binocular vision and ocular motility - semantic scholar€¦ · binocular vision and ocular...

BinocularVisionand OcularMotility

SIXTHEDITION

BinocularVisionand OcularMotilityTHEORY AND MANAGEMENTOF STRABISMUS

Gunter K. von Noorden, MDEmeritus Professor of OphthalmologyCullen Eye InstituteBaylor College of MedicineHouston, Texas

Clinical Professor of OphthalmologyUniversity of South Florida College of MedicineTampa, Florida

Emilio C. Campos, MDProfessor of OphthalmologyUniversity of BolognaChief of OphthalmologyS. Orsola-Malpighi Teaching HospitalBologna, Italy

MosbyA Harcourt Health Sciences CompanySt. Louis London Philadelphia Sydney Toronto

MosbyA Harcourt Health Sciences Company

Editor-in-Chief: Richard Lampert

Acquisitions Editor: Kimberley Cox

Developmental Editor: Danielle Burke

Project Manager: Agnes Byrne

Production Manager: Peter Faber

Illustration Specialist: Lisa Lambert

Book Designer: Ellen Zanolle

Copyright � 2002, 1996, 1990, 1985, 1980, 1974 by Mosby, Inc.

All rights reserved. No part of this publication may be reproduced or transmit-ted in any form or by any means, electronic or mechanical, including photo-copy, recording, or any information storage and retrieval system, without per-mission in writing from the publisher.

NOTICE

Ophthalmology is an ever-changing field. Standard safety precautions must befollowed, but as new research and clinical experience broaden our knowledge,changes in treatment and drug therapy may become necessary or appropriate.Readers are advised to check the most current product information provided bythe manufacturer of each drug to be administered to verify the recommendeddose, the method and duration of administration, and contraindications. It is theresponsibility of the treating physician, relying on experience and knowledge ofthe patient, to determine dosages and the best treatment for each individual pa-tient. Neither the publisher nor the authors assume any liability for any injuryand/or damage to persons or property arising from this publication.

Permission to photocopy or reproduce solely for internal or personal use is per-mitted for libraries or other users registered with the Copyright Clearance Cen-ter, provided that the base fee of $4.00 per chapter plus $.10 per page is paid di-rectly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers,Massachusetts 01923. This consent does not extend to other kinds of copying,such as copying for general distribution, for advertising or promotional pur-poses, for creating new collected works, or for resale.

Mosby, Inc.A Harcourt Health Sciences Company11830 Westline Industrial DriveSt. Louis, Missouri 63146

Printed in the United States of America.

Library of Congress Cataloging-in-Publication Data

Von Noorden, Gunter K., 1928–Binocular vision and ocular motility : theory and management of strabismus / Gun-ter K. von Noorden, Emilio C. Campos.—6th ed.

p. cm.

Includes bibliographical references and index.

ISBN 0–323–01129–2

1. Strabismus. 2. Binocular vision. 3. Eye—Movements. I. Title.

RE771.V62 2001 616.7�62—dc21 2001042586

01 02 03 04 05 / 9 8 7 6 5 4 3 2 1

HERMANN MARTIN BURIAN

1906-1974

Preface to the Sixth Edition

Amajor change with this edition is the additionof co-author Dr. Emilio Campos, who is oneof the leaders of European strabismology andwidely respected for his scientific contributions.Dr. Campos has written a new chapter on Chemo-denervation and assisted me with the review andrevision of this sixth edition. I selected Dr.Campos as a co-author because his scientific back-ground is similar to mine. His mentor Bruno Bag-olini was trained, as I was, by the late HermannBurian, with whom I co-authored the first edition.Because of this common heritage we agree on allmajor issues discussed in this text. Whenever anoccasional difference in opinions existed on minorsubject matters both of our views were stated.

As in previous editions, new material was addedand older text that had lost its relevance wasdeleted, except when it was of historical interest.Binocular Vision and Ocular Motility has becomea major source of references to the older strabis-mus literature that is not retrievable through elec-tronic search techniques. With this in mind, wehave used a conservative approach in deletingolder references so that they would remain avail-able to the researcher and interested clinician.

We have endeavored to improve clarity in thetext and tables, replaced several old figures withbetter examples, and added illustration of surgicaltechniques not covered in previous editions.

Ifeel deeply honored for having been asked byDr. Gunter von Noorden to collaborate withhim on the sixth edition of Binocular Vision andOcular Motility, and I consider this recognition asone of the highlights of my career.

I hope that my input to this edition has notinterfered with the homogeneity of this book andits original message.

Both Dr. von Noorden and I would appreciateany input from our readers that may help us tomake future editions even more useful.

I would like to express my gratitude to mycollaborators Drs. Costantino Schiavi and Costan-

The formerly voluminous chapter on sensoryadaptation and stereopsis has been divided intothree smaller chapters for easier access. Becausesensorial anomalies in strabismus are only brieflydealt with in current texts, or receive at best spuri-ous coverage in most teaching curricula for resi-dents, the comprehensive discussion of this sub-ject in this book appears to be fully justified.

The contributions and teaching of Hermann Bu-rian remain apparent throughout this text but espe-cially in Part One. We submit this volume notonly as his legacy but also that of his teacher,Alfred Bielschowsky, who has influenced strabis-mology during the first half of the 20th centurylike no one else.

My thanks are due to Mrs. Louise Thomas, myfaithful former secretary, for obtaining copies ofarticles from the local medical libraries and illus-trations through the Baylor Department of MedicalIllustrations, and to Mr. Mike Piorunski, librarianof the Friedenwald Library of the Wilmer Institute,for locating and verifying older references. Last,but not least, I thank my dear wife for her contin-ued support and patience during the work on thisedition.

The authors have no proprietary interest in anyof the commercial products, drugs, or instrumentsmentioned in this book.

Gunter K. von Noorden

tino Bellusci, who have helped me in the prepara-tion of clinical illustrations and surgical drawings.Many thanks also to Stefania Piaggi, C.O., forhaving located obscure references and for her helpwith the computer search of the literature.

I am grateful to all my collaborators and tothose close to me for their patience during thepreparation of the manuscript and ask their for-giveness for any lack of attention during this moststimulating but time-consuming venture.

Emilio C. Campos

Preface to the First Edition

He who is theoretic as well as practical istherefore doubly armed: able not only to provethe propriety of his design but equally so tocarry it into execution.

VITRUVIUS

This volume is the product of the cooperativeefforts of the two authors. Parts I and II werewritten by Burian, and Parts III and IV by vonNoorden; however, both authors take full responsi-bility for the complete text.

In this work, our aim is to provide the practic-ing ophthalmologist as well as the budding onewith the theoretic knowledge and practical know-how that will enable him to pursue the field ofneuromuscular anomalies of the eyes in the man-ner set forth in the precept of Vitruvius.

The sound physiologic tradition of Hering,Helmholtz, Donders, Tschermak, Hofmann, andtheir schools forms the solid ground upon whichwas built the clinical work of Javal, Worth,Bielschowsky, Duane, Lancaster, and, more re-cently, Harms, Cüppers, Lyle, Bagolini, ourselves,and many others. Our purpose has been to conveythis physiologic basis as concisely and simply as

possible, always with the practicing ophthalmolo-gist in mind and wherever possible emphasizingits immediate clinical application. But much hashappened in our field since the days of the oldmasters, and due consideration is given to theexciting and significant modern studies in the psy-chophysical and neurophysiologic areas as well asin the field of clinical management of strabismus.This volume is not a handbook or a system, how-ever, and is not intended to be systematically orhistorically complete. We, therefore, have omittedmany points that are to be found in referenceworks. Neither does this book supplant the Atlasof Strabismus by von Noorden and Maumenee,which continues to be a useful guide to the diag-nostic aspects of strabismus.

The theoretic foundation has served us as ameans to make the strictly clinical chapters both‘‘theoretic and practical,’’ telling the ophthalmolo-gist not only the ‘‘what and how’’ but also the‘‘why.’’ We hope that the long hours of laborexpended on this volume may be of real use-fulness in the study of strabismus, particularly tothe younger generation of ophthalmologists.

Hermann M. BurianGunter K. von Noorden

Contents

PA R T O N E

Physiology of the SensorimotorCooperation of the Eyes

1 General Introduction . . . . . . . . . . . . . . . . . . 3The Eyes as a Sensorimotor Unit 3

The Tasks of the Motor System 3

Nature and Control of Ocular Movements 3Voluntary and Involuntary Eye Movements 3Cybernetic Control of the Eye Movements 4Apparent Movement of the Environment 5

Empiricism and Nativism 5

2 Binocular Vision and SpacePerception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Fusion, Diplopia, and the Law of Sensory

Correspondence 7Relative Subjective Visual Directions 7Retinomotor Values 8Common Relative Subjective Visual Directions 9Retinal Correspondence 10Sensory Fusion 10Motor Fusion 11

Retinal Rivalry 11

Objective (Physical) and Subjective (Visual)Space 12Discrepancies of Objective and Subjective

Metrics 14

Distribution of Corresponding Retinal Elements 15The Foveae as Corresponding Elements 15The Horopter 16

Physiologic Diplopia 18Clinical Significance 18Suppression 19

Panum’s Area of Single Binocular Vision 20

Fixation Disparity 21

Stereopsis 21Physiologic Basis of Stereopsis 22Local vs. Global Stereopsis 23Stereopsis and Fusion 24Stereoscopic Acuity 25

xi

Monocular (Nonstereoscopic) Clues to SpatialOrientation 25Interaction of Stereoscopic and Monocular Clues 27Clinical Significance of Monocular Clues 27

Experimental Determination of the LongitudinalHoropter and the Criteria of RetinalCorrespondence 28Criterion of Single Vision 28Apparent Frontal Plane Criterion 28Criterion of Common Visual Directions 29Criterion of Highest Stereoscopic Sensitivity 29

Egocentric (Absolute) Localization 29Egocentric Localization and Convergence 29Egocentric Localization and Proprioception 30Clinical Significance of Relative and Egocentric

Localization 31

Theories of Binocular Vision 31Correspondence and Disparity 31Neurophysiologic Theory of Binocular Vision and

Stereopsis 31Older Theories of Binocular Vision 33

Advantages of Binocular Vision 35

3 Summary of the Gross Anatomyof the Extraocular Muscles . . . . . . . . 38Rectus Muscles 39

Muscle Pulleys 41

Oblique Muscles 42

Fascial System 44Tenon’s Capsule 44Muscle Sheaths and Their Extensions 45Ligament of Lockwood 47Check Ligaments 47Intracapsular Portion of the Muscle 47Functional Role of the Fascial System 48

Developmental Anomalies of Extraocular Musclesand the Fascial System 48

Innervation of Extraocular Muscles 49

Blood Supply of Extraocular Muscles 49

4 Physiology of the OcularMovements . . . . . . . . . . . . . . . . . . . . . . . . . . 52Basic Kinematics 52

Translatory and Rotary Movements 52Center of Rotation 52

xii Contents

Definitions of Terms and Action of IndividualMuscles 52

Further Considerations of Mechanics of ExtraocularMuscles 56

The Fundamental Laws of Ocular Motility 59Donders’ and Listing’s Laws 59Sherrington’s Law of Reciprocal Innervation 63Hering’s Law of Equal Innervation 64Experimental Studies of Integration of Ocular

Movements by Muscle Transposition 67

Survey of Ocular Movements and TheirCharacteristics 67Terminology of Ocular Movements 67Versions 68Vergences 71Characteristics of Version and Vergence

Movements 76

Fixation and the Field of Fixation 79Fixation 79Field of Fixation 79

5 The Near Vision Complex . . . . . . . . . . 85Accommodation 85

Mechanism of Accommodation 85Units of Measurement of Accommodation and

Definition of the Prism Diopter 86Sympathetic Innervation 86

Convergence 86Units of Measurement of Convergence 87Components of Convergence 88

Pupillary Constriction 99

6 Histology and Physiology ofthe Extraocular Muscles . . . . . . . . . . . 101Structure and Function of the Extraocular

Muscles 101General Histologic Characteristics 101Nerve Supply 102Physiologic and Pharmacologic Properties 102Slow and Fast Twitch Fibers 103

Structural and Functional Correlations 107

Muscle Spindles and Palisade Endings in theExtraocular Muscles 109

Electromyography 109

Sources of Tonus of the Extraocular Muscles 111

7 Visual Acuity, Geometric OpticalEffects of Spectacles, andAniseikonia . . . . . . . . . . . . . . . . . . . . . . . . . . 114Visual Acuity 114

Basic Physiologic Concepts 114Variables Affecting Visual Acuity 115

Geometric Optical Effects of Spectacles 118

Aniseikonia 119

PA R T T W O

Introduction to NeuromuscularAnomalies of the Eyes

8 Classification of NeuromuscularAnomalies of the Eyes . . . . . . . . . . . . . 127Heterophoria and Heterotropia 127

Relative and Absolute Position of Rest 128

Ocular Alignment 129

Direction of Deviation 129

Comitance and Incomitance 131

Constancy of Deviation 131

State of Vergence Systems 132

Type of Fixation 132

Time of Onset of Deviation 132

Paralytic Strabismus 132Paralysis and Paresis 132Muscles Affected 133Duration and Cause 133Seat of Lesion 133

Mechanical-Restrictive Strabismus 133

Orbital Strabismus 133

9 Etiology of Heterophoria andHeterotropia . . . . . . . . . . . . . . . . . . . . . . . . 134Factors Responsible for the Manifestation of a

Deviation 134Abnormalities of Fusion Mechanism 134Reflexologic Theories 137

Factors Causing the Underlying Deviation 138Mechanical (Muscular) Theories 138Structural Anomalies of Extraocular Muscles 139Role of Accommodation and Refraction in Comitant

Strabismus 139Fixation Disparity 140Other Innervational (Neurologic) Factors in Comitant

Strabismus 141Brain Damage 143Embryopathy 145Facial and Orbital Deformities 145

Genetics of Comitant Strabismus 145Summary 148

Concluding Remarks 148

10 Symptoms in Heterophoriaand Heterotropia and thePsychological Effectsof Strabismus . . . . . . . . . . . . . . . . . . . . . . . 153Asthenopia and Diplopia 153

Psychological Effects of Strabismus 156

11 Examination of the Patient—IPreliminaries . . . . . . . . . . . . . . . . . . . . . . . . 158History 158

Assessment of Visual Acuity in Children 159

Contents xiii

Estimation of Visual Acuity in Infants 159Measurement of Visual Acuity in Preschool-Age

Children 162Measurement of Visual Acuity in School-Age

Children and Adults 163

Refraction 163Changes of Refraction with Age 165

12 Examination of the Patient—IIMotor Signs in Heterophoria andHeterotropia . . . . . . . . . . . . . . . . . . . . . . . . . 168Inspection of the Eyes and Head Position 168

Inspection of the Lids and Lid Fissures 168Position of the Globes—Angle Kappa 169

Measurement of Angle Kappa 171Size of Angle Kappa 172Clinical Significance of Angle Kappa 172

Observation of Head Position 173

Determination of Presence of a Deviation—Coverand Cover-Uncover Tests 174

Measurement of Deviation 176Prism and Cover Test 177

Physiologic Basis 177Performance 178Limitations 181Prism and Cover Test in Diagnostic Positions of

Gaze 182Measurement with the Major Amblyoscope 183Corneal Reflection Tests 185Photographic Methods 186Brückner Test 187Subjective Tests 187

Diplopia Tests (Red-Glass Test and Others) 187Haploscopic Tests 190

Measurement of Cyclodeviations 194Qualitative Diagnosis Based on Position of Double

Images 194Maddox Double Rod Test 194Bagolini Striated Glasses 195Major Amblyoscope 196Ophthalmoscopy and Fundus Photography 196The New Cyclo Test 198Scotometry 198Determination of the Subjective Horizontal or

Vertical 198Measurement of Dissociated Vertical Deviations 198The Head Tilt Test 198

Examination of the Motor Cooperation of theEyes 199Ductions and Versions 199

Elevation or Depression of the Adducted Eye(Upshoot or Downshoot in Adduction) 201

Measurement of Vergences 202Measurement With Prisms 202Measurement With a Major Amblyoscope 206Fusional Movements Elicited by Peripheral Retinal

Stimuli in Strabismus 206Near Point of Convergence 206

Maintenance of Convergence 207

13 Examination of the Patient—IIISensory Signs, Symptoms,and Binocular Adaptationsin Strabismus . . . . . . . . . . . . . . . . . . . . . . . 211Confusion and Diplopia 212

Monocular Diplopia 213Binocular Diplopia 214

Suppression 215Mechanism and Seat 215Clinical Features 216Tests for Suppression 217

Binocular Perimetry and Haploscopy 217Prisms 218The Four-Prism Diopter Base-Out Prism Test 218Monocular Visual Acuity Measured Under

Binocular Conditions 219The Worth Four-Dot Test 219

Suppressing Versus Ignoring a Double Image 220Measurement of Depth of Suppression 221

Blind Spot Mechanism 221

Anomalous Correspondence 222Basic Phenomenon and Mechanism 222Tests 225

Afterimage Test 225Striated Glasses Test of Bagolini 227Testing With the Major Amblyoscope 228Diplopia Test 230Testing With Projection Devices 230Foveo-Foveal Test of Cüppers 230

Evaluation of Tests 231Neurophysiologic Basis 233Suppression and Anomalous Correspondence 233Development and Clinical Picture 234

Development 234Clinical Picture 235

Quality of Binocular Vision in AnomalousCorrespondence 239

Prevalence 239Theories 240Review and Summary 241

14 Examination of the Patient—IVAmblyopia . . . . . . . . . . . . . . . . . . . . . . . . . . . 246Prevalence, Social and Psychosocial Factors 246

Classification and Terminology 248Strabismic Amblyopia 249Anisometropic Amblyopia 250Visual Deprivation Amblyopia (Amblyopia Ex

Anopsia) 252Idiopathic Amblyopia 253Organic Amblyopia 253Amblyopia Secondary to Nystagmus 254

Clinical Features of Strabismic Amblyopia 254Fixation Preference 254Visual Acuity 255Fixation Pattern of the Amblyopic Eye 260The Sensitive Period 268

Pathogenesis and Pathophysiology ofAmblyopia 269Psychophysical Studies 269Higher Nervous Center Activities 277

xiv Contents

Eye Movements in Amblyopia 279Electrophysiologic Studies 279

Amblyopia vs. Suppression 282

Experimental Amblyopia in Animal Modelsand Histologic Abnormalities in Brainsof Human Amblyopes 282

The Essence of Amblyopia 286

15 Examination of the Patient—VDepth Perception . . . . . . . . . . . . . . . . . . . 298Development of Stereopsis 298

Stereopsis and Strabismus 298

Testing for Stereopsis 299Major Amblyoscope or Stereoscope 299Stereogram 299Titmus Stereo Test 299Random-Dot Stereograms 301TNO Test 302Lang Test 303Two-Pencil Test 304

PA R T T H R E E

Clinical Characteristics ofNeuromuscular Anomalies ofthe Eye

16 Esodeviations . . . . . . . . . . . . . . . . . . . . . . . 311Esophoria and Intermittent Esotropia 311

Etiology 311Clinical Signs 311Symptoms 312Sensorial Adaptation 312Diagnosis 312Therapy 313

Accommodative Esotropia 314Refractive Accommodative Esotropia (Normal AC/A

Ratio) 314Definition 314Etiology 314Clinical Characteristics 316Therapy 316

Nonrefractive Accommodative Esotropia (High AC/ARatio) 318

Definition 318Clinical Characteristics 318Therapy 318

Hypoaccommodative Esotropia 319Definition 319Clinical Characteristics 319

Partially Accommodative Esotropia 319Definition 319Clinical Characteristics 320Therapy 320

Nonaccommodative Esotropia 320Essential Infantile Esotropia 320

Definition 320Terminology, Prevalence, Etiology 320

Differential Diagnosis 321Clinical Characteristics 321Therapy 329

Nonaccommodative Convergence Excess Esotropia(Normal AC/A Ratio) 336

Definition 336Clinical Characteristics 336Treatment 336

Acquired or Basic Esotropia 336Definition 336Clinical Characteristics 337Therapy 337

Esotropia in Myopia 338Acute Acquired Comitant Esotropia 338

Acute Strabismus After Artificial Interruption ofFusion 338

Acute Esotropia Without Preceding Disruption ofFusion (Burian-Franceschetti Type) 339

Acute Esotropia of Neurologic Origin 339

Microtropia 340Historical Review 340Current Concepts and Clinical Significance 342Diagnosis 343Therapy 344

Recurrent Esotropia 345

Secondary Esotropia 345Sensory Esotropia 345

Etiology and Clinical Characteristics 345Therapy 346

Consecutive Esotropia 347

Management of Surgical Overcorrections 347

Esotropia Associated with Vertical Deviations 348Clinical Characteristics and Diagnosis 348Therapy 349

17 Exodeviations . . . . . . . . . . . . . . . . . . . . . . . 356Classification and Etiology 356

Primary Exodeviations 358Clinical Characteristics 358Therapy 365Surgical Treatment 367

Dissociated Exodeviations 372

Secondary Exodeviations 372Sensory Exotropia 372Consecutive Exotropia 372

18 Cyclovertical Deviations . . . . . . . . . . . 377Comitant Hyperdeviations 377

Etiology and Clinical Characteristics 377Therapy 378

Dissociated Vertical Deviations 378Terminology 378Clinical Characteristics 378Measurement 380Etiology 381Differential Diagnosis 383Therapy 383

Dissociated Horizontal Deviations 385

Elevation in Adduction (StrabismusSursoadductorius) 385

Contents xv

Clinical Characteristics 385Etiology 386Therapy 387

Depression in Adduction (StrabismusDeorsoadductorius) 387

Cyclodeviations 389Diagnosis 389Clinical Characteristics 389Therapy 391

19 A and V Patterns . . . . . . . . . . . . . . . . . . . 396Etiology 398

Horizontal School 398Vertical School 399Oblique School 399Orbital Factors 399

Craniofacial Anomalies 399Heterotropia of Muscle Pulleys 400

Anomalies of Muscle Insertions andCyclotorsion 401

Conclusions 402

Prevalence 404

Clinical Findings and Diagnosis 404

Treatment 406Indications for Surgery 406Surgical Methods 407

Surgery on the Horizontal Rectus Muscles 407Surgery on the Oblique Muscles 407Transposition of Horizontal or Vertical Rectus

Muscles 409Slanting of the Horizontal Muscle Insertions 410

Choice of Surgical Procedure 410

20 Paralytic Strabismus . . . . . . . . . . . . . . . 414Diagnosis and Clinical Characteristics 414

Ductions and Versions 415Measurement of the Deviation 415Head Tilt Test 416Compensatory Anomalies of Head Position 417Sensory Anomalies 421Past-Pointing 421Electromyography 422Neurogenic Paralysis vs. Myogenic or Structural

Restriction of Eye Movements 422Forced Duction Test 423Estimation of Generated Muscle Force 425Eye Movement Velocity 426Paralytic vs. Nonparalytic Strabismus 427Congenital vs. Acquired Paralysis 427Orbital Imaging Techniques 429Evaluation of Visual Impairment Caused by

Diplopia 429

Paralysis of Individual Extraocular Muscles 429Cranial Nerve III Paralysis 430Cranial Nerve IV Paralysis 434Cranial Nerve VI Paralysis 439

Skew Deviation 442

Double Elevator Paralysis 442

Double Depressor Paralysis 443

Supranuclear and Internuclear Paralysis 444

Therapy of Paralytic Strabismus 444Nonsurgical Therapy 445Surgical Therapy 445Alternative Methods 451

21 Special Forms of Strabismus . . . . . 458Retraction Syndrome (Duane Syndrome) 458

Laterality and Sex Distribution 458Etiology 459Clinical Findings and Diagnosis 461Therapy 465

Brown Syndrome 466Incidence, Laterality, and Heredity 466Associated Anomalies 467Natural History 467Etiology 467Diagnosis and Differential Diagnosis 470Therapy 470

Adherence Syndrome 471

Strabismus Fixus 471Clinical Findings and Etiology 471Therapy 472

Strabismus in High Myopes 473

Fibrosis of the Extraocular Muscles 474

Graves’ Endocrine Ophthalmopathy 476Etiology 476Diagnosis and Clinical Findings 476Therapy 478

Acute Orbital Myositis 480

Cyclic Heterotropia 480Clinical Findings and Etiology 480Therapy 482

Acquired Motor Fusion Deficiency 482

Fracture of the Orbital Floor 483Clinical Findings and Etiology 483Therapy 484

Fracture of the Medial Orbital Wall 486

Superior Oblique Myokymia 487Clinical Findings and Etiology 487Therapy 487

Ocular Myasthenia Gravis 488Clinical Findings 488Diagnosis 488Therapy 489

Chronic Progressive External Ophthalmoplegia(Ocular Myopathy of von Graefe) 489Clinical Findings and Etiology 489Therapy 490

22 Anomalies of Convergence andDivergence . . . . . . . . . . . . . . . . . . . . . . . . . . 500Anomalies of Convergence 502

Convergence Insufficiency 502Convergence Insufficiency Associated with

Accommodative Insufficiency 503Convergence Paralysis 503Convergence Spasm 504

Anomalies of Divergence 505Divergence Insufficiency 505Divergence Paralysis 505

xvi Contents

23 Nystagmus . . . . . . . . . . . . . . . . . . . . . . . . . . 508Manifest Congenital Nystagmus 508

Sensory and Motor Type 508Clinical Characteristics 509Compensatory Mechanisms 511

Latent and Manifest-Latent CongenitalNystagmus 516

Clinical Characteristics 516

Treatment 520Medical Treatment 521Surgical Treatment 522

PA R T F O U R

Principles of Therapy

24 Principles of NonsurgicalTreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . 537Optical Treatment 537

Refractive Correction 537Prisms 540

Pharmacologic Treatment 541Miotics 541Atropine 543Chemodenervation 543

Orthoptics 543Applications 543Indications and Contraindications 544Treatment of Amblyopia 545Red Filter Treatment 550Prisms 550Penalization 550Drugs 552Pleoptics 552CAM Treatment 553Other Types of Treatment 553Rationale for Treatment 553

25 Chemodenervation of ExtraocularMuscles—Botulinum Toxin . . . . . . . . 559Mechanisms of Action 559

Injection Technique 560

Indications 561Botox in Infantile Esotropia 561Botox in Other Forms of Comitant Strabismus 562Botox in Paralytic Strabismus 562Botox in Endocrine Ophthalmopathy and Other

Ocular Motility Disturbances 563Botox in Nystagmus 563Other Ophthalmologic Indications 563Alternatives to Botox for Chemodenervation 563

26 Principles of Surgical Treatment . 566History and General Comments 566

Choice of Operation 568Motility Analysis 569Symmetrical vs. Asymmetrical Operations 570Amount of Operation 571Prism Adaptation Test 572Operations to Weaken the Action of a Muscle 573Operations to Strengthen the Action of a

Muscle 579Combined Recession-Resection Operation 580

Single vs. Multiple Procedures 580

Preparation of Patient and Parents for Surgery 581

Anesthesia 581General Anesthesia 581Local Anesthesia 582

Instruments, Sutures, Needles 582

Surgical Techniques 583Preparation of the Eye 583Fixation of the Globe 584Conjunctival Incision and Exposure of a Rectus

Muscle 584Recession of a Rectus Muscle 587Resection of a Rectus Muscle 588Adjustable Sutures 591Marginal Myotomy of a Rectus Muscle 597Myectomy of the Inferior Oblique Muscle 598Recession of the Inferior Oblique Muscle 600Tenectomy of the Superior Oblique Muscle 602Recession of the Superior Oblique Muscle 603Tucking of the Superior Oblique Muscle 603Anterior and Lateral Displacement of the Superior

Oblique Tendon for Excyclotropia (Harada-ItoProcedure) 607

Posterior Fixation Suture 609Muscle Transposition Procedures 612Recession of Conjunctiva and Tenon’s Capsule 617Traction Sutures 617Use of Plastic Materials 618

Complications 618Surgical Complications 618Complications of Anesthesia 619Postoperative Complications 620

Overcorrections 623

Postoperative Care 623Length of Hospitalization and Postoperative

Checkups 623Dressing 624Medication 624

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633

P A R T onePhysiology of theSensorimotorCooperation ofthe Eyes

C H A P T E R 1General Introduction

The Eyes as a SensorimotorUnit

The two human eyes with their adnexa andnervous system connections form an indivisibleentity. This fact must always be kept in mind,but for the purpose of study a distinction be-tween the sensory and the motor systems is nec-essary.

Light stimuli, having gone through the changesimposed on them by the refractive media, reachthe peripheral organ of vision, the retina, andproduce physical and chemical alterations in theretinal receptors. In turn, these alterations provokein the retinal neurons physicochemical and electri-cal changes that are transmitted as impulses to thecentral nervous system. Eventually, visual sensa-tions of form, spatial relationships, and color ap-pear in our consciousness. This sequence of eventsmay be called the sensory aspect of the visualprocess. The events in the sensory part of thevisual system also precipitate a chain of responsesin the motor system of the eyes, in the central andperipheral nervous arrangements, and in the innerand outer muscles of the eyes.

In this unitary sensorimotor system, the sensorysystem transmits and elaborates the informationreceived about the outside world. The motor sys-tem has no independent significance and is en-tirely in the service of the sensory system, bywhich it is largely governed. Understanding ofthis system is essential for the interpretation ofthe neuromuscular anomalies of the eyes.

3

The Tasks of the MotorSystem

The tasks of the motor system are (1) to enlargethe field of view by transforming the field ofvision into the field of fixation, (2) to bring theimage of the object of attention onto the foveaand keep it there, and (3) to position the two eyesin such a way that they are properly aligned at alltimes, thereby ensuring the maintenance of singlebinocular vision.

Nature and Control of OcularMovements

Voluntary and Involuntary EyeMovements

In agreement with a time-honored classification, adistinction is made between voluntary and invol-untary eye movements. Voluntary simply impliesthat the movements are ‘‘willed’’ by the individ-ual, presumably as a result of a chain of impulsesthat originate in the cortex. Involuntary eye move-ments are not willed by the individual and, indeed,occur without awareness. They are elicited mainlyby stimuli arising from outside the body, for exam-ple, visual or auditory, or those arising from withinthe body, for example, vestibular. The former arereferred to as exteroceptive, the latter as interocep-tive stimuli.

When the illuminance of the retina changes,the pupil of the eye constricts or dilates. When we

4 Physiology of the Sensorimotor Cooperation of the Eyes

tilt our head to one shoulder, the eyes make aparallel movement around their anteroposterioraxes, so the vertical meridians of the retinas turnin the direction opposite that of the head. Theeyes attempt to right themselves. Both these motorreactions are highly useful unconditioned reflexes.The central nervous system structures that mediatethese reflexes are subcortical. The individual isnot aware they are taking place.

When a light stimulus reaches the retinal pe-riphery, the eye turns and causes the stimulus toimpinge on the area of highest resolving power,the fovea. If a binocularly fixated object ap-proaches the eyes, the visual axes converge tomaintain fixation. If for some reason the properalignment of the visual axes has been lost, correc-tive fusional movements occur and restore binocu-lar fixation. All these movements are highly use-ful, and most of them are also reflexive, but thereis a significant difference between them and reflexmovements.

If a person is lost in thought or concentratingon an object of regard, another object approachingfrom one side may not be noticed—at times withregrettable results. One can voluntarily stop con-vergence or voluntarily overconverge. In inatten-tive states, one may fail to make fusional move-ments. All these movements, then, thoughbasically reflexive, require the cooperation of thecerebral cortex, in particular a state of visual atten-tion. Hofmann and Bielschowsky,8 who publishedtheir classic study on fusional movements in 1900,clearly noted the reflex nature of these move-ments, but were also aware that they did not comeabout without the concurrence of attention. Theydesignated the fusional movements as psycho-op-tical reflexes. At the time Hofmann andBielschowsky published their paper, Pavlov hadjust begun his work on conditioned reflexes, andhis findings were not yet published. Today, reflexmovements that require cooperation of the cere-bral cortex are designated as conditioned reflexes.

In summary, all eye movements, insofar as theyare not voluntary, are unconditioned or condi-tioned reflexes performed in the service of thesensory system of the eyes, specifically in theinterest of clear, distinct vision and of binocularfixation.

Cybernetic Control of the EyeMovementsThe concept of reflex activity, with the neuron asthe unit of the anatomical and physiologic organi-

zation of the nervous system, for a long timehas been the cornerstone of neurophysiology andneurology and, consequently, also that of the sen-sorimotor system of vision. Chavasse1 introducedan extreme reflexologic view into the analysis ofneuromuscular anomalies of the eyes. He extendedthe concept of unconditioned reflexes, in the man-ner of Pavlov’s teaching on the higher nervousactivity, to include the sensory visual responses.Chavasse’s views are discussed in detail in laterchapters.

Control of the eye movements thus was inter-preted as resulting from exteroceptive and proprio-ceptive stimulations. More recently, a new way ofthinking and a new vocabulary have been devel-oping. Cybernetics and information theory, to-gether with spectacular advances in electronictechnology, have brought about a revolution thatcould not help have an influence on the interpreta-tion of biological phenomena. The terminology ofthe engineer has taken on a strangely biologicalcast, and the terminology of the biologist is in-creasingly borrowing terms from the engineer.‘‘Closed loops,’’ ‘‘open loops,’’ ‘‘feedback,’’ and‘‘servomechanisms’’ are words heard today ascommonly from biologists as from engineers.

The information received from the retina maybe designated as retinal error signal (the differencebetween the desired and received placement of theimage) or as outflow feedback. Signals sent outfrom tension sensors in the extraocular muscleswould then represent an inflow (proprioceptive)feedback. Inflow feedback is the common mecha-nism provided for in skeletal muscles, for exam-ple, the muscles of the limbs. Whether inflow fromthe extraocular muscles plays a role in oculomotorcontrol or space perception is discussed in Chap-ter 2.

Ludvigh,12 one of the first to propose a cyber-netic model for eye movements, stated that it istempting to hypothesize that the retina providesthe necessary feedback, since the visual environ-ment is ordinarily heterogeneous; therefore, move-ments of the eyes bring about changes in theretinal and neural pattern even in the absenceof any interoceptive sense. Ludvigh pointed out,however, that control of the eye movements can-not be based on retinal feedback alone.12 Thetemporal relations are such that entire large excur-sions of several degrees, so-called saccadic move-ments, may be initiated and completed by the eyesbefore there is time for any inflow or outflow

General Introduction 5

feedback to become effective. This reasoning maynot apply to the much slower fusional movements.

According to Ludvigh’s hypothesis12 a definiteinnervation sequence always follows when thestimulus has a specific extrafoveal position. This isan important concept well described by Hofmann,7

who spoke of a motor value of the retinal elementsproportional to the distance of the stimulated ele-ment from the fovea, whose retinomotor value isequal to zero (see Retinomotor Values in Chap-ter 2).

The cybernetic scheme proposed by Ludvigh12

is a qualitative one. Later authors2, 5, 15–17 haveworked out quantitative models for oculomotorcontrol. It is not useful to discuss them in thisbook; interested readers are referred to the originalpublications.

Apparent Movement of theEnvironment

When the eyes make a saccadic movement, theimage of the environment sweeps across the ret-ina, yet no movement is perceived. This phenome-non has been explained by von Holst and Mittel-staedt,9 Ludvigh,11 and others as follows.

The control system (the ‘‘space representationcenter’’ of Ludvigh12) is informed of the conjugateinnervation sent to the extraocular muscles. If themovement is accurately performed, the informa-tion from retinal feedback coincides with the in-formation about the conjugate innervation, and nomovement is perceived; but if the two disagree,an apparent movement of the visual environmentresults.

This can be shown by a simple experiment:close the left eye and push your right eye na-salward with your finger. Images will now sweepacross the retina, but since the control centerknows of no active innervation to the right medialrectus muscle, the environment appears to make ajump to the right. Likewise, if an extraocular mus-cle (e.g., the right lateral rectus muscle) is para-lyzed, an innervation impulse to abduct that eyewill not be executed at all or, if any abductionoccurs, the eye will not abduct fully. The controlcenter is informed of the innervation, but the ab-sence of the proper retinal feedback again causesan apparent movement of the environment to theright. This phenomenon is the basis of past-point-ing in paralytic strabismus, which is discussedfurther in Chapter 20.

Empiricism and Nativism

Historically, there were two opposing schools ofthought with regard to the origin and developmentof normal binocular vision and spatial orientation.One maintained that humans are born withoutbinocularity or spatial orientation and that binocu-larity and spatial orientation are learned functionsacquired by trial and error through experience andassisted by all the other senses, especially thekinesthetic sense. This is the theory of empiricism:that binocular vision depends on ontogenetic de-velopment. The other school held that binocularvision and spatial orientation are not learned func-tions but are given to humans with the anatomico-physiologic organization of his visual system,which is innate. This is the nativistic teaching:that binocular vision is acquired phylogeneticallyrather than ontogenetically.

The principal proponents of these two schoolswere Hering and Helmholtz who—with very littleexperimental evidence on either side—battledeach other fiercely during the second half of thenineteenth century. The intensity of this battle isunderstandable, because it is not restricted to thequestion of the development of binocular vision;indeed it is a battle between two attitudes towardlife and existence.

One may ask why philosophic ponderings onempiricism and nativism should be found in abook on strabismus. Surprising as it may seem,they are of basic importance in the managementof strabismus since the prognosis and the attitudetoward timing of treatment depend on this view.If one believes that binocular vision is a learnedskill and if a functional cure is sought, one willhave to operate very early in a child’s life. Anotherophthalmologist, more nativistically inclined, maybelieve that, given a normal sensorimotor anlage,early surgery is not absolutely essential, just as itis of no functional use if the anlage is not there.

There is no doubt that the anlage for normalbinocular vision is present at birth. No evidenceexists, for instance, that sensory fusion or stereop-sis are ‘‘learned’’ processes any more than theperception of color—as distinct from colornaming—is a learned process. Certain motor skillsof the eyes are learned and improvable, as are allmotor skills. The situation may be compared withthat of a musician. ‘‘Innate’’ musical talent isnecessary, but to be a pianist or violinist the motorskills of fingers and arms must be learned andcontinually reinforced through practice.


Animal research during the past three decadeshas actually provided support for both the nativis-tic and the empiricist schools of thought. The mostdirect evidence for the nativistic view came fromthe epochal work of Hubel and Wiesel,10 whoshowed with microelectrode recordings that visu-ally inexperienced kittens have striate neuronswith normal orientation sensitivity and a consider-able number of neurons that are responsive tostimulation from either eye. In fact, electrophysio-logic data from these kittens were strikingly simi-lar to those obtained from adult cats. The samedegree of complex functional differentiation of thevisual cortex is present in visually immature babymonkeys.18 These findings support a nativisticview, according to which many connections re-sponsible for the highly organized behavior of thestriate cortex must be present at birth or within afew days of it. On the other hand, we have alsolearned from animal experiments that the normalpostnatal development of the visual system de-pends on normal visual experience and that thisdevelopment can be adversely modified by abnor-mal visual input. For instance, environmental fac-tors are highly effective in tuning the spatial orien-tation of cortical neurons.6 Only brief disruptionsof binocularity, produced by suturing the lid ofone eye in a monkey14 or by creating artificialstrabismus,3 suffice to decimate or even abolishbinocular neurons in the striate cortex and thusthe ability to see stereoscopically.4 Thus, normalvisual experience is essential to preserve visualfunctions already present at birth and to promotetheir further development. The contradiction be-tween empiricism and nativism, with all its philo-sophical and social implications, may well be onlyan apparent one as far as the visual system isconcerned.13

REFERENCES1. Chavasse FB: Worth’s Squint or the Binocular Reflexes

and Treatment of Strabismus. Philadelphia, P Blakiston’sSon & Co, 1939.

2. Collins CC: The human oculomotor control system. InLennerstrand G., Bach-y-Rita P, ed: Basic Mechanisms ofOcular Motility and Their Clinical Applications. NewYork, Pergamon Press, 1975, p 145.

3. Crawford ML, Noorden GK. The effects of short-termexperimental strabismus on the visual system in Macacamulatta. Invest Ophthalmol Vis Sci 18:496, 1979.

4. Crawford ML, Noorden GK, von Meharg LS, et al. Binoc-ular neurons and binocular function in monkeys and chil-dren, Invest Ophthalmol Vis Sci 24:491, 1983.

5. Fender DH, Nye PW: An investigation of the mechanismsof eye movement control. Kybernetik 1 (July):81, 1961.

6. Hirsch HVB, Spinelli DN: Visual experience modifiesdistribution of horizontally and vertically oriented re-ceptive fields in cats. Science 168:869, 1970.

7. Hofmann FB.: Die Lehre vom Raumsinn des Auges. InAxenfeld T, Elschnig A, eds: Graefe-Saemisch’s Handbuchder gesamten Augenheilkunde, ed 2, vol 3. Berlin,Springer-Verlag, 1920–1923, p 208.

8. Hofmann FB, Bielschowsky A: Über die der Willkürentzogenen Fusionsbewegungen der Augen. Pflügers Arch80:1, 1900.

9. Holst E von, Mittelstaedt E: Das Reafferenzprinzip (Wech-selwirkung zwischen Zentralnervensystem und Peripherie).Naturwissenchaften 37:464, 1950.

10. Hubel DH, Wiesel TN: Receptive fields of cells in striatecortex of very young, visually inexperienced kittens. JNeurophysiol 26:994, 1963.

11. Ludvigh E: Possible role of proprioception in the extraocu-lar muscles. Arch Ophthalmol 48:436, 1952.

12. Ludvigh E: Control of ocular movements and visual inter-pretation of environment. Arch Ophthalmol 48:442, 1952.

13. Noorden GK von: Application of basic research data toclinical amblyopia. Ophthalmology 85:496, 1978.

14. Noorden GK von: Morphological and physiologicalchanges in the monkey visual system after short-term lidsuture. Invest Ophthalmol Vis Sci 17:762, 1978.

15. Robinson DA: Oculomotor control signals. In Lenner-strand G, Bach-y-Rita P, eds: Basic Mechanisms of OcularMotility and Their Clinical Applications. New York, Per-gamon Press, 1975, p 337.

16. Stark L, Kupfer C, Young LR: Physiology of the visualcontrol system. NASA CR-283, Washington, DC, June 1965.

17. Sunderhauf A: Untersuchungen über die Regelung derAugenbewegungen. Klin Monatsbl Augenheilkd 136:837,1960.

18. Wiesel TN, Hubel DH: Ordered arrangement of orientationcolumns in monkeys lacking visual experience. J CompNeurol 158:301, 1974.

C H A P T E R 2Binocular Vision andSpace Perception

Without an understanding of the physiologyof binocular vision it becomes difficult, ifnot impossible, to appreciate its anomalies. Thereader is well advised to study this chapter thor-oughly since important basic concepts and termi-nology used throughout the remainder of this bookare introduced and defined. It is of historical inter-est that most of these concepts and terms haveonly been with us since the nineteenth centurywhen they were introduced by three men who maybe considered among the fathers of modern visualphysiology: Johannes Müller, Hermann von Helm-holtz, and Ewald Hering. The basic laws of binoc-ular vision and spatial localization that were laiddown by these giants of the past form the veryfoundation on which our current understanding ofstrabismus and its symptoms and sensory conse-quences is based.

Fusion, Diplopia, and the Lawof Sensory Correspondence

Let us position an object at a convenient distancein front of an observer at eye level and in themidplane of the head. If the eyes are properlyaligned and if the object is fixated binocularly, animage will be received on matching areas of thetwo retinas. If the eyes are functioning normallyand equally, the two images will be the same insize, illuminance, and color. In spite of the pres-ence of the two separate physical (retinal) images,

7

only one visual object is perceived by the ob-server. This phenomenon is so natural to us thatthe naive observer is not surprised by it; he issurprised only if he sees double. Yet theopposite—single binocular vision from two dis-tinct retinal images—is the truly remarkable phe-nomenon that requires an explanation.

Relative Subjective VisualDirections

Whenever a retinal area is stimulated by lightentering the eye, the stimulus is perceived notonly as being of a certain brightness and colorand of a certain form but also as always beinglocalized in a certain direction in visual space.One cannot have a visual impression withoutseeing it somewhere. If the stimulated retinal areais located to the left of the fovea, it is seen in theright half of the field; if it is located to the rightof the fovea, it is seen in the left half of the field.

The direction in which a visual object is local-ized is determined by the directional, or spatial,values of the stimulated retinal elements. Thesedirectional values (the local signs of Lotze) are anintrinsic property inherent to the retinal elements,as are all the properties that lead to sensations ofbrightness, color, and form of a percept.

That the directional values are intrinsic proper-ties of the retinal elements and are not caused bythe location of the light stimulus in external spaceor by some other properties of the light stimulus


can be shown by using inadequate stimuli. If theretina is stimulated mechanically (pressure) orelectrically, the resulting sensation is localized inthe same specific direction in which it would belocalized if the retinal elements had been stimu-lated by light. For instance, if we apply fingerpressure near the temporal canthus through thelids of one eye, we will become aware of a posi-tive scotoma in the nasal periphery of that eye.

It must be made clear at this point that when-ever retinal elements, retinal points, or retinalareas are spoken of in this book, they are to beunderstood in the sense in which Sherrington85

used them. He defined these terms to mean ‘‘theretinocerebral apparatus engaged in elaborating asensation in response to excitation of a unit areaof retinal surface.’’ None of the ‘‘properties’’ spo-ken of ‘‘belong’’ to the retinal elements per se.Anatomical, physiological, biophysical, and bio-chemical arrangements and mechanisms withinthe retina give rise to excitations that ultimatelyresult in what we know as ‘‘vision.’’ We ‘‘see’’with our brain, not with our retina, but the firststep in elaboration of information received by theeye takes place in the retina. Without the retina,there is no vision. Since it is vastly easier for usto visualize the retina than the totality of theretinocerebral apparatus, retinal terminology is ad-hered to throughout this book.

Each retinal element, then, localizes the stimu-lus as a visual percept in a specific direction, avisual direction, but this direction is not absolute.It is relative to the visual direction of the fovea.The fovea, the area of highest visual acuity, isalso the carrier of the principal visual directionand the center to which the secondary visual direc-tions of all other retinal elements relate. This rela-tionship is stable, and this stability is what makesan orderly visual field possible. Since the localiza-tion of the secondary visual direction is not abso-lutely fixed in visual space but is fixed only asrelated to the visual direction of the fovea, itsdirection shifts together with the principal visualdirection with changes in the position of the eye.Strictly speaking, visual directions are subjectivesensations and cannot be drawn in a geometricconstruct. The objective correlates to visual direc-tions for the use in such drawings are the principaland secondary lines of directions. A line of direc-tion is defined as a line that connects an objectpoint with its image on the retina. Helmholtz44, vol.1, p. 97 defined it (the direction ray) also as a linefrom the posterior nodal point to the retina. All

FIGURE 2–1. Relative lines of direction. A, Eye instraight-ahead position. F, principal line of direction; N andP, secondary lines of direction. B, Eye turned to right.The sheath of lines of directions shifts with the positionof the eyes, but F� remains the principal line of directionand N� and P� remain the secondary lines of direction.

lines of direction therefore should meet in theanterior nodal point. For simplicity, the lines ofdirection are represented as straight lines in sche-matic drawings (Fig. 2–1).

Retinomotor Values

There is a further important result of this stableand orderly arrangement of the relative visual di-rections. The appearance of an object in the pe-riphery of the visual field attracts attention, andthe eye is turned toward the object so that itmay be imaged on the fovea. The resulting eyemovement, also called a saccade, is extraordi-narily precise. It is initiated by a signal from theretinal periphery that transmits to the brain thevisual direction, relative to the foveal visual direc-tion, where the peripherally seen object has ap-peared. Corresponding impulses are then sent tothe extraocular muscles to perform the necessaryocular rotation, mediated and controlled in a man-ner discussed in Chapter 4. This function of theretinal elements may be characterized by sayingthat they have a retinomotor value. This retinomo-tor value of the retinal elements increases fromthe center toward the periphery. The retinomotorvalue of the fovea itself is zero. Once an image ison the fovea, there is no incentive for ocularrotation. The fovea, then, in addition to its otherfunctions, is also the retinomotor center or retino-motor zero point. The retinal organization de-scribed here has an important clinical application:it makes it possible to measure ocular deviationsby means of the prism and cover test (see prismand cover test in Chapter 12).

Binocular Vision and Space Perception 9

FIGURE 2–2. A, The fixation point, F, and the objects L and R all lie on the geometric lines ofdirection Ffl and Ffr of the two foveae. F, L, and R therefore are seen behind each other in subjectivespace in the common relative subjective visual direction of the two foveae, f, as shown in B. Theimaginary ‘‘third’’ eye, the cyclopean eye, is indicated by dashed lines in A.

Common Relative Subjective VisualDirections

Thus far, only the single eye has been discussed.How do the relative subjective visual directions ofthe two eyes relate to each other?

Let a person with head erect fixate an object,F (Fig. 2–2), called the fixation point. Ffl and Ffrare the lines of direction of the two foveae and assuch are of special importance. They are alsocalled principal lines of direction or visual axes.Other synonyms are line of gaze, line of vision,and line of regard. If the two principal lines ofdirection intersect at the fixation point, it is saidthat there is binocular fixation. If only one princi-pal line of direction goes through the fixationpoint, fixation is monocular.

As we have seen, F, fixated binocularly (seeFig. 2–2), is seen not in the direction of theprincipal line of direction of either eye but in adirection that more or less coincides with themedian plane of the head. This holds true not onlyfor the fixation point but also for any object pointin the principal line of direction. L and R in Figure2–2, which lie on the principal lines of directionof the left and right eyes, therefore will appear tobe behind each other and in front of F, althoughall three are widely separated in physical space.All object points that simultaneously stimulate thetwo foveae appear in one and the same subjectivevisual direction. This direction belongs to both the

right and left foveae and therefore is called thecommon subjective visual direction of the foveae.

The two foveae have more than just a commonvisual direction; if an observer fixates F binocu-larly (Fig. 2–3), the object points, N and N�, ifproperly positioned, will be seen behind eachother, since the peripheral retinal points nl and nhave a common visual direction represented by b.What applied to nl and n applies to all other retinalelements. Every retinal point or area has a partner

FIGURE 2–3. A, Stimulating corresponding retinal ele-ments, objects N and N�, are localized in visual space inthe common relative subjective visual direction of nl andn�r and despite their horizontal separation are seen behindeach other in B, subjective visual space. F, fixation point.


in the fellow retina with which it shares a commonrelative subjective visual direction.

Retinal Correspondence

Retinal elements of the two eyes that share acommon subjective visual direction are called cor-responding retinal points. All other retinal ele-ments are noncorresponding or disparate with re-spect to a given retinal element in the fellow eye.This definition also may be stated in the followingway: corresponding retinal elements are those ele-ments of the two retinas that give rise in binocularvision to the localization of sensations in one andthe same subjective visual direction. It does notmatter whether a stimulus reaches the retinal ele-ment in one eye alone or its corresponding partnerin the other eye alone or whether it reaches bothsimultaneously (see Figs. 2–2 and 2–3).

The common visual direction of the foveae isagain of special importance. All visual directions,as has been seen, have a relative value in subjec-tive space. The common subjective visual direc-tions, too, have a fixed position relative only tothe principal common visual direction. They deter-mine the orientation of visual objects relative toeach other with the principal visual direction asthe direction of reference.

All common subjective visual directions can berepresented in a drawing as intersecting at onepoint with the principal visual direction. Thus,they form a sheaf that is the subjective equivalentof the two physical eyes and may be thought ofas the third central imaginary eye46, p. 348 or thebinoculus, or cyclopean eye44, vol. 3, p. 258 (see Fig.2–2). If the principal subjective visual directionlies in the median plane of the head, the physicalcorrelate of the point of intersection of the visualdirections, their origin, would be approximately inthe area of the root of the nose (whence ‘‘cyclo-pean’’ eye).

Corresponding retinal elements arranged in ho-rizontal and vertical rows provide the subjectivevertical and horizontal meridians. Meridians thatinclude the visual direction of the fovea are theprincipal corresponding horizontal and verticalmeridians.

The existence of corresponding retinal elementswith their common relative subjective visual direc-tions is the essence of binocular vision. It may becalled the law of sensory correspondence in anal-ogy with the law of motor correspondence, whichis discussed in Chapter 4.

The oneness of the directional sensory re-sponses originating in each eye is impressivelydemonstrated by means of afterimages. If one cre-ates an afterimage on the retina of one eye, it willappear in the binocular field of view in the com-mon visual direction of the stimulated retinal areaand in its nonstimulated partner in the other eye.It is difficult, indeed almost impossible, for theobserver to judge which eye carries the afterim-ages. It will continue to be seen and localized inthe same direction, whether the eyes are open orclosed or whether the stimulated eye is closed andthe other eye held open. In this latter situationsome authors19, 55 have spoken of an afterimagetransfer. This term is a misnomer as nothing isbeing transferred.43

If a horizontal afterimage is formed in one eyeby a strong horizontal light stimulus, leaving thefovea unstimulated, and if a similar verticalafterimage is created in the other eye, the resultingvisual percept is an afterimage in the form of across with a gap in its center.10, 49, p. 158 The gap isseen because of the lack of stimulation in thefoveae. The center of the horizontal and verticalafterimages is consequently a single spot localizedin the principal common visual direction. Thehorizontal and vertical legs of the afterimagesare oriented accordingly (Fig. 2–4). It is of greatimportance to understand clearly that the appear-ance of the afterimage cross is independent of theposition of the eyes. Once a lasting stimulus, suchas an afterimage, has been imparted, its localiza-tion in subjective space depends solely on thevisual direction of the retinal elements involved.One may topically anesthetize one eye and moveit passively with a forceps or push it in any direc-tion with one’s finger—the cross remains a cross.No change in the relative localization of the verti-cal and horizontal afterimage will occur. The useof afterimages has an important place in the diag-nosis of anomalous retinal correspondence (seeChapter 13). The principles underlying afterimagetesting must be fully understood to guard againstgross errors in interpretation.

Sensory Fusion

Sensory correspondence explains binocular singlevision or sensory fusion. The term is defined asthe unification of visual excitations from corres-ponding retinal images into a single visual per-cept, a single visual image. An object localized inone and the same visual direction by stimulation


FIGURE 2–4. A, Afterimages produced in the right and left eye, respectively. The fovea is repre-sented by the break in the afterimage. B, The combined binocular afterimage forms a cross. Thetwo gaps appear single.

of the two retinas can only appear as one. Anindividual cannot see double with correspondingretinal elements. Single vision is the hallmark ofretinal correspondence. Put otherwise, the stimu-lus to sensory fusion is the excitation of corre-sponding retinal elements.

Since both the central and peripheral parts ofthe retina contribute fusible material, it is mis-leading to equate sensory fusion with ‘‘central’’fusion (as opposed to ‘‘peripheral’’ or motor fu-sion). Fusion, whether sensory or motor, is alwaysa central process (i.e., it takes place in the visualcenters of the brain).

For sensory fusion to occur, the images notonly must be located on corresponding retinalareas but also must be sufficiently similar in size,brightness, and sharpness. Unequal images are asevere sensory obstacle to fusion. Obstacles tofusion may become important factors in the etiol-ogy of strabismus (see Chapter 9). Differences incolor and contours may lead to retinal rivalry.

The simultaneous stimulation of noncorres-ponding or disparate retinal elements by an objectpoint causes this point to be localized in twodifferent subjective visual directions. An objectpoint seen simultaneously in two directions ap-pears double or in diplopia. Double vision is thehallmark of retinal disparity. Anyone with twonormal eyes can readily be convinced of this factby fixating binocularly an object point and thendisplacing one eye slightly by pressure from afinger. The object point, which appeared singlebefore pressure was applied to the globe, is nowseen in diplopia because it is no longer imagedon corresponding retinal areas. Qualifications thatmust be made about equating disparate retinalelements and diplopia are discussed on page 20.Paradoxical diplopia with ordinarily correspond-

ing elements in cases of strabismus is discussedin Chapter 13.

Motor Fusion

The term motor fusion refers to the ability to alignthe eyes in such a manner that sensory fusion canbe maintained. The stimulus for these fusional eyemovements is retinal disparity outside Panum’sarea and the two eyes are moving in oppositedirections (vergences; see Chapter 4). Unlike sen-sory fusion, which occurs between correspondingretinal elements in the fovea and the retinal pe-riphery, motor fusion is the exclusive function ofthe extrafoveal retinal periphery. No stimulus formotor fusion exists when the images of a fixatedvisual object fall on the fovea of each eye.

Retinal Rivalry

When dissimilar contours are presented to corres-ponding retinal areas, fusion becomes impossible.Instead, retinal rivalry may be observed. This phe-nomenon, also termed binocular rivalry, must beclearly distinguished from local adaptation, orTroxler’s phenomenon.67

If a person looks into a stereoscope at twodissimilar targets with overlapping nonfusible con-tours, first one contour, then the other will beseen, or mosaics of one and the other, but notboth contours simultaneously. In Figure 2–5, takenfrom Panum,78 each eye sees a set of oblique lines,one going from above left to below right, seen bythe left eye, and another set going from aboveright to below left, seen by the right eye. Whenobserved in a stereoscope, these lines are not seenas crossing lines but as a changing pattern of


FIGURE 2–5. Rivalry pattern. A, Pattern seen by theleft eye. B, Pattern seen by the right eye. C, Binocularimpression. (From Panum PL. Physiologische Untersu-chungen über das Sehen mit zwei Augen. Kiels. Ger-many, Schwerssche Buchhandlung, 1858, pp. 52 ff. )

patches of oblique lines going in one or the otherdirection.

Binocular rivalry may also be produced byuniform surfaces of different color (color rivalry)and unequal luminances of the two targets. Manycombinations of contours, colors, and luminanceshave been studied exhaustively since the daysof Panum,78 Fechner,41 Helmholtz,44 and Hering.45

Review of the literature may be found in thereports of Hofmann,49 Ogle,76, p. 409 and Levelt.67

It is of interest that it takes a certain buildupof time (150 ms) before dissimilar visual input tothe eyes causes binocular rivalry. Dichoptic stim-uli were perceived as ‘‘fused’’ when presented forshorter periods.63

The phenomenon of retinal rivalry is basic tobinocular vision and may be explained as follows.Simultaneous excitation of corresponding retinalareas by dissimilar stimuli does not permit fusion;but since such excitations are localized in the samevisual direction and since two objects localized inthe same place give rise to conflict and confusion,one or the other is temporarily suppressed. Whichof the two is suppressed more depends on thegreater or lesser dominance of one eye rather thanon the attention value of the visual object seen byeach eye.17 In other words, it is the eye and notthe stimulus that competes for dominance under awide range of conditions. Stimulus rivalry occurs

only within a limited range of spatial and temporalparameters.59

The extent to which true fusion or monocularalternation in the binocular field governs normalvisual activity—in other words, the significance ofthe rivalry phenomena for the theory of binocularvision—is considered on page 31.

It is at once clear that rivalry phenomena, orrather their absence, must in some fashion berelated to what is known as suppression in strabis-mic patients. Suppression is discussed in detail inChapter 13. Here we state only that constant fo-veal suppression of one eye with cessation ofrivalry leads to complete sensory dominance ofthe other eye, which is a major obstacle to binocu-lar vision. Return of retinal rivalry is a requisitefor reestablishment of binocular vision.

The retinal rivalry phenomenon has been ex-plained in neurophysiologic terms by the presenceof separate channels for the right and left eyesthat compete for access to the visual cortex. Athird binocular channel is activated only by fusibleinput.27, 102 Because of this competition and theinhibition elicited, only fragments of the imageseen by each eye are transmitted to the striatecortex in the case of nonfusible binocular input.Competitive interaction occurs not only in theprimary visual cortex14 but continues at severalafferent levels of the visual pathway, well afterthe inputs to the two eyes have converged.64

Objective (Physical) andSubjective (Visual) Space

Certain terminological differentiations made ear-lier in this chapter will not have escaped the noticeof the attentive reader. For example, location ofan object point in physical (objective) space wasseparated from its localization in visual (subjec-tive) space. The (objective) lines of direction de-termine which retinal area will be stimulated; their(subjective) counterpart, the visual directions, de-termine the direction in which the object will beseen in visual space.

Clear distinctions between physical space andits subjective counterpart are essential both inthinking about spatial orientation and in the ex-pression of that thinking. Failure to do so has beenthe source of much confusion and error in thedescription of normal and abnormal binocular vi-sion. The naive observer gives little thought tovision. His thoughts are for the things he sees. Hetakes it for granted that he sees things as they are


and where they are. This instinctive approach isdeeply ingrained in all of us, and we act in accor-dance with it in practical life. In fact, however,we do not see physical objects. What takes placeis that energy in the form of light waves is ab-sorbed by photosensitive receptors in the retinaand is transformed into other forms of energy.Eventually this process leads in some manner toevents occurring in our consciousness; we callthis seeing. Thus, vision results from the activetransformation of the excitations produced initiallyin our retinas by energy emanating from a narrowband within the electromagnetic spectrum. In con-sciousness this builds up our world of light, color,and spatial orientation.

This view of vision is not shared by everyone.Some maintain that events in certain parts of thebrain are synonymous with vision and that whatwe experience in consciousness is an epiphenome-non. Others state that vision is nothing more thanan overt response of the organism to stimulation,a form of behavior, but all concede that we do notsee physical objects. What occurs in our brain arephysicochemical and electrical events. What weexperience in our consciousness are sense data. Injoining one sense datum to other sense data de-rived from the same or from different receptororgans, we proceed from sensation to perception.Relating these sense data to past experience isenormously complex, and each new sense datumbecomes either meaningful or not meaningful.

The sense datum is qualitatively different fromand is not commensurate with the physical processto which it is correlated. This is immediately clearwhen speaking of colors. Neither radiant energyof 640 mm nor the processes evoked by thisradiant energy in the retina, the optic nerve, or thebrain cells is ‘‘red.’’ Red is a sensation. It isnot immediately clear that similar considerationsapply to the perception of space. That they indeeddo apply will be evident throughout this book.

The scientific or philosophical validity of thevarious concepts of the nature of sensation andperception and of ‘‘reality’’ will not be arguedhere. The question under consideration is notwhich view is ‘‘true’’ or ‘‘correct’’—that is,verifiable—but which one gives the best descrip-tion of the phenomena and is most likely to helpin furthering the understanding and the advance-ment of clinical work. In this respect, the mostuseful view is that incorporated into the methodol-ogy termed exact subjectivism by Tschermak-Seysenegg.94 This view recognizes objective and

subjective factors in vision, that physical space,of which we and our visual system are a part, andsubjective space are built up from sense data.

The subjective space is private to each one ofus. A color-normal person can understand butnever experience how a color-blind person seesthe world, nor can a color-blind person ever expe-rience colors as a color-normal person does. Simi-larly, a person with a normal sensorimotor systemof the eyes may be able to understand but cannever experience certain phenomena that peoplewith abnormal sensorimotor systems may experi-ence in their subjective space (see Chapter 13).

The sensations of color and spatial localizationare not anarchic, however. Certain physical pro-cesses are always correlated with certain sensa-tions and perceptions. Known changes introducedinto the environment produce regular changes insensations and perceptions. These lawful relationsallow us to make quantitative determinations. Wehave no yardstick for the sensation ‘‘red,’’ and wehave no yardstick for subjective space; but we cancharacterize them quantitatively by changes in theenvironment with which they are correlated.

Each stimulus has certain characteristics: lumi-nance, wavelength, extent, and location in physicalspace. All these parameters, singly and combined,have an effect on the visual system; but how acolored object appears does not depend solely onthe wavelength it emits or reflects but also on thestate of the eye, particularly on the color to whichit has been previously adapted. The brightness ofa percept depends not only on the luminance ofthe stimulus but also on the state of the eye andits responsiveness. For instance, a stimulus that isbelow threshold for an eye adapted to bright lightmay appear very bright if the eye is adapted todarkness.

The ability of the eye to adapt to varying levelsof illumination is involved also in one of theconstancy phenomena. A white sheet of paperappears to be white not only at noon but also attwilight, although it reflects much more light intothe eye at noon. The smaller amount of light is aseffective in the dark-adapted eye as is the greateramount of light in the light-adapted eye. Up to acertain distance the size of a man remains constantas he walks away from us, although the retinalimage grows smaller (size constancy). Eventually,however, he will appear smaller, and as he recedesfarther he shrinks to a point and finally disappearsaltogether.

Most important, no stimulus is ever isolated. It


FIGURE 2–6. Retinal discrepancies.Subjective appearance of circles (bro-ken lines) contrasts with objectivecircle (solid lines). (From Tschermak-Seysenegg A Von: Der exacte Sub-jectivismus in der neueren Sinnes-physiologie, ed 2, Vienna, Emil, Haim,1932.)

has a surround, and this surround also has stimulusqualities. The effects of the surround, especiallyat the borders, lead to the phenomena of inductionand physiologic contrast, which play a great rolein visual discrimination and color vision.

Where a visual object is localized in subjectivespace relative to other objects does not depend onthe position of that object in physical space. Itdepends on the visual direction of the retinal area

FIGURE 2–7. Discrepancies between subjective vertical meridian, SVM, and plumb line in the twoeyes. No discrepancy exists between the subjective horizontal, SHM, and the objective horizontalmeridians. (From Tschermak-Seysenegg A Von: Der exacte Subjectivismus in der neueren Sinnesphy-siologie, ed. 2, Vienna, Emil Haim, 1932.)

that it stimulates. An object may be located inphysical space at any place. So long as it stimu-lates the foveae it is seen in their common subjec-tive visual direction.

Discrepancies of Objective andSubjective MetricsThe difference between the metric of physicalspace and the metric of the eye is emphasized by


the existence of so-called visual discrepancies. Ifone attempts to bisect a monocularly fixated linein an arrangement that excludes other visual cluesfrom the field, a constant error is detected. Theline is not divided into two objectively equal linesegments. If placed horizontally, the line segmentimaged on the nasal side of the retina, that is, theone appearing in the temporal half of the field, islarger than the temporally imaged retinonasal linesegment. This is the famous partition experimentof Kundt, a German physicist of the mid nine-teenth century.95, p. 137 The opposite phenomenon,described by Münsterberg,73 occurs only rarely.Similarly, the lower line segment (imaged retino-superiorly) is shorter than the upper (retinoinfer-ior) segment. In subjective space, therefore, theequivalent of a true circle fixated centrally is asomewhat irregular round figure, the smallest ra-dius of which points outward. Accordingly, a sub-jectively true circle does not correspond to a truecircle in physical space (Fig. 2–6). In general, thediscrepancies in the two eyes are symmetrical.They compensate each other, and the partition ofa line into two equal segments is more nearlycorrect in binocular fixation.

There are also directional discrepancies thatresult in a deviation of the subjective verticalfrom the objective vertical. A monocularly fixatedplumb line shows a definite disclination with thetop tilted templeward. This disclination is, as arule, approximately symmetrical in the two eyes(Fig. 2–7). In general, the angle of disclination isnot greater than 4� to 5�, but it has been reportedin isolated cases to be as high as 14�.

The discrepancies described are evidence thatthe retinal elements that physically have the sameeccentricity in the two eyes are not equivalentfunctionally. This is the basis of the Hering-Hille-brand horopter deviation (see p. 18).

Distribution of CorrespondingRetinal Elements

The Foveae as CorrespondingElements

That the foveae have a common subjective visualdirection is demonstrated by Hering’s fundamentalexperiment,46, p. 343 which in its classic simplicityis reminiscent of a bygone day when basic discov-eries in physiologic optics could be made with acandle, some cardboard, and a few strings and pul-leys.

Place yourself in front of a closed window withan open view. Close the right eye and look for anoutstanding, somewhat isolated object, say, a tree.Make an ink mark on the window pane at aboutthe midline of your head that will cover a spot onthe tree. Now close your left eye, open the righteye without moving your head, and fixate the inkspot. Observe what object it covers in the land-scape, say, a chimney on a house. Open both eyesand fixate the ink spot binocularly. You will notethat the chimney, the tree, and the ink spot appearin a line behind each other, approximately in themidline of your head. All those objects are seenin the common visual direction of the two foveae,even though they may actually be widely sepa-rated in physical space (Fig. 2–8). If you nowplace the point of a fine object (e.g., the tip of apencil) between one eye and the ink spot, it willalso appear in line with the objects seen outside

FIGURE 2–8. Hering’s fundamental experiment. (Modi-fied from Ogle KN: Researches in Binocular Vision. Phila-delphia, WB Saunders, 1950.)


FIGURE 2–9. A, Title page of the volume by Francis Aguilonius, S.J., Six Books on Optics Useful toPhilosophers and Mathematicians, published in Antwerp, 1613. B, First page of book II of Aguilonius’volume, which deals with the horopter � 30.

the window. This simple experiment shows con-vincingly the discrepancies that may exist betweensubjective and objective physical space.

The Horopter

Determining the distribution of the correspondingretinal elements throughout the retina is lessreadily achieved. For a long time the idea pre-vailed that the distribution of the correspondingretinal elements was strictly geometric. If thiswere indeed true, then corresponding points wouldbe retinal elements having the same horizontaland vertical distance from the fovea in the rightand left halves of the retinas. The following men-tal experiment clarifies the concept. Place the tworetinas one on the other so that the two foveae andthe geometric horizontal and vertical meridianscoincide. Imagine a needle placed through the tworetinas anywhere within the area subserving thefield of binocular vision. The needle should strike

corresponding points in the two retinas. On theassumption that this is in fact the case, the horo-pter was determined theoretically.

Horopter is a very old term, introduced in 1613by Aguilonius1 in his book on optics (Fig. 2–9)even though the basic concept of the horopter hadbeen known since the times of Ptolemy.36 In mod-ern usage it is defined as the locus of all objectpoints that are imaged on corresponding retinalelements at a given fixation distance.

The determination of the total horopter surfacewas approached mathematically by Helmholtz44,vol. 3, pp. 460 ff, on the basis of assumptions about thegeometric distribution of the corresponding retinalelements and about the position of the subjectivevertical meridians. For our purpose, we need beconcerned only with the horizontal distribution ofcorresponding retinal elements and to consider thelongitudinal horopter curve. This is the lineformed by the intersection of the visual plane(with head erect and eyes fixating a point straight


FIGURE 2–9 Continued. C, Pages 110 and 111 of the volume of Aguilonius in which he introducesthe term horopter and defines it as the line that delimits and bounds binocular vision. The pertinentparagraph is indicated by a box. (From the copy of the book of Aguilonius at Dartmouth College’sBaker Library. Courtesy Dartmouth College Photographic Service, Hanover, NH.)

ahead in symmetrical convergence) with the ho-ropter surface.

The term longitudinal horopter is an inadequatetranslation of the German term Längshoropter.Boeder, in his 1952 translation of Tschermak-Seysenegg’s Einführung zur physiologischen Op-tik (Introduction to Physiological Optics), sug-gested the term horopter of horizontal correspon-dence.95, p. 134 This much better but somewhatcumbersome term has not found general accep-tance. The term longitudinal horopter refers tothe locus in space of object points imaged on‘‘subjective longitudes’’ of the retina.

VIETH-MÜLLER CIRCLE. If corresponding pointshave a geometrically regular horizontal distancefrom the two retinas, the longitudinal horoptercurve would be a circle passing through the centerof rotation of the two eyes and the fixation point(Fig. 2–10). This would be true because by thetheorem of inscribed circles any lines drawn from

two points on a circle to any other pair of pointson its circumference include equal angles, asshown in the insert (see Fig. 2–10). This wasfirst pointed out by Vieth99 and later taken up byMüller,72 and this circle, which is the theoreticalor mathematical horopter curve, is also known asthe Vieth-Müller circle (see Fig. 2–10).

EMPIRICAL HOROPTER CURVE. By actual exper-imental determinations of the horopter curve, He-ring45, 46 and his pupil Hillebrand47 could showthat the Vieth-Müller circle does not describe thelongitudinal horopter. The empirical horoptercurve is flatter than the Vieth-Müller circle (seeFig. 2–10). This means that the distribution of theelements that correspond to each other is not thesame in the nasal and temporal parts of the tworetinas (e.g., the right half of each retina). Thecharacteristics of the horopter for each individualvary within certain limits; each person has hispersonal horopter.


FIGURE 2–10. Vieth-Müller circle. VMC, empirical horopter; EH, objective frontoparallel plane; OFPP,fixation point; F, inset, law of inscribed circles. Object P on EH is seen singly, but object PO onVMC elicits double vision because of discrepancies between the empirical and theoretical horopter(see text).

The discrepancy between the theoretical ho-ropter (the Vieth-Müller circle) and the empiricallyestablished horopter curve (the so-called Hering-Hillebrand horopter deviation) might be attributedto disturbing optical properties of the ocular media.However, Tschermak-Seysenegg95 has shown con-clusively that this is not the case.

A great deal of work has been expended onexperimental studies of the horopter. Interestedreaders are referred to the books by Tschermak-Seysenegg95 and Ogle.75 Only the broad outlinesof the information resulting from this work andthe experimental techniques are discussed on page28, but first other phenomena of binocular visionmust be presented.

Physiologic Diplopia

All object points lying on the horopter curve stim-ulate corresponding retinal elements. By defini-tion, all points on the horopter curve are seensingly. Also by definition, all points not lying onthe horopter curve are imaged disparately and,with certain qualifications, are seen double. Thediplopia elicited by object points off the horopteris called physiologic diplopia.

Physiologic diplopia can be readily demon-strated to anyone with normal binocular vision.

Hold a pencil at reading distance in front of yourhead in its midplane and select a conspicuous,somewhat isolated object on the wall in line withthe pencil. Fixate the more distant object, and thepencil will be seen double. Shut alternately oneeye and then the other. The contralateral doubleimage of the pencil will disappear; that is, theimage on the left will disappear if the right eye isshut, and the one on the right will disappear if theleft eye is shut. In other words, when fixating adistant object, a nearer object is seen in crossed(heteronymous) diplopia. Crossed diplopia is ex-plained by the fact that the nearer object is seenin temporal (crossed) disparity with reference toits fovea (or to a corresponding element in periph-eral vision if the nearer object is located in theperiphery of the visual field). This is shown inFigure 2–11, A.

If one now fixates the pencil binocularly it willbe seen singly, but the more distant object doublesup. By again alternately closing each eye, onefinds that the ipsilateral double image vanishes.There is uncrossed (homonymous) diplopia be-cause the more distant object is imaged in nasal(uncrossed) disparity (Fig. 2–11, B).

Clinical SignificancePhysiologic diplopia, a fundamental property ofbinocular vision, has a twofold clinical significance.


FIGURE 2–11. Physiologic diplo-pia. A, Crossed (heteronymous)diplopia of the object p�, closerthan the fixation point F, imagedin temporal disparity. B, Un-crossed (homonymous) diplopiaof the object P, more distant thanthe fixation point F and imaged innasal disparity.

Occasionally a person accidentally will becomeaware of physiologic diplopia. Since double visionmust appear as an abnormal situation, the individ-ual likely will seek the help of an ophthalmologist.If the ophthalmologist cannot establish the pres-ence of an acute paresis of an extraocular muscleor any of the other causes of diplopia mentionedin this book, one must conclude that all the patienthas experienced is physiologic double vision. Theophthalmologist must attempt to explain to thepatient that physiologic diplopia is a characteristicof normal binocular vision and evidence that thepatient enjoys normal cooperation of the two eyes.This is not always easy. Apprehensive, neuroticpatients may not accept the explanation and willreinforce the annoyance by constantly looking fora second image ‘‘that should not be there.’’ Manypatients have spent considerable amounts ofmoney looking for an ophthalmologist who willfinally rid them of their diplopia.

This is the undesirable clinical aspect of physi-ologic diplopia. The desirable use that can bemade of physiologic diplopia is both diagnosticand therapeutic. In diagnosing binocular coopera-tion, the presence of physiologic diplopia indicatesthat the patient is capable of using both eyes incasual seeing and presumably does so. In orthoptictreatment of comitant strabismus, physiologic di-plopia is an important tool (see Chapter 24).

Suppression

Physiologic diplopia is not just a trick producedin vision laboratories. It is a phenomenon inherent

to normal binocular vision. The question arises,why are we not always aware of diplopia?

From the first moment in which binocular vi-sion is established, we become accustomed orconditioned to the arrangements provided for bin-ocular seeing and hence to physiologic diplopia.We learn how to disregard it, and unless someabnormal process interferes we are never awareof diplopia.

If a patient acquires an acute lateral rectusparesis in one eye, the eye turns in. An objectpoint fixated by the other eye is now imaged on anasally disparate area in the deviated eye. Conse-quently, the patient experiences uncrossed diplo-pia. If he or she has acquired a medial rectusparalysis, the eye turns out and the fixation pointis imaged in temporal disparity. The patient hascrossed diplopia. These forms of diplopia in pa-tients with acute paralytic strabismus are to beexpected from what is known about physiologicdiplopia and are a normal response of the sensorysystem to an abnormal motor situation.

As

binocular vision and ocular motility - semantic scholar€¦ · binocular vision and ocular...

Documents