Quality of Vision : Essential Optics for the Cataract and Refractive Surgeon [1 ed.] 9781617116674, 9781556428012

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SLACK Incorporated

Quality of Vision Essential Optics for the

Cataract and Refractive Surgeon

Jack T. Holladay MD MSEE FACS

JACK T. HOLLADAY, MD, MSEE, FACS CLINICAL PROFESSOR OF OPHTHALMOLOGY BAYLOR COLLEGE OF MEDICINE HOUSTON, TEXAS

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ISBN-13: 978-1-55642-801-2 ISBN-10: 1-55642-801-4 Copyright © 2007 by SLACK Incorporated All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without written permission from the publisher, except for brief quotations embodied in critical articles and reviews. The procedures and practices described in this book should be implemented in a manner consistent with the professional standards set for the circumstances that apply in each specific situation. Every effort has been made to confirm the accuracy of the information presented and to correctly relate generally accepted practices. The authors, editor, and publisher cannot accept responsibility for errors or exclusions or for the outcome of the material presented herein. There is no expressed or implied warranty of this book or information imparted by it. Care has been taken to ensure that drug selection and dosages are in accordance with currently accepted/ recommended practice. Due to continuing research, changes in government policy and regulations, and various effects of drug reactions and interactions, it is recommended that the reader carefully review all materials and literature provided for each drug, especially those that are new or not frequently used. Any review or mention of specific companies or products is not intended as an endorsement by the author or publisher. SLACK Incorporated uses a review process to evaluate submitted material. Prior to publication, educators or clinicians provide important feedback on the content that we publish. We welcome feedback on this work. Contact SLACK Incorporated for more information about other books in this field or about the availability of our books from distributors outside the United States. Holladay, Jack T. Quality of vision : essential optics for the cataract and refractive surgeon / Jack T. Holladay. p. ; cm. Includes bibliographical references and index. ISBN-13: 978-1-55642-801-2 (alk. paper) ISBN-10: 1-55642-801-4 (alk. paper) 1. Eye--Surgery. 2. Physiological optics. I. Title. [DNLM: 1. Ophthalmologic Surgical Procedures--methods. 2. Optics. WW 168 H733q 2007] RE80.H65 2007 617.7059--dc22 2006029562 Published by:

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Dedication To my family Sharon, Taylor, and Courtney for their support, encouragement, and love.

Contents Dedication ................................................................................................. v Acknowledgments ..................................................................................... ix About the Author ...................................................................................... xi Preface .................................................................................................... xv Foreword by Richard L. Lindstrom, MD ............................................. xvii

Chapter 1

Understanding Optics..................................................1

Chapter 2

Astigmatism Analysis Vector Analysis to Chart Residual Astigmatic Error Can Improve the Accuracy of Refractive Surgery ............... 15

Chapter 3

Aspheric Treatments Reduce Spherical Aberration After Cataract, Refractive Surgery Implanting an Aspheric IOL or Incorporating a Prolate Laser Treatment Into Corneal Refractive Surgery Helps Reduce Spherical Aberration ..................................... 27

Chapter 4

Vertex Distance, Refraction and Intraocular Lens Power Calculations Measuring Vertex Distance and Performing Over-Refraction With a Soft Contact Lens for Higher Prescriptions Can Reduce Refractive Surprises After IOL Implantation.......... 39

Chapter 5

Intraocular Lens Calculations After Surgery Surgeons Implanting Intraocular Lenses in Patients Who Have Undergone Corneal Refractive Surgery Must Be Precise in Their Measurements and Calculations ................ 47

Chapter 6

Surgical Correction of Presbyopia Some Newer Refractive Surgeries Take Advantage of Pupil Size Changes and Other Factors to Provide Good Near and Distance Vision .................................................... 69

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Chapter 7

Optical Improvements in Excimer Laser Surgery Refinement of the Radial Compensation Function and Other Optical Concepts Have Helped to Improve LASIK Outcomes................................................................. 83

Chapter 8

Zernike and Fourier Polynomials Describing Surfaces ............................................................. 93

Chapter 9

Ocular and Topographic Wavefront ........................ 105

Chapter 10 Understanding Neural Adaptation Image-Enhancement Software in the Human Occipital Cortex Is a Key Component in Vision Correction ............. 115

Acknowledgments I greatly appreciate the hard work done by Tim Donald and Nicole Nader; their contributions are invaluable to this book. I'm indebted to their service. I'd also like to thank Elizabeth A. Davis, MD, FACS for her critical and helpful review and Richard L. Lindstrom, MD for his guidance and for writing the foreword. Finally, I would like to thank all those who have attended my lectures and asked the hard questions that made me think.

About the Author Jack T. Holladay, MD, MSEE, FACS was born on October 13, 1946, while his parents were stationed at Olathe Naval Base near Kansas City, Kansas. His father went to work for Ford Motor Company and typical of many families ascending the corporate ladder, the numerous relocations meant he attended 12 schools between kindergarten and high school. In 1961, the family moved to Dallas, Texas, where Dr. Holladay began his sophomore year at South Oak Cliff High School. In 1964, Dr. Holladay graduated from South Oak Cliff High School, receiving an academic and music scholarship for tuition and room at Southern Methodist University. He chose electrical engineering as his major and played solo trumpet with the Mustang Band along with Harry James, Jr. He worked in the student cafeteria for his meals, giving him the opportunity to meet many students. These many friends were instrumental in his successful campaigns for head cheerleader during his junior and senior years. In 1969, he received his Bachelor of Science degree in Electrical Engineering and was awarded a scholarship to graduate school. His work in the master’s program was primarily in computer science, where he developed software for the onboard aircraft computers to defeat Soviet radar systems. He also designed night vision optical devices using early IBM programs, which represented his first exposure to the field of optics. In 1971, Dr. Holladay received his Master of Science degree in Electrical Engineering from Southern Methodist University and started course work toward a doctorate. Attending classes at Southwestern Medical School was part of the biomedical engineering program, and this fostered an interest in the medical applications of his engineering background. As his interest grew, he decided to attend medical school. Dr. Holladay was accepted in the first on-campus class of 32 members at The University of Texas Medical School in Houston in 1971. In 1974, he received his Doctorate of Medicine, followed by a year of research developing instrumentation for measuring the electrical charge of the eye. He then began his residency in ophthalmology in 1975 at Hermann Hospital, the teaching hospital for The University of Texas Medical School at Houston. He completed his residency in ophthalmology in 1978 and was invited to join The University of Texas Medical School faculty. In addition to his teaching responsibilities and private practice, Dr. Holladay has invented the Brightness Acuity Tester, an instrument that is used by ophthalmologists all over the world to test the effects of glare on patients’ vision. He has also developed the Holladay “IOL Consultant” and “Refractive Surgery Consultant” software programs, which are currently used worldwide by ophthalmologists to help

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About the Author

restore patients’ vision following cataract removal and to obtain the best results following refractive surgery (laser in situ keratomileusis [LASIK]). Dr. Holladay specializes in refractive surgery, which includes LASIK-laser vision correction, photorefractive keratectomy (PRK), and conductive keratoplasty (CK). He is very active in the American Academy of Ophthalmology, serving as past Chairman of the Committee on Low Vision; Committee on Optics, Refraction and Contact Lenses; Ethics Committee; and the Committee for Ophthalmic Technology Development. Because of his service to the academy and his teaching contributions at the annual meeting, he received the Honor Award in 1985 and the Senior Honor Award in 1995, which is awarded to only 25 ophthalmologists a year. He has written over 96 scientific articles and 30 book chapters, authored or edited 5 books, and made several hundred scientific presentations. Dr. Holladay has been a visiting professor at many of the major ophthalmology programs internationally. In 1986, he received the Distinguished Service Award from the Commissioner of the Food and Drug Administration for his service on the Ophthalmic Device Panel. He has received the “Most Outstanding Lecturer in Ophthalmology” award from his medical students numerous times. In 1991, he was named the A. G. McNeese, Jr. Professor of Ophthalmology and was the second person to be recognized as a Distinguished Alumnus of The University of Texas Medical School at Houston. In 1992, he received the Binkhorst Medal Award from the American Society of Cataract and Refractive Surgery, which is given to one ophthalmologist each year. In 1995, he was honored with the Ridley Award from the European Society of Cataract and Refractive Surgery, which is given to only one ophthalmologist every 2 years. In 2001, he was the first recipient of the John Pearse Memorial Award from the United Kingdom & Ireland Society of Cataract & Refractive Surgeons (UKISCRS). He was acknowledged in 2002-2004 as one of the “Best Doctors in America” and has been recognized as one of the “Top Doctors in Houston” by Inside Houston Magazine. He is currently the Vice Chairman of the Executive Committee and member of the Board for the International Society of Refractive Surgery of the American Academy of Ophthalmology, Editorial Board Member of the Journal of Cataract and Refractive Surgery, and a Board of Director for the Council for Refractive Surgery Quality Assurance. He received the Barraquer Medal in 2005 and the Lifetime Achievement Award from the ISRS/AAO in 2006. Although Dr. Holladay’s professional activities are many, he still devotes a significant amount of time to the community and his family. He has served as a member of the Administrative Board, Council on Ministries, and Board of Trustees for the Bellaire United Methodist Church. He was a member of the Scientific Advisory Board for the Lion’s Eye Bank for 20 years. He is also very

About the Author

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proud of coaching and managing in Little League Baseball and in the Houston Youth Soccer Association from 1980 to 1992. In 1988, his son Taylor's baseball team won the Major League Championship, and he managed and coached the All-Star team, which placed second in the area play-offs that year. In 1989, he helped coach his son's soccer team to the Houston City Championship for 13-year-old boys. He was President of the Bellaire High School Baseball Booster Club in 1994, when his son’s team won the coveted State 5A Baseball Championship. Taylor received a baseball scholarship to The University of Texas at Austin. In 2000, he graduated with a Bachelor of Arts Degree from Houston Baptist University with honors. In July 2001, he graduated from the London School of Economics where he earned a Graduate degree in Business with honors. Taylor was inducted into the Bellaire Baseball Hall of Fame in January 2000. In April 2002, Taylor married Kimberly Bullen and they reside in Houston. After working as a senior analyst at Frost Bank for 2 years, he attended and graduated from the Rice University MBA program in May 2006. He is now employed for Nesbitt Corporation as an associate in investment banking. In 1990, his daughter Courtney’s softball team won the 12-year-old girls Major League Championship. Dr. Holladay managed and coached the AllStar team, which went on to win the District 16 Championship. In 1996, his daughter graduated from Bellaire High School as a four-year letter athlete and captain of the varsity soccer team that won the District 5A Championship for 4 years. She was also elected treasurer of the Bellaire High School Booster Club. Courtney graduated from Texas A & M University in May 2000 with honors. She received her Master’s degree in I/O Psychology in May 2002 and her PhD in May 2004 from Rice University and is now working at M.D. Anderson Hospital. In September 2006, Courtney married Mark Strong and they also live in Houston. Dr. Holladay strives for excellence in everything he does, but realizes that his greatest sources of happiness are his wife (Sharon), son (Taylor), daughter (Courtney), and their health, which are blessings for which he is most grateful.

Preface The purpose of this book is to convey the essential optical principles necessary for the cataract and refractive surgeon to maximize their surgical outcomes. Optics is a difficult subject for most surgeons, but a better understanding of the optical principles involved in corneal and lenticular surgery will translate directly into improved surgical techniques and utilization of diagnostic and therapeutic equipment. The explanations and illustrations have been refined from the valuable feedback received from 30 years of lectures to residents and practitioners that have faithfully attended my courses and presentations at state, regional, domestic, and international meetings. I have included those topics that are most relevant to clinical practice. Topics such as vertex distance calculations and astigmatic analysis are not new but are especially important today in refractive and cataract surgery, where the goal is to be independent of spectacles or contact lenses and to reduce—not induce—aberrations. Aspheric intraocular lenses, aspheric excimer laser treatments, multifocal lenses, and cataract surgery after prior refractive surgery are recent developments that require a greater understanding of selecting the correct procedure, device, and proper refractive target for a specific patient. The optics of the eye, the sensory pathway, image processing, and neural adaptation are all factors that when working in harmony allow us to perceive our world in all the exquisite detail that makes us treasure vision as the most important of our senses. Having our patients trust us with this treasure is a responsibility that every refractive and cataract surgeon recognizes and can also be the stimulus to persevere through the limited number of formulas and physics inherent in this subject to gain a better understanding of the eye as an optical system and how it relates to vision.

Foreword Optics… the bane of most ophthalmologists during their training years, and especially while sitting at their OKAPS, Written and Oral Board examinations. Yet, in the clinical world of today, the comprehensive ophthalmologist and cataract and refractive surgeon must have a strong understanding of optics. To practice effectively, the ophthalmologist must understand wavefront analysis; higher-order aberrations; corneal topography; aspheric, multifocal and accommodative intraocular lenses; IOL power calculations; small diameter aperture optics; photopic, mesopic and scotopic contrast sensitivity; light scatter; glare; halo; and neural adaptation to name a few. The list is daunting and growing every year. Fortunately, Jack T. Holladay, MD, MSEE, FACS of the Holladay LASIK Institute in Houston, Texas has come to the rescue with his book, Quality of Vision: Essential Optics for the Cataract and Refractive Surgeon, published by SLACK Incorporated. In 10 tightly written and well-illustrated chapters, Dr. Holladay brings the reader up-to-date on the core optics knowledge required to practice intelligently in today’s environment. Clinically relevant optics that can be applied daily in the practice of ophthalmology is the purpose of this amazingly easy-to-read book. For the reader desiring even greater depth of understanding, appropriate references are provided at the end of each chapter. This book is extremely timely and its content is a must-read for all ophthalmologists whose practice includes seeing patients who have or intend to undergo cataract or refractive surgery, which is nearly all of us. Thank you, Jack Holladay, for another outstanding job educating your colleagues. Richard L. Lindstrom, MD Adjunct Emeritus Professor of Ophthalmology University of Minnesota Founder and Attending Surgeon Minnesota Eye Consultants, P.A. Chief Medical Editor Ocular Surgery News

1 Understanding Optics To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. —Charles Darwin, The Origin of Species, Chapter 6, “Organs of Extreme Perfection and Complication”

Introduction Optics is not a subspecialty of ophthalmology; it is a branch of physics. However, optics is a subject that cuts across all subspecialties of ophthalmology because the physical characteristics of light and the optical elements of the visual system affect the way our patients perceive the world. This book explores how the field of optics affects ophthalmology, especially the subspecialties of cataract and refractive surgery, and how an understanding of optics can help the clinician achieve better quality of vision in his or her patients. To offer patients the best possible visual outcomes following cataract and refractive surgery, ophthalmologists must first attain a clear understanding of

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Chapter 1

optics and the role of optics in creating vision in the eye. Everyone working with human vision should understand the optics of the eye, how optics relates to vision, and how best to accurately measure the quality of that vision.

Quality of Vision The physiologic optics of the human eye affects the quality of vision. The term quality of vision, as used in this book, is a multifactorial concept that includes the entire visual system: optical, sensory and neural processing. Measurements such as visual acuity and contrast sensitivity measure the entire visual system, whereas wavefront aberrometry, topography and tomography evaluate only the optical portion of the visual system. We will discuss the appropriate use of each of these types of tests in the course of this book. Good vision is no longer defined by 20/20 Snellen acuity. Quality of vision is a comprehensive set of measures that includes visual performance at near and far distances and in variable light and contrast conditions. The necessity of moving beyond Snellen acuity in the evaluation of vision has been recognized by officials at the Food and Drug Administration, who now require contrast sensitivity and wavefront aberrometry measurements in most clinical trials related to vision. These requirements will help clinicians to better measure the performance of new devices and surgical procedures quantitatively. Before clinicians can accurately assess contrast sensitivity and other qualityof-vision measures, however, they must first understand the complexities of the human visual system and how optical aberrations and other factors can lead to poor quality of vision. The optics of the human eye, as Darwin acknowledged, is truly remarkable. We have clear media to admit light to our visual system and conduct it toward photosensitive cells; on the optical path to those photosensitive cells, we have an adjustable diaphragm (the pupil) to limit the amount of light admitted and an adjustable lens to focus the light. But the optics of vision goes beyond these well-known elements. There are complexities in the eye’s optical system that in some cases work to improve our vision and in some ways may work to the detriment of vision. The first part of this chapter reviews some of the physiological optical concepts at work in the human eye and how the optical properties of the eye can limit vision in some instances and improve it in others. The second part of the chapter explores some of the ways we assess the performance of the visual system.

Understanding Optics

3

Figure 1-1. The optical axis of the human eye extends from the anterior

vertex (pole) of the cornea to the posterior pole of the eye, and it is defined by the geometric centers of the two lenses of the eye, the cornea and the crystalline lens. The visual axis of the eye extends from the fovea through the nodal point of the eye and out through the cornea to an object, a point at “infinite” distance, such as a star. Angle alpha is the angle between the visual axis and the optical axis (angle A).

Part 1: Introduction to the Optics of the Eye ANGLE KAPPA VERSUS ANGLE ALPHA The optical axis of the human eye extends from the vertex of the cornea (anterior pole) to the posterior pole of the eye, and it is defined by the geometric centers of the two lenses of the eye, the cornea and the crystalline lens. The visual axis of the eye extends from the fovea through the nodal point of the eye and out through the cornea to an object, a point at “infinite” distance, such as a star (Figure 1-1). More often than not, these two axes are not defined by the same line. They are at a slight angle to each other. This optical and anatomical fact introduces some complexity in the planning of refractive surgery corrections.

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Chapter 1

Figure 1-2. The human eye on the average is tilted out 5.2° horizontally

and up 1.4° vertically from the optical axis (OC). This is the amount of tilt described by angle alpha (