Simplifying Strabismus : A Practical Approach to Diagnosis and Management [1st ed. 2019] 978-3-030-24845-1, 978-3-030-24846-8

Table of contents :
Front Matter ....Pages i-xv
Making Sense of Strabismus (Saurabh Jain)....Pages 1-7
Anatomy of the Extraocular Muscles (Saurabh Jain)....Pages 9-13
Applied Physiology of Eye Movements (Saurabh Jain)....Pages 15-22
Examining a Patient with Strabismus (Saurabh Jain)....Pages 23-40
Orthoptic Assessment of a Patient with Strabismus (Saurabh Jain)....Pages 41-62
Concomitant Strabismus (Saurabh Jain)....Pages 63-84
Paralytic Strabismus (Saurabh Jain)....Pages 85-108
Supranuclear Disorders (Saurabh Jain)....Pages 109-124
Alphabet Patterns in Strabismus (Saurabh Jain)....Pages 125-130
Strabismus in Systemic Disease (Saurabh Jain)....Pages 131-143
Other Forms of Incomitant Strabismus (Saurabh Jain)....Pages 145-158
Surgical and Non-surgical Treatment of Strabismus (Saurabh Jain)....Pages 159-174
Back Matter ....Pages 175-179

Citation preview

Simplifying Strabismus A Practical Approach to Diagnosis and Management Saurabh Jain

123

Simplifying Strabismus

Saurabh Jain

Simplifying Strabismus A Practical Approach to Diagnosis and Management

Saurabh Jain Royal Free London NHS Foundation Trust London UK

ISBN 978-3-030-24845-1    ISBN 978-3-030-24846-8 (eBook) https://doi.org/10.1007/978-3-030-24846-8 © Springer Nature Switzerland AG 2019 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Contents

1 Making Sense of Strabismus ������������������������������������������������������������������    1 1.1 Aetiology������������������������������������������������������������������������������������������    2 1.1.1 Heredity��������������������������������������������������������������������������������    3 1.1.2 Refractive Errors ������������������������������������������������������������������    3 1.1.3 Developmental Delay������������������������������������������������������������    3 1.1.4 Anatomical Causes���������������������������������������������������������������    3 1.1.5 Innervational Basis����������������������������������������������������������������    4 1.2 Classification of Strabismus��������������������������������������������������������������    4 1.3 Treatment of Strabismus ������������������������������������������������������������������    6 1.3.1 Occlusion Therapy for Amblyopia����������������������������������������    6 1.3.2 Correcting Refractive Errors������������������������������������������������    6 1.3.3 Occlusion and Prismatic Correction ������������������������������������    6 1.3.4 Botulinum Toxin ������������������������������������������������������������������    7 1.3.5 Extraocular Muscle Surgery ������������������������������������������������    7 References��������������������������������������������������������������������������������������������������    7 2 Anatomy of the Extraocular Muscles����������������������������������������������������    9 2.1 Pulley Systems����������������������������������������������������������������������������������   12 2.2 Blood Supply������������������������������������������������������������������������������������   12 3 Applied Physiology of Eye Movements��������������������������������������������������   15 3.1 Synergists������������������������������������������������������������������������������������������   15 3.2 Antagonists ��������������������������������������������������������������������������������������   15 3.3 Actions of the Extraocular Muscles��������������������������������������������������   17 3.4 Neurology of Eye Movements����������������������������������������������������������   19 3.4.1 Saccades��������������������������������������������������������������������������������   19 3.4.2 Smooth Pursuit����������������������������������������������������������������������   20 3.4.3 Optokinetic Movements��������������������������������������������������������   20 3.4.4 Vergence��������������������������������������������������������������������������������   21 3.4.5 Vestibulo-Ocular ������������������������������������������������������������������   21

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4 Examining a Patient with Strabismus����������������������������������������������������   23 4.1 Taking a Detailed History ����������������������������������������������������������������   23 4.1.1 Presenting Complaints����������������������������������������������������������   23 4.1.2 Previous Ophthalmic Treatment ������������������������������������������   24 4.1.3 Medical History��������������������������������������������������������������������   25 4.1.4 Family History����������������������������������������������������������������������   25 4.2 Examination��������������������������������������������������������������������������������������   25 4.2.1 Visual Acuity Assessment ����������������������������������������������������   26 4.2.2 Assessment of the Ocular Deviation������������������������������������   28 4.2.3 Corneal Reflex or Hirschberg’s Test ������������������������������������   30 4.2.4 Cover-Uncover Test��������������������������������������������������������������   31 4.2.5 Alternate Cover Test ������������������������������������������������������������   34 4.2.6 Ocular Motility Testing��������������������������������������������������������   35 4.2.7 Ductions and Versions����������������������������������������������������������   36 4.2.8 Park’s Three Step Test����������������������������������������������������������   38 4.2.9 Saccades and Pursuits ����������������������������������������������������������   40 5 Orthoptic Assessment of a Patient with Strabismus����������������������������   41 5.1 Bruckner’s Test ��������������������������������������������������������������������������������   41 5.2 Prism Cover Test ������������������������������������������������������������������������������   41 5.3 Prism Reflex Test������������������������������������������������������������������������������   43 5.4 Diplopia Charting������������������������������������������������������������������������������   44 5.5 Field of Binocular Single Vision������������������������������������������������������   44 5.6 Assessment of Binocular Status��������������������������������������������������������   46 5.7 Normal and Abnormal Retinal Correspondence ������������������������������   46 5.8 Testing Binocular Vision������������������������������������������������������������������   50 5.8.1 Simultaneous Macular Perception����������������������������������������   50 5.8.2 Fusion������������������������������������������������������������������������������������   51 5.8.3 Stereopsis������������������������������������������������������������������������������   54 5.9 Qualitative Tests��������������������������������������������������������������������������������   54 5.9.1 Lang Two Pencil Test������������������������������������������������������������   54 5.9.2 Synoptophore������������������������������������������������������������������������   54 5.10 Quantitative Tests������������������������������������������������������������������������������   54 5.10.1 TNO Test������������������������������������������������������������������������������   54 5.10.2 Wirt’s Fly Test����������������������������������������������������������������������   55 5.10.3 Frisby Stereotest�������������������������������������������������������������������   55 5.10.4 Lang Test������������������������������������������������������������������������������   55 5.11 Hess Charts ��������������������������������������������������������������������������������������   56 5.12 Postoperative Diplopia Test��������������������������������������������������������������   58 5.13 Prism Adaptation������������������������������������������������������������������������������   58 5.14 Measurement of Cyclotropia������������������������������������������������������������   58 5.15 Double Maddox Rods ����������������������������������������������������������������������   59 5.16 Synoptophore������������������������������������������������������������������������������������   59 5.17 Fundus Photographs��������������������������������������������������������������������������   59 5.18 Hess Screen��������������������������������������������������������������������������������������   62

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6 Concomitant Strabismus ������������������������������������������������������������������������   63 6.1 Classification������������������������������������������������������������������������������������   63 6.2 Exotropias ����������������������������������������������������������������������������������������   64 6.3 Intermittent Exotropia����������������������������������������������������������������������   65 6.3.1 Natural Course����������������������������������������������������������������������   65 6.3.2 Clinical Presentation ������������������������������������������������������������   65 6.3.3 Examination��������������������������������������������������������������������������   65 6.3.4 Orthoptic Testing������������������������������������������������������������������   66 6.4 Treatment of Exotropia ��������������������������������������������������������������������   67 6.5 Non Surgical ������������������������������������������������������������������������������������   68 6.5.1 Conservative��������������������������������������������������������������������������   68 6.5.2 Orthoptic Exercises��������������������������������������������������������������   68 6.5.3 Part Time Occlusion��������������������������������������������������������������   68 6.5.4 Overminus Lens Therapy������������������������������������������������������   68 6.5.5 Prisms������������������������������������������������������������������������������������   69 6.6 Surgical Intervention������������������������������������������������������������������������   69 6.6.1 Toxin ������������������������������������������������������������������������������������   69 6.6.2 Strabismus Surgery ��������������������������������������������������������������   69 6.7 Other Forms of Exotropia ����������������������������������������������������������������   70 6.7.1 Primary Constant Exotropia��������������������������������������������������   70 6.7.2 Consecutive Exotropia����������������������������������������������������������   70 6.7.3 Sensory Exotropia����������������������������������������������������������������   70 6.8 Esotropias������������������������������������������������������������������������������������������   71 6.9 Non-accommodative Esotropias ������������������������������������������������������   73 6.9.1 Early Onset Esotropia ����������������������������������������������������������   73 6.9.2 Pathogenesis��������������������������������������������������������������������������   74 6.9.3 Clinical Presentation ������������������������������������������������������������   74 6.9.4 Orthoptic Assessment�����������������������������������������������������������   74 6.9.5 Management of Infantile Esotropia��������������������������������������   75 6.9.6 Early Surgery������������������������������������������������������������������������   76 6.9.7 Delayed Surgery��������������������������������������������������������������������   76 6.9.8 Surgical Treatment����������������������������������������������������������������   76 6.10 Non Accommodative Late Onset Esotropia��������������������������������������   76 6.10.1 Clinical Presentation ������������������������������������������������������������   77 6.10.2 Treatment������������������������������������������������������������������������������   77 6.11 Acute Acquired Comitant Esotropia (AACE)����������������������������������   77 6.11.1 Clinical Presentation ������������������������������������������������������������   77 6.11.2 Treatment������������������������������������������������������������������������������   78 6.12 Cyclical Esotropia����������������������������������������������������������������������������   78 6.12.1 Clinical Presentation ������������������������������������������������������������   78 6.12.2 Aetiology������������������������������������������������������������������������������   78 6.12.3 Treatment������������������������������������������������������������������������������   79 6.13 The Role of Accommodation in Esotropias��������������������������������������   79 6.14 AC/A Ratio ��������������������������������������������������������������������������������������   79 6.14.1 Gradient Method ������������������������������������������������������������������   80

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6.14.2 Heterophoria Method������������������������������������������������������������   80 6.15 Accommodative Esotropia����������������������������������������������������������������   81 6.15.1 Fully Accommodative Esotropia������������������������������������������   81 6.15.2 Partially Accommodative Esotropia��������������������������������������   81 6.15.3 Convergence Excess Esotropia ��������������������������������������������   82 6.16 Treatment������������������������������������������������������������������������������������������   82 6.16.1 Optical����������������������������������������������������������������������������������   82 6.16.2 Surgery����������������������������������������������������������������������������������   83 References��������������������������������������������������������������������������������������������������   83 7 Paralytic Strabismus��������������������������������������������������������������������������������   85 7.1 Anatomy��������������������������������������������������������������������������������������������   85 7.2 Clinical Presentation ������������������������������������������������������������������������   86 7.3 Third Nerve Palsy ����������������������������������������������������������������������������   87 7.3.1 Anatomy��������������������������������������������������������������������������������   87 7.3.2 Presentation��������������������������������������������������������������������������   89 7.3.3 Nuclear Portion ��������������������������������������������������������������������   89 7.3.4 Fascicular Portion ����������������������������������������������������������������   90 7.3.5 Subarachnoid Space��������������������������������������������������������������   90 7.3.6 Cavernous Sinus Syndrome��������������������������������������������������   91 7.3.7 Orbital Portion����������������������������������������������������������������������   92 7.3.8 Investigation and Management ��������������������������������������������   93 7.3.9 Complete IIIrd Nerve Palsy��������������������������������������������������   93 7.3.10 Partial IIIrd Nerve Palsy ������������������������������������������������������   94 7.3.11 IIIrd Cranial Nerve Palsy in Children ����������������������������������   94 7.3.12 IIIrd Cranial Nerve Palsy in 18–50 Year Olds����������������������   94 7.3.13 IIIrd Cranial Nerve Palsy in over 50-Year Olds��������������������   95 7.3.14 Treating IIIrd Nerve Palsies��������������������������������������������������   96 7.4 Fourth Nerve Palsy����������������������������������������������������������������������������   96 7.4.1 Anatomy��������������������������������������������������������������������������������   97 7.4.2 Aetiology������������������������������������������������������������������������������   98 7.4.3 Presentation��������������������������������������������������������������������������   98 7.4.4 Site of Trauma����������������������������������������������������������������������   99 7.4.5 Investigation��������������������������������������������������������������������������   99 7.4.6 Clinical Assessment��������������������������������������������������������������   99 7.4.7 Bilateral Fourth Nerve Palsy������������������������������������������������  100 7.4.8 Management��������������������������������������������������������������������������  101 7.5 Sixth Nerve Palsy������������������������������������������������������������������������������  103 7.5.1 Anatomy��������������������������������������������������������������������������������  103 7.5.2 Presentation��������������������������������������������������������������������������  105 7.5.3 Subarachnoid Space��������������������������������������������������������������  106 7.5.4 Petrous Apex ������������������������������������������������������������������������  106 7.5.5 Cavernous Sinus��������������������������������������������������������������������  106 7.5.6 Orbit��������������������������������������������������������������������������������������  107 7.5.7 Management��������������������������������������������������������������������������  107

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7.5.8 Treatment������������������������������������������������������������������������������  108 References��������������������������������������������������������������������������������������������������  108 8 Supranuclear Disorders��������������������������������������������������������������������������  109 8.1 Conjugate Gaze Deviation����������������������������������������������������������������  110 8.2 Congenital Oculomotor Apraxia ������������������������������������������������������  111 8.2.1 Presentation��������������������������������������������������������������������������  111 8.2.2 Aetiology������������������������������������������������������������������������������  111 8.2.3 Treatment������������������������������������������������������������������������������  111 8.3 Internuclear Ophthalmoplegia����������������������������������������������������������  111 8.3.1 Presentation��������������������������������������������������������������������������  112 8.3.2 Aetiology������������������������������������������������������������������������������  113 8.3.3 Management��������������������������������������������������������������������������  114 8.4 One and a Half Syndrome����������������������������������������������������������������  114 8.5 Double Elevator Palsy����������������������������������������������������������������������  114 8.5.1 Aetiology������������������������������������������������������������������������������  114 8.5.2 Presentation��������������������������������������������������������������������������  114 8.5.3 Management��������������������������������������������������������������������������  115 8.6 Convergence Spasm��������������������������������������������������������������������������  116 8.6.1 Presentation��������������������������������������������������������������������������  116 8.6.2 Aetiology������������������������������������������������������������������������������  117 8.6.3 Management��������������������������������������������������������������������������  117 8.7 Dorsal Midbrain Syndrome or Parinaud’s Syndrome ����������������������  118 8.7.1 Aetiology������������������������������������������������������������������������������  118 8.7.2 Presentation��������������������������������������������������������������������������  118 8.7.3 Treatment������������������������������������������������������������������������������  121 8.8 Skew Deviation ��������������������������������������������������������������������������������  121 8.8.1 Ocular Tilt Reaction��������������������������������������������������������������  121 8.8.2 Aetiology������������������������������������������������������������������������������  122 8.8.3 Presentation��������������������������������������������������������������������������  122 8.8.4 Treatment������������������������������������������������������������������������������  123 8.9 Superior Oblique Myokimia ������������������������������������������������������������  123 8.9.1 Aetiology������������������������������������������������������������������������������  123 8.9.2 Presentation��������������������������������������������������������������������������  124 8.9.3 Management��������������������������������������������������������������������������  124 References��������������������������������������������������������������������������������������������������  124 9 Alphabet Patterns in Strabismus������������������������������������������������������������  125 9.1 Etiology��������������������������������������������������������������������������������������������  125 9.1.1 Horizontal Muscle Dysfunction��������������������������������������������  126 9.1.2 Vertical Recti Dysfunction����������������������������������������������������  126 9.1.3 Oblique Muscle Dysfunction and Cyclo-Torsional Effect����  127 9.1.4 Anatomical anomalies of orbits��������������������������������������������  127 9.1.5 Anomalies of Muscle Insertions ������������������������������������������  127 9.1.6 Anomalies of Muscle Pulley Action ������������������������������������  127 9.2 Presentation��������������������������������������������������������������������������������������  128

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9.3 Treatment of Pattern Strabismus����������������������������������������������������  128 9.3.1 Oblique Muscle Overaction����������������������������������������������  129 9.3.2 Horizontal Muscle Transposition��������������������������������������  129 9.3.3 Pulley Dystopia, Craniosynostoses etc.����������������������������  129 References ������������������������������������������������������������������������������������������������  130 10 Strabismus in Systemic Disease��������������������������������������������������������������  131 10.1 Myasthenia Gravis��������������������������������������������������������������������������  131 10.1.1 Pathophysiology����������������������������������������������������������������  131 10.1.2 Clinical Presentation����������������������������������������������������������  132 10.1.3 Diagnosing Myasthenia Gravis ����������������������������������������  133 10.1.4 Lambert Eaton Syndrome��������������������������������������������������  135 10.1.5 Management of Myasthenia Gravis����������������������������������  135 10.2 Thyroid Eye Disease ����������������������������������������������������������������������  136 10.2.1 Etiology ����������������������������������������������������������������������������  136 10.2.2 Risk Factors ����������������������������������������������������������������������  137 10.2.3 Natural History������������������������������������������������������������������  137 10.2.4 Presentation ����������������������������������������������������������������������  137 10.2.5 Ocular Motility������������������������������������������������������������������  138 10.2.6 Management����������������������������������������������������������������������  139 10.2.7 Non Surgical Management������������������������������������������������  140 10.2.8 Medical Treatment������������������������������������������������������������  140 10.2.9 Orbital Decompression������������������������������������������������������  141 10.2.10 Strabismus Surgery������������������������������������������������������������  141 10.2.11 Lid Surgery������������������������������������������������������������������������  142 10.3 Chronic Progressive External Ophthalmoplegia����������������������������  142 10.3.1 Etiology ����������������������������������������������������������������������������  142 10.3.2 Presentation ����������������������������������������������������������������������  142 10.3.3 Management����������������������������������������������������������������������  143 References��������������������������������������������������������������������������������������������������  143 11 Other Forms of Incomitant Strabismus������������������������������������������������  145 11.1 Blow Out Fracture��������������������������������������������������������������������������  145 11.1.1 Aetiology ��������������������������������������������������������������������������  145 11.1.2 Presentation ����������������������������������������������������������������������  146 11.1.3 Management����������������������������������������������������������������������  148 11.2 Browns Syndrome��������������������������������������������������������������������������  149 11.2.1 Aetiology ��������������������������������������������������������������������������  149 11.2.2 Presentation ����������������������������������������������������������������������  150 11.2.3 Investigation����������������������������������������������������������������������  151 11.2.4 Management����������������������������������������������������������������������  151 11.3 Acquired Brown Syndrome������������������������������������������������������������  152 11.4 Duanes Syndrome ��������������������������������������������������������������������������  152 11.4.1 Aetiology ��������������������������������������������������������������������������  152 11.4.2 Genetics ����������������������������������������������������������������������������  152

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11.4.3 Presentation������������������������������������������������������������������������  153 11.4.4 Management������������������������������������������������������������������������  155 11.5 Dissociated Vertical Deviation��������������������������������������������������������  156 11.5.1 Aetiology����������������������������������������������������������������������������  157 11.5.2 Presentation������������������������������������������������������������������������  157 11.5.3 Treatment����������������������������������������������������������������������������  157 References��������������������������������������������������������������������������������������������������  157 12 Surgical and Non-surgical Treatment of Strabismus����������������������������  159 12.1 Botulinum Toxin for strabismus ����������������������������������������������������  159 12.2 Method��������������������������������������������������������������������������������������������  160 12.2.1 Dysport��������������������������������������������������������������������������������  161 12.2.2 Botox/Xeomin��������������������������������������������������������������������  161 12.2.3 Complications ��������������������������������������������������������������������  161 12.3 Bupivacaine in Strabismus��������������������������������������������������������������  162 12.4 Surgery for Strabismus�������������������������������������������������������������������  162 12.4.1 Incisions Utilised in Strabismus Surgery����������������������������  163 12.5 Surgical Procedures������������������������������������������������������������������������  164 12.5.1 Weakening Procedures��������������������������������������������������������  164 12.5.2 Retroequatorial Myopexy (Faden’s Procedure)������������������  166 12.5.3 Strengthening Procedures ��������������������������������������������������  167 12.6 Calculating the Amount of Surgery to Perform������������������������������  170 12.7 Transposition����������������������������������������������������������������������������������  170 12.8 Yokoyama’s Procedure��������������������������������������������������������������������  171 12.9 Harada Ito Procedure����������������������������������������������������������������������  172 12.10 Anterior Transposition of the Inferior Oblique������������������������������  173 12.11 Complications of Strabismus Surgery��������������������������������������������  173 References��������������������������������������������������������������������������������������������������  174 Index������������������������������������������������������������������������������������������������������������������  175

List of Videos

Video 4.8

Cover test. A 70 year old man with a right large angle esotropia. On covering the left eye, he takes up fixation with the right but immediately switches back when the cover is removed suggesting this is a constant rather than an alternating form of strabismus Video 4.10b A 24 year old woman with a well controlled exophoria. Initially there is no obvious strabismus but this decompensates on alternate cover test to an alternating exophoria Video 4.11 A 64 year old woman with a left sixth nerve palsy, following a left MR recession. She has an esotropia in primary gaze and limitation of abduction bilaterally, left more than right Video 5.1 A 23 year old man with a left myopic esotropia, seen in primary position and confirmed by an initial cover test. Base out prisms of increasing power are placed in front of the left eye to neutralise the deviation and at the end, the only residual movement is a small hypertropia. As he is a high myope, the cover test is carried out with his glasses on which enables better fixation and true measurement of degree of deviation Video 6.2 A 75 year old man who previously underwent a left sided surgery for esotropia as a child. He now has a large left constant consecutive exotropia. On covering the right eye, he takes up fixation momentarily but switches back when the cover is removed. There is no significant change in the deviation on an alternate cover test Video 6.3 A 22 year old man who has undergone previous Right MR recession and now complains of diplopia in left gaze. There is no apparent strabismus in primary position on an alternate cover test but an alternating esotropia is obvious when this is carried out in laeveversion Video 6.4 A 25 year old man with consecutive exotropia following previous strabismus surgery. He has bilateral limitation of adduction (right greater than left) with a large angle of exotropia. He can take up fixation readily with either eye and the exotropia increases in lateral gazes as dem-

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Video 7.10

Video 7.12

Video 7.13 Video 7.14

Video 7.16 Video 8.3

Video 8.10 Video 10.1

Video 10.3 Video 10.6

List of Videos

onstrated by a cover-uncover test. Note the medial conjunctival scarring in both eyes subsequent to previous MR recessions A 42 year old man with a well controlled left hyperphoria in primary position with a slight right head tilt. However, in dextroversion an alternate cover test demonstrates an obvious left hypertropia secondary to significant IO overaction. The deviation almost disappears in laevoversion. There is a small exophoria when tilting the head to the right and left hypertropia when tilting it to the left Myectomy of the Left Inferior Oblique muscle: the muscle is identified and hooked, lateral to the IR. The muscle belly is held up by two squint hooks and central portion of 1 cm is cauterized at both ends and excised. The cut ends are inspected to ensure there are no residual connecting fibres The muscle tendon is identified and detached from the sclera as close as possible to the insertion. It is then reattached just lateral to the edge of the IR The Left eye has two marks put on at the limbus at 0 and 90° to ensure the baseline position is identified. A stay suture is put in, and the eye retracted inferomedially. The SO is identified after hooking the SR, the tendon is split and the anterior 25% isolated on a suture that is advanced 8 mm posterior and 2 mm superior to the LR insertion. Once the procedure is completed the marks show that the eye is now intorted compared to its original position A 87 year old patient with a right VIth nerve palsy with a prominent right esotropia that worsens in right gaze with associated loss of abduction A wheelchair bound patient with a right exotropia that alternates freely on a cover test. On Dextroversion there is limitation of left adduction and ataxic nystagmus of the right eye. On levoversion, there is limitation of left adduction and ataxic nystagmus of the left eye, suggestive of bilateral wall eyed internuclear ophthalmoplegia A 25  year old woman with complaints of episodic oscillopsia. On switching on the slit lamp beam, the right eye exhibits bursts of spasmodic, involuntary intorsion with intermittent depression of the eye A 55 year old man with bilateral ptosis, left more advanced than right, chin elevation and global reduction of eye movements. Following the application of an ice pack for 10 s there is an immediate improvement in both the lid position as well as the ocular motility A 65  year old lady with bilateral proptosis and right lid retraction, secondary to thyroid eye disease. There is bilateral limitation of upgaze due to IR fibrosis, more pronounced ion the right eye A 75 year old woman with bilateral ptosis and no manifest strabismus in primary gaze as evidenced by no movement on a cover-uncover test. However, she has significant limitation of eye movements in depression, dextroversion and laevoversion

List of Videos

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Video 11.4 A 78  year old man with a right sided blow out fracture. Note the frosted superior half of the lens in the right eye. He has no manifest strabismus in primary gaze but has prominent limitation of upgaze in the right eye leading to a right hypotropia in upgaze Video 11.5 A 10  year old girl with a small left hypotropia in primary position associated with a pseudoptosis. When she fixates with the left eye, the right eye elevates significantly behind the cover. This is due to the secondary deviation being more pronounced due to the extra innervation flowing to the right elevators when the left eye fixates. There is limitation of elevation of the left eye, more marked in adduction that abduction Video 11.8 A 16 year old boy with left exotropia and hypertropia in primary position. He has dense amblyopia in the left eye which does not take up fixation when the right is covered. On attempted dextroversion, the left eye elevates and retracts into the orbit due the miswiring of the MR and the SR Video 11.9 A 29 year old man with alternating hypertropia. The eye behind the cover elevates and then returns slowly to fixation when the cover is removed Video 12.3 Video depicting the use of fornix incision to approach the MR and LR with an explanation of the advantages Video 12.4 The use of a hang back adjustable suture on a bow tie while carrying out a LR recession Video 12.11 A 47 year old lady with left hypotropia, pseudoptosis and pseudoproptosis secondary to myopia. On a cover test in primary gaze with her myopic glasses o, she has a left small angle esotropia and left hyptropia. There is limitation of left elevation, most prominent in dextroelevation

Chapter 1

Making Sense of Strabismus

Strabismus, is misalignment of the visual axes that affects about 2.1% of the world’s population. It can be present since birth or may present acutely in late childhood or as an adult. Strabismus in children may be associated with amblyopia and loss of binocular vision and thus needs to be detected and treated early. It may rarely indicate an underlying serious ocular disorder such as congenital cataract, ocular malformations or retinoblastoma. Diplopia or double vision is commonly associated with acquired strabismus and should raise suspicion of a neurological etiology, especially if of new onset. Recent studies have demonstrated the psychosocial impact of strabismus in children and adults. Strabismus can create significant negative social prejudice with effect on social interaction and employability. Treating strabismus can be beneficial even if there is no improvement in binocularity but the appearance is improved. The predisposing features for development of strabismus in children include • Family history of strabismus, amblyopia and refractive errors especially hypermetropia. • Prematurity • Down’s syndrome • Developmental delay • Craniofacial syndromes • Fetal alcohol syndrome • Unilateral ocular disease • Cerebral palsy In adults or older children • Decompensation of childhood strabismus • Trauma • Myopia © Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_1

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1  Making Sense of Strabismus

Thyroid Eye disease Neurological disease Uniocular loss of vision Cranial Nerve palsies

1.1  Aetiology It is still unclear why some people develop strabismus and other don’t. The physiology of ocular motility involves not just the extraocular muscles but also the cranial nerves, supra nuclear pathways and the control centres and all of these have been implicated in the development of strabismus (Fig.  1.1) by various researchers. Claude Worth’s theory states that strabismus is the result of an inherent absence of cortical fusion potential. As a result, the brain is unable to sustain normal ocular alignment and any improvement in the motor alignment (by surgery, toxin, prisms etc.) is unlikely to improve this. Chavasse’s theory on the other hand postulates that it is the poor motor alignment that is the primary event that leads to a poor sensory status, if uncorrected. Thus, prompt restoration of normal alignment can lead to a sustained improvement in BSV and ocular alignment. This theory is favoured by many experts and as a justification for earlier surgery in conditions like infantile esotropia.

Cortical Control, BG, SC, thalamus, VA, Cerebellum

LEVEL 1: SUPRANUCLEAR

Brainstem, Ocular Motor Cranial Nerve Nuclei

Ocular motor nerves and Extraocular muscles

LEVEL 2:NUCLEAR

LEVEL 3: INFRANUCLEAR

Fig. 1.1  The pathways and structures implicated in the development of strabismus

1.1 Aetiology

3

1.1.1  Heredity Heredity plays an important part in the development of strabismus, particularly the intermittent and accommodative forms [1].

1.1.2  Refractive Errors It has been well established that refractive errors play a significant role in the etiology of strabismus. Hypermetropia is known to be associated with fully or partially accommodative esotropia and appropriate correction of the error can help in resolution of the strabismus. Further research has shown that concomitant esotropia is independently associated with significant anisohypermetropia. Comitant exotropia was found to be associated with astigmatism, myopia and hypermetropia [2].

1.1.3  Developmental Delay Children with psychomotor and/or developmental delay are more prone to developing strabismus. The prevalence of strabismus in this group has been variable estimated to be between 18 and 30%. Strabismus surgery in this group can have unpredictable results with some researchers noting increased effect of recessions and resections [3].

1.1.4  Anatomical Causes The anatomy of the orbit, of the connective tissue around the muscle, the position of the trochlea and the angle of insertion of the extraocular muscles onto the globe can all induce misalignment of the eyes either in primary position or in extremes of gaze. In craniosynsotosis syndromes the risk of strabismus varies from 40 to 90% [4] and can be due to many causes. A hypoplastic orbit may lead to abnormal muscle pathways, either by shortening of the muscles or torsion of the globe creating eccentric force vectors. These may also be associated with posterior displacement of the trochlea leading to apparent superior oblique underaction. One of the most common types of ocular misalignment in patients with craniofacial disorders is V-pattern strabismus characterised by apparent inferior oblique overaction. However, this overelevation in adduction is caused by the rotated orbit leading to the medial rectus being higher in position rather than inferior oblique overaction and surgical plans have to changed accordingly [5]. Exodeviations are common in hypertelorism.

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1  Making Sense of Strabismus

Another development in our understanding of strabismus is the concept of pulleys which are condensations of the connective tissue of the posterior Tenon’s capsule. Heterotopia or abnormalities of the pulley system can therefore lead to development of strabismus for example the inferior displacement of the lateral rectus being implicated in the sagging eye syndrome [6].

1.1.5  Innervational Basis The disproportionate contraction of muscles due to excessive innervation has also been postulated to be an etiological factor in certain forms of strabismus e.g. medical recti in infantile esotropia.

1.2  Classification of Strabismus Strabismus can be classified in various ways depending on the presentation, aetiology, pattern (Table 1.1) [7, 8]. A strabismus that is manifest is called a -tropia whereas one that is latent and appears only when fusion is disrupted is a -phoria. These may coexist so a manifest squint may have a latent component that becomes more apparent after dissociation of fusion. The ocular axes may diverge or point away from each other (exotropia/phoria) (Fig. 1.2) converge or point towards each other (esotropia/phoria) (Fig. 1.3). One eye may be elevated (Hypertropia/phoria) or depressed (hypotropia/phoria) (Fig. 1.4). In addition, the eyes may have the vertical axes rotated towards the nose (incyclotorsion) or away from the nose (excyclotorsion). The aetiology may be congenital or present since birth or acquired at any stage in later life. It may be due to an inherent lack of fusional capacity (central) or due to alterations in the cranial nerves, orbit or muscles that move the eye (peripheral). Neurogenic strabismus results from interruption in the neurological networks that Table 1.1  Classification of strabismus

Aetiology Congenital Central Neurogenic Type of deviation Intermittent Latent Comitant Accommodative Direction of deviation Horizontal -Eso/Exo

Acquired Peripheral Restrictive Constant Manifest Incomitant Non accommodative Vertical and cyclotorsional

1.2  Classification of Strabismus

5

Fig. 1.2  Left sided large angle exotropia following previous surgery for esotropia (Consecutive Exotropia)

Fig. 1.3  Right sided large angle esotropia

Fig. 1.4  Right sided hypotropia following a third nerve palsy

subserve ocular motility while restrictive strabismus is due to processes that mechanically limit the rotation of the eye. The deviation may be present at all times (constant) or may only be visible at certain times of the day, e.g. when the patient is tired or after visual effort or at certain distances. E.g. distance exotropias, accommodative esotropias etc. It may measure

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1  Making Sense of Strabismus

the same in all directions of gaze (comitant) or may differ markedly (usually by more than 10PD) with a larger deviation in the area of limitation or restriction (Table 1.1).

1.3  Treatment of Strabismus The primary aim of treatment of strabismus is to restore the ocular alignment. The secondary aims include treatment of amblyopia, maintaining binocularity and elimination of double vision or enlargement of the field of binocular single vision. The treatment of strabismus takes various forms. It includes:

1.3.1  Occlusion Therapy for Amblyopia Visual acuity is intricately linked with the occurrence of strabismus as eyes with poorer acuity tend to deviate more readily. Strabismus in children thus may initially may be treated using occlusion therapy to improve vision in the deviating eye that secondarily improves fixation and reduces the amount of strabismus.

1.3.2  Correcting Refractive Errors Refractive error correction is very important in these patients. Esotropias frequently coexistent with hypermetropia and may have an accommodative component. Prescription of the appropriate correction not only improves the vision but reduces the need to accommodate at all distances in an effort to overcome the refractive error with a reduction in the deviation. Similarly, a myopic prescription can stimulate accommodation and reduce an exotropic deviation.

1.3.3  Occlusion and Prismatic Correction Acquired strabismus in patients unsuitable for surgical correction can be managed using occlusion therapy e.g. Blenderm or Fresnel prisms that can be stuck on glasses. Fresnel prisms are thin strips of plastic that are most useful below 15PD as higher magnitude lenses are thicker and can distort vision significantly. If the deviation is stable, the prismatic correction can be built into glasses with the total deviation split between the two eyes to aid user acceptance.

References

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1.3.4  Botulinum Toxin Botulinum toxin can be used to correct the deviation by causing temporary paresis of extraocular muscles, with the effect lasting up to 4 months. Toxin may also be a permanent cure in some cases where it allows restoration of fusion.

1.3.5  Extraocular Muscle Surgery For more permanent correction, surgery is the treatment of choice. Muscles can be weakened by disinserting them and placing further away from the limbus (recession) and strengthened by shortening (resection or plication).

References 1. Maconachie GD, Gottlob I, McLean RJ. Risk factors and genetics in common comitant strabismus: a systematic review of the literature. JAMA Ophthalmol. 2013;131(9):1179–86. 2. Zhu, et al. Association between childhood strabismus and refractive error in Chinese preschool children. PLoS One. 2015;10(3):e0120720. 3. van Rijn LJ. Predictability of strabismus surgery in children with developmental disorders and/ or psychomotor retardation. Strabismus. 2009;17(3):117–2. 4. Carruthers JD.  Strabismus in craniofacial dysostosis. Graefes Arch Clin Exp Ophthalmol. 1988;226:230–4. 5. Tan KP, Sargent MA, Poskitt KJ, Lyons CJ. Ocular overelevation in adduction in craniosynostosis: is it the result of excyclorotation of the extraocular muscles? J AAPOS. 2005;9:550–7. 6. Oh SY, Clark RA, Velez F, Rosenbaum AL, Demer JL. Incomitant strabismus associated with instability of rectus pulleys. Invest Ophthalmol Vis Sci. 2002;43:2169–78. 7. https://www.rcophth.ac.uk/wp-content/uploads/2014/12/2012-SCI-250-Guidelines-for-Management-of-Strabismus-in-Childhood-2012.pdf 8. Olitsky E.  The negative psychosocial impact of strabismus in adults. J AAPOS. 1999;3(4):209–11.

Chapter 2

Anatomy of the Extraocular Muscles

The anatomy of the extraocular muscles is intimately linked with that of the orbit, eyelids and the fascia that surrounds them. All these components act harmoniously to bring about the various eye movements described in the next chapter. Each eye is moved by six extraocular muscles that are innervated by three different cranial nerves (Table 2.1). The recti muscles originate from the bony orbit and are inserted onto the eyeball in a spiral that begins at the origin of the medical rectus that’s closest to the limbus and rotates outwards. The two obliques arise from the surface of the orbital bones and pass beneath the corresponding vertical recti. The attachments of the recti muscles form the “Spiral of Tillaux” (Fig. 2.1). Unlike the well defined linear insertions of the recti, the obliques have insertions that spread out over the globe. The superior oblique passes through the bony trochlea which serves as the functional origin and determines its actions (Fig.  2.2) of intorsion, elevation and abduction. The inferior oblique is the shortest extra ocular muscle. It arises from the maxillary bone and not the ring of Zinn, passes beneath the inferior rectus and has a broad insertion that lies over the macula (Fig. 2.3). It is connected to the LR by condensation of the Tenon’s capsule called the intermuscular septum. The superior rectus muscle and the levator palpebrae superioris share a common sheath and tendon of origin. As a result, recession of the SR can lead to upper lid retraction unless they are meticulously dissected away. Similarly, the inferior rectus muscle has facial attachment to the lower lid retractors via the ligament of Lockwood (Fig.  2.4). A recession of the IR can lead to retraction of the lower lid if this is not divided.

© Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_2

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Table 2.1  Action and innervation of the extra ocular muscles Extraocular muscle Origin Medial rectus Both the upper and the lower parts of the common ring tendon and from the sheath of the optic nerve Lateral rectus Lateral part of the annular tendon or common tendinous ring Superior Annulus of Zinn at the orbital rectus apex Inferior Lower limb of the tendinous ring rectus Superior oblique Inferior oblique

Sphenoid bone at the orbital apex, superior to the optic foramen Orbital surface of the maxilla, lateral to the lacrimal groove

Insertion 5.5 mm from the limbus

Innervation Third nerve

7 mm temporal to the limbus

Sixth nerve

7.5 mm superior to the limbus

Third nerve

6.5 mm from the limbus in an arc, convex side forward, with the nasal side nearer the limbus Into the scleral through a wide diaphanous tendon on the outer posterior quadrant of the eyeball laterally onto the eyeball, deep to the lateral rectus overlying the macula

Third nerve

Fig. 2.1  Attachments of extra ocular muscles forming the spiral of Tillaux. (From Strabismus Surgery and its complications- David Coats- Rights obtained)

Fourth nerve Third nerve

Superior rectus

7.9 mm

6.9 mm

5.3 mm

Lateral rectus

Medial rectus

6.8 mm

Inferior rectus

2  Anatomy of the Extraocular Muscles

11

a

b SR

N

SO

T

Vortex v.

MR SO

LR

SR

LR

MR

Macula Vortex v. IO IR

From above

Fig. 2.2 (a, b) The trochlea serves as the functional origin of the superior oblique. The SO fans out into a widespread tendinous insertion beneath the superior rectus. When it contracts, the anterior 10–20% of the fibres incyclorotate the eye while the posterior 80–90% depress the eye. The posterior fibres are also responsible for abducting the eye due to the direction of travel. The SO has the longest tendon, measuring more than 30  mm. (Colour Atlas of Strabismus Surgery, Ken Wright- Rights obtained) Fig. 2.3  The Inferior Oblique spreads out over the posterior aspect of the globe, cradling it as it passes beneath the inferior rectus. As it contracts, it causes the eye to excyclorate, abduct and elevate. (Colour Atlas of Strabismus Surgery, Ken Wright- Rights obtained)

Visual axis 51˚

Muscle axis N

T

IO

MR

LR

IR

From below

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2  Anatomy of the Extraocular Muscles

Fig. 2.4 Fascial attachments between the IR and Lower lid retractors forming the Ligament of lockwood that needs to be dissected to avoid lower lid retraction following IR recession

2.1  Pulley Systems All recti have facial attachments to the obliques and to each other forming a complex structure called the Tenon’s capsule that aids as well as governs the movement of the eye. These bands of connective tissue can serve as functional origins or pulleys (Fig. 2.5) and aid in maintaining a stable position relative to the orbital wall. The fascial bands connect all the EOMs to each other apart from the medial rectus which can thus retract posteriorly during surgery if detached from the globe, and thus prove difficult to retrieve.

2.2  Blood Supply All of the extraocular muscles are supplied by the ophthalmic artery via the anterior ciliary arteries that also supply the anterior segment of the eye. The lateral recti have just one vessel while the other three rectus muscles have two each, making a total of seven (Fig. 2.6). Therefore, surgery to more than two muscles should be avoided due to the risk of disruption of multiple anterior ciliary arteries which can cause anterior segment ischemia. Vessel sparing surgery or partial tendon transposition can be utilised to try and avoid this complication, although they may not always be successful.

2.2  Blood Supply

13 Levator palpebrae superioris m.

Posterior Tenon's capsule

Anterior Tenon's capsule

Superior oblique tendon

Superior rectus m.

Inferior rectus m. Intraconal fat Extraconal fat

Sclera

Inferior oblique m.

Lockwood’s ligament

Conjunctiva

Fig. 2.5  Relationship between orbital fat, tenons capsule and the extra ocular muscles (From Strabismus Surgery and its complications- David Coats- Rights obtained) Fig. 2.6  Blood supply of anterior segment of the eye. Strabismus Surgery and its ComplicationsDavid Coats- Rights obtained

Superior rectus Anterior ciliary arteries

Lateral rectus

Medial rectus

Anterior ciliary arteries

Inferior rectus

Chapter 3

Applied Physiology of Eye Movements

Eye movements are complex and involve the two eyes moving together to focus a visual target on corresponding retinal points. They may also be used to follow or track an object of interest or to converge on an object at near. To achieve these, the muscles operate in harmony and their contraction and relaxation is mediated by the higher control centres. Some terms used to describe these eye movements are discussed below.

3.1  Synergists Each extraocular muscle has a synergist which is the corresponding muscle in the contralateral eye that helps it carry out a defined movement. For example, the Right MR and Left LR are synergist muscles that work together and in unison to move the eye to the left. These contralaterally paired extraocular muscles that work synergistically to direct the gaze in a given direction are called a Yoke muscle pair.

3.2  Antagonists An antagonist is a muscle that directly opposes the action of the one under consideration. So, for the Right MR, the Right LR serves as the antagonist. Similarly, for the Left IO, it would be the left SO and so on. Conjugate Movements: When both eyes move in the same direction, they do so by the action of the two synergists e.g. looking to the left when the right eye moves nasally and the left eye temporally by the action of the Right MR and Left LR which are a yoke muscle pair (Fig. 3.1). Disjugate movements: When both eyes move either towards (convergence) or away (divergence) from each other. © Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_3

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SYNERGISTIC

Elevation

Excycloduction

Superior Rectus

Medial Rectus

ANTAGONISTIC

Lateral Rectus

ANTAGONISTIC

Adduction ANTAGONISTIC

Inferior Oblique

Inferior Rectus

Superior Oblique

Abduction

SYNERGISTIC Depression

Incycloduction

Fig. 3.1  Movements of the eyes showing yoke muscle pairs

Ductions: Movements of one eye considered in isolation and can be described as: Adduction: looking inwards Abduction: looking outwards Elevation: looking upwards Depression: looking downwards Incycloduction: superior pole rotating towards the nose Excycloduction: superior pole rotating away from the nose Versions: These are movements of both eyes at the same time (Figs. 3.2 and 3.3) and can be described as: • Dextroversion: Looking to the right • Laevoversion: Looking to the left • Dextroelevation: Looking up and to the right • Laevoelevation: Looking up and to the left • Dextrodepression: Looking down and to the right • Laevodepression: Looking down and to the left

• • • • • •

3.3  Actions of the Extraocular Muscles

17 Supraversion

Dextroversion

Primary

Levoversion

Infraversion

Fig. 3.2  Versions are binocular eye movements; dextroversion right gaze; laevoversion left gaze; supraversion upgaze and infraversion downgaze. (From Handbook of Pediatric Strabismus and Amblyopia- Ken Wright-Rights obtained)

Superior rectus

Lateral rectus

Inferior rectus

Inferior oblique

Medial rectus

Superior oblique

Inferior oblique

Medial rectus

Superior oblique

Superior rectus

Lateral rectus

Inferior rectus

Fig. 3.3  Movements of the eyes showing yoke muscle pairs. The shaded pairs carry out specific eye movements (Blue- Dextrodepression, Green- Laevoversion, Orange- Dextroelevation)

3.3  Actions of the Extraocular Muscles The extraocular muscles have a variety of actions as summarized below (Table 3.1). Some like the MR and the LR have one primary function which makes it easy to detect their underactions. However, the situation is more complex when dealing with vertical recti and obliques. For example, in primary gaze, both superior oblique and inferior rectus depress the eye. Therefore, it may be difficult to distinguish which one of them is underacting if the eye was unable to move down adequately. To simplify the assessment of which muscle is underacting, one can utilise the relationship between the planes of the muscles and the axis of the globe. The common plane of the vertical recti, in primary position, forms an angle of 23° with the y-axis of the eye. Due to this, the recti muscle not only elevate or

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3  Applied Physiology of Eye Movements

Table 3.1  Actions of the EOMs Extraocular muscle Medial rectus Lateral rectus Superior rectus Inferior rectus Superior oblique Inferior oblique

Primary action Adduction Abduction Elevation Depression Incyclotorsion Excyclotorsion

Secondary action

Tertiary action

Incyclotorsion Excyclotorsion Depression Elevation

Adduction Adduction Abduction Abduction

A mnemonic to remember the actions of the vertical muscles is RADSIN where Recti Adduct, Superiors (i.e. SR & SO) Intort. The others do the opposite

a Muscle plane

b

Y axis

54˚

23˚ Axis of rotation

Superior oblique m.

Muscle plane

36˚

Y axis

Superior oblique m. Medial rectus m.

Medial rectus m. Lateral rectus m.

Lateral rectus m.

Superior rectus m.

Superior rectus m.

Origin of levator palpebrae superioris m.

Origin of levator palpebrae superioris m.

Fig. 3.4  Relationship of the muscle plane of the oblique muslces to the y-axis of rotation b. The superior oblique muscle functions to produce almost pure incycloduction when the eye is abducted to approximately 36 degrees and oure depression when it is adducted to 54 degrees

depress the eye but also cause rotation and adduction. However, when the eye is abducted to 23°, the superior recuts becomes a pure elevator and the inferior rectus a pure depressor. Thus, if the elevation was deficient in abduction, it can be attributed to underaction of the Superior rectus. Similarly, when the eye is adducted to 54°, the superior oblique becomes a pure depressor and the inferior oblique a pure elevator. Thus, if depression was deficient in adduction, it can be attributed to underaction of the Superior oblique (Fig. 3.4). Eye movements are governed by two basic laws of physiology Herrings Law of equal innervation: Whenever an eye movement is performed, equal and simultaneous flow of innervation occurs to the corresponding muscles of both eyes. For example, to facilitate laevoversion, equal innervation flows to the Right MR and Left LR.

3.4  Neurology of Eye Movements

LR +++

19

MR –––

MR +++

LR –––

Fig. 3.5  Herrings law: diagram of version movements to the left. As the left LR contracts (+++), the contralateral MR simultaneously contracts (+++). Also note that the left MR relaxes (−−−) and the right LR also relaxes (−−−). Handbook of Pediatric Strabismus and Amblyopia- Ken Wright rights obtained

This rule applies to all eye movements, whether voluntary or involuntary. Sherringtons law of reciprocal innervation states that when a muscle contracts its antagonist relaxes by an equal amount. When an extraocular muscle contracts its direct antagonist relaxes by an equal amount to allow a smooth movement. For example, to facilitate laevoversion, the Left LR contracts and there is an equal and simultaneous inhibition of innervation to the Left MR to enable the eyes to move left (Fig. 3.5).

3.4  Neurology of Eye Movements The eyes carry out the following forms of movements in order to visualize our surrounding environment,

3.4.1  Saccades Saccades are rapid, simultaneous movements that abruptly change the point of fixation. These can be reflexive when guided by visual clues or volitional, voluntary movements in the absence of such clues. Reflexive saccades are initiated subcortically by the Superior colliculi while volitional saccades are initiated cortically by the Frontal Eye Field (FEF).

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3  Applied Physiology of Eye Movements

3.4.2  Smooth Pursuit Smooth pursuit movements in contrast are much slower tracking movements of the eyes designed to keep a moving stimulus on the fovea. These are under voluntary control and really only take place to follow a moving target. To carry these out, the cortex (FEF), cerebellum and the vestibular nuclei need to coordinate to send information to the gaze centres and this is facilitated by the descending medial longitudinal fasciculus (MLF). The descending MLF arises from the vestibular nuclei and comprises of the medial and lateral vestibulospinal tracts.

3.4.3  Optokinetic Movements Optokinetic Movements utilise both saccadic and smooth pursuit eye movements in order to follow moving objects. They usually tested by using a Catford or Optokinetic (OKN) drum that has black and white alternating stipes that can be rotated towards or away from the observer. The eyes automatically follow a stripe until they reach the end of their excursion. There is then a quick saccade in the direction opposite to the movement, followed once again by smooth pursuit of a stripe leading to alternating slow and fast movement of the eyes called optokinetic nystagmus (Fig. 3.6).

Fig. 3.6  Using an OKR drum in a clinical setting. (From Osborne D et al. Supranuclear eye movements and nystagmus in children: A review of the literature and guide to clinical examination, interpretation of findings and age-appropriate norms. Eye. volume 33, pages 261–273 (2019). No changes made. License available at http://creativecommons.org/licenses/by/4.0/)

3.4  Neurology of Eye Movements

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3.4.4  Vergence Vergence movements line up the fovea of each eye with targets located at different distances from the observer. However, unlike in other types of eye movements wherein the two eyes move in the same direction (conjugate movements), vergence eye movements are disconjugate and involve either a convergence or divergence of the eyes.

3.4.5  Vestibulo-Ocular The Vestibulo ocular reflex consists of rapid eye movements in response to the movement of the head. By adjusting the position of the eyes to counteract the movement of the head, it stabilises the image on the retina and prevents blurring. The sensory cells in the semicircular canals are activated on change in head position, sending signals to the ipsilateral vestibular nuclei by the descending MLF which activates the appropriate cranial nerve nuclei contralateraly to initiate a gaze movement. The ocular movements are controlled by three cranial nerves which supply all the extra ocular muscles. The sixth nerve supplies the LR, fourth the superior oblique and the third, all the rest. The third, fourth, sixth cranial nerve nuclei are arranged in the brainstem as shown below. In order to carry out a synergistic gaze movement, these need to communicate with each other ipsilaterally and contralaterally. This takes place via the ascending medial longitudinal fasciculus that connects them all (Fig. 3.7). These coordinated gaze movements are coordinated by the gaze centres. The horizontal gaze centre is located in the Pons in the area of the parapontine reticular formation (PPRF) and the vertical one in the Midbrain reticular formation and the pretectal area

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3  Applied Physiology of Eye Movements

SEF PEF

FEF

PPC PC

Thalamus BG riMLF

III INC MLF PONS

IV

VI

PPRF DLPN

Cerebellum VN Medulla

Fig. 3.7  Structures involved in eye movement control. Higher centre control areas for both saccadic and pursuit eye movement include the frontal eye field (FEF) and posterior parietal cortex (PPC). The prefrontal cortex (PC), supplementary eye field (SEF), parietal eye field (PEF), thalamus, basal ganglia (BG) and the superior colliculus are specific for saccades and the lateral occipital cortex and angular gyrus for pursuit. Lower centre control areas include the pontine paramedian reticular formation (PPRF) for the horizontal saccadic movements and the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and interstitial nucleus of Cajal (INC) for vertical saccadic eye movements. The cerebellum plays an important role in saccadic and pursuit modulation and the dorsolateral pontine nuclei (DLPN) and vestibular nuclei (VN) are involved in pursuit eye movements (III third nerve nucleus, IV fourth nerve nucleus, VI sixth nerve nucleus, MLF medial longitudinal fasciculus)

Chapter 4

Examining a Patient with Strabismus

It is essential to cultivate a logical and structured approach for history taking and examination in strabismus patients. While each case is distinctive, using a logical approach will ensure that important clinical information is not missed, and an accurate diagnosis can be reached. Below is a suggested scheme that can be utilised for most cases. We recommend following all the steps initially and these can then be skipped with increasing proficiency.

4.1  Taking a Detailed History Strabismus patients will often present with an array of non-specific symptoms or at times due to an incidentally noted ocular deviation. It is important to obtain a comprehensive history to help guide diagnosis and management.

4.1.1  Presenting Complaints What is your main concern about your/your child’s eyes? Using an open question to start tends to encourage the patients to elaborate on exactly why they sought this appointment. Some may have noticed their eyes drift in, some out or vertically up or down. They may feel it limits their social interaction or career prospects. Others may have noticed double vision but may struggle to describe it so, using terms like ‘blurred vision’ instead. Some patients may have not Electronic Supplementary Material The online version of this chapter (https://doi. org/10.1007/978-3-030-24846-8_4) contains supplementary material, which is available to authorized users. © Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_4

23

24

4  Examining a Patient with Strabismus

noticed any symptoms themsleves but were informed of their deviation by friends, colleagues or optometrist. When was this first noticed? How has this changed over time? The majority of long standing strabismus is congenital or noted in the first few months of life, but it may initially be latent and only decompensate later in life and thus patients only become aware of it as they grow older. Rarely it may be a true, acquired form of strabismus and in those case, diplopia is a useful symptom to enquire about. Antecedent illness, fever, trauma, surgery, blood loss may all be linked to the sudden appearance of strabismus. Note: Diplopia, especially if of acute onset is a red flag and the possibility of an underlying neurological cause should be strongly considered. Which direction does the eye turn? Does it affect one eye or both? The patient may be unsure whether the eye turns in or out. It is important to also enquire whether the deviation is confined to just one eye or affects both. Alternating squints affect both eyes while in constant squints the same eye drifts all the time. In our experience, the parents are nearly always right about a noticed exotropia even if not visible in clinic. When is the squint most apparent? Is there anything that makes it more obvious? Anything that makes it better? People notice squint more often when their fusional reserves are diminished or when they are not actively concentrating on a target. This includes following illness, during day dreaming, when tired, after drinking alcohol etc. Plus or hypermetropic glasses help eso-deviations by relaxing accommodation and minus glasses exo-­ deviations by stimulating it. The fixation distance may also affect when the squint is more obvious e.g. convergence excess “when he looks at near things” or distance exo- when day dreaming or gazing into the distance. Are there any associated symptoms? Diplopia should always be asked about specifically although some patients may describe it as blurred or ghosted vision rather than double vision per se. Almost all acquired strabismus is associated with diplopia. Children and patients with longstanding strabismus develop suppression and thus don’t experience diplopia. However, those with intermittent squints such as exotropias may also experience this even though they are longstanding. Those with intermittent distance exotropia also sometimes close one eye in bright sunlight to avoid glare induced decompensation. Other associated symptoms include asthenopia or eye strain, headaches etc. Some patients may have noticed lid abnormalities such as retraction (Thyroid eye disease, Duane’s syndrome) or ptosis (third nerve palsy, myasthenia) etc. They may also be aware of an abnormal head posture.

4.1.2  Previous Ophthalmic Treatment Ask specifically about the use of glasses/contact lenses. At what age were they prescribed and how long have they been worn for? Does their use make the strabismus better?

4.2 Examination

25

Are they using any prisms in their glasses? Do they have a history of occlusion of either eye in childhood signifying underlying amblyopia? Have they any previous trauma to the eye? Any refractive or strabismus surgery? Previous trauma to either eye with loss of vision may lead to a sensory exotropia. Previous surgery may decompensate a squint (cataract, retinal detachment surgery, LASIK) or iatrogenically induce one (pterygium surgery, FESS). The history of previous strabismus surgery is very important as that helps decide if the squint is consecutive (opposite to the initial deviation) or residual (in the same direction). It is also helpful to know which eye was operated on and if possible the muscles as well, though that information may not be readily available.

4.1.3  Medical History Disorders such as hypertension, diabetes, previous cerebrovascular accidents as well as all vascular risk factors are important to enquire about. These are especially important in order to ascertain causation in cranial nerve palsies and also to decide on suitability for surgery if indicated. Most vascular nerve palsies recover in the first 6 months and therefore only require observation or noninvasive treatment. Other systemic conditions to be ruled out include: • Hyperthyroidism • Myasthenia Gravis The above two can mimic almost any strabismus disorder. Associated symptoms, signs of Graves’ disease and variability in symptoms should raise a suspicion. Rheumatoid disorders—Inflammation of the trochlea can lead to acquired Duane’s syndrome.

4.1.4  Family History The following should be enquired about • Strabismus • High refractive errors • Amblyopia

4.2  Examination All patients with strabismus require a complete ophthalmic examination including of the anterior and posterior segments, as well as assessment of their refractive status. Children in particular, need cycloplegic retinoscopy to rule out any hidden refractive errors.

26

4  Examining a Patient with Strabismus

Ophthalmic Examination • External—Facial asymmetry, Frontalis overaction, Ptosis, Telecanthus, Epicanthus, Hypereteleorism, dyskinetic phenomenon, Hypoglobus, Enophthalmos • Anterior Segment—Conjunctival scars from previous strabismus surgery, Underlying sutures, conjunctival cysts, Iris atrophy, transillumination defects, pupillary reactions, anisocoria • Posterior segment—macular anomalies, retinal periphery, optic nerve head swelling, pallor • Visual Fields Systemic Examination • Thyroid Dysfunction • Cranial nerve examination • Neurological examination Investigations (as needed) • BP • BM • Urinalysis • TFTs • Tensilon test • Single fibre EMG of the orbicularis • Anti acetylcholine receptor antibodies Imaging • CT • MRI • MRA • CTA The various steps of the ocular motility examination include:

4.2.1  Visual Acuity Assessment All patients need to have their best corrected uniocular visual acuity measured. If the vision is less than expected, a pinhole measurement will help to exclude refractive error. In patients with nystagmus with a latent component, covering one eye may exacerbate the nystagmus and reduce the measured visual acuity. In these cases, binocular visual acuity can be helpful. In young children, similarly due to

4.2 Examination

27

lack of cooperation binocular visual acuity may have to be accepted. Be aware that stuck on Fresnel prisms may reduce the visual acuity in those who are using them to control diplopia. It is important to use age appropriate vision tests and the following are the most commonly used. From birth onwards

6 months−2 years 18 months–3 years 18 months−5 years 3.5–6 years 4.5 years onwards

Fig. 4.1  Cardiff cards

Forced choice preferential looking (FCPL) Fixing and following Optokinetic Nystagmus Comparison of reaction to occlusion of either eye Ability to alternate or hold fixation with the usually squinting eye on cover test Cardiff cards (Fig. 4.1) Kays pictures (Fig. 4.2) LogMar crowded tests (Fig. 4.3), Keeler’s tests Sheridan Gardner with test type Snellen chart

28

4  Examining a Patient with Strabismus

Fig. 4.2  Kays pictures

Fig. 4.3  LogMAR crowded tests

Note: FCPL is not the same as a LogMar or Snellen’s test (Table 4.1) even if the reading is expressed in the same format. Single uncrowded optotypes generally give better results than linear optotypes and are likely to overestimate VA in amblyopia.

4.2.2  Assessment of the Ocular Deviation It is essential to cultivate a systematic method of assessing strabismus and the scheme below ensures that the relevant clinical information is gathered quickly and efficiently.

4.2 Examination Table 4.1  LogMAR to snellen conversion

29 LogMAR 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 −0.10 −0.20 −0.30

Snellen 6/60 6/48 6/38 6/30 6/24 6/19 6/15 6/12 6/9.5 6/7.5 6/6 6/4.8 6/3.8 6/3

Observe the patient to assess for • Facial Asymmetry • Head Posture which may be Chin Elevation or Depression, Head tilt to the right or left shoulder and Face turn to the right or left. If a head posture is not immediately apparent, it can be made more obvious by asking the patient to read a vision chart in the distance. Ask the patient to take off their glasses prior to commencing the examination. This serves as an excellent opportunity to inspect the glasses for the strength and type of refractive error and incorporated prisms. To do so, look at a straight line in the distance (corner of a room or edge of a wall serves well) and move the lens from side to side. If the lenses are convex, the line will move opposite to the movement of the glasses indicating hypermetropia and in concave or myopic glasses, it will move in the same direction. Prisms if used in glasses are placed with their apex pointing in the direction of the deviation and they tend to move the image towards the apex. Therefore, the line on the wall will appear to move towards the nose if the prism is Base Out (Esotropia) or towards the temple if it is Base In (Exotropia). A Base Down prism will move the line towards the top (Hypertropia) and a Base Up towards the feet (Hypotropia). Note: In some cases it might be preferable to commence the examination with the glasses on. If the patient is a child, you may wish to assess the deviation and perform a cover test initially with the glasses on as you might not get them on today. Also, patients with high refractive errors (particularly myopes) may not be able to see well enough without their glasses. Hypermetropes with an accommodative ­component also could be initially examined with the glasses on as it gives an indication of how their strabismus affects them in normal everyday conditions.

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4  Examining a Patient with Strabismus

4.2.3  Corneal Reflex or Hirschberg’s Test Shine a light from about 33 cm so that it can be seen reflected in both pupillary areas. This will immediately detect any obvious strabismus or ‘tropia’. It can also help estimate the size of deviation (30 dioptres if reflex is at edge of pupil, 45 dioptres if between pupil and limbus and 60 dioptres if at edge of limbus) (Figs. 4.4 and 4.5). The position of the corneal reflex is measured by the angle kappa (Fig.  4.6). which is the angle subtended between the visual and the central pupillary axes. If the fovea and posterior pole of the eye coincide, the angle is zero and the corneal reflex appears central. If the fovea is temporal to the posterior pole, it results in a positive angle kappa leading to a pseudo exotropia. This is commonly seen in hypermetropes. Similarly, a negative angle kappa which might be seen in myopia gives rise to a pseudoesotropia. + 15º = 30PD

+ 25º = 50 PD

+ 45º = 90 PD

Fig. 4.4  The relationship between the corneal light reflex and the amount of strabismus Fig. 4.5  Right Esotropia measuring around 30 PD detected using a corneal reflex test

Visual axis

Angle kappa

Pupillary axis

Fig. 4.6  Angle kappa is the angle subtended between the visual and the central pupillary axes

4.2 Examination

31

4.2.4  Cover-Uncover Test The next step is to perform a cover test wherein the fixating eye is covered to allow the deviating eye to take up fixation. It is preferable to use an accommodative target for near fixation such as a Lang stick. This ensures that the accommodation is controlled at all times during the assessment unlike a diffuse torch light which can be tricky for the patient to fixate on for a prolonged period. In ideal circumstances the fixation target (Fig.  4.7). whether for near or distance should be the smallest that the patient can see with the eye that has the least vision.

Fig. 4.7  Lang cube as a fixation target to assess strabismus

32

4  Examining a Patient with Strabismus

Once the fixing eye is covered, ask the patient to look at the target with the deviating eye. The eye should move in (Exotropia) or out (Esotropia) to take up fixation and the eye under the cover will deviate. The eye is then uncovered to assess the fixation response. If the previously deviated eye continues to now maintain fixation the patient has an alternating squint indicating good vision in both eyes and no fixation preference. If the eyes immediately switch to the initial position, it indicates a strong fixation preference and constant strabismus (Fig. 4.8). Using this test, you can determine the type of the deviation (horizontal, vertical or a combination), whether the deviation is more prominent in the right or left eye or is freely alternating and also estimate the size of the deviation (Fig. 4.9).

Fig. 4.8  The cover test. (a) Left exotropia, (b) the right eye is covered, (c) the abnormal left eye is observed for corrective movement as it takes up fixation. (Reproduced with permission from The Royal Australian College of General Practitioners from: O’Dowd C. Evaluating squints in children. Aus Fam Physican 2013;42(12):872–74. Available at www.racgp. org.au/afp/2013/december/ evaluating-squints)

a

b

c

4.2 Examination Fig. 4.9  The uncover test. (a) Alignment appears normal, (b) the abnormal left eye drifts into a deviated position when covered (In this case, a latent left exophoria), (c) the cover is removed and the newly uncovered eye is closely observed for corrective movement, (d) the abnormal eye resumes normal alignment. (Reproduced with permission from The Royal Australian College of General Practitioners from: O’Dowd C. Evaluating squints in children. Aus Fam Physican 2013;42(12):872–74. Available at www.racgp. org.au/afp/2013/december/ evaluating-squints)

33

a

b

c

d

34

4  Examining a Patient with Strabismus

4.2.5  Alternate Cover Test If there is no obvious deviation on the cover test, move on to the alternate cover test where each eye is covered in turn while fixating on a target. This will demonstrate the presence of any latent squint or ‘phoria’ as the alternate covering and uncovering disrupts fusion (Fig. 4.10). This test should be carried out even in the presence of a tropia as many patients will have an underlying latent component alongside a manifest squint. When this happens, the angle of deviation will increase on an alternate cover test. Using this test, you will be able to determine whether a latent component to the strabismus exists.

Fig. 4.10 (a) The cover/uncover test. Example of a right exotropia using a translucent occluder. (b) The alternate cover test in an exophoria using a translucent occluder. (Reproduced with permission from Alec Ansons, Helen Davis, Diagnosis and Management of Ocular Motility Disorders, 4th Edition, Wiley Blackwell)

4.2 Examination

35

After dissociating the eyes remove the cover and watch the recovery of the eyes to regain BSV (or small tropia), rapid recovery implies good control of the phoria. The patient may notice diplopia prior to recovery. The use of a transluscent occluder such as Spielman in the figures below may aid recognition of the clinical signs. Both these tests should be carried out for distance (6 m) and near fixation (1/3 m). In some conditions, like distance exotropia, testing at far distance which is infinity (or 20 m in practice) may also be useful. It is important to specify a target at these distances of fixation to encourage accurate measurement. For 6 m you can use the top letter of the fixation chart and for far distance, an object visible from the window.

4.2.6  Ocular Motility Testing This should be carried out in all cases of strabismus, in the cooperative patient the method can be as outlined below: Testing young children can be more challenging, a variety of interesting toys are essential, if the child resists all attempts to make them look around use doll’s head movements to elicit the movements. Ocular motility testing can be performed with a torch light or with the accommodative target used above. The advantage of using a torch is that the corneal reflections can be seen and compared, if you are unable to see the reflection in one eye this means that the patient will not be able to see the light with that eye and therefore will not be able to appreciate diplopia. A target can however be more comfortable for the patient over prolonged testing. Ensure that the target or torch light can be seen by the patient with either eye. Then with both eyes open and holding it on the primary position, ask them if they see it as single or double. If single, ask them to follow it with their eyes without moving their head. Move the target laterally and bring it back to the midline. This can then be repeated up and down and then diagonally, covering all nine directions of cardinal gaze. If the patient describes diplopia, ask them if it is vertical or horizontal (“are the images side by side or one on top of the other?”) which will help elucidate the type of deviation. Oblique diplopia signifies a vertical as well as a horizontal component. Torsional diplopia cannot be examined with a spot light but should be investigated separately with a linear target or a specially designed torsion test such as the double Maddox Rod. An increase in separation of diplopia indicates an increase in size of the deviation, which would be expected when the patient looks in the direction of action of the paralysed muscle or limitation. This can be confirmed by performing a quick cover test which would show a larger or more obvious deviation in the direction under question.

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4  Examining a Patient with Strabismus

Right 6th N. palsy Unable to abduct Rt eye. Strabismus worse

Rt eye turns medially

No obvious squint

Diplopia

Fig. 4.11  A right sixth nerve palsy may present with a small angle deviation and minimal diplopia in primary gaze. This increases in right gaze where the deviation is maximal and disappears in left gaze in the example above

For example, a patient with a right sixth nerve palsy may have a right convergent squint with a small deviation in primary gaze and horizontal diplopia. When they are asked to look at the right, the horizontal diplopia would get more pronounced with greater separation between the two images. A cover test performed in right gaze will demonstrate a larger esotropia than in primary gaze, confirming the diagnosis. When looking to the left, the deviation and separation of diplopia will reduce and single vision may be present (Fig. 4.11). Limitations or underactions of the medial recti are more unusual than LR but can occur in certain conditions (e.g. INO), they typically present with exo deviations and crossed diplopia, the separation of diplopia will increase on adduction and decrease on abduction.

4.2.7  Ductions and Versions Ductions are the movement of one eye considered in isolation while versions are the movements of both eyes in unison (Fig. 4.12). The methods described above primarily assesses the versions but it can be very helpful to evaluate the ductions as they can help differentiate between a restrictive and paralytic etiology. It is helpful to try and quantify the limitation of ductions as shown in Fig 4.12. The easiest way to do this is to first assess the degree of limitation of ocular motility in the direction of greatest deviation or diplopia with both eyes open. Following this, cover the contralateral eye and encourage the patient to overcome the limitation. If they can do this, and the duction movement is greater than the version, the underlying pathology is likely to be paralytic. This is due to the increased innervation that flows to the paretic muscle by this maneuver resulting in increased range of movement. In restrictive strabismus, the duction movement is the same as the version as the limiting force remains the same. Staying with the above example of a right sixth nerve palsy, the right eye will be limited in abduction. However, if the left eye is covered and the patient encouraged

4.2 Examination

37

Normal

a

-1 Limitation

-2 Limitation

b

c

-3 Limitation

-4 Limitation

d

e

Fig. 4.12  Ductions are monocular eye movements. (a) Normal abduction, (b) −1 limitation to abduction, (c) −2 limitation to abduction, (d) −3 limitation to abduction, (e) −4 limitation to abduction. (From Handbook of Pediatric Strabismus and Amblyopia- Ken Wright- Rights obtained)

to look further to the right, they will be able to move the eye a bit further out due to increased flow of innervation, thus indicating the underlying pathology is likely to be neurological rather than restrictive (Fig. 4.13). This principle also comes into play when discussing primary versus secondary deviation. Primary deviation is the deviation measured with the sound eye fixing (Primary deviation is the deviation of the paralysed eye). When the patient is encouraged to fix with the paralysed eye, in the example above, greater innervation will need to flow to the Left LR to move the eye to the midline. The same innervation will flow to the yoke muscle (right MR) by Herrings law. As a result of the overaction of the MR, the right esotropia will be larger than the left esotropia was

38

4  Examining a Patient with Strabismus Right gaze

Right gaze after covering left eye

Right 6th N. palsy Unable to abduct Rt eye. Improved abduction of the Rt eye

Fig. 4.13  Patient is unable to move the right eye into abduction due to a sixth nerve palsy. When the Left eye is covered and the patient encouraged to abduct further, an improvement is observed to an increased flow of innervation to the right LR

and this is the secondary deviation (Secondary deviation is deviation of the sound eye).

4.2.8  Park’s Three Step Test This is a useful test in the presence of a vertical deviation. The purpose of the test is localise an underacting muscle. This test is of limited value if more than one muscle is involved or if the underlying problem is restrictive rather than neurological in origin (Fig. 4.14). 4.2.8.1  Example R hypertropia pp with diplopia (remember that the higher eye sees the lower image so even if the deviation is slight it will be possible to tell which eye is hypertropic)— as the R eye is hypertropic we know that the underacting muscles must be either RIR or RSO (R depressors) or LSR or LIO (L elevators). This has immediately narrowed the possibilities from 8 muscles to 4 (you are half way there). Next ask the patient to look to the right and then to the left, look for any obvious increase or decrease in the deviation and ask if the vertical separation of the diplopia increases on R or L gaze (NB don’t ask “is the double vision wider apart” without specifying vertical separation as these cases often are associated with some degree of A or V pattern which can confuse the response). Confirm with a cover test. In this example the vertical deviation increases on left gaze, this must therefore be due to a vertical muscle which has its main action on left gaze i.e. the LSR or RSO (you are now down to two possibilities). Bielchowsky’s Head Tilt test is the last stage of the three step test. In order to perform this the head is tilted towards the right and then the left shoulder. In a RSO

4.2 Examination

a

39 Left Eye

Right Eye

Rt Med Rec

Rt Lat Rec

Rt Inf Rec

Lt Inf Obl

Rt Inf Obl

Rt Sup Rec

Rt Sup Obl

Lt Lat Rec

Lt Med Rec

Lt Sup Obl

Rt Sup Rec

Rt Lat Rec

Rt Inf Rec

Lt Inf Rec

Left Eye

Right Eye

b

Lt Sup Rec

Rt Inf Obl Rt Med Rec

Rt Sup Obl

Lt Inf Obl

Lt Med Rec Lt Sup Obl

Lt Sup Rec Lt Lat Rec

Lt Inf Rec

c SR

SO

SO SR

Fig. 4.14 (a) Step 1: Right hyperdeviation in primary gaze suggesting either the depressors of the right eye of the elevators of the left eye are underacting. (b) Step 2: The deviation increases in left gaze which helps narrow down the possible underacting muscle down to the two that are more active in left gaze. (c) Step 3: Diagram of a right superior oblique paresis with a positive head tilt in tilt right. As the head tilts to the right, the left eye extorts and the right eye intorts. The extorters of the left eye are the inferior rectus and the inferior oblique. Their vertical functions cancel each other, so there is no vertical overshoot. The intortors of the right eye are the superior rectus (SR) and superior oblique (SO) muscles. Because the right superior oblique is paretic, the elevation effect of the superior rectus is unopposed, and a right hypertropia occurs on tilt to the right

40

4  Examining a Patient with Strabismus

palsy the vertical deviation will increase on head tilt to the same side (This is why Obliques tilt Opposite) and vice versa for LSR. The reason for this phenomenon is when the head is tilted to the right, the right eye is extorted as the superior pole moves towards the ear. The ocular tilt reaction ensures that the eye needs to be intorted to bring it into alignment again. The two intortors of the Right eye are the SR and the SO. As the SO is weakened, the SR has to do the majority of the work and has a greater flow of innervation to accomplish this. However the primary action of the SR is elevation which leads to an increase in the amount of hypertropia. This effect disappears in left head tilt.

4.2.9  Saccades and Pursuits So far, all the duction and version movements assessed have been tracking or smooth pursuit movements. However, in certain cases saccades or rapid eye movements may need to be tested. Saccades are rapid eye movements that abruptly change the fixation of the eye and these might be of small amplitude, e.g. when moving fixation while reading or larger amplitude e.g. looking around a room. These can be assessed by asking the patient to rapidly switch fixation between targets held in each hand of the examiner. Paretic strabismus is associated with saccades of reduced velocity while restrictive strabismus is associated with normal saccades that come to an abrupt stop. Other examination may be guided by the initial findings and underlying medical conditions to include visual fields, field of binocular single vision, exophthalmometry etc. Some of these include. Summary of Clinical Assessment Assess the presence of an AHP Take off glasses and evaluate the Refractive error and look for incorporated Prisms Perform a Hirschberg’s test in primary position (PP) Switch to an accommodative target Cover—Uncover the deviated eye If no obvious deviation seen in PP, go straight to the Alternate cover test Ask the patient “Can you see one or two?” Move target around-“Let me know when it goes double”. “Side by side or one on top of the other?” Accessory tests based on results of above e.g. Saccades, convergence, ductions versus versions etc.

Chapter 5

Orthoptic Assessment of a Patient with Strabismus

In the UK orthoptists carry out the majority of the tests to assess patients with strabismus. However, a working knowledge of the tests used, and their interpretation is very useful for anyone seeing and treating these patients.

5.1  Bruckner’s Test This is one of the simplest tests that can be performed even in the most uncooperative of patients and usually yields significant information. A light from an Ophthalmoscope is shone into the pupils of both eyes from about a metre away in a darkened room time to compare the red reflex between the eyes. Normally, the red reflexes should be bilaterally symmetrical. If an eye is deviated or has a high refractive error, the reflex appears brighter in the affected eye.

5.2  Prism Cover Test Prisms tend to bend light towards the base and shift the image towards the apex. Thus, if a prism is placed in front an eye while fixating on an object, the object will appear to move towards the apex and the eye will follow to maintain fixation. In a patient with strabismus the power of this prism can be varied until the displacement of the image equals that caused by the ocular deviation. The purpose of a prism

Electronic Supplementary Material  The online version of this chapter (https://doi. org/10.1007/978-3-030-24846-8_5) contains supplementary material, which is available to authorized users. © Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_5

41

42

5  Orthoptic Assessment of a Patient with Strabismus

Fig. 5.1  Prism cover test for esotropia

a

X

F

b

X

F

X

c

X

F

Fig. 5.2  Diagram of the effect of a prism over one eye (a) patient fixates on the x (b) A prism is introduced and the image is displaced towards the base of the prism and off the fovea. Note that the patient will perceive the image to jump in the opposite direction. Thus a patient will perceive the image to jump in the direction of the apex of the prism. (c) Patient refixates to place the image on the fovea by rotating the eye towards the apex of the prism. (Handbook of Pediatric Strabismus and Amblyopia-Ken Wright rights Obtained)

cover test (PCT) is to measure this ocular deviation in prism dioptres. It may be carried out using a prism bar, loose prisms (Figs. 5.1, 5.2, and 5.3), a synoptophore or a combination of the above. The PCT is performed by placing a prism in front of the eye with the apex pointing in the direction of the deviation. An alternate cover test is then carried out

5.3 Prism Reflex Test

43

a

F

b

F

F

F

Fig. 5.3  Prism neutralisation (a) Patient with an esotropia (b) A prism is introduced to direct the image onto the fovea of the left eye, thus correcting or neutralising the deviation. (Handbook of Pediatric Strabismus and Amblyopia-Ken Wright rights Obtained)

with progressive increase in the power of the prism until there is no net movement. This is an indication of the amount of the ocular deviation and is usually carried out at near and distance fixation. The prism bar is held in the Prentice position wherein the posterior face of the prism is perpendicular to the line of sight of the deviating eye. Alternatively, the posterior face of the prism might be held in the frontal plane. It is essential the operator uses the same method throughout to avoid measurement error. To detect incomitant strabismus, the PCT must be performed in the nine diagnostic positions of cardinal gaze. In some cases, when the fixation is reduced in the deviating eye, a prism reflex test might be preferred.

5.3  Prism Reflex Test If the deviating eye has poor visual equity or the subject is unable to reliably maintain fixation (as in the case of children) the prism reflex test can be used as an alternative to PCT to carry out the measurements. This is done by observing the corneal

44

5  Orthoptic Assessment of a Patient with Strabismus

Fig. 5.4  Prism reflex test to measure a right sensory exotropia and hypertropia

reflection in the deviated eye from an appropriately placed penlight. Due to the deviation the corneal reflex will be de-centered in relation to the pupil. A prism is placed in front of the fixating eye and as a result of Herrings law, the deviated eye makes a corrective movement. Prisms of increasing power are then placed in front of the fixating eye to centre the reflex on the pupil to measure the deviation (Fig. 5.4). For example, in a left sensory exotropia, the prism would be placed in front of the right eye with the base in. As the image in front of the right eye is shifted to the apex of the prism (or to the right), it would make an outward movement, causing the left eye to swing inwards. As the power of the prism is increased, the corneal reflex would centre in the left eye, giving a measure of the deviation. It is important to maintain fixation during this test in the eye with good vision by using a Lang stick or similar (Fig. 5.5).

5.4  Diplopia Charting When patients have crossed eyes (esotropia) the diplopia is uncrossed, i.e. the right image appears on the right. When the eyes are uncrossed (exotropia), the diplopia is crossed, i.e. the right image appearing on the left. This can be charted using red green glasses (Fig. 5.6) where the red lens is usually placed in front of the right eye.

5.5  Field of Binocular Single Vision Each eye has a slightly different field of vision. The field of binocular single vision (BSV) is the area of the visual field where these images overlap and the foveal input from both eyes is amalgamated into a single image. It can be charted on a perimeter

5.5 Field of Binocular Single Vision

45

Fig. 5.5  Lang stick to aid fixation

Fig. 5.6  Red green glasses

that maps out the areas where BSV is maintained and where there is diplopia. This could be a Goldman or an Octopus fields machine and the binocular field that is free of diplopia can be represented as shown below. In patients with Incomitant strabismus, this field of BSV (Fig. 5.7) or the diplopia free field is moved away from the area of maximum limitation or overaction of the extraocular muscles. For example, in a left sixth nerve palsy, the patient will experience diplopia in left gaze, hence the field of BSV is shifted to the right. The purpose of intervention in these patients is to centre the field at the point of fixation to eliminate the compensatory head posture. If diplopia cannot be completely ­eliminated, it is important to try and achieve diplopia free binocular single vision at least in primary and down gazes as they are the most commonly utilised areas of the visual field.

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5  Orthoptic Assessment of a Patient with Strabismus

a

b

Fig. 5.7  Field of binocular single vision in unilateral LR palsy pre (a) and post (b) surgical treatment with bilateral MR recession. (Reproduced with permission under the Creative Commons Attribution 4.0 International License from Kaur S, Kamlesh, Rastogi A, Gupta P, Goyal G, Dash D, Dadeya S. Expansion of binocular fields in the treatment of lateral rectus paresis. Cli Exp Vis Eye Res J 2018;1(2):11-15)

5.6  Assessment of Binocular Status Binocular vision is the ability to use both eyes simultaneously to obtain a single image. This may be disrupted in acute or intermittent strabismus when the disparity in images seen by the two eyes cannot be fused, leading to diplopia. Childhood onset strabismus on the other hand leads to suppression of the image in the squinting eye which ensures they don’t experience diplopia. However, this also means that they can’t achieve binocularity as the brain utilises only one eye at a time. However, not all binocular subjects have an equal grade of binocularity. In a small angle squint, the fovea of one eye may correspond with a non-foveal point of the deviated eye to set up an abnormal correspondence that can provide an element of BSV that may not be high grade. Binocularity is a heterogenous attribute and patients can have some but not all of the following grades, first proposed by Worth: • Simultaneous macular perception • Fusion • Stereopsis

5.7  Normal and Abnormal Retinal Correspondence When we view an object, the fovea of one eye corresponds to the retinal elements of the fovea in the other eye. This foveal-foveal correspondence contributes to a shared cortical image as they share a common visual direction. This normal retinal correspondence (NRC) insures a high grade of binocular single vision.

5.7 Normal and Abnormal Retinal Correspondence

47

Sensory adaptation may take place when the fovea of one eye corresponds to an extrafoveal element in the other (Fig. 5.8). For example, in esotropia, the fovea of the non-deviating eye corresponds to the temporal retina of the deviating eye. Such cases of abnormal retinal correspondence (ARC) may still be able to demonstrate binocular single vision but to a lesser grade then in NRC. The presence of normal or abnormal retinal correspondence can be tested by using the following: • Bagolini’s striated glasses (Fig. 5.9) These glasses have no dioptric power but fine parallel striations at 45° on one and 135° on the other lens. When a spotlight is viewed with the glasses an image at 90° to the striations is produced. In normal BSV or NRC the patient will see a cross meeting in the centre. If the patient has diplopia, they will see an A or a V pattern. In suppression only one line is seen whereas a cross is seen in NRC, even in the presence of strabismus (Fig. 5.10).

Fig. 5.8 (a) This patient has a small angled constant right esotropia and the fovea of the left eye (FL) corresponds to the pseudo-fovea (P) in the right eye, with the fovea of the right eye (FR) being suppressed. This patient is likely to have some BSV and mild amblyopia in the deviating eye. (b) In a adult or late onset strabismus the fovea of the right eye (FR) is not suppressed. The image falls at a point P in the right eye, it does not correspond to the fovea of the left eye (FL) and projects to A′ resulting in diplopia

Fig. 5.9  Bagolini glasses exhibiting cross striations

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5  Orthoptic Assessment of a Patient with Strabismus

b

a

c

d

e

Fig. 5.10 Bagolini glasses responses. (a) Esotropia. (b) Exotropia. (c) Normal Retinal Correspondence (d) Microtropia with suppression scotoma (d) Suppression. (Reproduced with permission from Kai Leppanen, the copyright holder of this work, under the Creative Commons Attribution ShareAlike 4.0 license)

• Worth 4 dot test These consist of four lights in the form of circles arranged with one red light on top, two green ones in the middle and one white at the bottom. These are viewed through red green goggles with the red in front of the right eye. The patient is questioned about the number and colours of lights seen with both eyes open and then with each eye (Fig. 5.11). These are interpreted as below: • BSV or ARC—Four lights seen with the white light described as red or green depending upon dominance of the right or left eye

5.7 Normal and Abnormal Retinal Correspondence

49

a

b

c

d

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f

Fig. 5.11  Worth Four Dot Light test which provides information about the state of peripheral binocular cooperation. (a) The patient wears red green glasses with the red in front of the right eye and views a set of four lights, two green, one red and one white. The possible responses include (b) BSV or ARC—Four lights seen with the white light described as red or green depending upon dominance of the right or left eye, (c) Suppression of Left Eye—Two red lights, (d) Suppression of right eye—Three Green lights, (e) Esotropia—Uncrossed diplopia due to the deviation, leading to five lights with the red ones being to the right of the green ones and (f) Exotropia—Crossed diplopia, leading to five lights with the red ones being to the left of the green ones

• Suppression of Left Eye—Two red lights • Suppression of right eye—Three Green lights • Esotropia—Uncrossed diplopia due to the deviation, leading to five lights with the red ones being to the right of the green ones • Exotropia—Crossed diplopia, leading to five lights with the red ones being to the left of the green ones • Synoptophore The synoptophore or amblyoscope is an extremely versatile apparatus that can be used for assessment of the sensory status in strabismus in multiple ways. It can detect and quantify suppression, determine the presence of ARC, measure fusion potentials and amplitudes, measure the grade of stereopsis, measure torsion as well as the subjective and objective angles of strabismus in the nine cardinal gazes (Fig. 5.12).

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5  Orthoptic Assessment of a Patient with Strabismus

Fig. 5.12  Testing ocular deviation using the synoptophore

If on testing, the patient is asked to fix on objects alternately with the right and left eyes, in the presence of a squint the eyes will move out or in to take up fixation. The patient is asked to move the images using the handpiece, till there is no further movement of the eyes (subjective angle of strabismus). In NRC or no retinal correspondence this should be the same as the objective angle of strabismus. In ARC however, this differs, and the resultant angle of anomaly is indicative of the presence of ARC.

5.8  Testing Binocular Vision 5.8.1  Simultaneous Macular Perception This is the ability of both eyes to visualize an object at the same time. This can be tested on a synoptophore by using slides such as below (Fig. 5.13) where the two pictures are dissimilar to evaluate whether a patient can view them simultaneously. They are usually red in colour.

5.8 Testing Binocular Vision

51

Fig. 5.13  SMP Slide-lion and cage

5.8.2  Fusion This has two different components, motor and sensory fusion. 5.8.2.1  Sensory Fusion This is the ability to perceive two slightly dissimilar images from each eye and perceive them as one. This can be achieved via bifoveal fixation (central fusion) or through peripheral fixation in those with abnormal binocular single vision (peripheral fusion). • Worth Four Dot • Synoptophore Tested using superimposition slides where the majority of the picture is similar, but a few additional details are added in to make the complete picture (Fig. 5.14). These are usually green in colour to distinguish them from SMP slides. 5.8.2.2  Motor Fusion This is the ability of the binocular system to carry out eye movements or vergences that align the eyes to maintain binocular vision. It has four main components that include:

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5  Orthoptic Assessment of a Patient with Strabismus

Fig. 5.14  Fusion slide

• • • •

Convergence or positive fusional vergence Divergence or negative fusional vergence Vertical fusion Cyclovergence Motor fusion can be measured by the following methods:

• Fusion Range Measuring the amplitude across which fusion can be maintained gives valuable information about the ability to maintain binocularity and control the deviation. This can be done by using a prism bar to estimate the horizontal and vertical fusion range where objects are perceived as single when viewed through progressively increasing powers of prisms. Normal values of these the fusion ranges are as below Positive Fusion Range Negative Fusion Range Vertical Fusion Range

Near 35–40 PD 10 PD 3 PD up and down

Distance 15 PD 4–6 PD

• 20 PD Base Out Test A 20-dioptre prism is placed with the base out in front of one eye. This displaces the image nasally towards the apex of the prism in the eye covered leading the eye to move nasally. Due to Herring’s law, the contralateral eye makes an outward

5.8 Testing Binocular Vision

53

movement. However, this moves the image off the fovea in the contralateral eye and it has to make a refixation movement inwards to ensure the image falls on the fovea again. This simple test, that can even be performed on small babies, can give a quick indication of the presence of motor fusion and hence of the existence of binocular single vision and absence of a large ocular deviation (Fig. 5.15). • Controlled Binocular Acuity or CBA This test is used to monitor intermittent or latent deviations to assess the degree of control. The subject is asked to read a chart at the required distance and the examiner carefully observes the ocular alignment as this take place. The ­endpoint of the test is when the deviation becomes manifest and the level of visual acuity at which this happens is noted. This test can also be carried out for near and with and without glasses. The earlier the eyes dissociate while reading down the chart, the worse the control and this can used to guide further intervention in these patients. Fig. 5.15  The 20 PD BO test is used to assess motor fusion. In this figure, a 20 PD BO prism is placed in front of the left eye as the patient fixates on a target. The target seems to move to the apex of the prism and this the left eye adducts to maintain fixation. Due to Herings law, the right eye simultaneously abducts but then makes an adducting movement due to the resultant diplopia

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5  Orthoptic Assessment of a Patient with Strabismus

5.8.3  Stereopsis This is the highest grade of binocular single vision and relates to the perception of depth that arises from the disparity in images between the two eyes. It can be measured by assessing stereoacuity which is the minimal angle of binocular disparity necessary to appreciate stereopsis. The value obtained is in seconds of an arc and depends on the test being utilised and the method of conducting the test. Some tests commonly used in clinical practice are described below.

5.9  Qualitative Tests 5.9.1  Lang Two Pencil Test The patient is asked to place the tip of a pencil on the tip of a vertically held pencil by the examiner. This test is then repeated with one eye closed. In the presence of stereopsis, the performance should be much better with both eyes open. This test demonstrates the presence or absence of stereopsis but does not quantify it. Care must be taken to avoid monocular cues that may confound the result.

5.9.2  Synoptophore The presence or absence of stereopsis can be assessed using the yellow slides which consist of the same object but drawn slightly differently, so as to produce a three dimensional effect if viewed with both eyes in the presence of stereopsis.

5.10  Quantitative Tests 5.10.1  TNO Test This utilises random dot stereograms that are viewed though red green glasses. The test consists of three plates with different shapes on each. On each plate there is at least one image that can be viewed monocularly to serve as control. The book is held at 40 cm viewing distance to carry out the test that can measure stereo acuity between 480 and 15 s of an arc (Fig. 5.16).

5.10 Quantitative Tests

55

Fig. 5.16  TNO test

5.10.2  Wirt’s Fly Test This utilises vectographs and images that are polarized at 90° relative to the other eye when seen through the accompanying polarizing glasses. It is easy to test gross stereopsis with this test as it measures disparities ranging from 3000 to 40 s of an arc. Like the test above, it is performed at 40 cm, wearing polarising glasses. For young children, the fly is presented first and the effect can be quite startling if seen in 3D where it seems to hover off the page. The other plates consist of sets of circles to help refine the rest further if stereopsis is judged as being present.

5.10.3  Frisby Stereotest This is one of the most commonly performed stereopsis tests in clinics and consists of three plastic plates on which four squares of dots are presented. One of these contains a hidden circle and based on the thickness of the plates and the distance at which they are held from the patient, stereoacuities of 600 to 20 seconds of an arc can be tested (Fig. 5.17).

5.10.4  Lang Test The Lang test is based on the principle of stereograms which present different images to the two eyes by using cylinders or random dots. It is similar to the magic eye pictures which only show up hidden shapes if the observer views the image with

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5  Orthoptic Assessment of a Patient with Strabismus

Fig. 5.17  Frisby test

both eyes and has stereopsis (Fig. 5.18). It has the advantage of not requiring polarising or haploscopic glasses. It is particularly useful in young children who may not be able to cooperate with the above tests. The card is presented to the child who is encouraged to find the hidden objects using both eyes simultaneously. The test has the following figures with their attendant stereopsis values Star: always visible Moon: 200″ Truck: 400″ Elephant: 600″

5.11  Hess Charts This test utilises Herrings and Sherrington’s law to map out the range of ocular movements and can be used to evaluate the presence of incomitance or restrictive elements. It uses the haploscopic principle where a different object is presented to each eye simultaneously. This is carried out using a wall mounted chart with the two eyes dissociated with the help of a mirror or with red green glasses (Fig. 5.19). To be able to perform this test the subjects need to have good vision in both eyes and simultaneous perception with normal or abnormal regular correspondence. The commonest used variant is the Lee’s modification of the Hess screen, as shown below. It consists of two illuminated glass screens at right angles divided by a two-­ sided plane mirror. Each screen has a tangent grid that is intersected by dots at 15°and 30°. The examiner has stick with a pointer that is placed on the various dots and the patient places a ring at the end of a stick at the corresponding place on the other chart.

5.11 Hess Charts

Fig. 5.18  Lang test

Fig. 5.19  Performing ocular motility testing on a Lees screen

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5  Orthoptic Assessment of a Patient with Strabismus

The results are depicted on a chart that has inner and outer fields corresponding to the screens. Each square denotes 5° or 10 present diopters and this can be used to calculate the amount of deviation. Fields that are of similar size and shape indicate comitance whereas different sized feelings indicate incomitance. In patients with paretic strabismus, the field is smaller in the affected eye. Restrictive strabismus leads to fields that appear squashed. Hess charts cannot be used to measure torsion without a special adaptor.

5.12  Postoperative Diplopia Test This test is carried out in those patients who do not have binocular single vision. The aim of the test is to simulate the effect of surgery by correcting the alignment with the prison and assessing the presence of diplopia. The patient is asked to fixate on a target at near or distance and deviation corrected with the appropriate prism. If no diplopia is elicited at this point, the prismatic power can be increased or decreased to map out the diplopia free range which can then be used to plan the surgical dose. If the test results are equivocal, botulinum toxin can be used to simulate the effect of surgery and investigate the true risk of diplopia.

5.13  Prism Adaptation This is carried out to calculate the total amount of deviation in patients who have a latent deviation (phoria) underlying a manifest deviation (tropia). It is most useful in young myopic esotropes who have good vision in both eyes and are extremely symptomatic in the presence of an apparently small deviation. To perform this test a Fresnel prism of sufficient strength to restore single vision is stuck on to the patient’s glasses for a period of a few hours to days. The deviation is then re measured with the prism in situ and it will often be found that further deviation has appeared, or the patient has ‘eaten up the prism’. The prismatic power on the glasses is then increased and the above process repeated until there is no further change ad this will be the total amount of strabismus. The above can also be achieved by patching one eye for a few hours to completely disrupt fusion but care must be taken to position a prism in front of one eye prior to removing the cover to prevent accidental restoration of fusion.

5.14  Measurement of Cyclotropia Torsion is the subjective sensation of objects being tilted in the visual plane. It is usually but not always accompanied by cyclotropia where one or both eyes tilt around the visual axis. This is most commonly seen in fourth nerve palsy where a

5.17 Fundus Photographs

59

paralysed superior oblique is associated with an overaction of the inferior oblique which is a powerful extortor. However, torsion may also be seen in association with thyroid eye disease and abnormalities of the vestibular and reticular systems. Unlike horizontal deviation, the fusion amplitudes for torsion are very limited and patients with acquired torsion tend to be very symptomatic. Interestingly, primary inferior oblique overaction that develops in early childhood shows large amounts of fundus extorsion, but no subjective torsion because of complete sensory adaptation. Torsion can be measured objectively using the following methods

5.15  Double Maddox Rods Maddox rods consist of parallel cylinders that convert a point source of light to a straight line oriented at 90° to them. Thus, when the rods are oriented vertically, the patient sees a horizontal line and vice versa (Fig. 5.20). A Maddox rod is put up in front of each eye using a trial frame in such a way that each eye views a straight horizontal line when viewing a light source. If the patient has vertical strabismus and torsion with no suppression, they will see two lines. They are then asked to rotate the lenses in one or both eyes until the lines appear parallel and this can be read off from the scale on the trail frame as a measure of subjective torsion.

5.16  Synoptophore Torsion can be measured on the synoptophore using the “hot cross bun” slides (Fig. 5.21) in a similar manner to described above. The vertical deviation is first corrected using prisms and then the patient is directed to rotate the slides till the red cross appears superimposed within the green shapes and all lines are parallel. The advantage of this method is that it can be used to measure torsion in all nine positions of gaze.

5.17  Fundus Photographs When a horizontal line is drawn through the fovea to the optic disc, in the average person with no central nervous or peripheral extraocular muscle disease that could cause torsion, the line transects the disc approximately two-thirds from the top of the disc. When the fundus is intorted or extorted this relationship changes with the line bisecting the disc more superiorly in extorsion or inferiorly in intorsion (Figs. 5.21 and 5.22)

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5  Orthoptic Assessment of a Patient with Strabismus

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Fig. 5.20  Double Maddox Road test for cyclodeviation in a patient with Right IV Nerve palsy. The pateint sees two lines one of which is tilted as in Figure 5.20a. They are asked to rotate one of the lenses till the lines are aligned, as in Figure 5.20b.This amount of rotation of the lens helps measure the degree of subjective torsion (From Lanning B Kline. Neuro Ophthalmology Review Manual. Slack incorporated. Rights obtained)

5.17 Fundus Photographs

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Fig. 5.21  Hot Cross Bun Slides used to meaure torsion

Fig. 5.22  Disc foveal angle values. (Reproduced with permission under the Creative commons Attribution License from Le Jeune C, Chebli F, Leon L, Anthoine E, Weber M, et  al. (2018) Reliability and reproducibility of disc-foveal angle measurements by non-mydriatic fundus photography. PLOS ONE 13(1): e0191007 (Open Access))

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5  Orthoptic Assessment of a Patient with Strabismus

5.18  Hess Screen A Hess or Lees screen is not suitable to measure torsion unless a special adapter is used. A Lancaster red-green screen however can be used. Other clinical methods of measuring torsion include using Bagolini’s glasses, Harms wall or a torsionometer.

Chapter 6

Concomitant Strabismus

Concomitant strabismus is an ocular deviation that measures the same in all directions of gaze. It is associated with full or nearly full ocular motility and is primarily horizontal in nature. Most comitant squints are either congenital or arise in early childhood. Mechanical, restrictive and acquired squints are rarely comitant.

6.1  Classification Primary manifest strabismus may be esotropic (convergent) or exotropic (divergent). This arises in infancy or early childhood in the majority of cases and late onset should raise the possibility of a neurological etiology. Intermittent strabismus is present only at certain viewing distances or at certain times of the day and may be esophoric or exophoric. Constant strabismus is present at all times and tends to affect one eye, usually with lower vision. Consecutive strabismus is present when the direction of deviation reverses either spontaneously  with time or following intervention be it in the form of toxin or surgery. Residual strabismus is present when the original strabismus persists following intervention in the form of toxin or surgery. It may be reduced in magnitude from the original or primary deviation.

Electronic Supplementary Material  The online version of this chapter (https://doi. org/10.1007/978-3-030-24846-8_6) contains supplementary material, which is available to authorized users.

© Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_6

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6  Concomitant Strabismus

6.2  Exotropias Exotropia is the outward deviation of one or both eyes that may be latent or manifest and may present as a primary, residual or secondary deviation. It can be classified into various types (Figs. 6.1 and 6.2). One classification of exotropia utilises the near distance disparity of the deviation, i.e. the difference in deviation when measured at near and at distance fixation and can be divided into: • Non-specific or Basic exotropia: when the deviation is similar for near and distance • Convergence insufficiency exotropia: when the deviation is more for near than for distance • Divergence excess exotropia: the deviation is more for distance compared to near. • Simulated divergence excess: the deviation initially appears to be more for distance than near but equalises when the effect of accommodative convergence is neutralised using hypermetropic lenses. When +3 DS lenses are placed in front

Classification of Exotropia (XT) Primary

Constant

Early onset Decompensated Intermittent XT

Intermittent

Divergence Excess (Distance) XT Non-specific XT Convergence insufficiency (Near) XT Simulated Divergence Excess XT

Fig. 6.1  Classification of exotropias

Fig. 6.2  Left sided consecutive exotropia

Secondary

Consecutive

Early/ Late Onset

Spontaneous Postoperative

6.3  Intermittent Exotropia

65

of both eyes viewing a near target, they remove the need to accommodate and hence to converge. The exotropia at near then increases to become equal to the deviation at distance fixation.

6.3  Intermittent Exotropia This is one of the commonest forms of exotropia in children accounting for 50–90% of all exotropias that present before the second birthday.

6.3.1  Natural Course The natural course of intermittent exotropia is variable, and the condition may remain in a stable phoric state for a long time or rapidly progress to a constant exotropia. Consequences or signs of worsening include increasing frequency and duration of periods of diplopia or manifest deviation, reduction in the binocular visual acuity or fall in stereopsis. However not all forms of intermittent exotropia get worse with time and the deviation may remain stable for many years or even improve. Factors that predict long term stability include a small angle of deviation and a large fusional reserve and recovery [1].

6.3.2  Clinical Presentation It is usual for the deviation to be initially phoric and only present in special circumstances for example when the patient is tired, when daydreaming or after prolonged close work. Diplopia may not always be appreciated during these episodes, especially by younger patients. Another common symptom includes the closing of one eye in bright sunlight due to disruption of fusion and increased incident light in the deviated eye. With time, the  initial presentation of  an exophoria at distance can develop to a full-blown exotropia.

6.3.3  Examination On examination, the patient usually has good and equal visual acuity in both eyes. They demonstrate an exotropia where the deviation is more commonly seen at distance than for near. The exotropia may not be immediately visible and may need a prolonged cover uncover test to be rendered manifest. These patients tend to exhibit normal retinal correspondence with good stereopsis when aligned but suppression or abnormal correspondence when one eye is deviated.

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6  Concomitant Strabismus

The exotropia may be accompanied by inferior oblique overaction and rarely, lateral incomitance. The near stereoacuity may be normal or rarely reduced due to associated monofixation syndrome (11–55%). Recently, it was shown that for children with untreated intermittent exotropia, deterioration in near stereoacuity at 1 and 2 years is infrequent [2]. Refractive errors including anisomyopia, anisostigmatism and hypermetropia have all been shown to be associated with exotropia and the improvement in the retinal image by using the appropriate refractive correction can help control the exophoria. The fusional reserves for convergence are found to be decreased.

6.3.4  Orthoptic Testing 6.3.4.1  Measurement of the Angle of Deviation The variable amount of control and fusion can make the measurement of deviation challenging in these group of patients. To enhance the clinical assessment of deviation and ensure reproducibility, a few special clinical techniques can be used. This is especially relevant prior to planning surgical intervention. Patch test or Marlowe’s test whereby one eye is patched for 45 min–24 h is very helpful as the disruption of fusion reveals the total amount of deviation. Measurement of the deviation in far distance or 20 m is also useful and you can practically be achieved by asking the patient to focus on a distant object seen through an open window. The deviation is measured at near but the effect of convergence while accommodating might mask the true amount. This can be negated by using a +3.0 dioptre lens in front of each eye while fixing at near. 6.3.4.2  Assessment of Control The assessment of control or deviation during the day is important as a deterioration in control includes the need to intervene using surgical or nonsurgical methods. It has long been suggested that the presence of deviation for more than half the waking hours was an absolute indication for surgery. This can be assessed by taking a detailed history, using a validated control score and by measuring the controlled binocular acuity. The Controlled Binocular Acuity determines the level of vision for distance at which the eyes spontaneously diverge. The patient is asked to read down the chart at distance with both eyes open and the first line at which the eyes spontaneously diverge (i.e. without any dissociation) is noted. With increasing decompensation of the strabismus, this tends to occur earlier in the test or at lower levels of vision and may serve as an indicator for intervention. With further understanding of the nature of the condition, more sophisticated algorithms have been developed that take other factors into account to help monitor progression.

6.4  Treatment of Exotropia Table 6.1  The revised Newcastle control score

67 Score Home control  XT or monocular eye closure seen:   Circle appropriate score  Never  50% of time fixing in distance  >50% of time fixing in distance + seen at near Clinic control   Circle appropriate score near and distance  Near  Immediate realignment after dissociation

0 1 2 3

0

 Realignment with aid of blink or re-fixation  Remains manifest after dissociation/ prolonged fixation  Manifest spontaneously  Distance  Immediate realignment after dissociation

1

 Realignment with aid of blink or re-fixation  Remains manifest after dissociation/ prolonged fixation  Manifest spontaneously  Total NCS: (Home + Near + Distance)  =

1

2 3 0

2 3

Foremost among these is the Newcastle control score that includes both home and clinic assessment of control [3]. The initial score was an eight point scale ranging from 0 to 7 with higher scores indicating greater severity (Table 6.1). Recently, to increase sensitivity, this score has been modified to include more severe categories and now ranges from 0 to 9 as depicted above [4]. The total score is calculated by assessing the control at home from the clincial history and that in clinic on examoination. A score of more than 3 indicates the need for intervention. Jampolsky’s scoring system or the May Scale are alternatives to the NCS.

6.4  Treatment of Exotropia In spite of the common occurrence of this condition the treatment of exotropia remains challenging. This is due to the variable nature of the condition, the dependence on fusional reserves and the usually dissapointing long term response to surgery.

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6.5  Non Surgical 6.5.1  Conservative A large majority of patients with intermittent exotropia can be managed with observation alone if the deviation is controlled for the majority of the time and if they are stable and  asymptomatic. In some cases the deviation may spontaneously improve. The cure rate of untreated intermittent exotropia has shown to be around 12% whereas surgical cure rates in the same study were only 30% [5]. Various studies have reported the rates of those that remain stable from 25 [6] to 81% [7] and this probably reflects the heterogeneous nature of this condition.

6.5.2  Orthoptic Exercises Convergence exercises have been tried in those with remote near points of convergence or evidence of impaired fusion amplitudes for near. Exercises may be used to improve control of the deviation, usually in older children. Diplopia awareness and anti-suppression measures have also been advocated but in most cases are used to supplement rather than supplant surgical treatment.

6.5.3  Part Time Occlusion Part time occlusion of the non deviating eye in constant exotropia [8] or alternating occlusion of both eyes has been advocated to modify suppression responses and improve control [9]. However, response to these is very variable and at best these can be considered to be a temporising measure.

6.5.4  Overminus Lens Therapy All refractive errors in these patients should be corrected to ensure a blurred retinal image does not serve as a barrier to fusion. In addition, treating exotropia by over correcting refractive error with minus lenses is a well proven way to manage exotropia conservatively. Minus lenses tend to stimulate accommodation and thus induce convergence, lessening the exotropic deviation. This can be achieved by incorporating 1.5–2.5 dioptres of myopic prescription in the patient’s glasses. Researchers have shown variable efficacy of this treatment ranging from 46 to 100% [10]. There was initial concern [11] that over correcting myopia actually induces a myopic shift but there is no evidence of this effect [12].

6.6  Surgical Intervention

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6.5.5  Prisms Prisms may be used to correct or overcorrect the exodeviation but often large amounts of prism are required and compliance may be difficult. They are therefore not routinely used in the management of this condition apart from in temporary treatment of postoperative overcorrection [13].

6.6  Surgical Intervention The indications for surgery include worsening of the control of the deviation, reduction in binocular function and increase in the size of the deviation or  increasing psychosocial awareness. The aim of surgery is a complete correction of the exotropia and restoration of normal binocular alignment at distance and near fixation.

6.6.1  Toxin Botulinum toxin type A injected into one or both lateral recti can be used as an alternative to surgery and has been reported to produce comparable results in childhood intermittent exotropia [14, 15]. The reduction in the size of the deviation may help restore binocular single vision, which in turn stimulates improvement in the motor fusion range and better control of the remaining exophoria. This may even lead to an eventual cure. However, the results in adults and older children are not as promising and the effect seems to wear off more quickly.

6.6.2  Strabismus Surgery Depending on the size of the deviation and the presence of near distance disparity, the following types of surgical procedures can be carried out. 1. Two muscle unilateral surgery: the medial rectus muscle is resected and the lateral rectus muscle is recessed. 2. Bilateral surgery: the lateral rectus muscle is weakened on both eyes. 3. One muscle unilateral surgery: one lateral rectus muscle is weakened. The surgical method chosen depends on surgeon preference as well as the measurements obtained. When the exotropia is more for distance (Divergence Excess) unilateral or bilateral LR recession is chosen while for near exotropias (Convergence Insufficiency) MR resection can be utilised. Some surgeons, however, choose to perform a recess resect procedure for all types of exotropia and recent studies have shown no significant difference in outcomes (PEDIG IXT1 trial).

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Surgical success rates are disappointing with over and undercorrection reported in many studies. Eventual recurrence of the exotropia seems to be much commoner than consecutive esotropia that often recovers with time. Some authors have suggested that an initial overcorrection by 10–20 PD may help in better long term outcomes [16, 17]. The age at surgery is thought by some to influence success; some authorities advocate early intervention to avoid entrenched suppression and achieve an optimal result [18] while others suggest that surgery should be delayed until the child is older and others still have concluded that age at surgery makes no difference to the outcome [19].

6.7  Other Forms of Exotropia 6.7.1  Primary Constant Exotropia This is early onset exotropia that presents before the age of 6 months. It is usually a large angle deviation that may be freely alternating but with no binocular function and no significant refractive error. It is important to exclude an underlying developmental problem and to look for facial asymmetry and craniofacial abnormalities.

6.7.2  Consecutive Exotropia This is the development of a divergent squint where initially the patient was convergent and can occur iatrogenically following surgery or toxin or spontaneously in certain forms of esotropia [20]. This may be obvious in all positions or only in the direction gaze of the recessed muscle as illustrated in the two examples below. When the exotropia develops after surgery, assessment of the adduction of the deviating eye should be performed as it may be a consequence of a slipped medial rectus or a stretched scar (Figs. 6.3 and 6.4). The treatment in these cases is advancing the medial rectus to its original position and recessing the lateral rectus.

6.7.3  Sensory Exotropia This is the outward deviation of an eye that has lost all or most of its visual potential. It can be seen following dense amblyopia, trauma, development of a unilateral cataract or any cause leading to reduction vision in one eye. Treatment of the underlying cause may be sufficient to correct the deviation if vision is restored. The results of

6.8 Esotropias

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Fig. 6.3 Right consecutive exotropia, prominent in laeveversion. Note the limitation of right adduction (white arrow)

surgical correction of sensory exotropia are otherwise quite disappointing with frequent recurrence. Overcorrection by at least 10 PD should be the aim with the patient cautioned about possibility of recurrence of the deviation.

6.8  Esotropias As obvious from the classification below, Esotropias are a more heterogeneous group of disorders than exotropias (Fig. 6.5). Primary Esotropias may be constant or intermittent and may present from birth or in early childhood or be acquired in adulthood. Childhood esotropias are frequently comitant and may have an underlying accommodative component. Acquired esotropias tend to be secondary to neurological (sixth nerve palsy) or mechanical etiologies (myopia, TED) and are frequently incomitant. Secondary Esotropias are a consequence of poor vision in the deviating eye. Consecutive esotropias occur in patients who were initially exotropic and over time have developed a convergent squint. These may occur spontaneously or following surgery. Residual esotropia is a remaining esodeviation after surgery for esotropia. Pseudo Esotropias are common in childhood where a broad nasal bridge or prominent epicanthic folds can give the appearance of a convergent squint in an orthophoric child (Fig. 6.6).

Fig. 6.4  A 25 year old man with consecutive exotropia following previous strabismus surgery. He has bilateral limitation of adduction (right greater than left) with a large angle of exotropia. Note the medial conjunctival scarring in both eyes subsequent to previous MR recessions

72 6  Concomitant Strabismus

6.9  Non-accommodative Esotropias Concomitant Esotropia Classification of Esotropia (ET)

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Secondary

Primary

Intermittent

Constant

Accommodative Partally Accommodative ET

Consecutive

No-Accommodative Infantile or Congenital ET Nystagmus Blockage Late Onset ET Microtropia AACE or ANAET

Accommodative

Fully Accommodative Convergence Excess ET

No-Accommodative Near ET Distance ET Cyclical ET

Fig. 6.5  Classification of esotropia Fig. 6.6 Pseudoesotropia secondary to prominent epicanthic folds

Fig. 6.7  Right sided infantile esotropia

6.9  Non-accommodative Esotropias 6.9.1  Early Onset Esotropia The term congenital esotropia is used interchangeably with infantile esotropia but very few of these are actually noticed at birth. Infantile esotropia (Fig. 6.7) is the development of a non-accommodative, large angle convergent squint prior to 6 months of age in an otherwise healthy child.

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6.9.2  Pathogenesis The exact aetiology of this condition remains controversial and there are many theories to explain the development of a convergent squint in the first few months of life. According to Von Grafe (1854) mechanical factors are responsible for the deviation while Donders (1863) postulated that refractive errors through their link with accommodation lead to strabismus. Duane (1869) proposed that the causative defect was an excess in vergence innervation. None of these in isolation really explain the aetiology of infantile esotropia. Claude Worth in 1903 suggested that the development of esotropia was due a primary defect in the ability to fuse which led to be development of a convergent deviation. In contrast, in 1939 Chavasse proposed a motor theory that suggested the strabismus developed as a consequence of an excess reflexogenic action and that the primary defect was mechanical, which if corrected, the patient could develop binocularity. The latter has been considered the basis of early intervention in these cases but there is still considerable variation in management worldwide, and varied success in achieving binocularity after early surgery.

6.9.3  Clinical Presentation Infantile esotropia is characterised by the development of a large angle convergent squint measuring 40 dioptres or more before 6 months of age. There are no other visual or ocular concerns and usually no significant birth or family history. There is usually no other associated neurological or developmental abnormality.

6.9.4  Orthoptic Assessment The strabismus is a large angle concomitant esotropia, but patients may exhibit cross fixation in lateral gaze. Cross fixation is the phenomenon wherein the patient looks at objects on his left with right eye and on the left with the right, due to the

Looking Right

Looking Left

Fig. 6.8  Crossfixation in infantile esotropia on looking right and left giving the appearance of bilateral limitation of abduction

6.9  Non-accommodative Esotropias Table 6.2  Clinical features of infantile esotropia

75 •  Appearance before 6 months of age • Large angle deviation (usually greater than 40 PD BO) •  Manifest latent nystagmus •  Cross fixation •  Dissociated Vertical Deviation •  Inferior Oblique overaction •  Nasotemporal pursuit assymetry •  Age appropriate hypermetropia

large deviation (Fig. 6.8). This gives rise to the appearance of under action of both lateral recti and apparent limited abduction. To help distinguish this from a sixth nerve palsy, patching of one eye can demonstrate the abduction to be normal. In spite of the large deviation there is usually no underlying refractive error and these children don’t tend to develop amblyopia. They usually have age appropriate hypermetropia and if on refraction, a hypermetropia of more than 2.5 D is detected, the full prescription must be given to rule out an accommodative component. There is usually no demonstrable binocular function. The condition may be also associated with dissociated vertical deviation, latent or manifest latent nystagmus and bilateral inferior oblique over action. An assymmetric optokinetic response may also be demonstrable on testing with a rotating drum where the nasal to temporal pursuit movement is slowed or even absent, in comparison to the temporal to nasal movement which is normal (Table 6.2). Differential Diagnosis • Ciancia syndrome is variously regarded as a differential or even a variant of infantile esotropia. It consists of a large angle esotropia with nystagmus on attempted abduction and a head turn towards the adducting eye. • Nystagmus blockage syndrome is very similar although here the initial pathology is an esotropia with a null point in adduction that causes the appearance of a large angle convergent deviation. • Sixth Nerve Palsy • Duane’s Syndrome • Accommodative Esotropias

6.9.5  Management of Infantile Esotropia There is still significant controversy regarding the treatment of essential infantile esotropia. The Congenital Esotropia Study [21] suggested that the patients who met the following criteria were unlikely to spontaneously resolve and would benefit from early surgery

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• Initial appearance and persistence of esotropia between 10 weeks and 6 months of age • Constant esotropia of 40 PD or more on two examinations 2–4 weeks apart. • Refractive error of less than or equal to +3.0 DS.

6.9.6  Early Surgery Various researchers have shown that early surgery leads to better sensory outcomes with some showing the development of gross and even fine stereopsis. The duration of the strabismus seems to be the main determinant of whether the child will regain BSV with the success rate falling to only 4% after 12 months of misalignment [22]. The Early versus Late Infant strabismus surgery (ELISS) [23], a controlled, prospective, multicenter study also confirmed better sensory outcomes for surgery before 2 years of age.

6.9.7  Delayed Surgery The case for delayed surgery is  made because of difficulties with measuring the angle of deviation in young babies which affects the dose of surgery and concern regarding the stability of this deviation in young children. It has been shown that if the deviation is intermittent or variable and measures less than 40 prism dioptres spontaneous resolution is also possible. The other factors to consider are the anaesthetic risk and difficulties of operating on infant eyes. Early surgery is also associated with a higher rate of reoperations.

6.9.8  Surgical Treatment The author favours bimedial recession rather than recess resect due to the ease of operation, symmetrical nature of the procedure, possibility of readvancement in case of overcorrection and no loss of tissue. Due to the variation in anatomy, it is better to measure the amount of recession from the limbus rather than the muscle insertion.

6.10  Non Accommodative Late Onset Esotropia This is an esodeviation that appears after 6  months, and usually between 2 and 5 years of age.

6.11  Acute Acquired Comitant Esotropia (AACE)

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6.10.1  Clinical Presentation The esotropia is seen especially while focussing on near objects. The onset may be acute at times and 34% have a family history of strabismus. The child demonstrates, suppression of the deviating eye, amblyopia (41%), low hypermetropia or emmetropia (mean + 1.42 D) that usually doesn’t need correction and reduced binocular function.

6.10.2  Treatment Treatment includes a trial of full hypermetropic correction if indicated and Amblyopia treatment (occlusion, atropine, other penalisation techniques) if vision is found to be subnormal. If surgery is considered to restore ocular alignment, prism adaptation to uncover the maximal amount of strabismus must be carried out. Following surgery, restoration of binocular function is unusual, but good alignment with continued suppression would be considered a favourable outcome [24].

6.11  Acute Acquired Comitant Esotropia (AACE) This is an unusual presentation of esotropia that occurs in older children and adults where there is a sudden onset of a convergent squint where the eyes were aligned previously. It can cause significant parental and clinician anxiety and needs to be differentiated from other sinister causes of acute acquired esotropia such as sixth nerve palsy [25].

6.11.1  Clinical Presentation Three different types have been described according to the underlying aetiology • Type 1 AACE—Swan’s type occurs following occlusion of one eye, e.g. following trauma or after occlusion therapy for amblyopia. • Type II AACE—Burian-Franscheti’s type—Large angle, comitant esotropia with diplopia and mild to moderate hypermetropia, correction of which does not affect the strabismus. • Type III AACE—Reported by Bielchowsky and related to uncorrected myopia of −5.0DS or more, usually seen following a stressful episode. This variety is more advanced at distance and patients may be orthophoric for near.

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It is important that patients who present with acute onset of diplopia and comitant esotropia receive a careful history taking and a complete ophthalmologic and neurological examination to rule out cyclic esotropia, divergence insufficiency, paretic strabismus, and myasthenia gravis [26]. Any evidence of papailloedema, reduced vision or nystagmus should prompt neuroimaging to rule out a brain stem, cerebellum, pituitary or corpus callosum tumour [27].

6.11.2  Treatment Due to the sudden nature of the condition and the relatively large angles of strabismus, the primary treatment goal is to preserve stereopsis. This can be done by prescribing the full hypermetropic correction, using prisms while the deviation is developing or toxin to correct the deviation with eventual bimedial recession surgery.

6.12  Cyclical Esotropia This is a rare form of esotropia where the strabismus follows a recurring pattern with straight eyes or an esophoria alternating with a moderate to large angle esotropia.

6.12.1  Clinical Presentation The esotropia occurs in cycles that are usually 48 h (24 h of esotropia alternating with 24 h of straight eyes), but cycles of upto 5 days have been reported. The esotropia is acquired and manifests between 2 and 6 years of age and the child exhibits excellent binocularity on the days without strabismus and none on the misaligned days.

6.12.2  Aetiology The etiology is unknown with theories including decompensation of a latent strabismus or an aberration of the biological clock. The strabismus eventually tends to convert to a constant esotropia over months to years if untreated. Occlusion is not helpful and may actually hasten this conversion.

6.14  AC/A Ratio

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Fig. 6.9  Cyclical esotropia in a 3 year old boy

6.12.3  Treatment These patients respond well to surgery which is carried out to correct the largest deviation on the misaligned day and tends not to overcorrect during the straight days. Non-surgical options include toxin to the medial recti [28] or the use of prisms (Fig. 6.9).

6.13  The Role of Accommodation in Esotropias Our eyes converge in response to accommodation as part of the near reflex. This relationship between accommodation and convergence may cause esotropia in high hypermetropia where an increased accommodative effort results in increased convergence at near causing a near esotropia. This may be particularly marked in those with uncorrected hypermetropia but can also be seen in patients with an exaggerated convergence response to accommodation.

6.14  AC/A Ratio This is the ratio of Accommodative convergence (AC) induced per unit of Accommodation (A) and should be between 3 and 5:1 PD/D. It plays an important role in the development and prognosis to treatment of accommodative esotropias. People with a high AC/A ratio have more convergence when they accommodate at near which can induce an esotropia. In general, a high AC/A ratio is associated with

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earlier presentation, higher incidence of surgery and lower incidence of restoration of binocularity. AC/A is usually calculated using one of the following two methods.

6.14.1  Gradient Method Measure the angle of deviation at a fixed distance and then remeasure after relaxing the accommodation with plus lenses. The ratio then is AC / A = D − D′ / P

where

• D = Original deviation • D′ = Deviation with plus lenses • P = Plus lens power in dioptres Usually this is measured with fixation at 1/3 m, using +3 lenses. Example A 5  year old boy presents to clinic with an esotropia noticed for the past 6 months. On examination, he has a deviation of 50 PD BO for near and 20 for distance. The deviation for near decreases to 20 PD BO when it is measured with him wearing +3DS OU in a trial frame. The AC/A ratio then is

Dn − Dn′ / Power of lens = 50 − 20 / 3 = 10 : 1 PD / D

where • Dn = Deviation at near • Dn′ = Deviation at near with plus lenses • Power of lens = Power of plus lenses used Therefore, this child has a higher AC/A than normal. His esotropia can be treated with bifocal glasses which would reduce the accommodative effort for near and hence the esotropia.

6.14.2  Heterophoria Method This method utilises the measurement of the deviation at near and distance but also takes into account the interpupillary distance.

Ac / A = IPD ( in cm ) + Dn − Dd / D



6.15  Accommodative Esotropia

81

where • • • •

IPD = Interpupillary distance Dn = Deviation at near Dd = Deviation at distance D = Fixation distance at near

6.15  Accommodative Esotropia This form of esotropia usually presents between 2 and 4 years of age with increasing accommodative need and is directly linked to the amount of hypermetropia. Children with under or uncorrected hypermetropia need to exert a greater accommodative effort when viewing at near. If this is associated with a normal or increased AC/A ratio, this can lead to the development of an esotropia that is more obvious at near. In case of a low or normal AC/A ratio, they may remain orthophoric or become esophoric. Relaxing their accommodation using plus lenses, suspends this effort and with it the convergence response. The treatment is the prescription of the full ‘plus’ obtained after cycloplegic refraction. In those with a high refractive prescription, this may need to be stepped up to the full prescription or atropine drops used initially to aid compliance.

6.15.1  Fully Accommodative Esotropia Here, the refractive correction completely eliminates the ocular deviation and if corrected early enough in age, they have an excellent prognosis for development of stereopsis. As the child grows, the power of glasses used can be revised downwards and eventually replaced by contact lenses if desired but usually no other intervention is needed. An exception is those children who eventually just need a low prescription to control the deviation but can see as well without refractive correction. This particular group may benefit from surgery but have to be carefully counselled (Fig. 6.10).

6.15.2  Partially Accommodative Esotropia This is an acquired strabismus characterized by high hyperopia, a normal AC/A ratio, and a deviation that responds only partially to spectacle correction. Patients are treated by prescribing the maximal correction. If there is a significant residual angle, they may be suitable for surgery.

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a

6  Concomitant Strabismus

b

Fig. 6.10  Accommodative esotropia (a) Note eyes aligned with glasses, but (b) esotropia develops when the glasses are removed. (From Strabismus Surgery and its Complications—David Coats— Rights obtained)

Prior to the operation, the patient and parents have to be carefully counselled that the operation will only correct the angle of deviation visible with the glasses on and not the total amount as that risks a postoperative consecutive exotropia.

6.15.3  Convergence Excess Esotropia This is the term used to describe esotropia that measures more for near than distance after full hypermetropic correction with a near distance disparity of at least 8 PD [29]. The patient may be orthophoric or esophoric for distance with evidence of binocularity and only demonstrate manifest esotropia for near. This may be associated with high (51%), normal (48%) or uncommonly, even a low AC/A (1%) ratio [30].

6.16  Treatment 6.16.1  Optical Bifocals have long been used to control the near deviation in convergence excess esotropes as a safe and effective method. However, they only work in the subset of patients who have high AC/A ratios. For this, the patient needs to be prescribed the full distance hypermetropic correction after cycloplegic refraction. On top of this, bifocals can be prescribed as +3.00 add for all patients or, the smallest amount of add which controls the near deviation, up to a power of +3.5 DS [31]. It is important to ensure that the bifocals are not a half moon or D segment style but are of an

References

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‘Executive” style that bisect the pupil to ensure the child utilises the near add when looking at objects for near.

6.16.2  Surgery Bimedial recession can be an effective means of correction of strabismus in convergence excess esotropia but the amount of recession to be performed remains unclear. Both the near or the distance deviation have been used to calculate the amount of recession with similar results [32]. Another approach is to use an augmented medial rectus recession by adding in a posterior fixation suture that further boosts the effect of the surgery in near and also normalises the AC/A ratio [33].

References 1. Kwok JJSW, et al. The natural course of intermittent exotropia over a 3-year period and the factors predicting the control deterioration. Sci Rep. 2016;6:27113. 2. Holmes JM, et al. Stability of near stereoacuity in childhood intermittent exotropia. J AAPOS. 2011;15(5):462–7. 3. Buck D, Hatt SR, Haggerty H, Hrisos S, Strong NP, Steen NI, et al. The use of the Newcastle control score in the management of intermittent exotropia. Br J Ophthalmol. 2007;91:215–8. 4. Buck D, Clarke M, Haggerty H, et al. Grading the severity of intermittent distance exotropia: the revised Newcastle control score. Br J Ophthalmol. 2008;92:577. 5. Holmes JM, et al. Is intermittent exotropia a curable condition? Eye. 2015;29(2):171–6. 6. von Noorden GK, Campos EC. Binocular vision and ocular motility: theory and management of strabismus, vol. 6. St Louis: Mosby; 2002. p. 356–76. 7. Hiles DA, Davies GT, Costenbader FD. Long-term observations on unoperated intermittent exotropia. Arch Ophthalmol. 1968;80(4):436–42. 8. Freeman RS, Isenberg SJ. The use of part-time occlusion for early onset unilateral exotropia. J Pediatr Ophthalmol Strabismus. 1989;26(2):94–6. 9. Suh YW, Kim SH, Lee JL, Cho YA. Conversion of intermittent exotropia types subsequent to part time occlusion. Graefes Arch Clin Exp Ophthalmol. 2006;244(6):705–8. 10. Watts P, Tippings E, Al-Madfai H. Intermittent exotropia, overcorrecting minus lenses and the Newcastle scoring system. J AAPOS. 2005;9:460–4. 11. Rowe FJ, Noonan CP, Freeman G, et al. Intervention for intermittent distance exotropia with overcorrecting minus lenses. Eye. 2009;23:320–5. 12. Kushner BJ. Does overcorrecting minus lens therapy for intermittent exotropia cause myopia? Arch Ophthalmol. 1999;117:638. 13. Pratt-Johnson JA, Tillson G.  Prismotherapy in intermittent exotropia. Can J Ophthalmol. 1979;14(4):243–5. 14. Spencer RF, Tucker MG, Choi RY, McNeer KW. Botulinum toxin management of childhood intermittent exotropia. Ophthalmology. 1997;104(11):1762–7. 15. Razavi E, et  al. Efficacy of botulinum toxin in the treatment of intermittent exotropia. Strabismus. 2014;22(4):176–81. 16. Raab EL, Parks MM. Recession of the lateral recti. Early and late postoperative alignments. Arch Ophthalmol. 1969;82(2):203–8.

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17. Scott WE, Keech R, Mash AJ. The postoperative results and stability of exodeviations. Arch Ophthalmol. 1981;99(10):1814–8. 18. Pratt-Johnson JA, Tillson G. Management of strabismus and amblyopia: a practical guide, vol. 128. New York: Thieme; 1994. 19. Stoller SH, Simon JW, Lininger LL. Bilateral lateral rectus recession for exotropia: a survival analysis. J Pediatr Ophthalmol Strabismus. 1994;31(2):89–92. 20. Chatzistefanou KI, Droutsas KD, Chimonidou E. Reversal of unilateral medial rectus recession and lateral rectus resection for the correction of consecutive exotropia. Br J Ophthalmol. 2009;93:742–6. 21. PEDIG. The clinical spectrum of early-onset esotropia: experience of the Congenital Esotropia Observational Study. Am J Ophthalmol. 2002;133(1):102–8. 22. Birch EE, Fawcett S, Stager DR.  Why does early surgical alignment improve stereoacuity outcomes in infantile esotropia? J AAPOS. 2000;4(1):10–4. 23. Simonsz H.  Final report of the early vs. late infantile strabismus surgery study (ELISSS). Strabismus. 2005;13(4):169–99. 24. Jacobs SM, Green-Sims A, Diehl NN, Mohney BG.  Long-term follow-up of acquired non accommodative esotropia in a population based cohort. Ophthalmology. 2011;118(6):1170–4. 25. Lyons CJ, Tiffin PA, Oystreck D. Acute acquired comitant esotropia: a prospective study. Eye (Lond). 1999;13(Pt 5):617–20. 26. Clark AC, Nelson LB, Simon JW, et al. Acute acquired comitant esotropia. Br J Ophthalmol. 1989;73:636–8. 27. Hoyt CS, Good WV. Acute onset concomitant esotropia: when is it a sign of serious neurological disease? Br J Ophthalmol. 1995;79:498–501. 28. Jones A, Jain S. Botulinum toxin: a novel treatment for pediatric cyclic esotropia. J AAPOS. 2014;18(6):614–5. 29. Vivian AJ. Controversy in the management of convergence excess esotropia. Br J Ophthalmol. 2002;86(8):923–9. 30. Arnoldi KA. Convergence excess: characteristics and treatment. Am Orthopt J. 1999;49:37–47. 31. Von Noorden GK, Morris J, Edelman P. Efficacy of bifocals in the treatment of accommodative esotropia. Am J Ophthalmol. 1978;85:830–4. 32. West CE, Repka MX. A comparison of surgical techniques for the treatment of acquired esotropia with increased AC/A ratio. J Pediatr Ophthalmol Strabismus. 1994;31:232–7. 33. Leitch RJ, Burke JP, Strachan IM. Convergence excess esotropia treated surgically with Faden operation and medial rectus muscle recessions. Br J Ophthalmol. 1990;74:278–9.

Chapter 7

Paralytic Strabismus

Palsy or Paresis denotes incomplete limitation of action while paralysis, a complete absence of action of the affected muscle. Paralytic strabismus occurs when the IIIrd, IVth or Vth cranial nerves are involved and can be congenital or acquired.

7.1  Anatomy The IIIrd, IVth and VIth nerves supply the extraocular muscles responsible for all eye movements. The nuclei of these nerves lie in the midbrain and need to communicate with one another both ipsi- and contralaterally in order to coordinate synergistic eye movements. Communication between these nuclei occurs via the ascending medial longitudinal fasciculus and their actions are coordinated and controlled by the supranuclear centres. The vertical gaze centre lies in the midbrain (reticular formation and pretectal area) and the horizontal gaze centre in the pons (specifically, the PPRF). The descending MLF in the brainstem arises from the vestibular nuclei and is composed of the medial and lateral vestibulospinal tracts. The fascicular portion of the nerves lies within the brain stem and then these cranial nerves exit into cranial cavity where they are intimately associated with vascular and bony structures like the communicating artery and petrous temporal bone. These three nerves then join others to pass via the cavernous sinus and into the orbit to supply the extraocular muscles. An involvement of any of these structures or neurological pathways may affect these cranial nerves, either jointly or in isolation.

Electronic Supplementary Material  The online version of this chapter (https://doi. org/10.1007/978-3-030-24846-8_7) contains supplementary material, which is available to authorized users. © Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_7

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7.2  Clinical Presentation Acute paralytic strabismus is usually striking in presentation with new onset diplopia and is often easy to diagnose due to the typical history, classic motility findings and associated incomitance. Long standing paralytic strabismus however may pose more of a challenge as over time sequelae of muscle palsy develop that may make the clinical picture unclear. When a muscle is paralysed, the following changes tend to occur in sequence, leading to a “spread of comitance”. These include • • • •

Underaction of the paretic or paralytic muscle Overaction of the contralateral synergist by Herings law Overaction of the ipsilateral antagonist by Sherington’s law Inhibitional palsy of the antagonist of the contralateral agonist

This can be illustrated by using an example of a Left sixth nerve palsy (Fig. 7.1). The primary defect in Left sixth nerve palsy is limitation of abduction of the left eye. Due to Hering’s law, on attempted laevoversion, more innervation will flow both to the left LR but also to the right MR resulting in overaction in adduction of the right eye. The ipsilateral MR will overact as its antagonist (the LR) is relaxed and over time this can lead to contracture of the MR.

Fig. 7.1  Left Sixth Nerve Palsy Hess Chart displaying the sequelae of (a) Overaction of the contralateral synergist (Right MR), (b) Overaction of the ipsilateral antagonist (Left MR) and (c) Inhibitional palsy of the antagonist of the contralateral agonist (Right LR)

7.3  Third Nerve Palsy

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Fig. 7.2  Right Fourth Nerve Palsy Hess Chart displaying the sequelae of (a) Overaction of the contralateral synergist (Left IR), (b) Overaction of the ipsilateral antagonist (Right IO) and (c) Inhibitional palsy of the antagonist of contralateral agonist (Left SR)

There will be an inhibitional palsy of the right LR which is the antagonist of the right MR. With time, as these changes develop, the esotropia may measure the same in right as in left gaze, leading to a spread of comitance. As another example, let us consider a Right Fourth nerve palsy (Fig. 7.2). The primary defect is an underaction of the right fourth nerve leading to limitation of right depression in adduction. Due to Herring’s law, on attempted laevodepression, more innervation will flow both to the right SO but also to the left IR resulting in overaction and hypotropia of the left eye. The ipsilateral IO will overact as its antaonist (the SO) is relaxed leading to right hypertropia. There will be an inhibitional palsy of the left SR which is the antagonist of the left IR. Ina longstanding fourth nerve palsy, these changes may make it difficult to determine the primary pathology.

7.3  Third Nerve Palsy 7.3.1  Anatomy The oculomotor nerve (Figs. 7.3 and 7.4) originates from at the level of the superior colliculus in the midbrain, ventral to the cerebral acqueduct. It has two nuclei;

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GSE component of CN III

Edinger-westphal nucleus (CN III) Red nucleus Substantia nigra Crus cerebri

Ciliary muscle

Superior oblique

Superior rectus Lateral rectus

Cornea Pupillary constrictor muscle

Medial rectus Inferior rectus

Inferior oblique

Fig. 7.3  Diagram of the third nerve illustrating the supply to the extraocular muscles and the pupillary constrictor muscle

Superior Short Superior Ciliary rectus ciliary division muscle nerves ganglion of CN III

Oculomotor nerve (CN III)

Edingerwestphal nucleus

Oculomotor nuclear complex

Levator palpebrae superioris muscle Nerve to constrictor muscle Nerve to ciliary muscle Nerve to inferior oblique muscle Nerve to medial rectus muscle Nerve to inferior rectus muscle

Fig. 7.4  Course of the IIIrd Nerve

Ciliary ganglion

Nerve to inferior Inferior division oblique muscle of CN III (including visceral motor fibers)

Petrous temporal bone (cut)

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Oculomotor nucleus—controls all EOMs except LR and SO and striated fibres of the LPS. Edinger Westphal nucleus—Supplies parasympathetic fibres to the eye via the ciliary ganglion controlling sphincter pupillae affecting pupil constriction and the ciliary muscle affecting accommodation. The fibres from the two third nerve nuclei located on either side of the cerebral aqueduct then pass through the red nucleus, substantia nigra and exit through the interpeduncular fossa. The third nerve then passes between the superior cerebellar (below) and the posterior cerebral arteries (above), and then towards the cavernous sinus where it travels alongside (lateral) to the posterior communicating artery. An aneurysm at the junction of the PCA and internal carotid artery is the most common cause of a non traumatic isolated IIIrd nerve palsy with pupillary involvement. It traverses the cavernous sinus, above the other orbital nerves receiving in its course filaments from the cavernous plexus of the sympathetic nervous system, and a communicating branch from the ophthalmic division of the trigeminal nerve. As the oculomotor nerve enters the orbit it divides into a superior and an inferior branch, which enter the orbit through the superior orbital fissure along with other cranial nerves. 7.3.1.1  Superior Branch Supplies the superior rectus and levator palpebrae superioris 7.3.1.2  Inferior Branch Supplies the Medial rectus, Inferior rectus, Inferior oblique and the Ciliary ganglion which controls pupillary constriction and accommodation

7.3.2  Presentation The involvement of the IIIrd nerve at various anatomical sites is associated with characteristic signs and symptoms that may be helpful in localising the site of the lesion.

7.3.3  Nuclear Portion A discrete and isolated nuclear IIIrd nerve palsy is very rarely seen and is associated with dorsal midbrain infarction. The IIIrd nerve nucleus consists of four paired subnuclei, the most medial of which supply the SR that projects to the contralateral

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side. The rest of the sub nuclei only supply structures ipsilaterally. Thus, a nuclear lesion would cause a unilateral palsy of the third cranial nerve, weakness of the ipsilateral and contralateral superior rectus muscles, and bilateral incomplete ptosis due to LPS involvement. Involvement of discrete subnuclei can also cause isolated palsy of the Inferior rectus.

7.3.4  Fascicular Portion Once the IIIrd nerve has left the nucleus, the symptoms are localised to the same side as the nerve. Because of the proximity of the fascicular portion of the nerve to other structures in the midbrain, lesions typically produce typical neurologic symptoms some of which are described below. Syndrome Area involved Nothnagel’s Superior Cerebellar Peduncle Benedikt’s Red nucleus Weber’s Claude’s

Manifestation Ipsilateral IIIrd nerve paresis Ipsilateral IIIrd nerve paresis Cerebral peduncle Ipsilateral IIIrd nerve paresis Features of both Benedikt’s and Nothnagel’s syndromes

Manifestation Cerebellar ataxia Contralateral hemitremor Contralateral hemiparesis

7.3.5  Subarachnoid Space The IIIrd nerve exits the midbrain between the posterior cerebral and superior cerebellar artery and courses forward in the subarachnoid space. At this location, it is not in proximity to any of the other cranial nerves and if involved, the presentation tends to be isolated. The commonest lesion at this location is an aneurysm at the junction of the PCA and Internal carotid arteries that presses on the pupillomotor fibres which lie more superficially leading to an IIIrd nerve palsy with pupillary dilatation (Hutchinson’s sign) (Fig. 7.5). This is in contrast to a medical IIIrd nerve palsy that occurs due to involvement of the vasa nervorum secondary to microvascular disorders. As these vessels perforate the nerve to supply the deeper nerve fibres that don’t supply the pupil, the resultant IIIrd nerve palsy often doesn’t have associated pupillary abnormalities. On occasion, even in a compressive palsy, the pupillary involvement is slow to develop, and the patient must be carefully followed up for the first week to ensure the differentiation can be made. Other causes of IIIrd nerve palsy in this region include Ophthalmoplegic migraine, basal meningeal infection and neoplastic infiltration.

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Fig. 7.5  Blood supply to portions of the IIIrd nerve supplying the pupils and extraocular muscles

Vasa nervorum

Pupilomotor fibers

Internal carotid artery

Fibers to extraocular muscles and levator palpebrae

Cavernous sinus

Oculomotor nerve (CN III) Trochlear nerve (CN IV) Ophthalmic nerve (CN V1) Abducens nerve (CN VI) Maxillary nerve (CN V2)

Sphenoid sinus

Fig. 7.6  The arrangement of cranial nerves within the cavernous sinus

7.3.6  Cavernous Sinus Syndrome The IIIrd nerve runs laterally within the cavernous sinus (Fig. 7.6), entering it just below the interclinoid and above the petroclinoid ligament. It may be affected by both intrinsic disorders of the cavernous sinus and invasion from masses arising within the sella. More diffuse lesions within the cavernous sinus, often

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inflammatory in nature, typically give rise to simultaneous involvement of the III, IV, VI, and first two divisions of the V cranial nerves in various combinations with the VIth being the most commonly affected. Disorders of the pituitary leading to its enlargement such as adenoma tend to preferentially affect the IIIrd nerve as it is held between the relatively inflexible ligaments [1]. Caroticocavernous fistulas that lead to involvement of the internal carotid artery can also present with cranial nerve palsy.

7.3.7  Orbital Portion The IIIrd nerve enters the orbit via the superior orbital fissure (Fig. 7.7) and splits into two portions. The superior division innervates the SR and LPS and the inferior division the MR, IR, IO and the pupil (constriction via the sphincter muscle) and accommodation via the ciliary muscle. The cilliary ganglion is a parasympathetic ganglion that lies in the posterior orbit. It receives the parasympathetic output of the Edinger Westphal nucleus via the oculomotor nerve that contains these preganglionic fibres. The postganglionic fibres run in the short ciliary nerves and innervate the sphincter pupillae and the cillary muscles responsible for pupillary constriction and accommodation respectively. Pathology affecting the orbit, or the superior orbital fissure leads to multiple cranial neve involvement. It can also be associated with proptosis, raised intraocular pressure or involvement of the muscles themselves. An example of this is the Tolosa Hunt syndrome, a painful ophthalmoplegia caused by involvement of the cavernous sinus or superior orbital fissure. It is associated with idiopathic granulomatous

Superior rectus Levator palpebrae Superior Oblique Optic nerve and ophthalmic artery in optic foramen Medial rectus

Superior orbital fissure Common tendinous ring Lacrimal nerve (V) Frontal nerve (V) IV Superior ophthalmic vein III Nasociliary nerve (V)

Inferior rectus Inferior ophthalmic vein

Fig. 7.7  Diagram of nerves entering orbit through the superior orbital fissure

VI III Rectus lateralis

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inflammation and can affect any combination of the cranial nerves supplying the extraocular muscles. The International Headache Society criteria for Tolosa-Hunt syndrome include the following: (a) Unilateral orbital or periorbital headache fulfilling criterion C (b) Both of the following: 1. Granulomatous inflammation of the cavernous sinus, superior orbital fissure or orbit, demonstrated by MRI or biopsy 2. Paresis of one or more of the ipsilateral IIIrd, IVth and/or VIth cranial nerves (c) Evidence of causation demonstrated by both of the following: 3 . Headache is ipsilateral to the granulomatous inflammation 4. Headache has preceded paresis of the IIIrd, IVth and/or VIth nerves by ≤2 weeks, or developed with it (d) Not better accounted for by another ICHD-3 diagnosis. Some reported cases of Tolosa-Hunt syndrome had additional involvement of the Vth nerve (commonly the first division) or optic, VIIth or VIIIth nerves. Sympathetic innervation of the pupil is occasionally affected. It is diagnosed by neuroimaging which may be MRI with or without contrast which reveals inflammatory changes in the cavernous sinus, orbital apex and/or superior orbital fissure. It is treated using corticosteroids. Careful follow-up is required to exclude other causes of painful ophthalmoplegia such as tumours, vasculitis, basal meningitis, sarcoid or diabetes mellitus.

7.3.8  Investigation and Management The presentation of the IIIrd nerve palsy usually gives some clues to the etiology and guides further investigation and management. The major clinical determinants of management include: • • • • •

Size and reactivity of the pupil Age of patient Degree of lid involvement Periorbital pain Associated cranial nerve palsies

7.3.9  Complete IIIrd Nerve Palsy The eye is positioned in a down and out position with the only movements remaining being those of the LR (abduction) and SO (depression). The pupil is dilated, and the palsy is associated with loss of accommodation due to paralysis of the ciliary

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Fig. 7.8  Left Total IIIrd nerve Palsy—the field of the affected eye is markedly constricted

muscle. A Hess chart revels a significant abnormality with a reduced field of movement of the affected eye (Fig. 7.8).

7.3.10  Partial IIIrd Nerve Palsy The presentation depends on which division of the third nerve is involved. Superior division affected: ptosis, limitation of elevation Inferior division affected: Limitation of depression. Pupillary involvement

7.3.11  IIIrd Cranial Nerve Palsy in Children Aberrant regeneration or oculomotor synkinesis is more commonly seen in children due to the higher degree of neuroplasticity. Whereas the presence of mydriasis in III palsy suggests a compressive aetiology in adults, this is not the case in children. Half of all IIIrd cranial nerve palsies in children are congenital but 10–20% are due to an aneurysm or neoplasm with the rest being post traumatic and miscellaneous in cause [2]. Therefore, all children with a cranial neve palsy should undergo neuroimaging with a MRI, MRA or CTA based on local guidelines.

7.3.12  IIIrd Cranial Nerve Palsy in 18–50 Year Olds Within this age group, trauma, neoplasm and ischaemic changes are the main underlying causes. Irrespective of the degree of pupil involvement, neuroimaging in the form of MRI, MRA or CTA should be carried out.

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7.3.13  IIIrd Cranial Nerve Palsy in over 50-Year Olds Microvascular third nerve palsies become increasingly frequent at the beginning of the fifth decade of life and are largely responsible for the increase in incidence of acquired third nerve palsy in the sixth decade of life. Traditionally pupil involvement and periorbital pain are considered ominous signs of an underlying compressive lesion that requires more aggressive management. In a recent population-based study, the incidence of microvascular palsies was found to be much higher (42%) than expected from other studies (11–21%) and the authors postulate that referral bias may have contributed to the higher incidence of compressive third nerve palsies in other studies. Interestingly, 16% of patients with microvascular third nerve palsies had pupil involvement at time of presentation compared with 64% for compressive third nerve palsies. Therefore, anisocoria alone cannot definitively differentiate microvascular from compressive third nerve palsies. Pain was present in 61% of patients with microvascular third nerve palsies, a rate that did not differ from that of patients with aneurysm (78%). Therefore, pain is similarly unreliable to differentiate a microvascular etiology from aneurysmal compression. It was also noted that among the nine cases of aneurysmal third nerve palsies in the study, five were from cavernous sinus aneurysms. Cavernous sinus aneurysms seldom rupture, and if they do, they rarely cause life-threatening subarachnoid haemorrhage but rather cause carotid-cavernous fistula. Only three were from a PCA aneurysm but these have been reported far more frequently in literature as they are more likely to present as an acute neurosurgical emergency [3]. 7.3.13.1  Pupil Sparing Isolated IIIrd Cranial Nerve Palsy In the older age group, these palsies can be worked up in a similar manner to isolated sixth and fourth nerve palsies. In the first instance this includes a clinical examination and ischaemia work up including Blood Pressure, CBC, ESR, CRP, Blood Glucose and HbA1C. If the patient has Diabetes or Hypertension, it is important that these are controlled adequately and may necessitate a referral to their primary care provider. These patients need to be followed up closely over the next 5–7 days to ensure the pupil does not get involved after the initial presentation as maybe seen in evolving compressive lesions. The indications for neuroimaging in this group include; • • • •

Dilatation of the patient after initial presentation No improvement in symptoms over 3 months Signs of aberrant regeneration of the IIIrd nerve Other neurological findings or cranial nerve palsies.

Aberrant regeneration or oculomotor synkinesis is more commonly seen in children due to the higher degree of neuroplasticity as discussed above, but also secondary to trauma, tumours (cavernous or parasellar meningioma) and aneurysms

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(posterior communicating artery). This tends to occur when there is disruption of both the axon as well as the endoneurium. The most common clinical signs of aberrant regeneration consist of: • Elevation of the upper eyelid on attempted downward gaze (pseudo Von Grafe sign) when fibres to the IR innervate the levator. • Elevation of the upper eyelid on attempted adduction (Inverse Duane’s syndrome) when fibres to the MR innervate the levator. • Adduction of the eye on attempted upward or downward gaze, and • Constriction of the pupil on attempted adduction or downgaze (Presudo Argyll Robertson Pupil [4].

7.3.14  Treating IIIrd Nerve Palsies 7.3.14.1  Medical Microvascular palsies need monitoring to ensure the pupil does not become involved suggesting a compressive etiology, by close follow up within the first week. Prognosis for full recovery from isolated microvascular nerve palsies is  excellent  and occurs  typically over 8–12  weeks. Of microvascular third nerve palsies, 90.9% (20/22 patients) recovered completely within 12 months and 81.8% (18/22 patients) resolved within 3 months [5]. Management is primarily conservative consisting of adequate control of the underlying medical factors and occlusion or prisms for the paretic eye to control diplopia if ptosis is not complete. 7.3.14.2  Surgical For patients that do not resolve or do so partially, surgical management may become more appropriate. Most clinicians wait for at least 6  months following the acute presentation for recovery to take place and for stabilisation of the deviation. Surgical management of these patients is challenging due to the incomitant nature of the deviation. Associated factors such as pupil dilatation, loss of accommodation and partial or complete ptosis also need to be considered. The surgical options include: • Maximal resection of the MR and recession of the LR to correct the horizontal deviation. • Splitting the LR and transposition to the MR • Nasal transposition of the SO tendon

7.4  Fourth Nerve Palsy The trochlear nerve supplies just one extraocular muscle, the superior oblique which is responsible for intorsion (primary action), depression and abduction.

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7.4.1  Anatomy The fourth cranial nerve is unique in arising from the dorsal aspect of the brain stem, crossing over soon after its origin to supply the contralateral side and in having a long intracranial course that makes it susceptible to traumatic injury. The nucleus for the IVth nerve is located in the midbrain at the level of inferior colliculus. The trochlear nerves decussate in the roof of aqueduct before exiting from the dorsal aspect of midbrain. The nerve travels between the posterior cerebral and superior cerebellar arteries before entering the cavernous sinus. The fourth nerve then enters the orbit through the superior orbital fissure, outside the annulus of Zinn. It then crosses medially over levator palpebrae superioris and superior rectus muscles to finally supply the superior oblique muscle (Figs. 7.9 and 7.10).

Periaqueductal gray

Trochlear nerve Trochlear nucleus Superior cerebellar peduncle

Substantia nigra Crus cerebri

Superior oblique

Lateral rectus

Superior rectus Medial rectus

Fig. 7.9  The fourth nerve, which exits from the dorsal aspect of the brainstem, decussates and supplies the SO

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Fig. 7.10  A 42 year old man with a well controlled left hyperphoria in primary position with a slight right head tilt. In dextroversion an obvious left hypertropia secondary to significant IO overaction is visiible. The hyperdeviation almost disappears in laevoversion

7.4.2  Aetiology Fourth nerve palsy is less common than either IIIrd or VIth nerve palsy and may either be congenital or acquired. Congenital IVth nerve palsy may be associated with dysgenesis of the nucleus or the peripheral nerve. The commonest cause of an acquired fourth nerve palsy is idiopathic with trauma being the second most common cause. It is sustained in head trauma, often with associated loss of consciousness. Microvascular causes account for only 17% compared to 35% of all IIIrd nerve palsies.

7.4.3  Presentation 7.4.3.1  Congenital Children may present with abnormal head posture or intermittent elevation of one eye noted by the parents. In longstanding cases facial asymmetry may also be noticed. Decompensated fourth nerve palsy may present with worsening vertical diplopia especially when looking to the side in later age. Patients with congenital palsies have large, vertical fusional amplitudes on examination and lack of subjective torsion even in the presence of large amounts of fundus torsion. 7.4.3.2  Acquired Acquired fourth nerve palsy presents with acute onset of vertical diplopia and may be preceded by trauma or an ischaemic event. Patients tend to be more symptomatic as they haven’t had time to develop vertical fusional reserves unlike congenital

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palsies. Patients adopt a characteristic head tilt that is away from the affected side, to try and reduce the amount of diplopia.

7.4.4  Site of Trauma The fourth nerve can be affected during its long intracranial course. Unlike the IIIrd nerve, the lesions are rarely localising. Midbrain trauma, ischaemia or compression can cause a bilateral IVth nerve palsy. The fourth nerve is very susceptible to traumatic damage as it runs alongside the rigid tentorium for most of its course where it can be compressed by contrecoup forces. Tumours, aneurysms or other compressive lesions can affect the fourth nerve in the subarachnoid space, cavernous sinus or orbital apex where they may also involve adjacent cranial nerves and pupillary pathways.

7.4.5  Investigation If congenital and isolated, usually no neuroimaging is indicated. All acquired fourth nerve palsies with associated neurological signs however do need to be investigated more thoroughly.

7.4.6  Clinical Assessment 7.4.6.1  Three Step Test This test is carried out to isolate the underacting muscle involved in a vertical deviation and is frequently employed in the assessment of fourth nerve palsies. The three steps consist of the following: 1. What is the deviation in primary gaze? Taking a Right hypertropia as an example, this means either the two depressors of the right eye (SO and IR) or the two elevators of the left eye (SR and IO) are underacting. 2. How does the deviation change in lateral gaze? The position of the eyes is assessed in right and left gaze. Considering the example above, if the R/L increases in left gaze, we can narrow the possible muscles involved further to the Right SO or Left SR; the two of the four that are active in levoversion. Tip: By this stage the two muscles identified should both begin with the same letter, i.e. SO and SR or IO and IR.

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3. Bielschowsky’s Head Tilt Test The patient’s head is tilted to either side and the change in magnitude of deviation noted. In fourth nerve palsies, the deviation increases when the head is tilted to the same side, which is why they tend to adopt a head posture with a tile to the opposite shoulder (Obliques tilt Opposite is a handy mnemonic). Therefore, in the example above the vertical deviation will increase on a Right head tilt. The reason for this phenomenon is when the head is tilted to the right, the right eye becomes extorted and due the ocular tilt reaction needs to be intorted to bring it into alignment again. The two intortors of the Right eye are the SR and the SO. As the SO is weakened, the SR has to do the majority of the work and has a greater flow of innervation to accomplish this. However the primary action of the SR is elevation which leads to an increase in the amount of hypertropia. This effect disappears in left head tilt. 4. Supine test: Agnes Wong has described a fourth step which consists of repeating the measurements in a supine position. This negates the effect of the vestibulo ocular system and is helpful in distinguishing a fourth nerve palsy (no change) from a skew deviation (deviation decreases)

7.4.7  Bilateral Fourth Nerve Palsy The fourth nerve can be involved bilaterally, especially following road traffic accidents. The signs of a bilateral fourth can however be masked and need to be looked for carefully. These include • Significant V pattern esotropia leading to a chin down head posture (Fig. 7.11) • Alternating hypertropia in lateral gazes as the Right IO overacts in left gaze leading to a R/L and the opposite occurs in levoversion • Excyclotorsion more than 15° • Relative small vertical deviation in primary gaze • Head tilt can be to either side

Fig. 7.11  Hess chart showing bilateral superior oblique palsies, left more than right. Note the slightly tilted appearance and V type pattern esotropia

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7.4.8  Management 7.4.8.1  Conservative Can be managed with prisms if the deviation is small or the patient is asymptomatic. 7.4.8.2  Surgical The surgical modality used depends on the: • Presence of an anomalous head posture: Usually face turn and head tilt to the normal side. May have chin down if bilateral fourth nerve palsy which is associated with V pattern esotropia. • Angle of Deviation—Vertical and associated horizontal if any • Direction of gaze where the angle is the largest • Amount of Torsion The author prefers a nine gaze assessment on the synoptophore that helps quantify the above to enable a surgical decision to take place. As a rule of thumb, the muscles responsible for subserving the direction of gaze where the deviation is the most are tackled in the first instance. For example, if the deviation is most in laevodepression, either the left SO could be strengthened, or the right IR weakened. 7.4.8.3  Inferior Oblique Weakening • This is the commonest type of surgical procedure carried out for the treatment of fourth nerve palsy. The methods of IO weakening include • Disinsertion from the sclera which may not be very effective as the muscle re attaches variably • Myectomy of the muscle belly where about 1 cm of the muscle is excised and the cut ends buried within the tenons capsule (Video 7.12) a

b

Fig. 7.12 (a) The inferior oblique muscle is identified, clamped and disinserted from the sclera. (b) The muscle is reattached at Park’s point, avoiding the nearby vortex vein

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• Recession to Park’s point (3 mm posterior and 2 mm lateral to the lateral edge of the IR) (Fig. 7.12) • IO Anteriorisation where the muscle is detached and moved just lateral to the lateral insertion of the IR. This makes the IO a powerful anti elevator and can be a very effective cure of hypertropia (Video 7.13). 7.4.8.4  Superior Oblique Tendon Tuck This procedure is performed when the deviation is most in downgaze. It is technically more demanding than an IO weakening procedure. The SO tendon is more lax in congenital compard to acquired cases and a SO tuck is rarely performed for the latter (Fig. 7.13). Due to the induced restriction of upgaze in adduction following a SO tuck, it almost always induces an iatrogenic Brown’s syndrome which patients need to be warned about. 7.4.8.5  Harada Ito Procedure The SO tendon has an expansive insertion onto the sclera beneath the SR. The anterior 10–20% fibres are responsible for intorsion while the rest carry out depression and abduction. In cases where excyclotorsion is the main complaint, these anterior Fig. 7.13  Tucking the superior oblique tendon

7.5  Sixth Nerve Palsy Fig. 7.14 Fells modification of the Harada Ito Procedure: The SO tendon is split longitudinally and the anterior 25% that subserves intorsion is advanced to 8 mm posterior and 2 mm superior to the LR insertion

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fibres are moved down to the insertion of the LR which augments their intorting action (Fig. 7.14).

7.5  Sixth Nerve Palsy The sixth or abducens nerve innervates the lateral rectus that acts to abduct the eye.

7.5.1  Anatomy The nucleus is located in the pons, lateral to the medial longitudinal fasciculus. About 40% of its neurons project onto the ipsilateral MLF to cross over and supply the contralateral MR that is involved in adduction. Thus a nuclear sixth nerve palsy causes an inability to look towards the side of the lesion. The nerve emerges at the pontomedullary junction to enter the subarachnoid space and travels between the pons and clivus to enter Dorello’s canal. It travels upto the petrous apex where it enters the cavernous sinus and lies in close proximity to the internal carotid artery. It then travels through the superior orbital fissure to innervate the LR (Figs. 7.15, 7.16, and 7.17).

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Superior orbital fissure

Internal carotid artery

Abducens nucleus

Petrous temporal bone (cut)

Pons

CN VI exiting at the pontomedullary junction

Fig. 7.15  Course of the sixth nerve

Medial Longitudinal Fasciculus Fourth Ventricle Spinal Tract of V central sympathetic neurons VII Nucleus VII

VI Pyramidal Tract Paramedian Pontine Reticular Formation (PPRF)

Fig. 7.16  Diagram of the crossection of the lower pons through the VI nucleus and fascicle (highlighted in black). (From Lanning B Kline. Neuro Ophthalmology Review Manual.Slack incorporated. Rights obtained)

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Fig. 7.17  A 87 year old patient with a right VIth nerve palsy seen looking to the left (up), straight (middle) and right (bottom). She has a prominent right esotropia that worsens in right gaze with associated loss of abduction

7.5.2  Presentation 7.5.2.1  Adult Acquired Sixth Nerve Palsy Patients usually present with horizontal diplopia, worse in the direction of action of the paralysed muscle. They may also adopt a head posture with a face turn to the affected side to reduce diplopia. Depending on the aetiology, they may have a history of antecedent trauma, signs and symptoms of raised intracranial pressure, otitis media, nystagmus, giant cell arteritis etc. The location of involvement may also give rise to specific associations that are helpful in localisation of the site of the lesion.

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7.5.2.2  Nucleus and Fasciculus As the VIth nerve nucleus is closely associated with the following structures, they may be involved in the presentation Oculosympathetic neuron: ipsilateral Horner’s syndrome PPRF: Ipsilateral gaze palsy MLF: Ipsilateral INO Pyramidal tract: contralateral hemiparesis Associated syndromes include • Milliard-Gubler: VIth nerve paresis with ipsilateral VIIth nerve paresis and contralateral hemiparesis. • Raymonds syndrome: VIth nerve paresis with contralateral hemiparesis. • Foville’s syndrome: Horizontal conjugate gaze palsy with Ipsilateral V, VII and VIIIth crnial nerve palsies and Ipsilateral Horner’s syndrome.

7.5.3  Subarachnoid Space As the nerve is tethered at its exit from the pons, any rise in intracranial pressure may lead to stretching of the nerve causing a non localising palsy. This is commonly seen in idiopathic intracranial hypertension (IIH) but may also be secondary to haemorrhage, infection (viral, bacterial or fungal meningitis), inflammation (sarcoidosis) or infiltration (leukemia, lymphoma etc.).

7.5.4  Petrous Apex Gradinego’s syndrome occurs due to localised inflammation at the petrous apex following complicated otitis media and consists of:VIth nerve palsy with ipsilateral decrease hearing, facial pain and VIIth nerve paralysis. Pseudo Gradinego’s syndrome may be seen in nasopharyngeal carcinoma or a cerebellopontine angle tumour.

7.5.5  Cavernous Sinus Due to its proximity to other cranial nerves and the pituitary, the sixth nerve is very rarely affected in isolation due to lesions in this location. Common associations include involvement of the III, IV and ophthalmic division of the Vth (V1) cranial nerve, Horner’s syndrome and pituitary tumours.

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7.5.6  Orbit The sixth nerve may be affected at its entry into the orbit in the Orbital Apex syndrome. When this is secondary to inflammation there is associated pain on eye movements, it’s called Tolosa Hunt syndrome. It may also be associated with proptosis, conjunctival congestion with chemosis.

7.5.7  Management Patients presenting with a sixth nerve palsy should undergo systemic evaluation of their cardiovascular status including measurement of the blood pressure and routine haematological assessment such as a complete blood count, blood glucose levels, HB A1C and inflammatory markers. Patients under the age of 50 years should also be sent for neuro imaging as the aetiology is more likely to be secondary to neoplasms or a compressive vascular lesion. After the age of 50, it is most likely to be secondary to an ischaemic mononeuropathy. Therefore, in these patients imaging is only indicated if there are other associated neurological signs or no signs of resolution within 3 months. 7.5.7.1  Congenital Sixth Nerve Palsy Duane’s syndrome is the commonest form of congenital sixth nerve palsy and is covered in Chap. 10. Mobius syndrome is defined as congenital facial weakness (usually bilateral and complete) combined with VIth nerve involvement or a horizontal gaze palsy. These may be associated with hypogonadism, autism and dextrocardia. 7.5.7.2  Sixth Nerve Palsy in Childhood The abducens nerve is the most commonly affected cranial nerve in childhood acute acquired strabismus. Neoplasm as a cause is much more common than in adults (upto 45% in studies) and thus neuroimaging is mandatory [6]. Benign idiopathic VIth nerve palsy is another common presentation in childhood and is more often seen in girls with a left-sided preponderance and usually resolves in 2 mm proptosis Decrease in uniocular excursion in one direction of >8° Decrease of acuity equivalent to 1 snellen line

One point for each item. If score above 3/7 at the first examination or above 4/10 in successive examinations indicates active TED

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Oral steroids are very effective and should be considered in those with a CAS score of more than 3 at a high dose of 80–100 mg/day. Pulse Intravenous Methyl prednisolone can be used in severe disease with optic nerve compromise. Radiotherapy can be used for steroid non responsive cases or where their use is contraindicated. Immunomodulators such as Azathioprine have been used with variable effect and newer biological agents such as Rituximab are now being investigated. The Combined immunosuppression & radiotherapy in thyroid eye disease (CIRTED) investigated the efficacy of orbital radiotherapy (RT) and azathioprine (AZA) vs. placebo in combination with a standard 24-week tapering course of oral prednisolone in patients with active TED. They found no additional treatment benefit with RT and although completion rates of AZA treatment were low, those completing treatment derived substantial benefit at 48 weeks [6]. If surgical management of strabismus is necessitated, it should only be carried out in the inactive or quiescent phase of the disease. The surgical rehabilitation is carried out in the following order.

10.2.9  Orbital Decompression Proptosis is one of the most obvious sequelae of TED and may be associated with cosmetically unsightly disfigurement, corneal exposure, limitation of motility, globe luxation and optic nerve compromise. Orbital decompression is the procedure of choice which widens the orbital space by removal of one or more walls of the orbit, thereby reducing the proptosis. Of the four walls of the orbit (roof, floor, medial and lateral), up to three may be removed depending on the degree of severity of the proptosis. The roof is usually not operated upon due to the risk of serious complications [7].

10.2.10  Strabismus Surgery Management of diplopia in TED can be very challenging due the Incomitant nature of the strabismus. Surgery for strabismus should not be carried out until the condition has become inactive and any orbital decompression has been performed. The ocular deviation measurements should be stable for at least 6  months. For small deviation, botulinum toxin or prisms can be used as an alternative to surgery. If a decision to operate is made, a forced duction test should be carried out in order to assess the tightness of all the muscles. Surgery comprises recession of the tight muscles to increase the field of binocular single vision. Resection is rarely carried out [8].

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10.2.11  Lid Surgery Eyelid surgery should be delayed until after strabismus surgery as correction of hypo or hypertropia affects lid position. This consists of correction of upper and lower eyelid retraction. A transcutaneous levator recession is the most commonly used surgical procedure. It may be supplemented with a blepharoplasty, hyaluronic acid fillers and botulinum toxin injections [9].

10.3  Chronic Progressive External Ophthalmoplegia This is a disorder characterised by slowly progressive paralysis of the extraocular muscles with associated bilaterally symmetrical ptosis.

10.3.1  Etiology CPEO is a mitochondrial myopathy that preferentially affects the extraocular muscles due to their higher mitochondrial volume. It is secondary to mutations in the mitochondrial DNA and may occur in isolation or with associated skeletal muscle weakness. A variant is Kearns Sayre syndrome that is characterised by progressive external ophthalmoplegia, pigmentary retinitis and an onset before the age of 20 years. Other common features include deafness, cerebellar ataxia and heart block.

10.3.2  Presentation The signs and symptoms of CPEO typically begin in young adults between the ages of 18 and 40. The earliest manifestation is ptosis followed by ophthalmoplegia. The ptosis may be bilateral, unilateral or asymmetric and is associated with frontalis overaction and a chin up head posture. The ophthalmoplegia is global in nature and patients usually have no diplopia as the limitation tends to be symmetric between the two eyes (Fig. 10.6). Associations include neurological (cerebellar ataxia, vestibular symptoms) and endocrine diabetes, hypoparathyroidism, hypogonadism) and skeletal muscle (dysphagia) abnormalities.

References

143

Fig. 10.6  A 75 year old woman with CPEO, manifesting as bilateral ptosis and no obvious strabismus in primary gaze. She has significant limitation of eye movements in all directions of gaze including elevation, depression, dextroversion and laevoversion

10.3.3  Management There is no cure for CPEO and the management tends to be supportive. Patients usually do not require any intervention for ocular motility restriction due to lack of diplopia. Ptosis surgery is contraindicated due to the absence of a Bell’s phenomenon as it may lead to postoperative corneal exposure.

References 1. Bahn RS. Graves’ ophthalmopathy. N Engl J Med. 2010;362:726–38. 2. Mourits MP, Prummel MF, et  al. Clinical activity score as a guide in the management of patients with Graves’ ophthalmopathy. Clin Endocrinol. 1997;47:9–14. 3. Bartalena L, et  al. Consensus statement of the European Group on Graves’ Orbitopathy (EUGOGO) on management of GO. Eur J Endocrinol. 2008;158(3):273–85. 4. Marcocci C, et  al. Selenium and the course of mild Graves’ orbitopathy. N Engl J Med. 2011;364(20):1920–31. 5. Cawood T, Moriarty P, O’Shea D.  Recent developments in thyroid eye disease. BMJ. 2004;329(7462):385–90. 6. Rajendram R.  Combined immunosuppression and radiotherapy in thyroid eye disease (CIRTED): a multicentre, 2 × 2 factorial, double-blind, randomised controlled trial. Lancet Diabetes Endocrinol. 2018;6(4):299–309. 7. Naik MN, et  al. Minimally invasive surgery for thyroid eye disease. Indian J Ophthalmol. 2015;63(11):847–53. 8. Harrad R. Management of strabismus in thyroid eye disease. Eye. 2015;29(2):234–7. 9. Perros P, et al. Thyroid eye disease. BMJ. 2009;6:338.

Chapter 11

Other Forms of Incomitant Strabismus

11.1  Blow Out Fracture A blow out fracture involves traumatic injury to the orbit resulting in a fracture of one or more of the orbital walls. This may be associated with herniation or entrapment of the orbital contents into the sinuses resulting in enophthalmos and limitation of ocular motility. These most commonly involve the floor or less commonly the medial wall or a combination of the two and are caused by occlusion of the orbital opening by an object that is the same size e.g. ball, fist, kneecap etc. A pure fracture is one in which the orbital rim is not involved whereas an impure fracture involves the orbital rim in addition to the involvement of the orbital walls and is commonly seen in road traffic accidents (RTA).

11.1.1  Aetiology There are many proposed theories to explain the occurrence of blow out fractures in ocular trauma. One of the oldest is the bone-conduction theory, which suggests that a force, not powerful enough to fracture the rim, will propagate along the bone to fracture the weaker orbital floor (Le Fort). Pfeiffer proposed the “Globe-to-Wall Theory”, which is when a force pushes the globe into the orbit, it causes the globe to contact the orbital floor, resulting in a floor fracture.

Electronic Supplementary Material The online version of this chapter (https://doi. org/10.1007/978-3-030-24846-8_11) contains supplementary material, which is available to authorized users. © Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_11

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In contrast, another popular theory evokes the “hydraulic mechanism”, whereby the fracture is the result of increased intra-orbital pressure from the eye entering the orbit and not due to direct contact [1–3].

11.1.2  Presentation The main presenting complaints include: • A history of injury to the orbit or periorbital areas with varying degrees of periorbital echymosis, erythema and crepitus. • Diplopia which is usually vertical or oblique and can be due to limitation of upgaze if the IR is entrapped (Fig. 11.1) or downgaze if the IR is injured. If the medial wall and ethmoidal sinuses are involved, the diplopia is horizontal and abduction as well as adduction may be limited (Fig. 11.2). • Hypoesthesia in the distribution of the infraorbital nerve is found to be commonly associated. • Enophthalmos with or without hypoglobus, ptosis and deepening of the supratarsal crease (Figs. 11.3 and 11.4) Fig. 11.1  Posterior orbital floor fracture can not only restrict upgaze, but also alter the torque vector of the inferior rectus muscle, weakening its depressing action. (Strabismus-Burton Kushner-­Rights obtained)

11.1  Blow Out Fracture

147

Fig. 11.2  Hess chart depicting a Right sided medial wall blow out fracture leading to limitation of right abduction. Note the compressed nature of the field which indicates a restrictive rather than a neurological etiology

Fig. 11.3  A 70 year old lady who presented with trauma to the right eye. The photograph reveals enophthalmos and limitation of upgaze in the right eye, consistent with a blow out fracture involving the orbital floor

• Sequelae of injury to the globe- reduced visual acuity, disruption of structural integrity of the eye, commotio retinae, traumatic retinal detachment or optic neuropathy. A detailed ophthalmic examination in all patients with suspected blow out fractures is therefore indicated. Children tend to develop a trapdoor fracture or “white-eyed blowout” that is defined by the lack of displacement of the involved bones. These occur due to the

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Fig. 11.4  A CT scan of the Orbits of the lady above, displays a fracture of the right orbital floor with displacement of a bony fragment and orbital contents into the right maxillary sinus

pliant nature of orbital bones in children which lead to the fractured area springing back, trapping orbital tissue and in some cases the extraocular muscles. If the latter are involved (most commonly the IR), it leads to restriction of ductions in opposite gaze and severe autonomic reactions including nausea and vomitting. Timely release of entrapped tissue is vital to prevent permanent sequelae related to tissue ischemia, scarring and contraction.

11.1.3  Management Computed tomography of the orbits and face with thin cuts (1.5–2 mm) is the imaging option of choice for the evaluation of orbital and facial fractures. Coronal views can often show details of orbital floor fractures best. The shape of rectus muscles, extent of bony displacement, opacification of the maxillary sinuses and displacement of the globe can all give an indication of the size of the bony defect and help guide management [4] (Fig. 11.4). The timing of surgical intervention remains controversial. Initial oedema usually resolves within the first 2 weeks with improvement in ocular motility and infraorbital hypoesthesia and most experts advise waiting while this occurs [5]. The indications for early surgery include • Unresolved oculocardiac reflex with positive forced-duction testing and/or CT evidence of muscle entrapment (white-eyed blow-out fractures) • Diplopia within 30° of primary gaze • A pure orbital floor fracture involving more than 50% of the floor

11.2  Browns Syndrome

149

• Significant enophthalmos (>2 mm) or hypoglobus affecting facial symmetry If surgical repair is indicated, the orbital floor can be accessed via the cutaneous or transconjunctival approach. The repair involves • Fracture site exposure, • Freeing tissue prolapsed into the fracture site, and • Reapproximating the orbital wall support, usually with an implant that can repair the defect and restore integrity. Alloplastic implant materials are now more commonly used than autogenous tissues due to their ease in availability, the commonest being thin nylon foil (Supramid). Other implant materials include silicone, hydroxyapatite, polytetrafluoroethylene, titanium mesh etc.

11.2  Browns Syndrome This was first described by Harold Whaley Brown in 1950 after he came across a mother and child who were misdiagnosed with a paralysis of the inferior oblique. Brown’s syndrome is a mechanical disorder associated with a short superior oblique tendon which may be congenital or acquired.

11.2.1  Aetiology Brown’s syndrome was initially thought to be secondary to a tight superior oblique tendon or inelastic muscle-tendon complex [6]. However now various modes of causation have been described, with all leading to a limitation of elevation in adduction. Congenital Brown syndrome could be caused by a • Short anterior sheath of the SO tendon • A developmental abnormality of the tendon fibres that do now allow the normal telescoping movement through the trochlea. • Restrictive inferior orbital bands that adhere to the posterior globe • Lower location of the LR pulley system Acquired Brown syndrome can be associated with • Inflammation of the SO tendon or the trochlear region that hinder the movement of the tendon through the trochlea e.g. rheumatoid arthritis with trochlear involvement • Traumatic or iatrogenic damage to the trochlea (endoscopic sinus surgery, dog bites, Retinal detachment surgery, tooth extraction etc.)

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11.2.2  Presentation The most common presentation is an isolated limitation of elevation in adduction that improves in straight gaze and on abduction. In full adduction the affected eye cannot be raised above the mid-horizontal plane on voluntary eye movement. It tends to affect only one eye, more usually the right. There is usually widening of the palpebral fissure on adduction and V pattern exotropia may be seen on upgaze. Usually there is no strabismus in primary gaze and the condition only becomes apparent when the patient looks up. It may be associated with hypotropia, ptosis and a compensatory AHP but this is unusual and mostly seen in acquired cases (Fig. 11.5). On examination, there is a positive forced duction test with resistance to movement of the eye in elevation while adducted. The three step test is not useful is diagnosing Brown syndrome as it is a restrictive rather than a paralytic condition. A Hess chart depicts a normal sized field in the affected eye that is abruptly flattened superiorly, suggesting a restrictive disorder (Fig. 11.6).

Fig. 11.5  A 10 year old girl with a small left hypotropia in primary position associated with a pseudoptosis. There is limitation of elevation of the left eye, more marked in adduction than in abduction

Fig. 11.6  Hess chart in Left Brown Syndrome, depicting relatively normal sized fields in the affected eye but a superior flattening effect, consistent with a restrictive disorder

11.2  Browns Syndrome

151

11.2.3  Investigation If the signs are consistent with Brown syndrome, usually no further investigation is required. If associated with atypical features, pain or discomfort or a history of antecedent surgery or trauma, MRI of the orbits may be indicated. In cases of acquired nontraumatic Brown syndrome, tests to exclude inflammatory diseases, such as rheumatoid arthritis may need to be carried out.

11.2.4  Management Most cases of Congenital Brown syndrome are asymptomatic and require no active treatment. They are usually first noticed in early childhood as the child looks upwards towards their parents and this becomes less obvious with increasing age (and height). Spontaneous resolution of Brown syndrome has been described in upto 75% of cases and hence surgery is rarely indicated [7]. The indications for surgical intervention are • • • •

Significant hypotropia in primary gaze, Troublesome diplopia, Associated chin down head posture to maintain binocularity and Significant pain or discomfort on attempted elevation.

The principle of treatment is elongation of the superior oblique tendon to release the restriction in upgaze. This can be achieved by performing a tenotomy and inserting a segment of 240 retinal band between the cut ends. An alternative is using a suture bridge to achieve the elongation that eliminate the long term risk of exposure of the retinal band (Fig.  11.7). Other surgical techniques like SO recession or Z Fig. 11.7 Superior Oblique Tendon elongation utilising a retinal band for the treatment of Brown Syndrome

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tenotomy of the SO tendon usually lead to an under correction and a complete tenotomy of the tendon a SO palsy and are thus avoided.

11.3  Acquired Brown Syndrome If the symptoms are associated with pain and inflammation systemic and locally injected corticosteroids or non-steroidal anti-inflammatory agents (like ibuprofen) can be used.

11.4  Duanes Syndrome Duane Retraction Syndrome (DRS), also known as Stilling-Turk-Duane Syndrome, was originally described by Alexander Duane in 1905. It is a rare congenital, non-­ progressive form of strabismus characterised by variable horizontal duction deficits, narrowing of the palpebral fissure and globe retraction [8].

11.4.1  Aetiology Initially DRS was thought to be a mechanical disorder secondary to a tight LR or dual insertion of the MR. A study of the electric potentials generated by the extraocular muscles has led to a better understanding of the innervational basis of DRS. A congenital absence of the sixth nerve nucleus results in aberrant regeneration wherein the third nerve innervates both the LR and MR. As a result, the two recti co-contract in adduction and abduction leading to characteristic motility and palpebral aperture changes. This theory has been backed up by the finding of an absence of the left sixth nerve in a case of unilateral DRS using high resolution T1-weighted images on magnetic resonance imaging (MRI). This congenital absence of innervation to the muscles has been found to cause fibrotic changes in the extraocular muscles leading to abnormal motility. DRS is thus classified as a congenital cranial dissinervation disorder (CCDD) [9].

11.4.2  Genetics DRS is a sporadically inherited disorder in the majority but 10% may be inherited in an autosomal dominant manner associated with mutations in the CHN1 gene. It more commonly affects females (60%), the left eye (75–90%) and is more commonly unilateral (80%) than bilateral.

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153

Systemic associations. DRS has systemic associations in upto 30% of cases and can be associated with the following conditions. Radial Ray Anomalies Okihiro’s syndrome: Duane syndrome and radial ray defects. Holt-Oram syndrome: abnormalities of the upper limbs and heart. Head and Neck Anomalies Goldenhar syndrome: malformation of the jaw, cheek and ear, usually on one side of the face. Moebius syndrome: congenital paresis of facial and abducens cranial nerves. Wildervanck syndrome: Duane syndrome, Klippel-Feil anomaly, and deafness. Ophthalmic Anomalies Ocular colobomas. Morning Glory syndrome associated with abnormalities of the optic disc. Dysplasia of the iris stroma, pupillary anomalies, cataracts, ptosis, heterochromia, Marcus Gunn jaw-winking, and microphthalmos. Oculocutaneous albinism.

11.4.3  Presentation The strabismus is present since birth and tends to be non progressive. It is characterised by: • Limitation of ductions. Abduction is more commonly affected than adduction. As a result, esotropia is more common than exotropia although the patient can also be orthophoric in primary gaze. • Anomalous head posture in the direction of action of the limitation in an effort to preserve binocular vision can be seen in association with horizontal strabismus. • Narrowing of the palpebral aperture in adduction due to retraction of the globe and widening in abduction. The retraction occurs due to co contraction of both the MR and LR that pulls the globe within the orbit.

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• Upshoots and downshoots of the eye can occur when lateral or medial gaze is attempted. Mechanical forces, where the globe slips against a tight LR and contracting MR, are usually implicated. However, DRS patients may also exhibit an innervational upshoot that is slower in character and can occur in primary gaze, independent of attempted horizontal ductions (Fig. 11.8). The vision is well maintained in DRS but up to 30–80% of patients may have hypermetropic astigmatism and thus a full cycloplegic refraction remains an essential part of assessment. Ocular, aural, neural and skeletal anomalies as described above may be associated and should be screened for. DRS has been variously classified and Huber’s classification is most commonly used where it is divided into three types. • Type 1 where the abduction of the eye is limited whereas the adduction is full or nearly normal. There is retraction of the globe and narrowing of the palpebral aperture on attempted adduction. There may be associated esotropia with an associated head turn. • Type 2 in which the adduction of the affected eye is limited, whereas abduction of the eye is normal or only slightly reduced and may be associated with an ­exotropia. As above, there is retraction of the globe and narrowing of the palpebral aperture on attempted adduction. • Type 3 where both the abduction and adduction are limited. a

Fig. 11.8 (a) A 16 year old boy with left exotropia and hypertropia in primary position. He has dense amblyopia in the left eye which does not take up fixation when the right is covered. On attempted dextroversion, there is narrowing of the palpebral aperture and the left eye elevates and retracts due co contraction of the MR and the LR. This effect can be better observed in (b), where the eye is seen to retract into the orbit inducing a temporary enophthalmos

11.4  Duanes Syndrome

155

b

Fig. 11.8 (continued)

11.4.4  Management 11.4.4.1  Investigation In typical DRS no investigations are necessary. In atypical forms or where the diagnosis is in doubt, EMG recordings from the LR may be obtained which show firing during adduction confirming the diagnosis.

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11.4.4.2  Treatment As the condition is non progressive, isolated mild forms of DRS require no more than a cycloplegic refraction to rule out refractive error and follow up as requested by the family or patient. A mild head turn can be managed by prismatic glasses and strabismus by toxin although the results can be frequently unexpected. The indications for surgical intervention include a marked head posture, significant strabismus, unsightly upshoots or downshoots or globe retraction. The primary procedure is recession of the ipsilateral MR which can correct esotropia, improve the head posture and also increase the range of abduction. Resection of the lateral rectus muscle is avoided because it increases retraction and does not improve abduction. In significant retraction and up/downshoots both the LR and MR may need to be recessed. Alternatively, a Y split of the LR may be carried out which increases the area of insertion and thus stabilises the globe (Fig. 11.9). Recession of the contralateral MR has been utilised to match the abduction defect and to reduce diplopia in the affected gaze. Abduction may be improved by transposition of the vertical recti along the spiral of Tillaux but care must be taken not to induce a vertical or rotational deviation.

11.5  Dissociated Vertical Deviation This is a condition in which one eyes drifts upwards while the other one is fixating. It is bilateral but usually assymetric.

LR

Original LR Insertion Crest

8 mm 20 mm

Fig. 11.9  Depiction of Y splitting of the LR to anchor the muscle and prevent the globe from slipping up or down. (From Strabismus-Burton Kushner-Rights obtained)

References

157

11.5.1  Aetiology The etiology of DVD is not well understood and variously thought to be a vestigial righting reflex, nystagmus blocking mechanism or a result of unbalanced cortical input to subcortical pathways [10].

11.5.2  Presentation DVD is seen in early childhood, usually in the non-dominant or amblyopic eye which tends to drift upwards from the primary position. When tested for however, the condition is frequently bilateral if asymmetric. It is not associated with diplopia as the image from the hypertropic eye is suppressed but may have a head tilt to compensate. It may be associated with infantile esotropia (90%), sensory tropias or DRS. Frequently DVD coexists with IO overaction (IOOA) from which it must be differentiated. DVD results in the slow upward drift of either eye when the other fixates. The eye exhibits slow excyclotorsion while elevating and incyclotorsion while regaining fixation. However, these movements are all in primary gaze. In contrast IOOA leads to rapid elevating movements of the eye, which are more pronounced in adduction.

11.5.3  Treatment Patients with DVD can be managed conservatively with routine observation or optical blur to change fixation. Toxin to the superior rectus has been utilised but carries the risk of inducing a ptosis. Surgical treatment of DVD can be carried out by • Inferior oblique anteriorisation—Changing the position of the IO also changes its action into an anti-elevator • Superior Rectus Recession—Moderate to large Sr recessions with or without a posterior fixation suture can be used. Care must be taken to avoid upper lid retraction and involvement of the SO fibres • Inferior rectus resection-uncommonly used. In assymetric DVD, operating on one eye is frequently associated with unmasking of the condition in the other so ideally both eyes need to be operated upon, even if the deviation has been noticed by the patient in just one.

References 1. Pfeiffer RL. Traumatic enophthalmos. Trans Am Ophthalmol Soc. 1943;41:293–306. 2. Smith B, Regan WF Jr. Blow-out fracture of the orbit; mechanism and correction of internal orbital fracture. Am J Ophthalmol. 1957;44(6):733–9.

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3. King EF, Samuel E. Fractures of the orbit. Trans Ophthalmol Soc U K. 1944;64:134–53. 4. Grob S. Orbital fracture repair. Semin Plast Surg. 2017;31(1):31–9. 5. Tang DT. Delayed immediate surgery for orbital floor fractures: less can be more. Can J Plast Surg. 2011;19(4):125–8. 6. Manley DR. Brownʼs syndrome. Curr Opin Ophthalmol. 2011;22(5):432–40. 7. Dawson E. Spontaneous resolution in patients with congenital Brown syndrome. J AAPOS. 2009;13(2):116–8. 8. Kekuunya R.  Duane retraction syndrome: causes, effects and management strategies. Clin Ophthalmol. 2017;11:1917–30. 9. Parsa CF, Grant E, Dillon WP, du Lac S, Hoyt WF. Absence of the abducens nerve in Duane syndrome verified by magnetic resonance imaging. Am J Ophthalmol. 1998;125(3):399–401. 10. Hatt S.  Interventions for dissociated vertical deviation. Cochrane Database Syst Rev. 2015;(11):CD010868.

Chapter 12

Surgical and Non-surgical Treatment of Strabismus

A variety of methods can be utilised to treat strabismus. The non surgical methods commonly used in the acute stage or when the deviation is variable include: • Occlusion using Blenderm, Bangerter graded occlusion foil, Occlusive contact lenses and intraocular lenses • Prismatic correction using Fresnel prisms, incorporated prisms in glasses etc. and • Orthoptic exercises. These have all been discussed in the previous chapters alongside the relevant conditions. Once the deviation has stabilised, more permanent treatment modalities may be considered. Although the etiology of strabismus is multifactorial, treatment is uniformly directed towards either weakening or strengthening the extraocular muscles. The former may be achieved using surgery or toxin and the latter by surgery or bupivacaine.

12.1  Botulinum Toxin for strabismus Botulinum toxin type A is a purified neurotoxin that acts by inhibiting the release of acetylcholine from presynaptic nerve terminals leading to temporary weakening of the muscle. It was first used for the treatment of strabismus in 1980 by Dr. Alan Scott in San Francisco, USA [1].

Electronic Supplementary Material The online version of this chapter (https://doi. org/10.1007/978-3-030-24846-8_12) contains supplementary material, which is available to authorized users. © Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8_12

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Fig. 12.1  Botulinum toxin being injected into the medial rectus in a child with infantile esotropia

In the treatment of strabismus, toxin can be used to weaken the LR, MR and IR. It can be used for the SR in rare cases but carries the risk of inducing ptosis. It is generally not useful for treating the obliques. Some indications for the use of toxin in strabismus include Diagnostic • To investigate the risk of postoperative diplopia • To demonstrate presence of binocularity Therapeutic • To preserve binocularity in acute onset strabismus • To treat consecutive or residual small angle strabismus • As substitute for those unfit or unwilling for surgery It can be used in children specifically for the treatment of acute onset esotropia and infantile esotropia [2, 3] (Fig. 12.1).

12.2  Method Botulinum toxin injection should be carried out under electromyographic control when injected into extraocular muscles. This optimises placement of the toxin and minimises side effects. The dose strength used depends on the muscles to be injected as well as the preparation of toxin used. The commonly used preparations in the U.K. include Botox, Xeomin and Dysport where 1 Unit of Botox/Xeomin is equal in potency to approximately 4 U of Dysport. The author’s preferred dosage patterns are as below:

12.2 Method

161

12.2.1  Dysport Vertical muscles, and for horizontal strabismus of less than 20 prism dioptres: • 5–10 U. Horizontal strabismus of 20 to 50 prism dioptres: • 10–20 U. • (max range = 4–50 U)

12.2.2  Botox/Xeomin Vertical muscles, and for horizontal strabismus of less than 20 prism dioptres: • 1.25–2.5 U. Horizontal strabismus of 20 to 50 prism dioptres: • 2.5–5.0 U. • (max range = 1–12.5 U) The toxin is injected using a needle electrode (37 mm × 27 G), which is connected to the EMG machine. Electrodes are placed on the patient’s forehead and the side of the eye to be injected and also connected. The requisite dose is drawn up in 0.1 mL, using a 1 mL tuberculin syringe ensuring the smallest possible volume is injected to minimise extravasation and unwanted deviations. The patient is asked to look away from the muscle to be injected and the needle placed so that the bevel faces the muscle. The needle is then inserted transconjunctivally 8–10  mm from limbus and pushed 5–6  mm posteriorly until it enters the anterior tendon. The patient is then asked to move the eye in the direction of the injected muscle and the needle is advanced to the loudest sound. This is achieved by advancing at 45° for the LR and 90° for the MR, following the orbital walls. The toxin is then injected, and the needle left for 15–30 s before withdrawal. The procedure above leads to temporary loss of action of the muscle injected, with the effect manifesting 48–72 h after the injection, peaking at 2 weeks and gradually wearing off within the next 3–4 months.

12.2.3  Complications Patients should be warned about the possibility of • Under or overcorrection of strabismus • Diplopia

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• Effect on surrounding muscles inducing a new vertical or horizontal deviation. Injecting the MR more commonly causes hypertropia and the LR more commonly hypotropia. This may be utilised for treatment planning, but the effects are variable and unpredictable. • Adies pupil • Retrobulbar haemorrhage (0.2%) • Vertical deviation or partial ptosis (25%, most commonly MR) • Perforation of globe (1:1000)

12.3  Bupivacaine in Strabismus Bupivacaine when injected into a muscle can lead to an initial weakening but long term strengthening effect. It can therefore be injected into extraocular muscles to attempt correction of the angle of deviation. Bupivacaine hydrochloride is a sodium channel blocker local anaesthetic that also displaces calcium from membrane binding sites and increases cytoplasmic Ca2+ level. This results in a particular myotoxicity that leaves the basal lamina, satellite cells, nerve fibers and vessels intact allowing regeneration of muscle fibers. These regenerated muscle fibres have greater contractile strength and intrinsic elastic stiffness, with consequent effects on eye alignment. Initially described by Alan Scott, a concentration of 0.75–3% was used in a volume of 2–3 mL. The Bupivacainne injection was supplemented with an injection of botulinum toxin to the antagonist muscle [4]. In the UK, bupivacaine hydrochloride injection containing 0.5 g/dL bupivacaine, in individual dose of 4.5–5 mL has been used as the enhanced concentrations are not available readily. The authors reported a mild improvement and a qualitative success rate of 37% [5].

12.4  Surgery for Strabismus Extraocular muscles have a complicated surgical anatomy that has been covered earlier. Any strabismus surgeon needs to be aware of the relationship between the muscles and fascia forming the pulley systems, effect of previous surgery as well as the surrounding structures such as lid retractors prior to carrying out any surgical procedure. Principles of surgery • • • •

To reduce the angle of deviation and improve the aesthetic appearance. Reduction or elimination of Diplopia Correction of associated anomalous head posture Widening the field of binocular single vision

12.4  Surgery for Strabismus

163

12.4.1  Incisions Utilised in Strabismus Surgery The EOMs can be accessed via different incisions. Limbal incision was popularised by Harms. It is created by a peritomy at the limbus and two radial relaxing incisions. It allows excellent visualization of the muscle undergoing the procedure and avoids excessive scarring and bleeding by avoiding surgery directly over the muscle tendon. Some common postoperative complications include discomfort, interpalpebral conjunctival redness, corneal dellen, and the possibility of a tenon’s capsule prolapse (Fig. 12.2). Swan’s incision is performed directly over the insertion of the muscle and has largely been abandoned apart from for the vertical recti. Fornix incision, described by Park, is placed in the superior or inferior fornix and allows access to the muscle by stretching the conjunctiva over it. Although initially challenging to learn, it avoids the risk of perilimbal scarring and dellen formation and carries the advantages of more rapid recovery and a small, nearly invisible scar in the fornix. This technique may be difficult to perform in children because of their prominent Tenon’s capsule, in cases with significant preexisting scarring, and in older patients with inelastic conjunctiva (Fig. 12.3). Minimally invasive strabismus surgery (MISS): Gobin developed a technique utilising two small incisions placed on either side of the recti to perform hang back recessions and this was further refined by Daniel Mojon to develop minimally invasive strabismus surgery (MISS). This method involves performing strabismus ­surgery through keyhole openings to decrease tissue trauma, minimize postoperative complications and patient discomfort, and improve surgical outcomes. MISS is more difficult to perform and needs the operating surgeon to use a microscope to perform the surgery. It is trickier in children with abundant Tenon’s tissue but can be carried out in adults with poor conjunctival elasticity.

Fig. 12.2 Diagram depicting the Harm’s limbal incision (red) and Swan’s incision (black)

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Fig. 12.3 Diagram depicting an inferior fornix incision (green) and paired minimally invasive surgery incisions (black)

12.5  Surgical Procedures Strabismus surgery is usually carried out under general anaesthesia but if the patient has medical constraints, it can be performed with a periocular block or under topical anaesthesia. The oculocardiac reflex is a significant deterrent to routine local anaesthesia surgery. Also, infiltration of local anaesthetic can distort the tissue planes making surgery more challenging.

12.5.1  Weakening Procedures Recession is the process of weakening the effect of a muscle by disinserting it and moving it away from the limbus, thus decreasing the arc of contact and the power of the muscle. The muscle is disinserted from its original attachment and placed posteriorly by a pre determined amount. It may be sutured directly to the sclera or anchored to the original insertion in a hang back fashion. Hang back recession has the advantage of a lower rate of scleral perforation as the suturing is carried out anteriorly with better access and visibility (Figs. 12.4 and 12.5). Adjustable sutures can be used to fine tune the results of the strabismus surgery when the patient has regained consciousness and the fusion mechanisms are active. The recessed (and sometimes the resected) muscles are placed on a hangback suture with an adjustable, securing knot as below. If the correction of the deviation is nonideal, the bow tie is undone and the muscle moved to try and achieve the desired correction. It thus serves as way to optimise surgical results avoiding further surgery.

12.5  Surgical Procedures

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a

b

Aterior segment of muscle resected

Fig. 12.4  a) Recession: The rectus muscle is secured by a suture and disinserted from its insertion. It can then be attached to the sclera through a fixed hang back anchored to its original insertion or secured on to the sclera, posterior to the insertion, resulting in weakening of its action. Resection: the muscle is secured on a suture at predetemined distance from the instertion, shortened and reinserted at the original insertion resulting in strengthening of its action

Myectomy is the process of disinserting a muscle that is allowed to retract into its capsule and not attached at a specific point on the sclera. It is only really routinely used for Inferior oblique weakening procedures. Rarely, a LR myectomy is performed in third nerve palsy where the muscle is attached to the periosteum.

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a

b

Fig. 12.5  Hangback recession on an adjustable slipknot

Myotomy is the weakening of a muscle by partial division of the muscle fibres or removing a portion of the tendon. It tends to have a non-predictable effect and is not commonly used.

12.5.2  Retroequatorial Myopexy (Faden’s Procedure) The muscle is fixed to the sclera posterior to the equator. As a result, the lever arm is shortened with consequent reduced force generation but only when the muscle is used. There is no effect in primary position but a reduction in movement in the direction of action of the muscle. This can be used very effectively in incomitant strabismus where there is a deviation in particular direction of gaze but none in primary gaze (Figs. 12.6 and 12.7). As an alternative a combined recession-resection or Scott’s Procedure can be carried out which offers the advantage of also being an adjustable procedure.

12.5  Surgical Procedures

a

167

b

A

B

c

A

B

C

B

Fig. 12.6 (a)The drawing shows the normal length of the moment arm when the eye is in the primary position (A-B) (b) A faden pinning the rectus muscle 12  mm posterior to the muscles insertion leaves the moment arm unchanged in the primary position (A-B) (c) When the eye rotates towards the fadened muscle, the moment arm is significantly shortened (C-B) leading to a reduced rotational force. (K.W.Wright, YNJ Strube.Color Atlas of Strabismus Surgery. Rights obtained)

12.5.3  Strengthening Procedures Resection is a strengthening procedure wherein the muscle is shortened and then reattached to the original insertion (Fig. 12.8). Plication or tucking achieves the same result as resection without the need to detach the muscle and thus preserves the blood supply. It consists of folding the muscle over and suturing it in place to shorten it. It also possesses the advantage of being potentially reversible by dividing the fixing sutures. However, some surgeons feel it is not quite as effective as resection and so surgical amounts may need to be increased. While performing a recession or resection, it is important to be aware of their secondary effects as they might have unintended consequences. After recession, the effect of a muscle is weakened in primary position but is even further weakened in the direction of action of the muscle. For example, following a right MR recession for esotropia, the deviation is corrected in primary position. However, when the person looks to the left, there is an enhanced weakening effect potentially leading to an exotropia in left gaze.

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Fig. 12.7  Scotts procedure: A combined recession-resection on the same muscle has the effect of a Faden’s procedure but can be adjusted postoperatively. (Strabismus-Burton Kushner-Rights obtained)

6mm res

6mm res

a

6mm res

b

3mm res

12.5  Surgical Procedures

169

SR

a

LR

b

SR

LR

IR

IR

SR

c

d

LR

SR

LR

IR

Fig. 12.8  Horizontal transposition of the vertical recti laterally (a) Whole muscle transposition (b) Hummelsheim operation where the lateral halves of the SR and IR are transposed laterally (c) Jensens Procedure, The LR, SR and IR are split longitudinally and apposed (d) Foster suture augmentation of a whole muscle transposition. Alec Ansons, Helen Davis, Diagnosis and Management of Ocular Motility Disorders, 4th Edition, Wiley Blackwell Rights obtained

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Similarly, after resection, the muscle behaves like a tight leash as it has been shortened. When the patient looks away from the muscle that a been operated there is a potential bridle action leading to an enhanced effect. For example, following a right LR resection for esotropia, the deviation is corrected in primary position. However, when the person looks to the left, there is an enhanced effect due to the pull of a tight LR, potentially leading to an exotropia in left gaze.

12.6  Calculating the Amount of Surgery to Perform There are many surgical tables available that try to estimate the amount of recession-­ resection to be carried out for a given deviation. A few principles are helpful to keep in mind while deciding on these values. • On average recession is more effective than resection. • Procedures on the MR are more effective than those on the LR. Surgery on the MR corrects between 3 and 4 PD/mm and LR 2–3 PD/mm. • When these are both carried out on the same eye, there is an additive effect of 25%. For example, carrying out a 5  mm MR recession and 7  mm LR resection as in the example below will give an approximate correction of 36.25  PD (5 × 3 = 15 + 7 × 2 = 14 + 25% of 29 = 7.25). Excessive amounts of surgery on any of the recti can lead to limitations of ocular rotation due to mechanical effects. Excessive recession can place the insertion of the muscle behind the equator resulting in a significant reduction in its action. Similarly, an over enthusiastic resection can convert the muscle to an inelastic tether. On average the amount of surgery on a MR should not exceed 7 mm and the LR 9 mm. Therefore, the maximum horizontal deviation.

12.7  Transposition There are occasions where a muscle has no power to carry out its designated action e.g. LR following a complete sixth nerve palsy. Resecting such a muscle is rarely useful as it has no action that can be strengthened. A neighbouring muscle can be recruited to assist in the action of the paralysed muscle. This can be done by either moving the whole muscle or part of the tendon. The latter emerged as an option in an effort to preserve the blood supply of the anterior segment. The extraocular muscles are supplied by the muscular branches of the ciliary artery that gets disrupted when the muscle is detached. Vessel sparing procedures or partial tendon transposition can help avoid anterior segment ischaemia by preserving the blood supply.

12.8  Yokoyama’s Procedure

171

Fig. 12.9  Assymetrical myopic fixus with marked left esotropia and hypotropia. Elevation and abduction are severely restricted on the left eye. Reproduced with permission from Alec Ansons, Helen Davis, Diagnosis and Management of Ocular Motility Disorders, 4th Edition, Wiley Blackwell

Some examples include • Full tendon • Lateral transposition of the SR and IR to the LR in sixth nerve palsy. • Lateral transposition of the SR the LR in sixth nerve palsy with an augmentation suture between the two muscles that potentiates the effect (Crouch’s procedure) • Partial tendon • Hummelscheim Procedure • Jensens Procedure (Fig. 12.9).

12.8  Yokoyama’s Procedure Heavy Eye syndrome or myopic fixus is a condition where there is progressive development of hypotropia and esotropia in a highly myopic eye (Fig. 12.10). It is thought that the large globe prolapses between the SR and the LR displacing them nasally and inferiorly respectively. The loop myopexy procedure was first described by Yokoyama for the treatment of this condition. The LR and SR muscle bellies are sutured together to reform the muscle cone without involving the sclera or splitting the muscles with good results (Fig. 12.11).

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a

b

Fig. 12.10  Plication of the LR and the SR to reform the muscle cone in the Yokoyama procedure. Strabismus-Burton Kushner-Rights obtained

Fig. 12.11  A 47 year old lady with left hypotropia, pseudoptosis and pseudoproptosis secondary to myopia. On a cover test in primary gaze with her myopic glasses on, she has a left small angle esotropia and left hyptropia. There is limitation of left elevation, most prominent in dextroelevation

12.9  Harada Ito Procedure The anterior 10% fibres of the SO tendon are responsible for carrying out its incylorotating function. In fourth nerve palsy where excyclorotation is the main finding, these fibres can be transposed inferiorly and laterally towards the LR to help augment incyclorotation.

12.11  Complications of Strabismus Surgery

173

Fig. 12.12 Anterior transposition of the IO. (Strabismus-Burton Kushner-Rights obtained)

12.10  Anterior Transposition of the Inferior Oblique The inferior oblique is an elevator of the eye. However, in the treatment of DVD and fourth nerve palsy, it can be converted into an anti-elevator by changing its course. The muscle is detached near its insertion and reattached just lateral to the IR at the same level as its tendon (Fig. 12.12). A recognized risk of anteriorization of the inferior oblique muscle is the potential for postoperative limitation of elevation ­during abduction, resulting in an apparent inferior oblique overaction in the contralateral eye, often accompanied with Y-pattern exodeviation, or AES [6].

12.11  Complications of Strabismus Surgery These are uncommon but may be serious when they do occur. Globe perforation is the commonest severe complication of strabismus surgery, reported in 0.13–1% of cases. In the BOSU study, the incidence was 1:1000 and was more common in children and myopes. Even if perforation occurs, sight threatening complications like endophthalmitis and retinal detachment are relatively uncommon if treatment is instituted promptly.

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Lost muscle is significant reduction or absence of action of a muscle immediately postoperatively, which is usually due to the sutures giving way. It requires immediate exploration and reattachment of the muscle. In contrast, a slipped muscle is seen weeks or even months following the surgery when a stretched scar or pseudotendon leads to a persistent weakness of the muscle. The scar or pseudotendon needs to be excised and the muscle reattached. Other complications include orbital infection, endophthalmitis and surgically induced necrotising scleritis.

References 1. Scott AB. Botulinum toxin injection of eye muscles to correct strabismus. Trans Am Ophthalmol Soc. 1981;79:734–70. 2. Rowe FJ, Noonan CP.  Botulinum toxin for the treatment of strabismus. Cochrane Database Syst Rev. 2017;3(3):CD006499. Published 2017 Mar 2. 3. Solebo AL, Austin AM, Theodorou M, Timms C, Hancox J, Adams GGW. Botulinum toxin chemodenervation for childhood strabismus in England: National and local patterns of practice. PLoS One. 2018;13(6):e0199074. Published 2018 Jun 14). 4. Scott AB, Miller JM, Shieh KR. Treating strabismus by injecting the agonist muscle with bupivacaine and the antagonist with botulinum toxin. Trans Am Ophthalmol Soc. 2009;107:104–9. 5. Ziahosseini K, Marsh IB. Single injection of bupivacaine for correction of strabismus. Med Hypothesis Discov Innov Ophthalmol. 2015;4(4):157–61. 6. Stager D.  Uses of the inferior oblique muscle in strabismus surgery. Middle East Afr J Ophthalmol. 2015;22(3):292–7.

Index

A Abduction, 153 Aberrant regeneration, 95 Abnormal retinal correspondence (ARC), 47 AC/A ratio, 79 Accommodative esotropia, 81–82 Acquired brown syndrome, 149, 152 Acute acquired comitant esotropia (AACE), 77, 78 Acute non accommodative esotropia (ANAET), 77–78 Alphabet patterns aetiology, 125–127 arrow pattern, 125 diamond pattern, 125 lambda pattern, 125 presentation, 128 treatment of, 128–129 X pattern, 125 Y pattern, 125 Alternate cover test, 34–36 Amblyopia, 1 Amblyoscope, 50 Anisomyopia, 66 Anisostigmatism, 66 Antiacetylcholine esterase inhibitors (AchE), 135 Antiacetylcholine receptor antibodies (AChR-Abs), 131 Azathioprine (AZA), 135, 141 B Bagolini’s glasses, 61 Bielchowsky’s Head Tilt test, 38 Bifocals, 82 Botulinum toxin, 7, 108

Botulinum toxin type A, 69 Brown’s syndrome acquired and congenital, 149 investigation, 151 management, 151 presentation, 150 Bruckner’s test, 41 Bupivacaine hydrochloride, 162 C Cavernous sinus syndrome, 91–92 Chavasse’s theory, 2 Childhood esotropias, 71 Chronic progressive external ophthalmoplegia (CPEO), 142, 143 Ciancia syndrome, 75 Claude Worth’s theory, 2 Cogan’s ocular motor apraxia, 111 Combined immunosuppression & radiotherapy in thyroid eye disease (CIRTED), 141 Comitant exotropia, 3 Concomitant strabismus classification, 63 esotropias AACE/ANAET, 77, 78 AC/A ratio, 79–81 accommodation, role of, 79 accommodative esotropia, 81–82 bimedial recession, 82, 83 cyclical esotropia, 78, 79 delayed surgery, 76 non accommodative late onset esotropia, 77 non-accommodative esotropias, 73–76 exotropia

© Springer Nature Switzerland AG 2019 S. Jain, Simplifying Strabismus, https://doi.org/10.1007/978-3-030-24846-8

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176 Concomitant strabismus (cont.) botulinum toxin type A, 69 classification of, 64 consecutive exotropia, 70, 72 conservative, 68 convergence exercises, 68 intermittent exotropia, 65–66 Newcastle Control Score, 67 orthoptic testing, 66, 67 overminus lens therapy, 68 part time occlusion, 68 primary constant exotropia, 70 prisms, 69 sensory exotropia, 70–71 surgery, 69, 70 surgical intervention, 69 Congenital brown syndrome, 149 Conjugate movements, 21 Convergence excess esotropia, 82 Convergence insufficiency exotropia, 64 Convergence spasm, 116–118 Cover-uncover test, 31–34 Craniosynsotosis syndromes, 3 Cyclical esotropia, 78, 79 D Diplopia, 1 Divergence excess exotropia, 64 Double elevator palsy, 114–117 Duane retraction syndrome, 152 E Early versus late infant strabismus surgery (ELISS), 76 Edrophonium (Tensilon) test, 133 European Group of Graves' Orbitopathy (EUGOGO), 140 Extraocular muscles anatomy of action and innervation of, 10 blood supply, 12, 13 bony trochlea, 9 levator palpebrae superioris, 9 pulley systems, 12 recti muscles, 9 ring of Zinn, 9 Spiral of Tillaux, 9 surgery, 7 Eye movements actions of EOMs, 17, 18 antagonist, 15

Index conjugate movements, 15 disjugate movements, 15 ductions, 16 herrings law, 18 optokinetic movements, 20 saccades, 19 sherringtons law, 19 smooth pursuit movements, 19 synergist, 15 vergence movements, 21 versions, 16 vestibulo ocular, 21 F Fornix incision, 163 Foville’s syndrome, 106 Frisby stereotest, 55–56 Frontal eye field (FEF), 19 Fully accommodative esotropia, 81 Fundus photographs, 61 G Globe-to-wall theory, 145 Goldenhar syndrome, 153 Gradinego’s syndrome, 106 Graves' disease, 137 Grove sign, 138 H Heredity, 3 Herring’s law, 44, 53, 86, 87 Herrings and Sherrington’s law, 56 Hess charts, 56, 58 Hess/Lees screen, 61 Holt-Oram syndrome, 153 Horner’s syndrome, 106 Huber’s classification, 154 Hydraulic mechanism, 146 Hypermetropia, 3, 66 Hyperthyroidism, 138 I Ice test, 133–134 Incomitant strabismus blow out fracture aetiology, 145–146 management, 148, 149 presentation, 146–148 brown’s syndrome

Index acquired and congenital, 149 investigation, 151 management, 151 presentation, 150 dissociated vertical deviation, 156, 157 Duane retraction syndrome etiology, 152 genetics, 152, 153 investigation, 155 presentation, 153, 154 treatment, 156 Intermuscular septum, 9 Internuclear ophthalmoplegia (INO), 111–114 J Jampolsky’s scoring system, 67 L Lambert eaton syndrome, 135 Lang test, 56 Lang two pencil test, 54 Limbal incision, 163 LogMAR, 29 M Maddox rods, 59 Marlowe’s test, 66 May Scale, 67 Milliard-Gubler syndrome, 106 Minimally invasive strabismus surgery (MISS, 163 Mobius sign, 138 Monocular elevation deficit syndrome (MEDS), 114 Myasthenia gravis clinical presentation, 132–133 diagnosing edrophonium (Tensilon) test, 133 ice test, 133–134 immunological testing, 133 single-fiber electromyography, 134, 135 management of, 135 pathophysiology, 131 TED etiology, 136, 137 imaging, 139 immunosupression, 140–141 lid signs, 138 lid surgery, 142

177 natural history, 137 non surgical management, 140 ocular motility, 138–139 orbital decompression, 141–142 proptosis, 138 risk factors, 137 selenium, 140 strabismus surgery, 141 symptoms of, 137 Mycophenolate mofetil, 135 N Non-specific or basic exotropia, 64 Normal retinal correspondence (NRC), 47 Nystagmus blockage syndrome, 75 O Oculomotor synkinesis, 95 Okihiro's syndrome, 153 Optokinetic movements, 20 Orbital apex syndrome, 107 Orbital radiotherapy (RT), 141 Orthoptic assessment ARC and NRC, 47, 49, 50 binocular vision, 46 binocular vision testing macular perception, 51 motor fusion, 52–54 qualitative test, 54 quantitative tests, 55, 56, 58, 59, 61 sensory fusion, 51–52 stereopsis, 54 Bruckner’s test, 41 diplopia charting, 44 field of BSV, 45 prism cover test, 41–43 prism reflex test, 44 Overminus lens therapy, 68 P Paralytic strabismus anatomy, 85 clinical presentation, 86, 87 fourth nerve palsy acquired fourth nerve palsy, 98, 99 aetiology, 98 anatomy, 97 bilateral fourth nerve palsy, 100–101 clinical assessment, 99, 100 congenital palsies, 98

178 Paralytic strabismus (cont.) Harada Ito procedure, 103 investigation, 99 management, 101, 102 site of trauma, 99 sixth nerve palsy adult acquired sixth nerve palsy, 105 anatomy, 103, 104 cavernous sinus, 106 course of, 104 management, 107 nucleus and fasciculus, 106 orbital apex syndrome, 107 petrous apex, 106 subarachnoid space, 106 treatment, 107, 108 third nerve palsy anatomy, 87, 89 cavernous sinus syndrome, 91–92 in children, 94 complete and partial, 93, 94 in 18-50 year olds, 94 fascicular portion, 90 investigation and management, 93 microvascular palsies, 96 nuclear portion, 89–90 orbital portion, 92–93 in over 50-year olds, 95–96 presentation, 89 pupil sparing isolated IIIrd cranial nerve palsy, 95–96 subarachnoid space, 90 surgical options, 96 Paramedian pontine reticular formation (PPRF), 110, 113 Parapontine reticular formation (PPRF), 21 Parinaud’s syndrome, 118–120 Partially accommodative esotropia, 81 Patch test, 66 Primary esotropias, 71 Prism cover test, 41–43 Prism reflex test, 44 Prisms, 69 Pseudo Gradinego’s syndrome, 106 Pulley systems, 12 Q Quantitative tests cyclotropia measurement, 59 Frisby stereotest, 55–56 fundus photographs, 61 hess charts, 56, 58

Index hess/lees screen, 61 Lang test, 56 Maddox rods, 59 postoperative diplopia test, 58 prism adaptation, 58–59 synoptophore, 59 TNO test, 55 Wirt’s fly test, 55 R Raymonds syndrome, 106 Refractive errors, 3, 66 Retroequatorial myopexy, 166 Rituximab, 135 Rundle’s curve, 137 S Scotts procedure, 168 Secondary esotropias, 71 Sherringtons law, 19 Simulated divergence excess, 64 Single-fiber electromyography, 134, 135 Smooth pursuit movements, 19 Snellen Conversion, 29 Stellwag sign, 138 Stilling-Turk-Duane syndrome, 152 Strabismus aetiology of, 2–4 amblyopia, 1 botulinum toxin, 7 classification of, 4–6 correcting refractive error, 6 diplopia, 1 extraocular muscle surgery, 7 loss of binocular vision, 1 occlusion and prismatic correction, 6 occlusion therapy, 6 orthoptic assessment (see Orthoptic assessment) patient examination alternate cover test, 34–36 complaints, 23–25 cover-uncover test, 31–34 ductions, 36, 37 Hirschberg’s test, 30 medical history, 25 ocular deviation assessment, 28, 29 ocular motility testing, 35, 36 ophthalmic examination, 26 Park’s three step test, 38, 40 patient history, 23

Index saccades and pursuit, 40 versions, 36, 37 visual acuity assessment, 26–31 predisposing features, 1, 2 surgical and non-surgical treatment (see Strabismus, surgical and non-­surgical treatment) treatment of, 5 Strabismus, surgical and non-surgical treatment botulinum toxin acute onset esotropia, 160 Botox/ Xeomin, 161 complications, 161–162 Dysport, 161 electrodes, 161 infantile esotropia, 160 bupivacaine Fornix incision, 163 Limbal incision, 163 myotoxixcity, 162 surgery for, 162 surgical procedures, 164–165 Swan’s incision, 163 transposition, 171 weakening procedures, 164–168 complications of, 173 excessive recession, 169, 170 Harada Ito procedure, 172 inferior oblique, 172 occlusion, 159 orthoptic exercises, 159 prismatic correction, 159 strengthening procedure, 166, 167 transposition, 170 Yokoyama’s procedure, 170–172 Strabismus,patient examination, Hirschberg’s test, 30 Supranuclear disorders cogan’s ocular motor apraxia, 111 conjugate gaze deviation, 110 convergence spasm, 109, 116–118 dorsal midbrain syndrome, 118–120 double elevator palsy, 109, 114–117 horizontal gaze, 109 INO, 111–114

179 one and half syndrome, 114 parinaud’s syndrome, 118–120 skew deviation, 109, 120–122 superior oblique myokimia, 122–123 vertical gaze, 109 Swan’s incision, 163 Synoptophore, 50, 54, 59 T Tenon’s capsule, 12 Thyroid eye disease (TED), 136 etiology, 136, 137 imaging, 139 immunosupression, 140–141 lid signs, 138 lid surgery, 142 natural history, 137 non surgical management, 140 ocular motility, 138–139 orbital decompression, 141–142 proptosis, 138 risk factors, 137 selenium, 140 strabismus surgery, 141 TNO test, 55 Tolosa-Hunt syndrome, 92, 93, 107 20 PD base out test, 53 V Vergence movements, 21 Vestibulo ocular, 21 Vigouroux sign, 138 Von Grafe’s sign, 138 V-pattern strabismus, 3 W Wildervanck syndrome, 153 Wirt’s fly test, 55 Y Yoke muscle pair, 15