. Preetha R, Goel P, Patel N, et al. Clear lens extraction with intraocular lens implantation for hyperopia. J Cataract Refract Surg 2003;29(5):895–899 35. Pop M, Payette Y. Refractive lens exchange versus irisclaw Artisan phakic intraocular lens for hyperopia. J Refract Surg 2004;20(1):20–24

22. Hoffman RS, Fine IH, Packer M. Refractive lens exchange as a refractive surgery modality. Curr Opin Ophthalmol 2004;15(1):22–28

36. Kolahdouz- Isfahani AH. Rostamian K, Wallace D, Salz JJ: CLE with IOL implantation for hyperopia. J Refract Surg 1999;15:316–323 https://www.ncbi.nlm.nih.gov/ pubmed/10367573

23. Wang JK, Chang SW. Optical biometry intraocular lens power calculation using different formulas in patients with different axial lengths. Int J Ophthalmol 2013;6(2):150–154

37. Sun XY, Vicary D, Montgomery P, Griffiths M. Toric intraocular lenses for correcting astigmatism in 130 eyes. Ophthalmology 2000;107(9):1776–1781, discussion 1781–1782

24. Gabrić N, Dekaris I, Karaman Z. Refractive lens exchange for correction of high myopia. Eur J Ophthalmol 2002;12(5):384–387

38. Ruíz-Mesa R, Carrasco-Sánchez D, Díaz-Alvarez SB, Ruíz-Mateos MA, Ferrer-Blasco T, Montés-Micó R. Refractive lens exchange with foldable toric intraocular lens. Am J Ophthalmol 2009;147(6):990–996, 996.e1

25. Ravalico G, Michieli C, Vattovani O, Tognetto D. Retinal detachment after cataract extraction and refractive lens exchange in highly myopic patients. J Cataract Refract Surg 2003;29(1):39–44 26. Fernández-Vega L, Alfonso JF, Villacampa T. Clear lens extraction for the correction of high myopia. Ophthalmology 2003;110(12):2349–2354

39. Jaimes M, Xacur-García F, Alvarez-Melloni D, GraueHernández EO, Ramirez-Luquín T, Navas A. Refractive lens exchange with toric intraocular lenses in keratoconus. J Refract Surg 2011;27(9):658–664 40. Leccisotti A. Refractive lens exchange in keratoconus. J Cataract Refract Surg 2006;32(5):742–746

Refractive Lens Exchange 179 41. Pop M, Payette Y, Amyot M. Clear lens extraction with intraocular lens followed by photorefractive keratectomy or laser in situ keratomileusis. Ophthalmology 2001;108(1):104–111 42. Barraquer C, Cavelier C, Mejía LF. Incidence of retinal detachment following clear-lens extraction in myopic patients. Retrospective analysis. Arch Ophthalmol 1994;112(3):336–339

43. Alió JL. Lens surgery (cataract and refractive lens exchange) and retinal detachment risk in myopes: still an issue? Br J Ophthalmol 2011;95(3):301–303 44. Neuhann IM, Neuhann TF, Heimann H, Schmickler S, Gerl RH, Foerster MH. Retinal detachment after phacoemulsification in high myopia: analysis of 2356 cases. J Cataract Refract Surg 2008;34(10): 1644–1657

180 Chapter 11

Case-based Approach For a better understanding of the indications and patient section, here are two cases where RLE was selected as the treatment option.

Case 1

His aim was to get rid of contact lens or bulky spectacles

A 42-year-old teacher presented to a refractive clinic for

multifocal IOL but was concerned with the risk of dyspho-

removal of spectacles. He had used spectacles since 6

topic symptoms.

years of age. He had stable refraction for the past 5 years. Slit-lamp examination and tear-film assessment revealed no abnormality. He had previously undergone retinal laser for lattice degeneration in both eyes, with fundus examination revealing no new lesions. Patient parameters are given in Table 11.3. Pentacam of both eyes is as shown in Fig. 11.7a, b. The patient has been using contact lenses for

while he had no problem with near glasses. He considered

Postoperatively, a UCVA of 6/9 in the right eye and 6/6 in the left eye was achieved with near vision of N-6 with +3 DS near add. Improvement in one-line vision was likely due to the elimination of the minification effect of the concave lens in his spectacles. The patient is on regular follow-up for anterior segment and fundus examination.

the past 10 years on occasion but is unhappy with the idea of daily routine. He started using near spectacles of +2 DS near

Table 11.3  Patient parameters for Case 1

add for the past 2 years.

Parameter

OD

OS

Uncorrected visual acuity (UCVA)

1/60

1/60

Best-corrected visual acuity (BCVA) with spectacles

6/12

6/9

Cycloplegic refraction

–22 DS/–1.5 DC @100

–20 DS/–1 DC @ 90

Keratometry (K) 1, D

42.5

43

K2, D

44

44

Axis, degrees

108.6

102.4

K mean, D

43.3

43.5

Thinnest pachymetry, μm

579

573

Pupillary diameter, mm

3.37

3.15

Posterior elevation

+5

+4

D value

0.68

0.47

Specular count, cells/mm

3256

3214

White-to-white (WTW), mm

11.9

11.8

Endothelial anterior chamber depth (endo ACD), mm

2.97

2.95

Surgical treatment options were discussed with the patient: ••The patient is suitable for RLE. The option of monofocal and multifocal IOLs was given with the advantages and disadvantages of both. The risks of RD and intraocular procedure were discussed. ••Phakic IOL can be considered given the refractive error. Any residual refractive error can be treated with corneal refractive surgery (bioptics). ••Near correction can also be performed using corneal refractive surgery such as PRESBYOND®. A need for cataract surgery at a later stage (~10–15 years later) was explained. The patient chose the option of RLE with monofocal IOL. The decision was made on the basis of him not wanting to undergo more than one refractive procedure in each eye.

2

Refractive Lens Exchange 181

a

b Fig. 11.7 (a, b)  Corneal Topography of Case 1 patient OD and OS respectively.

182 Chapter 11

Case 2 A 36-year-old lady presented to a refractive clinic for

The patient chose to use contact lens for a few years till her accommodation is preserved. She has been on regular follow ups.

removal of spectacles. She had used spectacles since 5 years of age. She had stable refraction for the past 12 years. Slitlamp examination and tear-film assessment revealed no abnormality. Both eyes fundus examination revealed no new lesions. Patient parameters are given in Table 11.4. Pentacam of both eyes showed no abnormality. Anterior

Table 11.4  Patient parameters for Case 2 Parameter

OD

OS

UCVA

3/60

3/60

BCVA with spectacle

6/9

6/9

Cycloplegic refraction

+15 DS

+15 DS

Refractive options were discussed with the patient:

K1, D

41.5

41.9

••Corneal refractive surgery is not possible since refrac-

K2, D

42

42.3

Axis, degrees

89

97

K mean, D

41.8

42.1

Thinnest pachymetry, μm

513

521

Pupillary diameter, mm

3.1

3.01

performed using monofocal or multifocal IOL. Possible

Posterior elevation

+11

+9

complications of intraocular surgery are discussed.

D value

1.06

0.89

The loss of accommodation was discussed.

Specular count, cells/mm2

3024

3108

WTW, mm

11.6

11.5

Endo ACD, mm

2.63

2.56

segment optical coherence tomography (ASOCT) is shown in Fig. 11.8a, b. The patient has been using spectacles and has never used contact lenses.

tive error is beyond the limit. ••Phakic IOL (Implantable Collamer Lens [ICL]) is contraindicated due to endo ACD < 2.8 mm. ••RLE is the only refractive surgical option. RLE can be

••Contact lens can also be tried since she has never used contact lens in the past.

Refractive Lens Exchange 183

a

b Fig. 11.8 (a, b)  ASOCT showing endo ACD of Case 2 OD and OS respectively.

Chapter 12 Hyperopic Refractive Surgery

Introduction.....................................................................................186 Preoperative Considerations.......................................................186 Laser-assisted In Situ Keratomileusis for Hyperopia.......... 187 Femto Second Lenticule Extraction (FLex)............................. 188 Phakic IOLs for Hyperopia...........................................................188 Photorefractive Keratectomy for Hyperopia.......................... 189 Refractive Lens Exchange for Hyperopia................................. 189 Retreatment/Enhancements and Bioptics for Hyperopia.................................................................. 190 Conclusion........................................................................................190 Case-based Approach....................................................................192

12. Hyperopic Refractive Surgery Yogita Gupta, Chirakshi Dhull and Sudarshan Khokhar

Introduction

technique has been accepted as the standard treatment for

Hyperopia is often associated with short axial-length or weak

pia have been listed in Box 12.1. Factors to consider when

focusing-mechanism such as a flat cornea or a combination

deciding between these options include the degree of hyper-

of the two factors. Refractive surgical options, such as laser-

opia, the patient’s age, lens opacification, accommodative

assisted in-situ keratomileusis (LASIK), are being explored

ability, keratometry (K), corneal topography, and endothe-

to address these anatomic factors in hyperopic eyes. For low

lial status.3

hyperopia.2 Various refractive surgical options for hypero-

degrees of hyperopia, these procedures show good efficacy and predictability. However, regression and lower predictability is reported with higher degrees of hyperopia. This chapter summarizes the current perspectives on the treatment options for hyperopia. Hyperopia is the optical term for farsightedness, a condition in which parallel light rays focus behind the retina, making near objects appear blurred. This refractive error has a reported prevalence of 25.2% to 31.8% in adults.1 Hyperopia

Preoperative Considerations After a thorough clinical history and ocular examination, a cycloplegic refraction must be performed to determine the exact amount of hyperopia to be corrected. The stability of refraction must be ensured for the last one year. Contact lenses must be removed prior to the pre-op examination for

can be categorized into low (≤ 3.00 D), moderate (3.00–5.99 D), and high (≥ 6.00 D). It may be due to short axial length or weak focusing mechanisms for the given axial length of the eye, e.g., low refractive power of the cornea (a flat cornea) or crystalline lens. Refractive surgical options have been designed with the aim of increasing the overall focusing power of the eye, either by altering the corneal curvature (corneal refractive surgery) or by placing an artificial lens implant (phakic intraocular lens [IOL]) in the eye. While the refractive surgical correction for myopia has evolved continuously since the introduction of 193 nm excimer laser, the refractive treatment of hyperopia has lagged behind due to regression and unpredictability. Although collagen shrinkage techniques, e.g., conductive keratoplasty and laser thermal keratoplasty, have been devised for correcting hyperopia, these result in significant regression of the refractive error, and are, thus, fading out from clinical practice today. Refractive surgical treatment for hyperopia remains a challenge for a refractive surgeon and no single

Box 12.1  Refractive surgical options for correction of hyperopia Laser techniques ▪▪Surface laser treatment: Photorefractive keratectomy (PRK), laser subepithelial keratomileusis (LASEK), Epi-LASIK ▪▪Lamellar treatment: Laser-assisted in situ keratomileusis (LASIK) using microkeratome or femtosecond laser ▪▪Femtosecond laser alone: Small incision lenticule extraction (SMILE), Femtosecond lenticule extraction (ReLEx FLEx) Intraocular techniques ▪▪Phakic intraocular lens (Phakic IOL)—angle supported, iris-claw, or posterior chamber phakic IOLs ▪▪Refractive lens exchange (RLE) Collagen shrinking techniques ▪▪Conductive keratoplasty ▪▪Laser thermal keratoplasty using holmium YAG (yttrium aluminum garnet) laser Combination of techniques ▪▪Bioptics ▪▪Trioptics

Hyperopic Refractive Surgery 187 a minimum of 7–14 days for soft contact lenses and 3 weeks

use of appropriate IOL power formula as per the axial

for rigid gas permeable lenses. Any other past significant

length (Hoffer Q/Haigis/Holladay–I).

ocular or systemic history must be ruled out. A post-mydriatic test must then be performed after the

••The presence of any amount of cataract in the eye should prompt a surgeon to plan an RLE surgery.

effect of the cycloplegic agent wears off. Both manifest and cycloplegic refraction are recommended to select appropriate surgical treatment. Determination of pupil size, keratometry, pachymetry, white-to-white diameter, and corneal endothelial cell counts help in careful patient selection. Anterior chamber depth (ACD) measured from endothelium (endo ACD) is an important consideration before planning intraocular surgery in hyperopes. A few points that must be carefully noted by the surgeon when planning procedure in hyperopes are: ••Cyclopleged refractions should be performed and used for correction in all hyperopes to avoid any residual refractive error due to latent hyperopia. ••If planning a phakic IOL procedure, endo ACD 46 D should be carefully reviewed to rule out any keratectatic disease, as corneal steepness would only increase after hyperopic laser vision correction (LVC), causing loss of postoperative best-corrected visual acuity (BCVA) and lower patient satisfaction.

Laser-assisted In Situ Keratomileusis for Hyperopia Laser-assisted in situ keratomileusis (LASIK) is currently the most commonly performed surgery for hyperopia. An excimer laser is used for the ablation of the paracentral cornea to steepen the central cornea (i.e., create a more prolate cornea; thereby increasing the corneal eccentricity as measured by Q value) (Fig. 12.1). For mild ( 47 D, there is higher chances of regression. ••The patient was explained about the additional risk of dry eyes and possible regression due to steep Km along with the usual ectasia associated with corneal refractive surgery. Patient chose LASIK surgery with explained risk for regression over time.

Postoperative Outcome

Specular count, cells/mm

2

Abbreviations: ACD = anterior chamber depth, BCVA = best corrected visual acuity, OD = oculus dextrus, OS = oculus sinister, K1 = flat keratometry, K2 = steep keratometry, K max = maximum keratometry, PMT = post mydriatic test, PTA = percentage tissue ablation, RSBT = residual stromal bed thickness, UCVA = uncorrected visual acuity, WTW = white-to-white diameter.

The patient gained satisfactory visual outcomes with no

Table 12.3  Postoperative parameters for Case 1

complications and mild dry eyes treated with lubricant

Parameter

OD

OS

UCVA 1 day post LASIK

6/6

6/6

UCVA 3 months post LASIK

6/6

6/6

UCVA 6 months post LASIK

6/6

6/6

UCVA 1 year post LASIK

6/6

6/6

drops (Table 12.3, and Fig. 12.4a, b).

Hyperopic Refractive Surgery 193

a

b Fig. 12.3  (a, b) Corneal topography maps of Case 1 for OD and OS respectively. Note the normal topography in both eyes with steep Km > 44 D in both.

194 Chapter 12

a

b Fig. 12.4  (a, b) One-year postoperative corneal topography maps of Case 1 for OD and OS respectively. Note that the cornea has become steeper, but there is no significant change in posterior corneal curvature.

Chapter 13 Corneal Incision Surgery

Introduction.....................................................................................196 Incisional Correction of Myopia................................................ 196 Incisional Correction of Astigmatism...................................... 197 Types of Corneal Incision for Astigmatism Correction.........................................................................................197 Incisional Correction of Post-Keratoplasty Astigmatism.....................................................................................202 Phacoincisions: Refractive Aspects........................................... 202

13. Corneal Incision Surgery Abhidnya Surve, Chirakshi Dhull, Yogita Gupta and Sudarshan Khokhar

Introduction

Prospective evaluation of radial keratotomy (PERK) study in 1982 included 435 patients with myopia from –2.00 D to

Corneal incisions have an important refractive asset. It forms

–8.75 D with 1.50 D or less of astigmatism and showed the

a crucial aspect of phacoemulsification surgery and is impor-

continued long-term instability of the procedure. The 90%

tant for treating refractive errors including astigmatism.

prediction interval at 4 years was 4.42 D, which is a wide

The use of incisional refractive surgery today is, however,

range.1 Fifty-three percent of cases had >20/20 uncorrected

limited in the treatment of astigmatism. Femtosecond laser

visual acuity (UCVA) and 85% of cases had 20/40 UCVA at

platforms have also been increasingly used for the same.

the end of 10 years. The clear corneal zone was the only variable, and statistics showed significant association with

Incisional Correction of Myopia Radial Keratotomy Radial Keratotomy (RK) formed an important component of refractive surgery in the past but is presently obsolete because of the innovation of later forms like laser-assisted in situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE). The accuracy and predictability of correction by later procedures have outmatched the older ones. But unlike these procedures, RK does not involve the

the hyperopic shift. A hyperopic shift of 1 D or greater was noted in 43% of eyes between 6 months to 10 years. Further, this percentage increased 5% annually after 10 years.2 At the end of the 11-year follow-up of a subset of PERK population, persistent diurnal changes in refraction, corneal curvature, and visual acuity was observed.3 This lack of predictability and stability of the procedure is the reason it is not used as the first choice for refractive correction. Various complications related to the procedure include transient pain for 24–48 hours, glare, light sensitivity, fluctuating visual acuity, keratitis, and risk of traumatic

removal of corneal tissue. It redistributes the corneal power from center to periphery. Radial corneal incisions severe the stromal collagen fibers. This leads to wound gape, with midperipheral bulging of the cornea. This leads to compensatory flattening of the central cornea, thereby a decrease in the corneal power leading to a decrease in myopia (Fig. 13.1). The angle, sharpness of cutting edge, width of the blade, and design of the footplate influence both the depth and the contour of the incision. The ideal depth of an RK incision is 85–90% of corneal thickness. The number of incisions and the clear optical zone maintained depend on the amount of refractive correction needed. The amount of refractive error corrected is more with a larger number of incisions, longer incisions, and lesser clear optical zone.

Fig. 13.1  Radial keratotomy incisions in a myopic patient.

Corneal Incision Surgery 197 rupture of the globe through the weakened keratotomy

corneal power. Thus, it is important to differentiate between

scars. Other persistent complications included overcorrec-

the amounts of corneal and lenticular astigmatism.

tion, undercorrection, and instability over a period of time.

4

Before surgery, an accurate manifest refraction, topography, and keratometry are required. The manifest or

Incisional Correction of Astigmatism

cycloplegic refraction provides us with the total refractive

Surgical management of astigmatism with corneal incision

us with the corneal astigmatism and axis.7,8 It is also impor-

is one of the oldest refractive procedures. Astigmatism is a form of refractive error that causes a decrease in visual acuity and has magnitude and direction. Some amount of astigmatism is usually seen in 95% of the population, and the definition for its significance level has been varying. The prevalence of astigmatism increases with age and changes from with-the-rule to against-the-rule or oblique astigma-

astigmatism, while the keratometry and topography provide tant to know that surgically induced astigmatism (SIA) gets created while making cataract incisions (Fig. 13.2). Corneal topography and elevation mapping allow for the assessment of any corneal pathology.8 These cases have unpredictable postoperative results and may not be a good candidate for limbal relaxing incision (LRI) or astigmatic keratotomy (AK). Patients with systemic inflammatory diseases such as rheu-

tism with advancing age.5

matoid arthritis have an increased risk of peripheral ulcera-

Prerequisite

thinning and increased risk of perforation.

During refractive error correction, taking into consideration

Types of Corneal Incision for Astigmatism Correction

tive keratitis and predisposition of the cornea to peripheral

the amount and cause of astigmatism is of prime importance for its appropriate management. It can be due to asymmetry of the anterior corneal surface, posterior corneal surface, or lens.6 Corneal incisions can correct or induce astigmatism by altering anterior corneal surface, leading to change in

The types of corneal incision used for astigmatism correction are given in Flowchart 13.1.

Fig. 13.2 Construction of phacoin­cisions for minimal sur­ gically induced astigmatism.

Placement of the phaco incision Peripheral enough to barely nick limbal vessels

Good form 180°

• Great long-term sealing • Further from visual axis • Less astigmatic effect

Poor form 180°

• Weaker long-term sealing • Closer to visual axis • More astigment effect

198 Chapter 13

Clear corneal incision

Tangential (Transverse)

Manual Astigmatism correction Femtosecond assisted

Arcuate (Curved)

Limbal relaxing incision (LRI)

RUIZ

Flowchart 13.1  Types of corneal incisions used for astigmatism correction.

Corneal coupling effect 45.00 × 090

43.00 × 180

44.00 × 090

44.00 × 180

Before corneal incisions

After corneal incisions

MRx –3.00 + 2.00 × 090 Spherical equivalent –1.50 K 45.00 × 090 / 43.00 × 180

MRx –1.50 spherical Spherical equivalent –1.50 K 44.00 × 090 / 44.00 × 180

Fig. 13.3  Example of coupling effect seen following limbal relaxing incision.

Astigmatic Keratotomy

effect. The coupling ratio is the amount of flattening to the

The Astigmatic Keratotomy (AK) incisions are known to

a coupling ratio of 1 indicates that there is no change in the

be safe and effective but are of limited use because of the

overall spherical equivalent, the coupling ratio greater than

unpredictability related to the procedure and development

1 indicates a hyperopic shift.5,11 Longer and transverse inci-

of newer technology and lenses.9,10 However, it is still used

sions have more effect but do tend to produce a coupling

in the correction of astigmatism mainly during cataract

ratio greater than 1, leading to a hyperopic shift. Thus,

surgery and post-keratoplasty. The common principle is

with a higher amount of astigmatism, especially >2.0 D,

the placement of incision in the steep axis, leading to flat-

the coupling ratio tends to be on the higher side. The inci-

tening in the same meridian and steepening of the merid-

sional keratotomy can correct between +0.75 and +3.50 D of

ian perpendicular to it. This effect is called the coupling

astigmatism (Fig. 13.4).

amount of steeping in the respective axis (Fig. 13.3). While

Corneal Incision Surgery 199

Addressing corneal astigmatism 45.00 × 090

44.00 × 180

45.25 × 090

43.75 × 180

Before surgery 1.0 D of WTR corneal astigmatism

44.50 × 090

44.50 × 180

After phaco incision: 1.5 D of WTR corneal astigmatism

After LRIs at 90°: 0.0 D of corneal astigmatism

Fig. 13.4  Limbal relaxing inci­sion for management of corneal astigmatism during cataract surgery.

Tangential (transverse/straight) and arcuate (curved) keratotomy are different types of astigmatic keratotomy. Transverse keratotomy (TK) is used in combination with RK to correct myopia. Arcuate keratotomy (AK) is used to correct astigmatism during or after cataract surgery and intraocular lens (IOL) implantation as well as after refractive procedure such as LASIK and photorefractive keratectomy (PRK).

Femtosecond Laser-Assisted Femto Second Laser Assisted Correction of Astigmatism The femtosecond laser was first used to treat high levels of astigmatism with arcuate incisions in cases with operated penetrating keratoplasty. Now, they have been approved for the treatment of corneal astigmatism in the form of AK. The incisions can be performed safely with precision. They

Limbal Relaxing Incision

can be penetrating or intrastromal (Fig. 13.5). Twenty mil-

Limbal Relaxing Incision (LRI) does not change the spherical equivalent, and thus, does not affect the IOL power. LRI is useful in cases where the astigmatism is outside the range of toric lenses or where the toric lens could not be implanted. It can also be used in cases where the astigmatism axes are asymmetric and nonorthogonal, and in those patients who cannot afford premium IOL. Also, LRI is useful in cases where presbyopic lenses are implanted. LRI have lesser chances of

limeters of the anterior cornea are uncut in intrastromal incisions and can be opened later using Sinskey hook if additional treatment is required. This allows for titration of the effect of intrastromal incisions. One can also rely on the Optiwave refractive analyzer to predict the need to open the incision intraoperatively. These incisions also decrease the risk of discomfort and infection as the epithelium remains intact. The femtosecond laser allows for precise planning of the incision anterior, posterior, depth, length, angle, and

developing aberrations leading to glare and discomfort. The

location. The centration of the pupil is important while plac-

healing is faster, and the results are more predictable but

ing the suction ring on the cornea. During cataract surgery,

less effective compared to AK.

the SIA is more predictable because of the uniformity of the

12

Depending on the amount

of correction required, LRI can be single or paired. If an astig-

incisions.13,14

matic bow tie is seen on corneal topography, the LRI inci-

On comparison of manual and femtosecond laser-assisted

sions should be altered with longer incision at the larger arm

LRI, it was seen that the femtosecond AK provided signifi-

and shorter incision at the smaller arm.

cant improvement in uncorrected and best corrected visual

200 Chapter 13

Cornea Side view

Penetrating arcuate incision (2shown)

Arcuate incision

Ciliary body

Iris

Iris

Fig. 13.5  Illustration show­ ing (a) penetrating arcuate incision and (b) intrastomal arcuate incision.

Ciliary body

Lens

Penetrating arcuate incision (2shown)

Cornea Side view

Ciliary body

a

Iris

Iris

b

acuity, which could be attributed to the increased accuracy and precision of femtosecond technology and the reduced

Ciliary body

Lens

limbus at ~600 mm depth or 50 mm less than the thinnest pachymetry measurement at the limbus.

complication rates.15 Cases of post-keratoplasty astigmatism

••Meridian of the incision: The incision placed on the

correction of 0.5 to 6 D using femtosecond laser have been

horizontal meridian has twice the astigmatic effect as

documented in the literature.

the incision placed on the vertical meridian.

16,17

Various complications

with femtosecond lasers include micro corneal perforation and low-grade inflammation at the incision site.

Factors Affecting Outcome of the Astigmatic Keratotomy Procedure Different parameters of the incisions affect the outcome of the procedure (Fig. 13.6) : 18

••Although linear incisions are easier to make, they may induce more irregular astigmatism than arcuate incisions. ••Length of the incision: TK incisions are usually 2–3 mm in length while AK incisions can vary from 30 to 90 degrees. ••Placement of the incision: Smaller the central optical zone greater the astigmatic effect. These incisions are

••Number of incisions: Paired incisions at the steep axis can be used to correct a higher amount of astigmatism. Low astigmatic errors (≤2.75 D) can be corrected by limbal incisions (11 mm optical zone), while the addition of 8 mm optical zone incision is intended for corrections >3.0 D. ••Age of patient: Younger patients usually experience less effect than older patients for a given incision; so, the expected result is decreased by 2% per year for ages below 30 and increased by 2% per year for ages over 30. ••Opening of incisions: The incisions can be titrated. Only a part of an incision can be opened initially and can be extended later if greater astigmatic correction is required.

usually placed at a 7 mm optical zone. This allows the

Different nomograms based on various factors including

maintenance of an optimal clear central zone to avoid

the age of the patient, the amount of preoperative cylinder,

any glare symptoms. Also, the risk of astigmatism

and axis of astigmatism have been developed. Lindstrom’s

increases with a smaller optical zone. LRI is placed at

nomogram has adjustment for the patient’s age. After deter-

the most peripheral area of the clear cornea. Placing

mining the magnitude and axis of astigmatism, the nomo-

incisions at a more peripheral cornea or over surgical

gram can help to determine the length and location of the

limbus has a lesser effect.

LRI.19 The surgeon should try multiple nomograms, record

••Depth of incisions: They are usually of 95% depth or

their postoperative results, and modify the nomograms to

20 mm less than the thinnest depth measured at the

fit their surgical technique. Nomograms that plan incisions

point of the incision. LRI are placed just anterior to the

based upon degrees of arc are thought to be most accurate.19

Corneal Incision Surgery 201

Larger incision = more flattening 44.50 × 090

Central incision = more flattening

44.00 × 090

43.50 × 180

44.00 × 180

Smaller incision = less flattening This cornea still has 1 diopter of residual astigmatism

44.50 × 090

43.50 × 180

Larger incision = more flattening This cornea has no residual astigmatism

This cornea still has 1 diopter of residual astigmatism

Longer tunnels = less flattening Astigmatically neutral incisions

Central incision = more flattening The same sized incision placed more centrally result in no residual astigmatism

For non-penetrating incisions

Shorter tunnels = more flattening

44.00 × 180

44.00 × 180

Peripheral incision = less flattening

For penetrating incisions

44.00 × 090

44.00 × 090

Deeper cuts = more flattening 44.50 × 090

43.50 × 180

Short tunnels = more flattening Incision is nearly pe rpendicular to the corneal surface

44.00 × 090

43.50 × 090

44.50 × 180

44.00 × 180

Shallow cuts = less flattening Cuts less than 50% depth have very little effect on corneal power

Deeper cuts = more flattening Cutting deeper than 90% of corneal pachymetry may result in perforation

Fig. 13.6  Understanding corneal incisions and their impact on corneal astigmatism.

Procedure AK or LRI can be done in combination or performed with cataract surgery, PRK, and LASIK surgery. However, better results are obtained if one performs astigmatic correction

The incisions can be performed before entering the eye or can be performed in eyes filled with viscoelastic agents. The firmness of the eye allows for a regular and accurate incision. A diamond or disposable blade with a footplate set to

after the achievement of refractive stability. For any astig-

a depth of 550 or 600 mm is most often used. It is important

matic correction, it is important to mark the axis preopera-

to use a single-footplate double-cutting blade that provides

tively to avoid error due to cyclotorsion. The patient should

full visualization of the blade during the cut. This allows the

be upright and looking straight ahead with no head tilt. After

surgeon to visualize the depth of the cut and allows early

instillation of topical anesthesia, the 3, 6, and 9 o’clock posi-

recognition of corneal perforation in case of adverse events.

tion at limbus are marked using a fine-tipped marking pen. The slit lamp can be used to mark preoperatively. The horizontally oriented slit-lamp beam should overlap the central corneal reflex at the visual axis. This confirms the centration and allows marking at a specific position. The commercially

Complications ••Predictability: AK incision results were often more unpredictable.

available bubble-level marker is another method. The image-

••Undercorrection: Various factors associated with inci-

guided method is found to be more a accurate alignment but

sion can lead to undercorrection. Lack of adequate

with comparable results.20,21 On the operating table, using

incision depth is the most commonly associated cause.

these references, the steep axis is identified and marked.

In the case of significant undercorrection, the wounds

202 Chapter 13 can be opened or extended. Excimer laser refractive

mixed astigmatism.12,19 Several studies have compared inci-

surgery can also be performed if required.

sional keratotomy and toric IOL for correcting astigmatism.

••Overcorrection; It can be more disabling, especially

Toric IOL was found to be more effective and predictable, but

when the axis is flipped. It can be corrected with exci-

a few studies have found both modalities to be comparable

mer laser refractive surgery if required. Addition of

in cases with mild to moderate astigmatism.23–25

more incisions should be avoided. ••Ocular surface disruption: AK incisions were more frequently associated with glare and foreign body

Astigmatic Keratotomy and LASIK

sensation.22 LRI may have increased foreign body sen-

In cases with naturally occurring astigmatism, especially

sation in the first 24 hours until the epithelium heals.

those >3.00 D of astigmatism, the use of AK or LASIK alone

Frequent use of lubricants is effective in alleviating the

is less accurate and predictable. These cases can be managed

symptoms.

by reducing the cylindrical component first with AK and

••Aberrations: AK incisions being closer to the center

then correcting myopia and residual cylinder using LASIK.26

of the cornea compared with LRI had a tendency to

However, care should be taken that the incisions are away

induce aberrations, especially trefoil.

from the optical zone.

12,22

••Perforation and wound leak: Perforation can occur due to blade abnormalities or due to unrecognized corneal thinning at the site of incision. In the case of a self-sealed wound, nothing is required to be done, but in a case with significant wound leak due to perforation, corneal suture must be placed. A bandaged contact lens may be placed to cover both self-sealed and sutured wounds. ••Risk of infection: Perforation and wound leak increases the risk of infection. Aggressive antibiotic therapy is recommended. ••Irregular astigmatism: Irregular incisions can lead to irregular astigmatism. It can occur with either AK or LRI but is more common with AK because of its close proximity to the corneal center. ••Ocular surgery after arcuate keratotomy and limbal relaxing incisions: While performing penetrating keratoplasty in a case with extensive AK, the wounds may have to be sutured before trephination of the cornea.

Incisional Correction of PostKeratoplasty Astigmatism In post-keratoplasty astigmatism, AK can correct low to high amount of astigmatism up to 10 D. Such a high amount of astigmatism cannot be corrected by an excimer laser, and thus, AK can be very useful in such cases.26 The incisions can be limbal, arcuate, or transverse. AK incisions used to correct post-penetrating keratoplasty astigmatism are often made in the graft or in the graft–host junction. Care must be taken to avoid perforation. Making the incision in the host tissue has a lesser effect. Also, when combining the two procedures, an initial overcorrection is desired to compensate for wound healing. Also, as described above, it depends on numerous other factors including length, optical zone, and depth of incisions. They thus have less predictability.27–29 The astigmatic effect of the incisions varies according to the preoperative astigmatism.30 Various nomograms are devised but they also have less predictive capacity.31–33

Efficacy The Astigmatism Reduction Clinical Trial (ARC-T) of AK used a 7-mm optical zone and varying arc lengths. A reduction of 1.6 ± 1.1 D astigmatism in cases with preoperative astigma-

Phacoincisions: Refractive Aspects

tism of 2.8 ± 1.2 D was documented. Studies have shown a

Refractive outcome is an important component of cataract

UCVA of 20/40 in 65–80% of eyes. Studies of LRIs are limited,

surgery. Corneal astigmatism can be managed during phaco-

but these incisions are frequently used with seemingly good

emulsification by considering corneal incisions. The various

results in astigmatic patients undergoing cataract surgery. A

incisions used in phacoemulsification include clear corneal

few patients have showed a change of 1.72 ± 0.81 D in cases

incision and limbal incision. The clear corneal incision is

with astigmatism. One study showed an absolute change in

typically 2.7–3.2 mm wide to accommodate the foldable

refractive astigmatism of 1.72 ± 0.81 D after LRI in cases with

IOL after incision. The incisions can be placed superiorly,

9

Corneal Incision Surgery 203 temporally, or at the steepest axis of the cornea. The incision can also be uniplanar or multiplanar.

34,35

••Shorter tunnel has a more flattening effect compared

These incisions are

to a longer tunnel.

usually watertight, but their integrity also depends on the

••Larger the size of the incision more the flattening

distortion of the wound in the subsequent phacoemulsifica-

effect.

tion steps. The astigmatism created while placing this inci-

••A 3 mm, biplanar, hinged, clear corneal wound has a

sion is known as surgically induced astigmatism (SIA) and is

greater astigmatic effect than a 3 mm, single-plane,

particularly important while placing toric IOL. SIA is one of

corneal incision. Thus, the construction of the wound

the factors considered in determining the power and axis of

also influences its astigmatic effect.

36

the lens.

Preoperative astigmatism can be reduced by consider-

During phacoemulsification, the induction of astigmatism depends on various factors

34–38

:

••The closer the incision is to the center of the cornea, the higher the chance of inducing astigmatism. ••The radial incision has minimal effect compared to the oblique entry.

ing the appropriate placement of incisions. A low amount of astigmatism—up to 1 to –1.5 D—can be effectively managed by corneal incisions, while moderate to high amount of astigmatism require toric IOL. The main phacoincision, if possible, should be placed at the steeper axis. Further paired LRI or clear corneal phacoincision can be placed in the

••The temporal limbus is farther away from the visual

steeper meridian to reduce astigmatism. The addition of an

axis compared to the superior incision and thus has

opposite clear corneal incision (OCCI) is found to be a more

less amount of SIA. Also, many elderly patients have

effective, easy, safe, and predictable procedure in managing

against-the-rule astigmatism, which increases with

mild to moderate amounts of astigmatism.39 This enhances

age, and placing the incisions temporally benefits

the flattening effect; the method is called paired OCCIs

such cases.

(Fig. 13.7a–d). OCCIs are self-sealing wounds and have no

a

b

c

d

Fig. 13.7  (a–d) Opposite clear corneal incision (OCCI) in an albinism patient (a) Marking of steep axis with toric marker using guide of 0 and 180 degree marking in sitting position; (b) Switch to superior incision during phacoemulsification to align incision with steep axis; (c) OCCI is done at the marked opposite axis; (d) At the completion, there is no requirement to hydrate the OCCI.

204 Chapter 13 added risk of complications other than the usual risk of endophthalmitis and wound-related infection.

38,40,41

These

corneal incisions can be placed manually or using femtosecond laser. In a few studies, femtosecond laser-assisted keratotomy has shown better results than LRI during conventional phacoemulsification.42

References 1. Waring GO III, Lynn MJ, Fielding B, et al; Perk Study Group. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. JAMA 1990;263(8):1083–1091 2. Waring GO III, Lynn MJ, McDonnell PJ. Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery. Arch Ophthalmol 1994;112(10):1298–1308 3. McDonnell PJ, Nizam A, Lynn MJ, Waring GO III; The PERK Study Group. Morning-to-evening change in refraction, corneal curvature, and visual acuity 11 years after radial keratotomy in the prospective evaluation of radial keratotomy study. Ophthalmology 1996;103(2):233–239 4. Rashid ER, Waring GO III. Complications of radial and transverse keratotomy. Surv Ophthalmol 1989;34(2): 73–106 5. Lindstrom RL. The surgical correction of astigmatism: a clinician’s perspective. Refract Corneal Surg 1990;6(6): 441–454 6. Sheridan M, Douthwaite WA. Corneal asphericity and refractive error. Ophthalmic Physiol Opt 1989;9(3): 235–238 7. Kanellopoulos AJ, Asimellis G. Distribution and repeatability of corneal astigmatism measurements (magnitude and axis) evaluated with color light emitting diode reflection topography. Cornea 2015; 34(8):937–944 8. Miyata K, Miyai T, Minami K, Bissen-Miyajima H, Maeda N, Amano S. Limbal relaxing incisions using a reference point and corneal topography for intraoperative identi­ fication of the steepest meridian. J Refract Surg 2011; 27(5):339–344 9. Price FW, Grene RB, Marks RG, Gonzales JS; ARC-T Study Group. Astigmatism reduction clinical trial: a multicenter prospective evaluation of the predictability of arcuate keratotomy. Evaluation of surgical nomogram predictability. Arch Ophthalmol 1995;113(3):277–282 10. Kwitko ML, Jovkar S, Yan H, Rymer S. Arcuate kerat­ otomy to correct naturally occurring astigmatism. J Cataract Refract Surg 1996;22(10):1439–1442

11. Thornton SP. Astigmatic keratotomy: a review of basic concepts with case reports. J Cataract Refract Surg 1990; 16(4):430–435 12. Monaco G, Scialdone A. Long-term outcomes of limbal relaxing incisions during cataract surgery: aberrometric analysis. Clin Ophthalmol 2015;9:1581–1587 13. Chang JSM. Femtosecond laser-assisted astigmatic keratotomy: a review. Eye Vis (Lond) 2018;5:6 https:// www.ncbi.nlm.nih.gov/pmc/articles/PMC5853056/ cited2019May22 [Internet] 14. Aristeidou A, Taniguchi EV, Tsatsos M, et al. The evolution of corneal and refractive surgery with the femtosecond laser. Eye Vis (Lond) 2015;2:12 https:// www.ncbi.nlm.nih.gov/pmc/articles/PMC4655461/ cited2019May22 [Internet] 15. Bahar I, Levinger E, Kaiserman I, Sansanayudh W, Rootman DS. IntraLase-enabled astigmatic keratotomy for postkeratoplasty astigmatism. Am J Ophthalmol 2008;146(6):897–904.e1 16. Kymionis GD, Yoo SH, Ide T, Culbertson WW. Femtosecond-assisted astigmatic keratotomy for postkeratoplasty irregular astigmatism. J Cataract Refract Surg 2009;35(1):11–13 17. Kook D, Bühren J, Klaproth OK, Bauch AS, Derhartunian V, Kohnen T. [Astigmatic keratotomy with the femto­ second laser: correction of high astigmatisms after keratoplasty]. Ophthalmologe 2011;108(2):143–150 18. Raviv T, Epstein RJ. Astigmatism management. Int Ophthalmol Clin 2000;40(3):183–198 19. Cristóbal JA, del Buey MA, Ascaso FJ, Lanchares E, Calvo B, Doblaré M. Effect of limbal relaxing incisions during phacoemulsification surgery based on nomogram review and numerical simulation. Cornea 2009;28(9): 1042–1049 20. Elhofi AH, Helaly HA. Comparison between digital and manual marking for toric intraocular lenses: a randomized trial. Medicine (Baltimore) 2015;94(38): e1618 21. Mayer WJ, Kreutzer T, Dirisamer M, et al. Comparison of visual outcomes, alignment accuracy, and surgical time between 2 methods of corneal marking for toric intraocular lens implantation. J Cataract Refract Surg 2017;43(10):1281–1286 22. Montés-Micó R, Muñoz G, Albarrán-Diego C, RodríguezGalietero A, Alió JL. Corneal aberrations after astigmatic keratotomy combined with laser in situ keratomileusis. J Cataract Refract Surg 2004;30(7):1418–1424 23. Hirnschall N, Gangwani V, Crnej A, Koshy J, Maurino V, Findl O. Correction of moderate corneal astigmatism during cataract surgery: toric intraocular lens versus peripheral corneal relaxing incisions. J Cataract Refract Surg 2014;40(3):354–361

Corneal Incision Surgery 205 24. Mingo-Botín D, Muñoz-Negrete FJ, Won Kim HR, Morcillo-Laiz R, Rebolleda G, Oblanca N. Comparison of toric intraocular lenses and peripheral corneal relaxing incisions to treat astigmatism during cataract surgery. J Cataract Refract Surg 2010;36(10):1700–1708 25. Poll JT, Wang L, Koch DD, Weikert MP. Correction of astigmatism during cataract surgery: toric intraocular lens compared to peripheral corneal relaxing incisions. J Refract Surg 2011;27(3):165–171 26. Güell JL, Vazquez M. Correction of high astigmatism with astigmatic keratotomy combined with laser in situ keratomileusis. J Cataract Refract Surg 2000;26(7): 960–966 27. Krachmer JH, Fenzl RE. Surgical correction of high post­ keratoplasty astigmatism. Relaxing incisions vs wedge resection. Arch Ophthalmol 1980;98(8):1400–1402 28. Hoffart L, Proust H, Matonti F, Conrath J, Ridings B. Correction of postkeratoplasty astigmatism by femto­ second laser compared with mechanized astigmatic keratotomy. Am J Ophthalmol 2009;147(5):779–787, 787.e1 29. Ho Wang Yin G, Hoffart L. Post-keratoplasty astigmatism management by relaxing incisions: a systematic review. Eye Vis (Lond) 2017;4:29 https://www.ncbi.nlm. nih.gov/pmc/articles/PMC5725940/ cited2019Jun18 [Internet] 30. Wilkins MR, Mehta JS, Larkin DFP. Standardized arcuate keratotomy for postkeratoplasty astigmatism. J Cataract Refract Surg 2005;31(2):297–301 31. Hanna KD, Hayward JM, Hagen KB, Simon G, Parel JM, Waring GO III. Keratotomy for astigmatism using an arcuate keratome. Arch Ophthalmol 1993;111(7):998– 1004 32. Al Sabaani N, Al Malki S, Al Jindan M, Al Assiri A, Al Swailem S. Femtosecond astigmatic keratotomy for postkeratoplasty astigmatism. Saudi J Ophthalmol 2016;30(3):163–168

33. Cleary C, Tang M, Ahmed H, Fox M, Huang D. Beveled femtosecond laser astigmatic keratotomy for the treatment of high astigmatism post-penetrating keratoplasty. Cornea 2013;32(1):54–62 34. Langerman DW. Architectural design of a self-sealing corneal tunnel, single-hinge incision. J Cataract Refract Surg 1994;20(1):84–88 35. Fine IH. Clear corneal incisions. Int Ophthalmol Clin 1994;34(2):59–72 36. Vasavada V, Vasavada AR, Vasavada VA, Srivastava S, Gajjar DU, Mehta S. Incision integrity and postoperative outcomes after microcoaxial phacoemulsification performed using 2 incision-dependent systems. J Cataract Refract Surg 2013;39(4):563–571 37. Tejedor J, Pérez-Rodríguez JA. Astigmatic change induced by 2.8-mm corneal incisions for cataract surgery. Invest Ophthalmol Vis Sci 2009;50(3):989–994 38. Bazzazi N, Barazandeh B, Kashani M, Rasouli M. Opposite Clear Corneal Incisions versus Steep Meridian Incision Phacoemulsification for Correction of Pre-existing Astigmatism. J Ophthalmic Vis Res 2008;3(2):87–90 39. Tadros A, Habib M, Tejwani D, Von Lany H, Thomas P. Opposite clear corneal incisions on the steep meridian in phacoemulsification: early effects on the cornea. J Cataract Refract Surg 2004;30(2):414–417 40. Lever J, Dahan E. Opposite clear corneal incisions to correct pre-existing astigmatism in cataract surgery. J Cataract Refract Surg 2000;26(6):803–805 41. Khokhar S, Lohiya P, Murugiesan V, Panda A. Corneal astigmatism correction with opposite clear corneal incisions or single clear corneal incision: comparative analysis. J Cataract Refract Surg 2006;32(9):1432–1437 42. Roberts HW, Wagh VK, Sullivan DL, Archer TJ, O’Brart DPS. Refractive outcomes after limbal relaxing incisions or femtosecond laser arcuate keratotomy to manage corneal astigmatism at the time of cataract surgery. J Cataract Refract Surg 2018;44(8):955–963

Chapter 14 Presbyopia Correction

Introduction.....................................................................................208 Nonsurgical Methods for Correction of Presbyopia............ 209 Surgical Methods for Correction of Presbyopia.................... 210 Laser Assisted Presbyopia Corrections.................................... 216 Conclusion........................................................................................217

14. Presbyopia Correction Pulak Agarwal, Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

Introduction

(AP). Thus, it proposes loss of lens capsule elasticity as the main cause of loss of accommodation.

Loss of accommodative amplitude due to aging is known as presbyopia. Symptoms include diminution of vision for near sight, headache, asthenopia, and eye strain. Many plausible mechanisms in the form of theories have been proposed for accommodation (Fig. 14.1),

Schachar Theory3 It proposes that during ciliary contraction, the tension in equatorial zonular fibers increases, which leads to steepening of anterior lens capsule. With aging, the distance between

Helmholtz Theory1,2

ciliary body and the equatorial lens capsule decreases, which

It proposes that when the ciliary body is relaxed, the

based interventions are based on this theory.

causes ineffective tension generation. Most of the scleral-

zonules are stretched, which lead to flattening of anterior lens capsule and decrease in the diameter (AP) of the lens. As opposed to when the ciliary body contracts, zonules are

Catenary Theory

slackened; due to lens capsule elasticity, the anterior cap-

It proposes ciliary body, zonules, lens, and anterior vitreous,

sule steepens, which causes an increase in lens diameter

as a part of diaphragm. Contraction of ciliary body causes

Ciliary muscle

Zonules

Contracts

Contracts

All zonules relax and curl

Centre zonules become tight

Central part of lens becomes thicker and more steeply curved

Tension in lens causes it to become rounder

Front and back zonules relax and curl

Unaccommodated lens

Accommodated lens Helmholtz theory

Fig. 14.1  Illustration depicting various mechanisms of accommodation.

Accommodated lens Schachar theory

Presbyopia Correction 209 increase in vitreous pressure, which leads to anterior shift of lens and, thus, accommodation.

Spectacles They come in a variety of designs and materials. A person

What Happens with Age?

can use different sets for near and distance vision. If this is

The reason for the age-related decline in the amplitude of

correction in the same pair of glasses.

tedious, near vision can be incorporated over the distance

accommodation is not fully understood. Evidence suggests ciliary muscle atrophy and increase in connective tissue over time may lead to ciliary muscle weakening.4,5

The drawback being that it does not account for intermediate vision. To account for this problem, many designs have come up. Bifocal, trifocal, and progressive are few of the

In addition to this, lens becomes thicker and stiffer with age, which may contribute to reduced accommodation.

6

commonly used designs (Fig. 14.2). In the latter category, there can be hard progression or soft progression, depending on the refractive error and near add transition. In cases

Nonsurgical Methods for Correction of Presbyopia Although in this chapter, our main focus is on the surgical

of hard progression, there is a significant complaint of image jump, which patients have great difficulty in adapting to. Also micromonovision can be used with spectacles to varying success.

correction methods of presbyopia, there is also a brief overview of more conventional methods in this section.

Single vision lens

A

Distance or Near

Bifocal lens

B

Distance near

C

Distance near

D

Distance near

Trifocal lens

E

Distance Intermidate Near

Progressive lens

F

Distance Near

Fig. 14.2  A monofocal lens B, C, D. Bifocal lens– C-shaped, D-shaped, and executive bifocal lens C. Trifocal lens D. Progressive lens.

210 Chapter 14

Contact Lens Contact lenses can be used in many different ways to help with the problem of presbyopia:

associated with these designs are induction of aberrations, reduced contrast sensitivity, glare, halos, etc. Modified micromonovision can be used with the multifocal lenses, in which one eye can be corrected for distance,

Monovision

and the other eye can have multifocal multifocal near add.

It is the method most commonly resorted to. Dominant

can be used either with same design (center distance or

eye is corrected for distance and nondominant eye for near vision. Acceptance rate is generally good. Optimum addition is generally + 1.5D. Addition more than this may cause difficulty in stereopsis and less than this may not solve the purpose of near add altogether.

Multifocal Contact Lenses Soft bifocal or multifocal contact lenses are available in different designs (center distance/center near; two rings/multiple rings; Fig. 14.3). It has varying acceptance rates among patients. It is a pupil dependent method. The main problems

Also, simultaneous multifocal contact lenses in both eyes center near) or crossover designs. Crossover designs may have a little more success as compared with the former. There is a limited research that has been conducted on rigid gas permeable (RGP) lenses with multifocality. The diffractive component can be added in those to increase the range of focus. Recent literature reports use of contact lens with pinhole.7 Near vision and intermediate vision improves with no negative effect on binocular visual field and distance visual acuity; although, contrast sensitivity decreases at certain frequencies.

Surgical Methods for Correction of Presbyopia A

On the Basis of Cornea Inlays Various corneal inlays have been used for correction of presbyopia (Fig. 14.4). Below are few which are commonly used.

B

Kamra Inlay It is a Food and Drugs Administration (FDA)–improved corneal implant. It is an opaque implant inserted in the corneal pocket created using femtosecond laser technology (depth of 200 μm). It is generally inserted in the nondominant eye.

C

This polyvinylidene fluoride inlay has around 8400 micro pinholes which lead to adequate perfusion anterior and posterior to the inlay. It increases the depth of focus with minimal effect on the distance visual acuity. It works on the principle of pinhole effect and causes increase in depth of focus. It can be used with simultaneous laser-assisted in-situ

Fig. 14.3  Types of presbyopic contact lens A. Bifocal D shaped lens B.D Centre design (Distance/ Near) C. Multiple ring Design.

keratomileusis (LASIK) surgery as well and can be implanted in nondominant eye. The main side effects are glare, halos, difficulty in subsequent cataract surgery, and LASIK flap- and

Presbyopia Correction 211

8,400 holes (5–11µm)

3.8 mm diameter

Thickness: 15 µm

Profile view

6 µm thin

1.6 mm aperture

Made from polyvinylidene fluoride (PVDF)

Fig. 14.4 

Corneal inlays.

pocket-related complications (vascularization and epithelial

that are being performed. This implant is no longer recom-

ingrowth). Keratitis has also been reported. In cases with

mended for presbyopia correction.

8

unsatisfactory results, the inlay can be explanted. It should be avoided in patients who require night time driving. The results have been very encouraging with good gain in near vision and good patient satisfaction.9 On long-term follow-up as well, the vision remained stable with no signifi-

Icolens12 It is the most recent addition to the inlay family. It is made up of hydrophilic acrylic hydrogel. It is very similar to flexivue inlay and is under FDA trials.

cant change in refractive errors.10

Small Incision Lenticule Extraction Lenticule

Flexivue Inlay11

Animal study on primates shows good results for presbyopia

It is a hydrophilic acrylic polymer implant with an overall diameter of 3.2 mm. It has a central disk with no power, which provides for distance vision and surrounding that are multiple rings of increasing power providing multifocality. It is a transparent inlay. It has a central hole which provides nutrition through diffusion. It is currently under FDA trials.

Rain Drop Inlay

correction using small incision lenticule extraction (SMILE) lenticule. Central cornea steepens and shape becomes prolate. There is no postoperative corneal haze at 6 months. The drawbacks include thinning of the lenticule in the postoperative period, with regression after a few months. There is also theoretical risk of rejection of the lenticule by the host body. Jacob et al reported using SMILE lenticule for presbyopia

It is a corneal reshaping inlay with no power of its own. It

in four patients with good visual outcome. All the patients

was FDA-approved in 2016 but has been recalled due to

had good near vision (J2), decent intermediate vision, and

significant corneal haze in postoperative period. Due to

good distance visual acuity. There was no gross ocular dis-

this haze, there is an increasing number of inlay removals

comfort, glare, halos, or rejection.13

212 Chapter 14 a disadvantage in that it leads to excessive loss of

Laser Vision Correction

corneal tissue due to myopia correction in central

PresbyLASIK

cornea.

Correction of presbyopia at the corneal plane by creating a

Epstein et al reported 92% and 89% of spectacle

multifocal ablation profile using excimer laser is achieved by

independence in myopic and hyperopic patients at

a procedure known as PresbyLASIK. It can be of two types:

1-year follow-up. Higher order aberrations (HOAs)

1. Central PresbyLASIK: It is achieved by creating a

were increased in both the groups.15

hyperpositive area in the central cornea which helps in near vision; the peripheral area is left for distance

Supracor

vision. As miosis occurs during the near vision triad,

It is an algorithm developed by Technolas Perfect Vision

this approach seems very practical, as the central

GmbH, Munich, Germany. It optimizes aberrations while

area is left for near vision. It can be used in hyper-

creating a hyperpositive area in the central 3 mm of cornea

opes, myopes, and emmetropes. The drawback being

(+ 2 near add; Fig. 14.6). It can be treated in a symmetri-

the centration of the ablated area over the visual axis,

cal or asymmetrical manner. In the former, both the eyes

which can often be unsatisfactory, as more often

are treated for near vision. In the latter, the dominant eye

than not, the pupillary axis does not coincide with

is treated for distance (plano) and the nondominant eye is

the visual axis.

treated for near.



Alio et al reported the outcomes with 72% of the 25

Ryan et al reported that binocular UNVA better than 0.2

eyes having uncorrected near visual acuity (UNVA)

logMar in 91% of the patients undergoing hyperopic presby-

better than 20/40. Contrast sensitivities decreased

opic LASIK (Supracor). HOAs were increased but there was

uniformly.14

no significant increase in trefoil and coma.16 The majority

2. Peripheral PresbyLASIK: In this procedure, a nega-

(96%) of patients were happy with the procedure in this

tive spherical aberration is induced in the peripheral

study.

cornea. Thus, the peripheral cornea is utilized for near vision and the central cornea is used for distance

PresbyMax

vision (Fig. 14.5). This procedure is mainly used for

PresbyMAX

hyperopes. In myopic patients, this procedure is at

Kleinostheim, Germany) biaspheric corneal surface is

Near vision

Far vision

(SCHWIND

eye-tech-solutions

GmbH,

Near vision

Cornea Iris

Lens

Fig. 14.5  Illustration showing ablation pattern in peripheral PresbyLASIK. Abbreviation: LASIK, laser in-situ keratomileusis.

Presbyopia Correction 213

Intermediate and distance zone

Near addition zone

Intermediate and distance zone

Pre-op cornea Near and far in focus Post-op cornea

Central near addition

Fig. 14.6  Supracor presbyopia correction. Near add is central followed by transition zone and distance vision zone. created and multifocality is achieved by creating a hyper-

Postoperatively, there are three stages of recovery which

positive area from + 0.75D to + 2.50D. The area peripheral to

overlap between swelling, healing, and adaptation. The

this area is ablated for distance vision.

adaptation part can take up to 3 to 4 months.

Uthoff17 reported good visual outcomes with 90% of

It was reported that in emmetropic, myopic, and astig-

emmetropic patients and 80% of the myopic and hyperopic

matic patients, 96% achieved vision better than J2 (Jaeger

patients having UNVA better than 0.3logRAD.

scores).19,20 In hyperopic patients, only 81% achieved near

Luger18 reported 84% of all the patients treated using PresbyMax had UNVA of 0.1logRAD or better.

vision of J3 or better.21

Conductive Keratoplasty

Laser-blended Vision

It is based on the premise that heat denatures collagen.

Presbyond Laser Blended Vision (Carl Zeiss Meditec, Jena,

Eight spots are placed circumferentially at 6 mm, 7 mm,

Germany) is a type of monovision in which the dominant

and 8 mm from the center of optical zone. Thus, when the

eye is corrected for distance and the nondominant eye is

collagen denatures, it contracts and flattens the cornea in

corrected for near (around 1.5D; Fig. 14.7). It is a refined

the center. Stahl et al22 reported that after 1-year follow-up,

version, with the refinement being that it is a wavefront-

patients had good near vision. The vision improved from J10

optimized ablation which leads to low aberration profile.

to J1. There were no complaints of postoperative discomfort

Preoperative workup includes: ••Best-corrected near visual acuity (BCVA) and pupillary reactions. ••Manifest refraction. ••Dominance test (hole test, finger pointing test, camera test, and rifle shooting test). ••Tolerance test (to test for cross blur). ••Schirmer’s test and tear film breakup time (TBUT; more chances of dry eye in adults). ••Corneal topography, tomography, and corneal biomechanics (ocular response analyzer).

as well. However, the major drawback is the regression overtime with this procedure and majority of the patients returning to their baseline error. Due to this reason conductive keratoplasty is not extensively in use currently.

On the Basis of Intraocular Lenses Phakic Multifocal IOLs There is limited literature on use of phakic multifocal intraocular lenses (IOLs) in presbyopia correction.

214 Chapter 14

Distance

Distance

Sharp distance vision

Combined good intermediate vision

BLEND ZONE

Sharp near vision

NEAR Dominant eye ± 0.0 D

NEAR Non- dominant eye − 1.5 D

Fig. 14.7  Principle of Presbyond by Zeiss Meditech; blended vision where dominant eye is treated for distance and nondominant eye is treated for near.

They can be angle-supported or implantable collamer lenses (ICLs). The angle-supported IOL has haptic of polymethylmethacrylate (PMMA) material and optic of hydrophilic acrylic material. It has a four-point fixation. With this, IOL results were satisfactory but inferior to refractive IOLs.23 Complication rate was low. But in patients with slight lens opalescence, there was marked reduction in visual acuity.

Refractive Lens Exchange/Multifocal IOLs This approach is the most widespread and accepted treatment modality for presbyopia. Multifocal IOLs has passed through generation of modifications to reach the present level and there is still ongoing research to improve and refine it even further. Initially, they used to be refractive in nature with mul-

The other type of phakic IOL for presbyopia is implant-

tiple rings of refraction. The center of the IOL can either be

able collamer lens with central hole. Due to the presence of

for near or distance. The refractive multifocal IOL is pupil-

central hole, iridotomy is not needed to prevent pupillary

dependent and patients may have complaints of glare, halos,

block and the chances of development of cataract are low.

and loss of contrast sensitivity.

Preoperative workup has to be done properly with anterior

Recent designs use diffractive designs (Fig. 14.8). They

chamber (AC) depth of a minimum of 3 mm. It is tried as

have two foci. One for near and one for distance. The dif-

a monovision therapy. The postoperative results are satis-

fractive steps are added on to the anterior or posterior sur-

factory with reduction in spectacle dependence and good

face to provide for the near focus. The distance between the

vision in near and intermediate distance.24

steps determine the power of add and height of the steps

Presbyopia Correction 215

Fig. 14.8  Diffraction steps (L) and apodization (R). determine the division of amount of light diffracted to near

It can be achieved by using conventional method, crossover

and distance foci. Some IOLs have an apodised design of

method, and hybrid method. In conventional method, the

diffraction steps, which means that the height of the steps

dominant eye is corrected for plano, and the nondominant

decreases toward the periphery. So, in mesopic conditions,

eye is corrected for myopia and vice versa in crossover

when more of diffraction rings are exposed, more of the light

design. Generally, for successful monovision, −1.5D is an

is focused for distance rather than near. This, in turn, leads

acceptable myopia in the nondominant eye. For minimono-

to a drawback: in dim lit situations, it is difficult to work for

vision, dominant eye is implanted with monofocal IOL for

near with multifocal IOLs.

emmetropia. Nondominant eye is implanted with the aim

More recently, trifocal lenses which provide focus for intermediate distance as well have been developed with good success rates. The most recently FDA-approved IOL is a type of extended range of vision or extended depth of focus. It has an echelette type of design. It has nine echelettes at the back of the IOL which are not exactly perpendicular but slightly angled. The slight angulation leads to extended focus for intermediate visual acuity rather than two foci for near and distance as in most multifocal IOLs (Fig. 14.9). Although, the complaints of glare and halos drastically decrease with this IOL but it is not altogether eliminated. Although patients are to be counseled about need of glasses for near vision, they will have good vision for most of the intermediate range of vision and distance vision. Chromatic aberrations are also very less with this type of IOL. Also, patient has to be counseled about a period of neuroadaptation that is required after implantation of this IOL. The most important criteria in successful multifocal IOL implantation is patient selection.

Pseudophakic Monovision

of residual myopia of around − 0.75D. In hybrid monovision, dominant eye is implanted with monofocal IOL and nondominant eye is implanted with multifocal IOL. It is especially useful for people younger than 60 years. Studies have reported that spectacle independence with monovision was comparable with multifocal IOLs. However, multifocal IOLs are generally superior in this respect. Reading ability may be better with this approach as compared with multifocals. Contrast sensitivity is better as compared with multifocal IOLs. Also, night time problems of glare and halos are a little less with this approach. Drawbacks are poor stereoacuity and low-clarity in near and intermediate vision as compared with multifocal IOLs.

Accomodating IOLs Although accommodating IOLs are not used in our setup, this chapter wouldn’t be complete without their mention. These IOLs are based on the premise of changing their shape in response to ciliary body contraction, contraction of lens bag, and positive vitreous pressure. Crystalens and Trulign toric IOL are the only two accommodating IOLs approved by FDA. Crystalens, Tetraflex, and IO human optics are the most commonly used accommodating IOLs. They are all

With increasing demand of spectacle independence and

single optic. They have good visual outcomes; however, bag

affordability, a considerable issue (especially in developing

contraction with loss of accommodating ability of the IOL is

countries), pseudophakic monovision is a very viable option.

very common.

216 Chapter 14

Echelette side view

Elongated focus Light

Focal length

Fig. 14.9  Principle of extended depth of focus; diffractive echelette design.

and bag filling technology. These are still under research.

Laser Assisted Presbyopia Corrections25,26

On the Basis of Sclera

The LaserACE system uses erbium-yag laser. They use 600 μm

Other IOLs in development on the same lines are Nu lens

The scleral approaches are based on the premise of Schachar theory of accommodation. According to Schachar, due to aging, the lens grows in equatorial diameter, which leads to decrease in distance between lens equator and ciliary body. The decreased distance leads to inadequate pull on zonules which, in turn, leads to inadequate zonular tension and consequent loss of accommodation. The decrease in distance has been proven on magnetic resonance imaging (MRI). The extraocular approaches are considered safer, as they don’t have decrease in distance vision, loss of contrast, halos, glare, etc.

spot size. Nine spots in a diamond matrix pattern are ablated using fiber optic hand piece in nine oblique quadrants of the eye. The postulated mechanism is that it decreases the scleral rigidity and reduces the distance between scleral spur and ora serrata. The latter helps in restoring the anatomical relation of the accommodating mechanism. Preliminary reports are encouraging with improvement in near vision and good patient satisfaction.

Scleral Implant-based Approach It is based on the concept that if the distance between cili-

On the above-stated premise, LaserACE (Ace Vision

ary body and the lens equator is increased by pulling the

Group, Silver Lake, Ohio, USA) and VisAbility Implant System

sclera outward in an area of the ciliary body, effective ten-

Surgery Scleral Implants (Refocus Group, Dallas, Texas, USA)

sion on zonules can be increased. Thus, VisAbility Implant

were developed and are still under trials for actual mecha-

System Surgery Scleral Implants27 (Refocus Group, Dallas,

nism of action and efficacy.

Texas, USA) are rice grain-sized implants which are placed

Presbyopia Correction 217 in scleral tunnels 4 mm from limbus. The procedure requires 360 degrees conjunctival peritomy and formation of scleral tunnels. Preliminary results of the trial show improvement in near vision but prolonged ocular surface recovery.

Conclusion In the current era, various modalities are available for correction of presbyopia. A cornea based or lens based approach may be used based on the age, requirement, amount of refractive error and nucleus status. Monovision using corneal procedure or lens based procedure is a fairly common procedure with low cost and good outcomes. In older patients requiring permanent correction, multifocal IOLs may provide a more suitable alternate. Hence, consideration of variety of patient and surgery related factors can help in achieving excellent outcomes.

References 1. Michaels DD. Visual optics and refraction: a clinical approach, 3rd ed. St. Louis, MO: CV Mosby; 1985; Chap. XVIII 2. Fincham EF. The mechanism of accommodation. Br J Ophthalmol Monogr Suppl 1937; 8 3. Schachar RA. Cause and treatment of presbyopia with a method for increasing the amplitude of accommodation. Ann Ophthalmol 1992;24(12):445–447, 452 4. Pardue MT, Sivak JG. Age-related changes in human ciliary muscle. Optom Vis Sci 2000;77(4):204–210 5. Borish I. Clinical Refraction. Chicago, IL: The Professional Press Inc; 1975 6. Weeber HA, Eckert G, Pechhold W, van der Heijde RG. Stiffness gradient in the crystalline lens. Graefes Arch Clin Exp Ophthalmol 2007;245(9):1357–1366 7. Park SY, Choi YJ, Jung JW, et al. Clinical efficacy of pinhole soft contact lenses for the correction of presbyopia. In Seminars in ophthalmology. Mar 10 (pp. 1–9). Taylor & Francis; 2019 8. Duignan ES, Farrell S, Treacy MP, et al. Corneal inlay implantation complicated by infectious keratitis. Br J Ophthalmol 2016;100(2):269–273 9. Seyeddain O, Riha W, Hohensinn M, Nix G, Dexl AK, Grabner G. Refractive surgical correction of presbyopia with the AcuFocus small aperture corneal inlay: twoyear follow-up. J Refract Surg 2010;26(10):707–715 10. Dexl AK, Jell G, Strohmaier C, et al. Long-term outcomes after monocular corneal inlay implantation for the

surgical compensation of presbyopia. J Cataract Refract Surg 2015;41(3):566–575 11. Limnopoulou AN, Bouzoukis DI, Kymionis GD, et al. Visual outcomes and safety of a refractive corneal inlay for presbyopia using femtosecond laser. J Refract Surg 2013;29(1):12–18 12. Bouzoukis DI, Kymionis GD, Panagopoulou SI, et al. Visual outcomes and safety of a small diameter intrastromal refractive inlay for the corneal compensation of presbyopia. J Refract Surg 2012;28(3):168–173 13. Jacob S, Kumar DA, Agarwal A, Agarwal A, Aravind R, Saijimol AI. Preliminary evidence of successful near vision enhancement with a new technique: PrEsbyopic Allogenic Refractive Lenticule (PEARL) corneal inlay using a SMILE lenticule. J Refract Surg 2017;33(4): 224–229 14. Alió JL, Amparo F, Ortiz D, Moreno L. Corneal multifocality with excimer laser for presbyopia correction. Curr Opin Ophthalmol 2009;20(4):264–271 15. Epstein RL, Gurgos MA. Presbyopia treatment by monocular peripheral presbyLASIK. J Refract Surg 2009; 25(6):516–523 16. Ryan A, O’Keefe M. Corneal approach to hyperopic presbyopia treatment: six-month outcomes of a new multifocal excimer laser in situ keratomileusis pro­ cedure. J Cataract Refract Surg 2013;39(8):1226–1233 17. Uthoff D, Pölzl M, Hepper D, Holland D. A new method of cornea modulation with excimer laser for simultaneous correction of presbyopia and ametropia. Graefes Arch Clin Exp Ophthalmol 2012;250(11):1649–1661 18. Luger MH, Ewering T, Arba-Mosquera S. Oneyear experience in presbyopia correction with biaspheric multifocal central presbyopia laser in situ keratomileusis. Cornea 2013;32(5):644–652 19. Reinstein DZ, Carp GI, Archer TJ, Gobbe M. LASIK for presbyopia correction in emmetropic patients using aspheric ablation profiles and a micro-monovision protocol with the Carl Zeiss Meditec MEL 80 and VisuMax. J Refract Surg 2012;28(8):531–541 20. Reinstein DZ, Archer TJ, Gobbe M. LASIK for myopic astigmatism and presbyopia using non-linear aspheric micro-monovision with the Carl Zeiss Meditec MEL 80 platform. J Refract Surg 2011;27(1):23–37 21. Reinstein DZ, Archer TJ, Gobbe M. Aspheric ablation profile for presbyopic corneal treatment using the MEL80 and CRS Master Laser Blended Vision module. J Emmetropia 2011;2(3):161–175 22. Stahl JE. Conductive keratoplasty for presbyopia: 1-year results. J Refract Surg 2006;22(2):137–144 23. Baïkoff G, Matach G, Fontaine A, Ferraz C, Spera C. Correction of presbyopia with refractive multifocal phakic intraocular lenses. J Cataract Refract Surg 2004;30(7):1454–1460

218 Chapter 14 24. Kamiya K, Takahashi M, Takahashi N, Shoji N, Shimizu K. Monovision by implantation of posterior chamber phakic intraocular lens with a central hole (Hole ICL) for early presbyopia. Sci Rep 2017;7(1):11302 25 U.S. National Institutes of Health Clinical Trials. LaserACE Procedure Restore Visual Function and Range of Accommodation LaserACE Procedure. NCT01491360

26. Hipsley A, Ma DH, Sun CC, Jackson MA, Goldberg D, Hall B. Visual outcomes 24 months after LaserACE. Eye Vis (Lond) 2017;4:15 27. U.S. National Institutes of Health Clinical Trials. A Clinical Trial of The VisAbility Micro Insert System for Presbyopic Patients

Chapter 15 Bioptics

Introduction.....................................................................................220 History...............................................................................................220 Indications........................................................................................220 Bioptics with Phakic IOL..............................................................221 Bioptics with Refractive Lens Exchange.................................. 221 Conclusion........................................................................................222 Case-based Approach....................................................................223

15. Bioptics Chirakshi Dhull, Yogita Gupta, and Sudarshan Khokhar

Introduction

With the passage of time, bioptics has been performed in patients in various combinations as listed in Table 15.1. The

Bioptics refers to the combination of cornea-based and lens-

order depends on the surgeon’s preference. Since lens-based

based procedures for the correction of refractive errors not

procedures offer a larger range of correction than cornea-

fully correctable by a single procedure.1–3 Surgery is per-

based procedures, most surgeons prefer them first, followed

formed in a sequential manner for the correction of large

by a more precise cornea-based procedure. In some cases,

refractive errors. The aim is to correct the maximum possi-

where there is inadvertent residual error following pri-

ble refractive error in a predictable manner while preserving

mary surgery, bioptics with phakic IOL may be performed

corneal asphericity. To achieve this, a combined approach

(unplanned bioptics).5,6 Surgery is performed in two steps in

for refractive correction using lens- and cornea-based pro-

most cases. In the past, a three-stage surgery was proposed

cedures is ideal. If a very large amount of refractive correc-

where flap creation was followed by phakic IOL implantation

tion is performed on cornea only, it will cause an increase

and then laser ablation.7,8 In patients with iris-claw phakic

in higher-order aberrations as well as risk of ectasia. Lens-

IOL, there was a concern for endothelial touch or IOL disloca-

based correction alone may not correct refractive error fully

tion during suction generation for flap formation. This has

due to limitation in available power for phakic intraocular lens (IOL).

not been reported, hence, at present, two-stage procedures are preferred. Corneal retreatment following a cornea-based

Table 15.1 gives an overview of the procedures included

refractive surgery should not be considered bioptics. This

in bioptics.

has been discussed in detail in chapter 9 on retreatment.

History

Indications

The first report of bioptics was published by Maloney et

Table 15.2 lists the indications for bioptics. Bioptics poten-

al in 1995, where photorefractive keratectomy (PRK) was

tially covers a wide range of refractive errors and virtually

performed for residual myopia in patients operated for

makes refractive surgery possible for everyone. Incomplete

cataract. Zaldivar gave the term “bioptics”, while using

correction following a single procedure offers much lower

the same for extreme myopia, as a combination of phakic

patient satisfaction and does not eliminate the burden

IOL with LASIK. It has also been referred to as “adjustable

of spectacles completely. In these patients, bioptics is

refractive surgery”.

worth trying.

4

2

4

Table 15.1  Various procedures included in bioptics First procedure

Phakic IOL

Refractive lens exchange with IOL

Laser-assisted in situ keratomileusis (LASIK)/photorefractive keratectomy (PRK) (reverse bioptics)

Second procedure

LASIK/PRK/ intracorneal rings

LASIK/PRK/intracorneal rings

Phakic IOL/refractive lens exchange with IOL

Bioptics 221

Bioptics with Phakic IOL

following Intacs and found refraction with 1 D in all patients

Bioptics following angle-fixated, iris-fixated, and posterior

phakic IOLs can provide good outcomes in select cases.

with keratoconus.14 Using a combination of Intacs with

chamber phakic IOL have been published in literature with good outcomes.8–11 The biggest advantage of this procedure is the preservation of accommodation and a reduction in the risk of retinal detachment compared to refractive lens exchange. Indications for the procedure have been listed in Table 15.2. Zaldivar et al have shown the safety and predictability of bioptics in myopia and myopic astigmatism.11 They found no added risk of retinal complications in extreme myopes. In addition, target refraction achieved was +/− 0.5 D and it was stable over 4 years. Many hyperopes may be unsuitable for phakic IOLs due to shallow anterior chamber depth (ACD). When ACD is adequate, bioptics can be planned in these patients. Munoz et al used Artisan iris-claw phakic IOL with LASIK for correction of high hyperopia.12 They found bioptics to be effective and predictable in high hyperopes. One-third of the patients had a one-line reduction in best corrected visual acuity likely due to loss of the magnification effect of spectacles. This should be discussed preoperatively. No vision-threatening complications were observed but glare and haloes were a concern. A good preoperative counseling can help improve patient satisfaction. Combining intracorneal rings with phakic IOL has also been reported in the literature for keratoconus patients.13,14 In both studies, Intacs were implanted first. An interval of 6 to 10 months was kept between the first and second

Bioptics with Refractive Lens Exchange Combining corneal refractive surgery with refractive lens exchange (RLE) is relatively rarely planned. It may be required in situations where there is extreme myopia or hyperopia and IOL power is a limiting factor. More commonly, it is performed following RLE or cataract surgery where there is residual refractive error (unplanned bioptics). Indications for the same have been listed in Table 15.2. Problems and complications are mainly related to intraocular surgery, including loss of accommodation, retinal complications, etc.15 Its advantage is that it covers a wider range of corrections and ACD is not a limiting factor. Zaldivar et al have shown the safety and efficacy of bioptics using RLE in myopia and myopic astigmatism.11 Correction of myopia been reported in the range of –18 to –35 D.2 Hyperopia is an important indication for bioptics with RLE since phakic IOLs are not feasible in many cases. RLE with LASIK or PRK yields good results in hyperopia and hyperopic astigmatism, with stable correction in most cases.16,17 Similar procedures can be employed for presbyopia as well.18 RLE using multifocal IOL has also been successfully combined with LASIK or PRK.19,20 This provides accurate correction for distance as well as near vision and reduces the need for near glasses in patients.

procedures. Phakic IOL was then implanted for myopia and

Reverse bioptics, where corneal surgery is performed

myopic astigmatism. El-Raggal found good outcomes with

first followed by lens-based procedure, have also been per-

Intacs followed by Verisyse phakic IOL in 8 eyes with kera-

formed. In most cases, the lens-based procedure is a better

toconus, with final equivalent between –1.75 D to +1 D.

option or the only option following corneal refractive sur-

Coskunseven et al used toric implantable Collamer lens

gery, where corneal retreatment is not ideal.

13

Table 15.2  Indications for bioptics Type of bioptics procedure

Indications

Phakic IOL-based bioptics

Planned bioptics: High myopia, hyperopia, or astigmatism (beyond the range of phakic IOL-only correction) Unplanned bioptics: Myopic progression or unexpected refractive error following phakic IOL implantation; regression following corneal surgery (reverse bioptics)

Refractive lens exchange-based bioptics

Planned bioptics: High myopia, hyperopia, or astigmatism (unsuitable for phakic IOL, such as low anterior chamber depth) Unplanned bioptics: Unexpected refractive error following IOL surgery

222 Chapter 15

Conclusion With the advancement in refractive procedures, combining lens-based procedures with cornea-based procedures treats refractive error in a much wider range compared to a single procedure. It offers the advantage of providing a full refractive correction. Complications are primarily similar to that in individual procedures and no additional risk is reported. Hence, it can be considered a safe and predictable method for the correction of high refractive errors.

References 1. Güell J, Vázquez M. Bioptics. Int Ophthalmol Clin 2000; 40(3):133–143 2. Zaldivar R, Davidorf JM, Oscherow S, Ricur G, Piezzi V. Combined posterior chamber phakic intraocular lens and laser in situ keratomileusis: bioptics for extreme myopia. J Refract Surg 1999;15(3):299–308 3. Dvali ML, Tsinsadze NA, Sirbiladze BV. Bioptics with LASIK flap first for the treatment of high ametropia. J Refract Surg 2009; 25(1, Suppl)S160–S162 4. Güell J. The adjustable refractive surgery concept (ARS). [letter] J Refract Surg 1998;14(3):271 5. Maloney RK, Chan WK, Steinert R, Hersh P, O’Connell M; Summit Therapeutic Refractive Study Group. A multi­ center trial of photorefractive keratectomy for residual myopia after previous ocular surgery. Ophthalmology 1995;102(7):1042–1052, discussion 1052–1053 6. Güell JL, Gris O, de Muller A, Corcostegui B. LASIK for the correction of residual refractive errors from previous surgical procedures. Ophthalmic Surg Lasers 1999;30(5):341–349 7. Bleckmann H, Jørgensen J, Lamcke I, Keuch R. Bioptik Ein Verfahren der refraktiven Chirurgie zur Korrektur der hohen und extremen Myopie. Ophthalmologe 2002; 99(12):936–940 8. Güell JL, Vázquez M, Gris O. Adjustable refractive surgery: 6-mm Artisan lens plus laser in situ keratomileusis for the correction of high myopia. Ophthalmology 2001;108(5):945–952 9. Güell JL, Vazquez M, Gris O, De Muller A, Manero F. Combined surgery to correct high myopia: iris claw

phakic intraocular lens and laser in situ keratomileusis. J Refract Surg 1999;15(5):529–537 10. Sánchez-Galeana CA, Smith RJ, Rodriguez X, Montes M, Chayet AS. Laser in situ keratomileusis and photorefractive keratectomy for residual refractive error after phakic intraocular lens implantation. J Refract Surg 2001;17(3):299–304 11. Zaldivar R, Oscherow S, Piezzi V. Bioptics in phakic and pseudophakic intraocular lens with the Nidek EC-5000 excimer laser. J Refract Surg 2002; 18(3, Suppl)S336– S339 12. Muñoz G, Alió JL, Montés-Micó R, Albarrán-Diego C, Belda JI. Artisan iris-claw phakic intraocular lens followed by laser in situ keratomileusis for high hyperopia. J Cataract Refract Surg 2005;31(2):308–317 13. El-Raggal TM, Abdel Fattah AA. Sequential Intacs and Verisyse phakic intraocular lens for refractive improve­ ment in keratoconic eyes. J Cataract Refract Surg 2007; 33(6):966–970 14. Coskunseven E, Onder M, Kymionis GD, et al. Combined Intacs and posterior chamber toric implantable Collamer lens implantation for keratoconic patients with extreme myopia. Am J Ophthalmol 2007;144(3):387–389 15. Alió JL, Grzybowski A, El Aswad A, Romaniuk D. Refractive lens exchange. Surv Ophthalmol 2014;59(6):579–598 16. Velarde JI, Anton PG, de Valentin-Gamazo L. Intraocular lens implantation and laser in situ keratomileusis (bioptics) to correct high myopia and hyperopia with astigmatism. J Refract Surg 2001; 17(2, Suppl)S234– S237 17. Probst LE. Refractive lensectomy and cross-cylinder laser in situ keratomileusis for the correction of extreme hyperopic astigmatism. J Cataract Refract Surg 2004; 30(5):1136–1138 18. Leccisotti A. Secondary procedures after presbyopic lens exchange. J Cataract Refract Surg 2004;30(7):1461– 1465 19. Piñero DR, Ayala Espinosa MJ, Alió JL. LASIK outcomes following multifocal and monofocal intraocular lens implantation. J Refract Surg 2010;26(8):569–577 20. Santhiago MR, Ventura BV, Ghanem RC, Kara-Junior N, Moraes HV Jr, Ghanem E. Predictability and vector analysis of laser in situ keratomileusis for residual errors in eyes implanted with different multifocal intraocular lenses. Cornea 2016;35(11):1404–1409

Bioptics 223

Case-based Approach A 31-year-old software engineer presented to a refractive

The disadvantages are a significant cost burden

clinic for removal of spectacles. He had used spectacles from

and an increased risk of retinal detachment in the

9 years of age. He had a stable refraction for the last 3 to

future. The risk of haloes and glares is also present.

4 years. A slit-lamp examination and tear-film assessment

4. Phakic IOL alone: The advantage is that it is a single

revealed no abnormality. He had previously undergone

procedure where the power of glasses will be reduced. The cost burden is less compared with bioptics.

retinal laser for lattice degeneration in both eyes, with no new lesions. Patient parameters are given in Table 15.3.

The disadvantage is incomplete correction. The

Pentacam of both eyes is as shown in Fig. 15.1a, b.

power of glasses is reduced significantly, but the patient will have to wear glasses most of the time.

The patient has been using contact lenses for the past 5 years on occasion but is unhappy with the idea of a daily

The pros and cons of all the procedures were discussed with the patient. The final decision has to be made by the

routine.

patient. He is currently planned for bioptics, where Toric

Discussion

phakic T-ICL was done in the first stage, followed by cor-

The refractive error in the patient is very high, it cannot be

an advantage in this patient as maximum correction can be

treated fully with a single procedure.

performed in the first surgery. The second surgery was done

Surgical Options 1. Bioptics: Phakic IOL followed by cornea-based surgery for residual refractive error. The advantages of this technique are: preserved accommodation, lesser retinal complica-

neal refractive surgery in the second sitting. T-IOL offers

for residual error after an interval of 3 months. The residual error after T-ICL was OD -6.5DS and OS-6DS. This was corrected using LASIK surgery. UCVA at 1 week and 1 month was OD 6/6, OS 6/6. Patient is currently under follow-up.

tions, and potentially full correction without added

Table 15.3  Patient parameters

complications.

Parameter

OD

OS

Uncorrected visual acuity (UCVA)

1/60

1/60

Best corrected visual acuity (BCVA)

6/12

6/9

Cycloplegic refraction

–24 DS/–1.5 DC @110

–24DS/–1 DC @100

Keratometry (K) 1, D

42.5

43

K2, D

44

44

advantage is that it is a single-step procedure with

Axis, degrees

108.6

102.4

fast rehabilitation. The cost burden is also much less.

K max, D

43.3

43.5

Thinnest pachymetry, μm

579

573

and a permanent need to wear glasses at a young age.

Pupillary diameter, mm

3.37

3.15

There is also an increased risk of retinal detachment

Posterior elevation

+5

+4

in the future.

D value

0.68

0.47



The disadvantage is that it is a two-step procedure

and will require a 3–6 month gap for interval surgery and complete rehabilitation. The second concern is the cost. Since two procedures are required, there is a significant cost burden. 2. Refractive lens exchange with monofocal IOL: The

The disadvantage is the loss of accommodation

3. Refractive lens exchange with multifocal IOL: The

3256

3214

advantage is that it is a single-step procedure and

White-to-white (WTW), mm

11.9

11.8

there is no/reduced need for near use of spectacles

Endothelial anterior chamber depth (ACD), mm

2.97

2.95

for near work glasses.

Specular count, cells/mm

2

224 Chapter 15

a

b Fig.15.1  (a, b) Pentacam of the patient in Table 15.3 showing normal topography.

Appendix: Patient Information and Consent

Patient Information

Consent Forms for Refractive Surgery

More often than not, a refractive surgeon deals with the

The various consent forms which could be used for obtain-

eyes of “normal” individuals and not “patients.” A refractive

ing a written informed consent from patients undergoing

surgeon must counsel patients well before planning any

refractive surgeries are provided henceforth. These should

refractive surgery. Individuals should be counseled to avoid

be handed over to the patients to allow them to read them

dissatisfaction regarding any unrealistic expectations. The

fully, discuss, and then decide for or against their surgery.

merits and demerits, nature of reversibility, cost, success

Depending on individual’s requirements and situations,

rates, and complication rates of all suitable options should

these consent forms may be modified.

be well-communicated to the individuals undergoing refractive surgery. Proper counselling will help the surgeon understand individual’s needs and would also help answer their queries.

Consent for laser-assisted in situ keratomileusis (LASIK) surgery Name of Patient ........................................................................................... Age/Sex .......... Patient ID .............................. Date ............................. Son/Daughter of .................................................................................................. Address ......................................................................................................................................................................... Tel................................................. LASIK reshapes the cornea; it involves raising a thin flap of corneal tissue using a blade/femtosecond laser and remodeling the corneal shape using an excimer laser. During the procedure, the patient is required to fix his/her gaze at the blinking light to ensure proper centration. A clicking sound is heard and a smell similar to that of charring of hair is perceived. Expected benefits– I understand the purpose of LASIK is to reduce short sightedness, long sightedness and/or astigmatism to provide me much better unaided vision than I presently have without spectacles or/and contact lenses. However, I understand that an excellent unaided vision may not be guaranteed. I understand that continuous use of spectacles and/or contact lenses can provide excellent vision and LASIK is an alternative to decrease the dependence on spectacles and/or contact lenses. Possible side effects, risks, and complications– Undercorrection or overcorrection. I understand that calculations used in this surgery are based on previous experience of a large number of patients and they use average values. Thus, depending on the individual variations in response to the procedure, there might be some undercorrection or overcorrection. As a result, I may require some spectacles to achieve best possible vision for distance and/or near. If repeat LASIK treatment may be required, a period of 6 months must elapse between it and the original surgery. Presbyopia. I understand that as I get older (45 years or older), there is a likelihood of requiring spectacles for reading which is based on natural age-related changes in the eye on which there is no direct bearing of the LASIK procedure. Glare, starbursts and double vision. These may occur, more so, in the first 24 hours. In most cases, they disappear in 1 to 4 weeks. Rare complications– infection, inflammation, corneal edema, loss

226 Appendix: Patient Information and Consent or damage to the corneal flap. Long-term changes– there may be alteration in power, requiring spectacles or contact lenses. Technical failure– it may lead to abandoning the procedure and performing a repeat procedure at a later date. I certify that I have fully understood the implications of the above consent and authorize the doctors to perform the procedure on my R/L eye. I have had all the questions answered to my satisfaction. Signature/thumb impression of patient: ............................................................................................................................................................ Name: ............................................................................................................................................................................................................................ Address: ........................................................................................................................................................................................................................ Phone Number (Office) ................................................................................ (Residential) ................................................................................ (Mobile Number) ............................................................................... Date ...................................................... Declaration by doctor– I declare that I have explained the nature and consequences of the procedure to be performed and discussed the risks that particularly concern the patient. I have given the patient an opportunity to ask questions and I have answered these. Doctor’s signature ................................................................ Doctor’s name ....................................................................... Date .......................................................................................... Witness 1

Witness 2

Name: ...........................................................................................

Name: ...........................................................................................

Signature: ...................................................................................

Signature: ...................................................................................

Address: ......................................................................................

Address: ......................................................................................

Phone number: .........................................................................

Phone number: .........................................................................

Date: .......................................

Date: .......................................

Appendix: Patient Information and Consent 227

Consent for small incision lenticule extraction (SMILE) surgery Name of Patient ........................................................................................... Age/Sex .......... Patient ID .............................. Date ............................. Son/Daughter of .................................................................................................. Address ......................................................................................................................................................................... Tel................................................. The SMILE procedure uses the femtosecond laser which is also used to create a LASIK flap. The femtosecond laser cuts out a thin lenticule (small lens) of tissue beneath the corneal surface which is then removed through a smaller incision than LASIK. The SMILE procedure is FDA-approved to be used in patients over 21 years of age for a treatment of myopia ranging from − 1.00 to − 10.00 Diopters (D) in power, astigmatism of -0.75 to − 3D in power and spherical equivalent of up to − 10D in power. A good candidate for refractive surgery such as LASIK would also be a good candidate for SMILE. Like all surgeries, there are some risks involved in this procedure too. Most of the potential complications and side effects listed in the consent for bladeless LASIK also apply to the SMILE procedure (except for flap complications). In addition to these risks, few considerations are specific to the SMILE procedure. If the lenticule has to be successfully created with femtosecond laser, suction needs to be maintained on each eye for about 40 seconds. The suction part of procedure is not felt by most of the patients and they have to look at fixation light during this time. If a patient excessively squeezes their eyelids during this time, there is a chance that suction could be broken. If this lasts for about 15 seconds, the procedure would need to be terminated without completion. Other times during the procedure, the suction can be reapplied and the procedure is successfully completed. If the procedure remains incomplete, the vision should return to its presurgical state. LASIK or photorefractive keratectomy (PRK) can be an alternative which can be performed either the same day or at another time. If you wish to get the alternative procedure done, a separate consent will need to be reviewed and signed giving your permission for the same. At the time of surgery, if the surgeon feels that a patient is unable to maintain suction during the entire procedure, then he may choose to recommend bladeless LASIK instead of SMILE. It will be your option whether to proceed with this alternative treatment. Other complications include the lenticule being torn during removal, perforation of cornea, or a small part of the lenticule being left behind. In majority of the cases, outcome is not affected, but the remaining parts of the lenticule may have to be removed by second surgery, or subsequent surgical procedure might be required to restore vision. As compared to LASIK, SMILE limits the type of retreatments that can be performed to further improve the vision.

Patient’s statement of acceptance and understanding I have read the consent for LASIK using the femtosecond laser and understand that all of the risks associated with this surgery also apply to the SMILE procedure. [

] I am electing to have SMILE performed, but in the event that my surgeon feels that it is unsafe to proceed with SMILE, I consent to have femtosecond LASIK performed.

[

] If the surgeon performs SMILE surgery and my procedure cannot be completed, I request to have the femtosecond LASIK surgery substituted at the same surgery session.

[

] I understand that I may have to return for an alternative procedure at another date.

228 Appendix: Patient Information and Consent The details of the procedure known as SMILE, as well as alternative surgeries such as bladeless LASIK, have been presented to me. My ophthalmologist and staff have answered all of my questions to my satisfaction. I have been offered a copy of this consent form and therefore I consent to SMILE on: Signature/thumb impression of patient: ............................................................................................................................................................ Name: ............................................................................................................................................................................................................................ Address: ........................................................................................................................................................................................................................ Phone Number (Office) ................................................................................ (Residential) ................................................................................ (Mobile Number) ............................................................................... Date ...................................................... Declaration by doctor– I declare that I have explained the nature and consequences of the procedure to be performed and discussed the risks that particularly concern the patient. I have given the patient an opportunity to ask questions and I have answered these. Doctor’s signature ................................................................ Doctor’s name ....................................................................... Date .......................................................................................... Witness 1

Witness 2

Name: ...........................................................................................

Name: ...........................................................................................

Signature: ...................................................................................

Signature: ...................................................................................

Address: ......................................................................................

Address: ......................................................................................

Phone number: .........................................................................

Phone number: .........................................................................

Date: .......................................

Date: .......................................

Appendix: Patient Information and Consent 229

Consent for photorefractive keratectomy (PRK) Name of Patient ........................................................................................... Age/Sex .......... Patient ID .............................. Date ............................. Son/Daughter of .................................................................................................. Address ......................................................................................................................................................................... Tel................................................. In giving my permission for PRK, I understand the following: The long-term risks and effects of PRK surgery are unknown. The goal of PRK with the excimer laser is to reduce dependence upon or need for contact lenses and/or eyeglasses; however, I understand that as with all forms of treatment, the results in my case cannot be guaranteed. For example: 1. I understand that an overcorrection or undercorrection could occur, causing me to become farsighted or nearsighted or increase my astigmatism and that this could be either permanent or treatable. I understand an overcorrection or undercorrection is more likely in people over the age of 40 years and may require the use of glasses for reading or for distance vision some or all of the time. 2. If I currently need reading glasses, I will likely still need reading glasses after this treatment. It is possible that dependence on reading glasses may increase or that reading glasses may be required at an earlier age if I have PRK surgery. 3. Further treatment may be necessary, including a variety of eye drops, the wearing of eyeglasses or contact lenses (hard or soft), or additional PRK or other refractive surgery. 4. My best vision, even with glasses or contacts, may become worse. 5. There may be a difference in spectacle correction between eyes, making the wearing of glasses difficult or impossible. Fitting and wearing contact lenses may be more difficult. 6. I have been informed, and I understand, that certain complications and side effects have been reported in the posttreatment period by patients who have had PRK, including the following:

A. Possible short-term effects of PRK surgery: The following have been reported in the short-term posttreatment period and are associated with the normal posttreatment healing process including mild discomfort or pain (first 72 to 96 hours), corneal swelling, double vision, feeling something is in the eye, ghost images, light sensitivity, and tearing.



B. Possible long-term complications of PRK surgery: ••Haze: Loss of perfect clarity of the cornea, usually not affecting vision, which usually resolves over time. ••Starbursting: After refractive surgery, a certain number of patients experience glare, a “starbursting” or halo effect around lights, or other low-light vision problems that may interfere with the ability to drive at night or see well in dim light. Although there are several possible causes for these difficulties, the risk may be increased in patients with large pupils or high degrees of correction. For most patients, this is a temporary condition that diminishes with time or is correctable by wearing glasses at night or taking eye drops. For some patients, however, these visual problems are permanent. I understand that my vision may not seem as sharp at night as during the day and that I may need to wear glasses at night or take eye drops. I understand that it is not possible to predict whether I will experience these night vision or low-light problems, and that I may permanently lose the ability to drive at night or function in dim light because of them. I understand that I should not drive unless my vision is adequate. These risks in relation to my particular pupil size and amount of correction have been discussed with me. ••Loss of best vision: a decrease in my best vision even with glasses or contacts. ••Intraocular pressure (IOP) elevation: An increase in the inner eye pressure due to posttreatment medications, which is usually resolved by drug therapy or discontinuation of posttreatment medications.

230 Appendix: Patient Information and Consent ••Mild or severe infection: Mild infection can usually be treated with antibiotics and usually does not lead to permanent visual loss. Severe infection, even if successfully treated with antibiotics, could lead to permanent scarring and loss of vision that may require corrective laser surgery or, if very severe, corneal transplantation. ••Keratoconus: Some patients develop keratoconus, a degenerative corneal disease affecting vision that occurs in approximately 1/2000 in the general population. While there are several tests that suggest which patients might be at risk, this condition can develop in patients who have normal preoperative topography (a map of the cornea obtained before surgery) and pachymetry (corneal thickness measurement). Since keratoconus may occur on its own, there is no absolute test that will ensure a patient will not develop keratoconus following laser vision correction. Severe keratoconus may need to be treated with a corneal transplant while mild keratoconus can be corrected by glasses or contact lenses.

C. Infrequent complications. The following complications have been reported infrequently by those who have had PRK surgery: itching, dryness of the eye, foreign body feeling in the eye, double or ghost images, patient discomfort, inflammation of the cornea or iris, persistent corneal surface defect, persistent corneal scarring severe enough to affect vision, ulceration/infection, irregular astigmatism (warped corneal surface which causes distorted images), cataract, drooping of the eyelid, loss of bandage contact lens with increased pain (usually corrected by replacing with another contact lens), and a slight increase of possible infection due to use of a bandage contact lens in the immediate post-operative period.



I understand there is a remote chance of partial or complete loss of vision in the eye that has had PRK surgery.

I understand that it is not possible to state every complication that may occur as a result of PRK surgery. I also understand that complications or a poor outcome may manifest weeks, months, or even years after PRK surgery. I understand this is an elective procedure and that PRK surgery is not reversible. For women only: I am not pregnant or nursing. I understand that pregnancy could adversely affect my treatment result. I have spoken with my physician, who has explained PRK, its risks and alternatives, and answered my questions about PRK surgery. I therefore consent to having PRK surgery. Signature/thumb impression of patient: ............................................................................................................................................................ Name: ............................................................................................................................................................................................................................ Address: ........................................................................................................................................................................................................................ Phone Number (Office) ................................................................................ (Residential) ................................................................................ (Mobile Number) ............................................................................... Date ......................................................

Appendix: Patient Information and Consent 231 Declaration by doctor– I declare that I have explained the nature and consequences of the procedure to be performed and discussed the risks that particularly concern the patient. I have given the patient an opportunity to ask questions and I have answered these. Doctor’s signature ................................................................ Doctor’s name ....................................................................... Date .......................................................................................... Witness 1

Witness 2

Name: ...........................................................................................

Name: ...........................................................................................

Signature: ...................................................................................

Signature: ...................................................................................

Address: ......................................................................................

Address: ......................................................................................

Phone number: .........................................................................

Phone number: .........................................................................

Date: .......................................

Date: .......................................

232 Appendix: Patient Information and Consent

Consent for phakic intraocular lens (IOL) Name of Patient .............................................. Age/Sex .......... Patient ID .............................. Date ............................. Son/Daughter of ........... ....................................................................................... Address ........................................................ Tel................................................................ …………. Nature of the phakic IOL procedure– Surgical implantation of a phakic IOL is one of a number of alternatives for correcting nearsightedness. In phakic implant surgery, an artificial lens (such as the implantable collamer lens [ICL] or Verisyse phakic intraocular lens) is surgically placed inside your eye. The lens is made from material similar to the type used for IOL currently being implanted in the eye to correct vision after cataract surgery. The difference between phakic implant surgery and other intraocular lens implants is that your natural lens is not removed during phakic implant surgery. The phakic lens is inserted in addition to your natural lens. The procedure is performed under local anesthesia for a peribulbar block. Indications and expected benefits– If you have myopia, hyperopia or astigmatism, phakic implant surgery may improve your natural vision without the use of glasses or contacts. Further, they have the advantage of removability and maintaining a more natural corneal shape. Phakic IOL cannot be felt by the patient, require no maintenance, and are less visible than a contact lens to the naked eye. Patients who elect to have phakic IOL implants are not “locked in” to the procedure forever, as are patients who undergo other refractive procedures such as LASIK or PRK. Alternative Treatment– I understand that continuous use of spectacles and/or contact lenses can provide good vision and phakic IOL is an alternative to decrease the dependence on glasses and/or contact lenses. Possible side effects, risks and complications vision threatening complications– Anesthetic complications: In most cases, the surgery will be accomplished with use of an injection around the eye for anesthesia. Very rare complications from injections include damage to the eye muscles, perforation of the eye, and damage to the retina or optic nerve leading to loss of vision. Infection: I understand that mild or severe infection is possible. Mild infection can usually be treated with antibiotics and usually does not lead to permanent visual loss. Severe infection, even if treated with antibiotics, could lead to permanent scarring and loss of vision. Iris atrophy: I understand that I could experience damage to the iris (the colored portion of the eye), leading to iris atrophy, or develop a rise in the pressure in my eye (secondary glaucoma). I may require iridotomy, if this occurs, or eye drops to control the pressure. Retinal detachment: I understand that I could develop a retinal detachment, a separation of the retina from its adhesion at the back of the eye, which usually results from a tear in the retina and could lead to vision loss. Patients with moderate to high levels of nearsightedness have a higher risk of retinal detachment when compared to the general population. This risk level may be increased with implantation of the phakic IOL. Cataract: I understand that I may develop a cataract, or a clouding of the eye’s natural lens, which impairs normal vision, and may require removal of the lens and phakic implant, and insertion of an artificial lens. Corneal involvement: I understand that I may develop corneal swelling (edema) and/or ongoing loss of cells lining the inner surface of my cornea (endothelial cells). These cells play a role in keeping the cornea healthy and clear. Corneal edema and loss of endothelial cells may result in a hazy and opaque appearance of the cornea, which could reduce vision and may require a corneal transplant. Glaucoma: I understand that I may develop glaucoma, which is an increase in the pressure of the eye caused by slowed fluid drainage. Glaucoma can lead to vision loss and may require treatment with long-term medications or surgery.

Appendix: Patient Information and Consent 233 I understand that other complications could threaten my vision, including, but not limited to, iritis or inflammation of the iris (immediate and persistent), uveitis, bleeding, swelling in the retina (macular edema), and other visual complications. Although rare, certain complications may result in total loss of vision or even loss of the eye. Complications may develop days, weeks, months, or even years later. Nonvision-threatening side effects– glare or halos: I understand that there may be increased sensitivity to light or night glare. I also understand that at night there may be a “star bursting” or halo effect around lights. The risk of this side effect may be related to the size of my pupil, and larger pupils may put me at increased risk. Under/overcorrection: I understand that an overcorrection or undercorrection could occur, causing me to become farsighted, remain nearsighted, or increase my astigmatism, and this could be either permanent or treatable with either glasses, contact lenses, or additional surgery. Repeat surgery: I understand that the phakic lens may need to be repositioned, removed surgically, or exchanged for another lens implant. The lens may change position (decentration), or I may require a different size or power of lens than that of the implanted lens. Potential complications of additional surgery include all of the complications possible from the original surgery. Protective glasses: I understand that, after phakic implant surgery, the eye may be more fragile to trauma from impact. I understand that the treated eye, therefore, is somewhat more vulnerable to all varieties of injuries. I understand it would be advisable for me to wear protective eyewear when engaging in sports or other activities in which the possibility of a ball, projectile, elbow, fist, or other traumatizing object contacting the eye may be high. Presyopia: I understand that if, I currently need reading glasses, I will still likely need reading glasses after this treatment. It is possible that dependence on reading glasses may increase or that reading glasses may be required at an earlier age if I have this surgery. I understand that the correction that I can expect to gain from phakic implant surgery may not be perfect. I understand that it is not realistic to expect that this procedure will result in perfect vision, at all times, under all circumstances, for the rest of my life. I understand I may need glasses to refine my vision for some purposes requiring fine detailed vision after some point in my life, and that this might occur soon after surgery or years later. I understand that, since it is impossible to state every complication that may occur as a result of any surgery, the list of complications in this form may not be complete. I understand that because I have a phakic lens, it is important for me to be seen at all follow-up visits as felt necessary by my surgeon. I hereby give permission to release/publish medical data and/or video/audio record/photograph the current procedure and the procedures performed in subsequent/follow-up visits for the advancement of medical knowledge. In signing this consent form for insertion of phakic IOL, I am stating that I have read this consent form (or it has been read to me) and I fully understand the nature and the purpose of and the possible side effects, risks and complications of this procedure. Although it is impossible for the doctor to inform me of every possible complication that may occur, the doctor has answered all my questions to my satisfaction. I give permission to perform phakic IOL insertion on my R/L/both eye(s). Signature/thumb impression of patient: ............................................................................................................................................................ Name: ............................................................................................................................................................................................................................ Address: ........................................................................................................................................................................................................................ Phone Number (Office) ................................................................................ (Residential) ................................................................................ (Mobile Number) ............................................................................... Date ......................................................

234 Appendix: Patient Information and Consent Declaration by doctor– I declare that I have explained the nature and consequences of the procedure to be performed and discussed the risks that particularly concern the patient. I have given the patient an opportunity to ask questions and I have answered these. Doctor’s signature ................................................................ Doctor’s name ....................................................................... Date .......................................................................................... Witness 1

Witness 2

Name: ...........................................................................................

Name: ...........................................................................................

Signature: ...................................................................................

Signature: ...................................................................................

Address: ......................................................................................

Address: ......................................................................................

Phone number: .........................................................................

Phone number: .........................................................................

Date: .......................................

Date: .......................................

Suggested Readings 1. FDA. Available at: https://www.accessdata.fda.gov/cdrh_docs/pdf15/P150040C.pdf. Accessed January 17, 2020. 2. FDA. Available at: https://www.accessdata.fda.gov/cdrh_docs/pdf6/P060004d.pdf. Accessed January 17, 2020. 3. American Academy of Ophthalmology Guidelines and Consent forms 4. Consent Forms Booklet, DOS, AIOS Publication

Index Note: Page numbers followed by f and t indicate figures and tables, respectively. A Aberrometry, 26, 28 Ablation depth (AD), 31–32 Accommodation age-related decline in amplitude of, 209 mechanisms of, 208–209 Anterior chamber bubbles, 85 Anterior chamber depth (ACD), slit-lamp examination for, 18 Argon fluoride (ArF) excimer laser, 56 Artemis (Arcscan), 22 Astigmatic keratotomy (AK), 2, 198–199, 199f, 200 Astigmatism, 177 Astigmatism, incisional correction of astigmatic keratotomy (AK) incisions, 198–199, 199f, 200 complications, 201–202 efficacy, 202 femtosecond laser-assisted, 199–200 LASIK, 202 limbal relaxing incision (LRI), 199 phaco incisions, 197f prerequisite, 197 procedure, 201 types of, 197–198 Autorefractometer, 16f B Bandage contact lens (BCL), 128 Biomechanical properties, 130–131 Bioptics case-based approach, 223–224 definition, 220 history, 220 indications for, 220, 221t procedures included in, 220, 220t with phakic IOL, 221 with refractive lens exchange, 221 Black spots, 108 Buttonhole flap, 82 C Cap parameters, 99, 100f Cap tear, 112, 113f Cassini topographer, 22 Cataract, 164 Catenary theory of accommodation, 208–209 Cavitation bubbles, 5f Central islands, 92 Central toxic keratopathy, 90

Chronic uveitis, 164 Chung’s swing technique, 105 Conductive keratoplasty, 213 Consent forms for LASIK surgery, 225–226 for phakic intraocular lens, 232–234 for PRK, 228–231 for refractive surgery, 225 for SMILE surgery, 227–228 Continuous curvilinear lenticulorhexis technique, 105 Contrast sensitivity, 130 testing chart, 16f Corneal aberrations, 130 Corneal apical scarring, 91–92 Corneal biomechanics, 29 Corneal ectasias, 18 Corneal endothelial cell count, 31 Corneal flaps, 4 Corneal haze, 62, 62f Corneal incision surgery astigmatism, incisional correction of AK incisions, 198–199, 199f, 200 complications, 201–202 efficacy, 202 femtosecond laser-assisted, 199–200 LASIK, 202 limbal relaxing incision, 199 phaco incisions, 197f prerequisite, 197 procedure, 201 types of, 197–198 myopia, incisional correction of, 196–197 phacoincisions, 202–204 post-keratoplasty astigmatism, incisional correction of, 202 Corneal inlays, 210–211, 211f Corneal perforation, 82 Corneal refractive surgery. See Refractive surgery Corneal stroma, 5 Corneal topography systems arc scanning with high-frequency ultrasound, 22 colored light-emitting diode topographer, 22 optical coherence tomography based systems, 22 placido disk-based systems, 20 scanning slit system, 20

Scheimpflug technology, 20 Pentacam AX, 21–22 Pentacam HR tomographer, 21 Pentacam system, 21 Corvis ST, 29, 30f D Decentered ablation, 112 Decentered flap, folded flap, 87 Decision-making, in refractive surgery case-based approach, 39–54 factors influencing, 36 parameters, 38t range of correction for procedures, 36, 37t stepwise flowchart for, 37f suitable candidate selection, 36, 36t Diffuse lamellar keratitis (DLK), 89 Dissection, difficulty in, 108–109, 109f Docking, 101, 103 Dry eye disease, 62, 90, 131 E Early Treatment Diabetic Retinopathy Study (ETDRS) chart, 15f Ectasia Risk Score System, 32 Endothelial cell loss, 164 Enhancements after refractive surgery, 136–142 case-based approach for, 144–156 indications and considerations for, 136–137 retreatment after LASIK, 138 retreatment after phakic intraocular lens insertion, 137 retreatment after SMILE incidence of, 138 VisuMax® circle treatment, 138–139, 139f, 140f, 141f retreatment in surface ablation procedures, 137–138 Epithelial defect, 84 after photorefractive keratectomy, 62f Epithelial ingrowth, 91 Epithelial LASEK, 57 Epithelial LASIK, 57 Excimer lasers beam delivery systems, 6 FDA-approved indications for use of, 63t indications for use of, 63t photoablation principle, 6, 6f

235

236 Index F Femtosecond laser-assisted correction of astigmatism, 199–200 Femtosecond laser-related complications intraoperative problems anterior chamber bubbles, 85 decentered flap, folded flap, 87 difficulty in flap lifting, 82–83 epithelial defect, 84 interface debris, 86–87 opaque bubble layer (OBL), 83 subconjunctival hemorrhages, 85–86 suction loss, 82 vertical gas breakthrough (VGBT), 83–84 late postoperative central islands, 92 corneal apical scarring, 91–92 epithelial ingrowth, 91 optical aberrations, 92 postLASIK corneal ectasia, 91–92 rainbow glare, 91 residual refractive error, 92 vitreoretinal complications, 92 postoperative problems central toxic keratopathy, 90 diffuse lamellar keratitis (DLK), 89 dry eyes, 90 flap dislodgment, 87–88 flap edema, 89 flap striae or folds, 88–89 good acuity plus photosensitivity (GAPP) syndrome, 90 interface haze, 90 post LASIK keratitis, 90–91 pressure-induced stromal keratitis (PISK), 90 steroid-induced glaucoma, 90 transient light photosensitivity syndrome (TLPS), 90 Femtosecond lasers, 128 creation, 5 delivery, 103 evolution of, 4–5 Femto second lenticule extraction, 188 Femto second refractive lenticule extraction (FLEx), 5 Flap dislodgment, 87–88 Flap edema, 89 Flap lifting, difficulty in, 82–83 Flap related intraoperative complications buttonhole flap, 82 corneal perforation, 82 flap subluxation, 82 free flap, 82 incomplete flap, 82 thin flap, 81–82 Flap striae or folds, 88–89

Flap subluxation, 82 Fluorescein strip, 18, 18f Free flap, 82 G Good acuity plus photosensitivity (GAPP) syndrome, 90 H Helmholtz theory of accommodation, 208 Higher-order aberrations (HOA), 80 Hyperopia, 176–177 bioptics for, 190 categorization of, 186 definition of, 186 preoperative considerations for, 186–187 prevalence of, 186 refractive surgical options. See Hyperopic refractive surgery retreatment/enhancements for, 190 Hyperopic ICL (HICL), 163 Hyperopic refractive surgery case-based approach, 192–194 challenges associated with, 186 factors to be considered for, 186 femtosecond lenticule extraction, 188 hyperopic photorefractive keratectomy, 189 LASIK surgery, 187–188, 187f phakic IOLs, 188–189 preoperative considerations, 186–187 refractive lens exchange, 189–190 refractive lenticule extraction, 188 SMILE, 188, 189f I Iatrogenic aberrations, 61–62 Implantable Collamer Lens (ICL), 159, 160 complications, 164 outcomes, 163–164 sizing of, 161–162, 162t surgical technique of, 162–163 Incisional bleeding, 112 Incomplete flap, 82 Interface debris, 86–87 Interface haze, 90 Intraocular lens power considerations, 174–175 types of, 175 Intraoperative ASOCT, 112f Intraoperative mitomycin C (MMC), 62 IOLs, accommodating for presbyopia correction, 215–216 Irregular astigmatism, 61 K Keratomileusis, 3 KISA index %, 22

L Lans, Lendert Jan, 2 LaserACE system, 216 Laser in situ keratomileusis (LASIK), 56, 96, 128 complications, 130 femtosecond laser-related, 82–91 flap related intraoperative, 81–82 late postoperative, 91–92 consent forms for, 225–226 development, 3 FDA approved limits of, 74t for hyperopia, 75, 187–188, 187f for incisional correction of astigmatism, 202 instruments for, 75, 76f for myopia, 74–75outcomes of biomechanical properties, 130–131 contrast sensitivity, 130 corneal aberrations, 130 dry eyes, 131 visual outcome, 130 principle behind, 74 retreatment after, 138 case-based approach for, 149–153 surgical procedure LASIK operating room, 75 steps, 128 treatment, 78 topography customized ablation treatment, 80–81 topography-guided, 80–81 treatment approval and customization, 128 treatment parameters for excimer laser ablation, 77f flap of femtosecond LASIK, 77f recommended, 79t wavefront-optimized LASIK, 78f, 79f treatment planning applications for performing, 75 fluence test, 75 wavefront-optimized and wavefrontguided, 80 Laser microkeratomes, 4 Laser parameters, 99, 100f, 101f, 102f, 103f Laser physics cavitation bubbles, 5, 5f in corneal stroma, 5 excimer lasers beam delivery systems, 6 photoablation principle, 6, 6f femtosecond laser creation, 5 Lasers, evolution of, 3 Laser subepithelial keratomileusis, 57 Laser vision correction, 212–213 Lens-based surgery, 158 Lensometer, 16f

Index 237 Lenticule dissection and extraction, 103–105 Lenticule parameters, 99, 100f, 101f Limbal relaxing incision (LRI), 199 M Macrostriae, 88 Massachusetts Eye and Ear Infirmary criteria (MEEI criteria), 22, 25f Mechanical microkeratomes advancements in development of, 4 classification of, 3–4, 4t complications related to, 3t components, 4f for creating corneal flaps, 4 Hansatome microkeratome, 3–4 Microstriae, 88 Monovision, 210 Multifocal IOLs for presbyopia correction, 214–215 Myopia, 176 incisional correction of, 196–197 O Opaque bubble layer (OBL), 83, 108 Optical aberrations, 92 Optical coherence tomography (OCT) anterior segment, 25 available, 25 based systems, 22 principle of, 26f in refractive surgeries, 25–26 Outcomes of refractive surgery biomechanical properties, 130–131 contrast sensitivity, 130 corneal aberrations, 130 dry eyes, 131 visual outcome, 130 P Pachymetry, 26 Patient examination anterior segment and external examination, 17–18 combined topography/tomography, 22 convergence near-point test, 17 corneal biomechanics, 29–30 corneal diameter, 31 corneal endothelial cell count, 31 corneal evaluation, 18 corneal sensations, 19 corneal tomography, 20–26 corneal topography, 20 dilated fundus examination, 19 Ectasia risk score system, 32 intraocular pressure, 19 Miles test, 17 ocular dominance, 16 ocular motility, 18

orthoptic testing, 17 pachymetry, 26 percentage tissue ablation, 32 pupil size, 18 RSBT, 31–32 tear film assessment, 18–19, 18f visual acuity and refraction, 15–16 wavefront analysis, 26–29 wavefront analysis systems, 22 Patient information, 225 Patient positioning, 99, 101 Patient selection and patient counseling, 99 Patient support system, 98 Pentacam clinical aspects, 27 refractive display of map, 23f, 24f Percentage of tissue ablated (PTA), 32 Phacoincisions, 202–204 Phakic intraocular lens (pIOL), 158 acrysof AC, 159 advantages of, 164t anterior chamber, 158, 160f artiflex/veriflex, 160f artisan/verisyse, 159 bioptics with, 221 case-based approach of, 167–170 consent forms for, 232–234 history of, 158–159 for hyperopia, 188–189 ICL. See Implantable Collamer Lens (ICL) inclusion and exclusion criteria for, 161t insertion, retreatment after, 137 iris-fixated anterior chamber, 158, 159, 160f Kelman Duet AC, 159 posterior chamber, 158–159 for presbyopia correction, 213–214 Phakic refractive lens, 161 Photorefractive keratectomy (PRK), 3, 18, 56 consent forms for, 228–231 retreatment after, 137–138 Phototherapeutic keratectomy (PTK), 18 Pigment dispersion and glaucoma, 164 Post-corneal refractive surgery residual error, 136t Post-keratoplasty astigmatism, incisional correction of, 202 Post-LASIK corneal ectasia, 91–92 Post-LASIK keratitis, 90–91 Presbyopia, 208 Presbyopia correction laser assisted, 216–217 nonsurgical methods for contact lenses, 210 multifocal contact lenses, 210 spectacles, 209, 209f surgical methods for

accommodating IOLs, 215–216 conductive keratoplasty, 213 corneal inlays, 210–211, 211f laser vision correction, 212–213 multifocal IOLs, 214–215 phakic multifocal IOLs, 213–214 pseudophakic monovision, 215 refractive lens exchange, 214–215 scleral approaches, 216 Pressure-induced stromal keratitis (PISK), 90 Pseudophakic monovision, 215 Pupillary reactions, 18 Push-up and push-down techniques, 105 R Radial keratotomy (RK), 2, 2f, 196–197 Rainbow glare, 91 Ray tracing, 28 Refractive correction, 128 Refractive lens exchange (RLE), 158 bioptics with, 221 case-based approach of, 180–183 complications, 177 history of, 172 for hyperopia, 189–190 indications and contraindications for, 172t outcome of, 176–177 for presbyopia correction, 214–215 procedure, 172 surgical consideration in capsulorhexis, 173 femtosecond laser-assisted cataract surgery, 173 hydrodissection, 173 incision, 172–173 intraocular lens power, 174–175 phacoemulsification and irrigation/ aspiration, 173 special, 173–174 Refractive lenticule extraction (ReLEx), 96, 96f, 188 Refractive surgery. See also Phakic intraocular lens (pIOL); Refractive lens exchange (RLE); Transepithelial photorefractive keratectomy (PRK) abbreviations commonly used in, 12t advancements in, 10 classification of, 10, 11t consent forms for, 225–234 contraindications to, 15 corneal incision surgery. See Corneal incision surgery cycloplegic agents used for, 17t decision-making in. See Decisionmaking, in refractive surgery definition, 2 early work in, 2

238 Index FDA approval for, 129t goal of, 10 history of, 7f hyperopic. See Hyperopic refractive surgery implications in, 29–30 incisional correction of astigmatism. See Astigmatism, incisional correction of laser in situ keratomileusis. See Laser in situ keratomileusis (LASIK) optical aberrations after, 29 outcomes evaluated to quantify success in, 12t outcomes of. See Outcomes of refractive surgery patient examination. see Patient examination phakic intraocular lens. See Phakic intraocular lens (pIOL) photorefractive keratectomy. See Photorefractive keratectomy (PRK) preoperative evaluation eyelid abnormalities, 18 ocular examination, 14 patient history, 14–15 screening for lesions of conjunctiva, 18 small incision lenticule extraction. See Small incision lenticule extraction (SMILE) surgery surface ablation procedures. See Surface ablation procedures surgically induced magnification in, 158 surgical steps of, 128, 129f Regression, 61 Residual refractive error, 92, 136 Retained lenticule, 110, 112 Retinal detachment (RD), 164 Retreatment rates in refractive surgery, 136 S Schachar theory of accommodation, 208 Schirmer’s tear strip, 18, 18f Scleral approaches of presbyopia correction, 216 Scleral implant-based approach, 216–217 Side cut tears, 112, 113f Small incision lenticule extraction (SMILE) surgery, 5, 96f, 128 case-based approach, 116–126 consent forms for, 227–228 dependence on environmental factors, 132 for hyperopia, 188, 189f

intraoperative complications of, 130 black spots, 108 cap tear and side cut tears, 112, 113f decentered ablation, 112 difficult dissection, 108–109, 109f incisional bleeding, 112 opaque bubble layer, 108 retained lenticule, 110, 112 subconjunctival hemorrhage, 112 suction loss, 106–108 outcomes of, 105 biomechanical properties, 130–131 contrast sensitivity, 130 corneal aberrations, 130 dry eyes, 131 visual outcome, 130 postoperative complications of, 110t, 113 precursors to, 96 preoperative risk factors, 106 principle of, 96 procedure docking, 101, 103 femtosecond laser delivery, 103 laser parameters, 99, 100f, 101f, 102f lenticule dissection and extraction, 103–105 machine and laser settings, 98 patient positioning, 99, 101 patient selection and patient counseling, 99 patient support system, 98 surgical steps, 129f treatment pack, 98–99 retreatment after case-based approach for, 144–148, 154–156 incidence of, 138 VisuMax® circle treatment, 138–139, 139f, 140f, 141f Starbursts-like visual phenomenon, 2f Steroid-induced glaucoma, 90 Subconjunctival hemorrhage, 112 Subconjunctival hemorrhages, 85–86 Suction loss, 82, 106–108 Surface ablation procedures, 128 case-based approach, 66–71 complications, 61–63 complications in, 130 epithelial LASEK, 57 epithelial LASIK, 57 excimer laser systems, indications for use of, 63t laser in situ keratomileusis (LASIK), 56

laser subepithelial keratomileusis, 57 outcomes of biomechanical properties, 130–131 contrast sensitivity, 130 corneal aberrations, 130 dry eyes, 131 visual outcome, 130 photorefractive keratectomy (PRK), 56 principle of, 56 retreatment in, 137–138 topography-guided photorefractive keratectomy (TG-PRK), 58, 61 transepithelial photorefractive keratectomy, 56–57 surgical procedure of, 57–58, 58f treatment parameters used for, 59f, 60f treatment approval and customization, 128 Surgically induced magnification, 158 T Tear film osmometer test equipment, 19, 19f Thermohygrometer, 76f Thin flap, 81–82 Topography-guided photorefractive keratectomy (TG-PRK), 58, 61 Toric ICL (TICL), 163 Transepithelial photorefractive keratectomy (PRK), 56–57 surgical procedure of, 57–58, 58f treatment parameters used for, 59f, 60f Transient light photosensitivity syndrome (TLPS), 90 Treatment pack, 98–99 V Vertical gas breakthrough (VGBT), 83–84 Visual aberrations, 61 Visual outcome, 130 VisuMax femtosecond LASER system, 98, 98f docking, 101, 103 femtosecond laser delivery, 103 laser parameters, 99, 100f, 101f, 102f, 103f lenticule dissection and extraction, 103–105 treatment pack, 98–99 Vitreoretinal complications, 92 W Wavefront analysis of aberrometry, 26, 28