Ebook Clinical orthoptics: Part 1

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Clinical Orthoptics

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Dedication
This book is dedicated to my family

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Clinical Orthoptics
Third Edition

Fiona J. Rowe
PhD, DBO, CGLI CertEd
Senior Lecturer, Directorate of Orthoptics and Vision Science,
University of Liverpool, Liverpool, UK

A John Wiley & Sons, Ltd., Publication

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This edition first published 2012
C 1997, 2004 by Blackwell Publishing Ltd
C 2012 by Wiley-Blackwell
Wiley-Blackwell is an imprint of John Wiley & Sons, formed by the merger of Wiley’s global Scientific,
Technical and Medical business with Blackwell Publishing.
Registered office:

John Wiley & Sons, Ltd, The Atrium, Southern Gate, Chichester,
West Sussex, PO19 8SQ, UK

Editorial offices:

9600 Garsington Road, Oxford, OX4 2DQ, UK
The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
2121 State Avenue, Ames, Iowa 50014-8300, USA

First edition published 1997 by Blackwell Science
Second edition published 2004 by Blackwell Publishing Ltd
Third edition published 2012 by Wiley-Blackwell

For details of our global editorial offices, for customer services and for information about how to
apply for permission to reuse the copyright material in this book please see our website at
www.wiley.com/wiley-blackwell.
The right of the author to be identified as the author of this work has been asserted in accordance with
the UK Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or
otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior
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brand names and product names used in this book are trade names, service marks, trademarks or
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vendor mentioned in this book. This publication is designed to provide accurate and authoritative
information in regard to the subject matter covered. It is sold on the understanding that the publisher
is not engaged in rendering professional services. If professional advice or other expert assistance is
required, the services of a competent professional should be sought.
Library of Congress Cataloging-in-Publication Data
Rowe, Fiona J.
Clinical orthoptics / Fiona J. Rowe.—3rd ed.
p. ; cm.
Includes bibliographical references and index.
ISBN 978-1-4443-3934-5 (pbk. : alk. paper)
I. Title.
[DNLM: 1. Ocular Motility Disorders–Outlines. 2. Craniosynostoses–Outlines.
3. Orthoptics–methods–Outlines. 4. Strabismus–Outlines. WW 18.2]
617.7’62–dc23
2011037444
A catalogue record for this book is available from the British Library.
Set in 10/12.5pt Sabon by Aptara R Inc., New Delhi, India
1 2012

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Contents

Preface
Acknowledgements
List of Figures
List of Tables
SECTION I

xi
xii
xiii
xvii
1

1

Extraocular Muscle Anatomy and Innervation
Muscle pulleys
Ocular muscles
Innervation
Associated cranial nerves
References
Further reading

3
3
5
10
12
15
16

2

Binocular Single Vision
Worth’s classification
Development
Retinal correspondence
Physiology of stereopsis
Fusion
Retinal rivalry
Suppression
Diplopia
References

Further reading

17
17
17
19
20
23
24
24
25
27
28

3

Ocular Motility
Saccadic system
Smooth pursuit system
Vergence system
Vestibular-ocular response and optokinetic response
Brainstem control
Muscle sequelae
Past-pointing
Bell’s phenomenon
References
Further reading

29
29

31
33
35
37
39
40
41
41
43


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Contents

Orthoptic Investigative Procedures

Visual acuity
Cover test
Ocular motility
Accommodation and convergence
Retinal correspondence
Fusion
Stereopsis
Suppression
Synoptophore
Aniseikonia
Fixation
Measurement of deviations
Hess charts
Field of binocular single vision
Uniocular field of vision
Measurement of torsion
Parks-Helveston three-step test
Diplopia charts
Bielchowsky phenomenon (dark wedge test)
Forced duction test
Forced generation test
Orthoptic exercises
References
Further reading

SECTION II

45
45
60

64
68
73
77
82
89
91
97
98
99
105
108
110
111
113
113
115
115
115
115
119
124
129

5

Heterophoria
Classification
Aetiology
Causes of decompensation

Esophoria
Exophoria
Hyperphoria/hypophoria
Alternating hyperphoria
Alternating hypophoria
Cyclophoria
Incomitant heterophoria
Hemifield slide
Investigation of heterophoria
Management
References
Further reading

131
131
131
132
132
132
133
133
133
133
133
133
134
135
136
137

6

Heterotropia
Esotropia
Factors necessary for development of binocular single vision
Constant esotropia with an accommodative element
Constant esotropia without an accommodative element
Accommodative esotropia

138
138
139
140
141
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Contents

vii

Relating to fixation distance
Exotropia
Hypertropia
Hypotropia
Cyclotropia
Dissociated vertical deviation
Dissociated horizontal deviation
Quality of life
Pseudostrabismus
References
Further reading

151
155
168
168
169
170
172
173
174
175
184

7

Microtropia

Terminology
Classification
Investigation
Management
References
Further reading

189
189
190
191
194
194
195

8

Amblyopia and Visual Impairment
Classification
Aetiology
Investigation
Management
Eccentric fixation
Cerebral visual impairment
Delayed visual maturation
PHACE syndrome
References
Further reading

197

197
197
198
199
205
205
206
207
207
212

9

Aphakia
Methods of correction
Investigation
Problems with unilateral aphakia
Management
References
Further reading

215
215
215
216
216
218
219

SECTION III

221

10

Incomitant Strabismus
Aetiology
Aid to diagnosis
Diplopia
Abnormal head posture
References
Further reading

223
223
225
226
227
230
231

11

A and V Patterns
Classification
Aetiology

232
232
232

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Contents

Investigation
Management
References
Further reading

236
238
241
243

12

Accommodation and Convergence Disorders
Accommodative disorders
Presbyopia – physiological
Presbyopia – premature (non-physiological)
Accommodative insufficiency
Accommodative fatigue
Accommodative paralysis
Accommodative spasm
Accommodative inertia
Micropsia
Macropsia
Convergence anomalies
Convergence insufficiency
Convergence paralysis
Convergence spasm
Specific learning difficulty
References
Further reading

245
245
245
246
247
248
248
249
250
251
251

251
252
254
254
254
255
257

13

Ptosis and Pupils
Ptosis
Marcus Gunn jaw-winking syndrome
Lid retraction
Pupils
References
Further reading

259
259
263
264
264
269
271

14

Neurogenic Disorders
III (third) cranial nerve

IV (fourth) cranial nerve
VI (sixth) cranial nerve
Multiple sclerosis
Acquired motor fusion deficiency
Non-accidental injury
Premature visual impairment
Ophthalmoplegia
References
Further reading

272
272
280
288
292
293
294
295
296
300
307

15

Mechanical Paralytic Strabismus
Congenital cranial dysinnervation disorders
Brown’s syndrome
Adherence syndrome
Moebius syndrome
Strabismus fixus syndrome

Thyroid eye disease

310
312
319
324
325
327
327


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Contents

ix

Orbital injuries
Blow-out fracture
Soft tissue injury

Supraorbital fracture
Naso-orbital fracture
Zygoma fracture
Conjunctival shortening syndrome
Retinal detachment
Cataract
Macular translocation surgery
References
Further reading

333
334
339
341
341
341
342
342
343
344
344
350

16

Myogenic Disorders
Thyroid eye disease
Chronic progressive external ophthalmoplegia
Myasthenia gravis
Myotonic dystrophy

Ocular myositis
Kearns–Sayre ophthalmoplegia
References
Further reading

354
354
354
355
358
358
359
359
361

17

Craniofacial Synostoses
Plagiocephaly
Brachycephaly
Scaphocephaly/dolichocephaly
Occipital plagiocephaly
Apert’s syndrome
Craniofrontonasal dysplasia
Crouzon’s syndrome
Pfeiffer syndrome
Saethre–Chotzen syndrome
Unicoronal syndrome
General signs and symptoms
Ocular signs and symptoms

Management
References
Further reading

362
362
362
362
362
363
363
363
363
364
364
364
365
365
366
367

18

Nystagmus
Aetiology
Classification
Investigation
Management
References
Further reading

368
368
368
373
375
378
380

19

Supranuclear and Internuclear Disorders
Saccadic movement disorders
Smooth pursuit movement disorders

382
382
384


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Contents

Vergence movement disorders
Gaze palsy
Optokinetic movement disorders
Vestibular movement disorders
Brainstem syndromes
Skew deviation
Ocular tilt reaction
Ocular investigation
Management options
References
Further reading
SECTION IV

Appendices

385
386
394
395
395
397
398
398
400

401
405
407

Diagnostic Aids

409

Abbreviations of Orthoptic Terms

418

Diagrammatic Recording of Ocular Motility

424

Diagrammatic Recording of Nystagmus

426

Glossary

428

Case Reports

441

Index

459


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Preface

Clinical Orthoptics has become established as a basic reference text providing
fundamental information on anatomy, innervations and orthoptic investigation,
plus diagnosis and management of strabismus, ocular motility and related visual
disturbances. As with previous editions, the third edition is not designed to provide
in-depth discussion of the content as it is recognised that this can be found in other
excellent texts, in systematic reviews and in journal literature.
Following the revision of previous editions, this third edition, in addition to many
of the original illustrations, contains new figures, tables and flowcharts designed to
enhance the written text. Reference and further reading lists for each chapter have
been extended and include up-to-date literature.
The layout of the text remains similar to that of the previous edition. Section I
concentrates on anatomy and innervations of extraocular muscles including muscle
pulley systems and associated cranial nerves. Ocular motility and orthoptic investigative techniques have been updated to include new assessments and reference to

normative data. Section II refers to concomitant strabismus and Section III to incomitant strabismus. There has been considerable revision to add new information
on conditions not previously included. A new chapter on craniofacial synostosis
syndromes has been added. Section IV includes an updated list of abbreviations
and glossary of definitions with additions to the information provided on diagnostic aids, flowcharts and illustrative case reports.


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Acknowledgements

Thanks are due to my colleagues and undergraduate students at the University of
Liverpool, whose discussions provoke enquiry and understanding of orthoptics.
Thanks are due to Addenbrooke’s Hospital, Cambridge, for permission to use patient photographs and to the patients and parents for their consent to use these
images. The glossary incorporates terminology from the British and Irish Orthoptic
Society, and thanks are due to the Society for permission to use the glossary terminology. Finally, a thank you to the team at Wiley-Blackwell, the publisher, for
their input to this text.


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List of Figures

1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8

3.1
3.2
3.3
3.4
3.5
3.6
3.7
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9

Orbital apex
Extraocular muscles
Medial rectus action
Lateral rectus action
Superior rectus action
Inferior rectus action
Superior oblique action
Inferior oblique action
Extraocular muscle insertions
Cardinal positions of gaze – position of main action of
extraocular muscles
Projection in normal retinal correspondence
Projection in abnormal retinal correspondence

Projection in heteronymous diplopia
Projection in homonymous diplopia
Horopter
Right convergent strabismus with suppression
Right convergent strabismus with pathological diplopia
Right convergent strabismus with paradoxical diplopia
Saccadic eye movement control pathways
Smooth pursuit eye movement control pathways
Vergence eye movement control pathways
Vestibulo-ocular and optokinetic response control pathways
Sagittal cross section of brainstem; schematic representation
Coronal cross section of brainstem; schematic representation
Sagittal view of cortical areas; schematic representation
Optics of visual acuity
Forced choice preferential looking
Teller cards
LogMAR test
LEA symbols
Snellen test
Sheridan Gardiner test
Kay’s pictures
Cardiff acuity cards

4
4
5
6
7
7
8

9
9
9
20
20
21
22
23
25
26
26
32
34
35
36
37
38
39
46
47
48
48
49
50
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51
52


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List of Figures

4.10
4.11
4.12
4.13
4.14
4.15
4.16
4.17
4.18
4.19
4.20
4.21
4.22
4.23
4.24

4.25
4.26
4.27
4.28
4.29
4.30
4.31
4.32
4.33
4.34
4.35
4.36
4.37
4.38
4.39
4.40
4.41
4.42
4.43
4.44
4.45
4.46
4.47
4.48
4.49
4.50
4.51
4.52
4.53

Vistech chart
LEA contrast numbers
Heidi contrast faces
Hypermetropia
Myopia
Astigmatism
Occluders
Fixation targets
Cover/uncover test in manifest strabismus
Cover/uncover test in latent strabismus
Alternate cover test
Rotation of the eye
Optokinetic nystagmus Drum
RAF rule
Flipper lenses
Bagolini glasses
Results with Bagolini glasses
Worth’s four lights test
Risley prism (a): Prism bars and loose prisms (b)
Response to overcome a base out prism
Lang two pencil test
Frisby stereotest
FD2 stereotest
Lang stereotest
TNO stereotest
Titmus/Wirt stereotest
Randot stereotest
Sbisa bar
Amsler chart
Synoptophore

Optics of the synoptophore
Maddox slides
Simultaneous perception slides
Fusion slides
Stereopsis slides: (a) gross stereopsis; (b) detailed stereopsis
Angle kappa
Angle kappa slide assessment
Fixation
Fusion response with 4 dioptre prism test
Suppression scotoma response with 4 dioptre prism test
Prism position
Hirschberg’s corneal reflections
Maddox rod
Maddox wing

55
55
56
57
57
58
60
61
62
63
63
65
67
69
70

74
74
75
79
79
84
84
85
86
87
88
88
89
91
92
92
93
94
95
96
96
97
98
99
99
101
103
103
105

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List of Figures

4.54 Hess screen
4.55 Lees screen
4.56 Arc perimeter
4.57 Goldmann perimeter
4.58 Octopus perimeter
4.59 Six vectors for uniocular rotations
4.60 Objective assessment of torsion
4.61 Diplopia chart of IV nerve palsy
4.62 Diplopia chart of VI nerve palsy
4.63 Bar reading
4.64 Stereograms
5.1
Post-fixational blindness
6.1
Classification of esotropia

6.2
Infantile esotropia
6.3
Intermittent fully accommodative esotropia
6.4
Intermittent convergence excess esotropia
6.5
Classification of exotropia
6.6
Constant exotropia
6.7
Intermittent distance exotropia
6.8
Hypertropia
6.9
Pseudostrabismus
8.1
Neutral density filter bar
11.1
A pattern
11.2
V pattern
14.1
Right III nerve palsy
14.2
Hess chart of right III nerve palsy
14.3
Hess chart of left inferior rectus palsy
14.4
Hess chart of right inferior oblique palsy

14.5
Left IV nerve palsy
14.6
Hess chart of left IV nerve palsy
14.7
Field of binocular single vision of left IV nerve palsy
14.8
Right VI nerve palsy
14.9
Hess chart of right VI nerve palsy
14.10 Field of binocular single vision of right VI nerve palsy
15.1
Duane’s retraction syndrome
15.2
Hess chart of Duane’s retraction syndrome
15.3
Field of binocular single vision of Duane’s retraction
syndrome
15.4
Right Brown’s syndrome
15.5
Hess chart of right Brown’s syndrome
15.6
Field of binocular single vision of right Brown’s syndrome
15.7
Thyroid eye disease
15.8
Hess chart of thyroid eye disease
15.9
Hess chart of unilateral thyroid eye disease

106
106
109
109
110
111
112
114
114
116
117
134
139
142
147
149
156
157
160
172
174
200
233
234
274
275
276
277
282

283
284
290
290
291
314
315
315
321
322
323
329
330
331

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List of Figures

15.10
15.11
15.12
15.13
15.14
18.1
18.2
18.3
19.1
19.2

Field of binocular single vision of thyroid eye disease
Left orbital floor fracture
Hess chart of left orbital floor fracture
Hess chart of right medial wall fracture
Field of binocular single vision of left orbital floor fracture
Nystagmus; early onset
Nystagmus; late onset
Nystagmus velocity
Hess chart of right internuclear ophthalmoplegia
Field of binocular single vision of right internuclear
ophthalmoplegia
19.3
Internuclear ophthalmoplegia and one and a half
syndrome – site of lesions
Chart 1 Eso-deviations

Chart 2 Exo-deviations
Chart 3 Microtropia

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335
336
337
337
369
371
374
388
389
390
415
416
416


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List of Tables

1.1
4.1
10.1
10.2
10.3
14.1
14.2

Primary, secondary and tertiary muscle actions
Age-related visual acuity norms
Differences between congenital and acquired defects
Differences between neurogenic and mechanical defects
Torticollis differential diagnosis
Differences of superior oblique and superior rectus palsy
Differences of unilateral and bilateral superior oblique palsy

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50
225
225
229
285
285


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SECTION I

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Extraocular Muscle Anatomy

and Innervation

This chapter outlines the anatomy of the extraocular muscles and their innervation
and associated cranial nerves (II, V, VII and VIII).
There are four rectus and two oblique muscles attached to each eye. The rectus
muscles originate from the Annulus of Zinn, which encircles the optic foramen and
medial portion of the superior orbital fissure (Fig. 1.1). These muscles pass forward
in the orbit and gradually diverge to form the orbital muscle cone. By means of a
tendon, the muscles insert into the sclera anterior to the rotation centre of the globe
(Fig. 1.2).
The extraocular muscles are striated muscles. They contain slow fibres, which
produce a graded contracture on the exterior surface, and fast fibres, which produce
rapid movements on the interior surface adjacent to the globe. The slow fibres contain a high content of mitochondria and oxidative enzymes. The fast fibres contain
high amounts of glycogen and glycolytic enzymes and less oxidative enzymes than
the slow fibres. The global layer of the extraocular muscles contains palisade endings in the myotendonous junctions, which are believed to act as sensory receptors.
Signals from the palisade endings passing to the central nervous system may serve
to maintain muscle tension (Ruskell 1999, Donaldson 2000).

Muscle pulleys
There is stereotypic occurrence of connective tissue septa within the orbit and
stereotypic organisation of connective tissue around the extraocular muscles
(Koornneef 1977, 1979). There is also stability of rectus extraocular muscle belly
paths throughout the range of eye movement, and there is evidence for extraocular
muscle path constraint by pulley attachment within the orbit (Miller 1989, Miller
et al. 1993, Clark et al. 1999). High-resolution MRI has confirmed the presence of
these attachments via connections that constrain the muscle paths during rotations
of the globe (Demer 1995, Clark et al. 1997). CT and MRI scans have shown
that the paths of the rectus muscles remain fixed relative to the orbital wall during
excursions of the globe and even after large surgical transpositions (Demer et al.

Clinical Orthoptics, Third Edition. Fiona J. Rowe.
C 2012 John Wiley & Sons, Ltd. Published 2012 by Blackwell Publishing Ltd.


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Clinical Orthoptics

Figure 1.1 Orbital apex.

1996, Clark et al. 1999). It is only the anterior aspect of the muscle that moves
with the globe relative to the orbit.
Histological studies have demonstrated that each rectus pulley consists of an
encircling ring of collagen located near the globe equator in Tenon fascia attached to
the orbital wall, adjacent extraocular muscles and equatorial Tenon fascia by slinglike bands, which consist of densely woven collagen, elastin and smooth muscle
(Demer et al. 1995, Porter et al. 1996). The global layer of each rectus extraocular
muscle, containing about half of all extraocular muscle fibres, passes through the
pulley and becomes continuous with the tendon to insert on the globe. The orbital

layer containing the remaining half of the extraocular muscle fibres inserts on the
pulley and not on the globe (Demer et al. 2000, Oh et al. 2001, Hwan et al. 2007).

Figure 1.2 Extraocular muscles.


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Extraocular Muscle Anatomy and Innervation

5

The orbital layer translates pulleys while the global layer rotates the globe through
its insertion on the sclera. The inferior oblique muscle also has a pulley that is
mechanically attached to the inferior rectus pulley (Demer et al. 1999).
The general arrangement of orbital connective tissues is uniform throughout
the range of human age from foetal life to the tenth decade. Such uniformity
supports the concept that pulleys and orbital connective tissues are important for the
mechanical generation and maintenance of ocular movements (Kono et al. 2002).

Ocular muscles
Medial rectus muscle
This muscle originates at the orbital apex from the medial portion of the Annulus
of Zinn in close contact with the optic nerve. It courses forward for approximately
40 mm along the medial aspect of the globe and penetrates Tenon’s capsule roughly
12 mm from the insertion. The last 5 mm of the muscle are in contact with the
eye and the insertion is at 5.5 mm from the limbus with a width of 10.5 mm. The
muscle is innervated by the inferior division of the III nerve, which enters the muscle
on its bulbar side. Its function is adduction of the eye (Fig. 1.3).

Lateral rectus muscle
This muscle arises by two heads from the upper and lower portions of the Annulus of Zinn where it bridges the superior orbital fissure. It courses forward for
approximately 40 mm along the lateral aspect of the globe and crosses the inferior
oblique insertion. It penetrates Tenon’s capsule at roughly 15 mm from the insertion and the last 7–8 mm of the muscle is in contact with the eye. The insertion is at

Figure 1.3 Medial rectus action.


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Clinical Orthoptics

Figure 1.4 Lateral rectus action.

7 mm from the limbus with a width of 9.5 mm. The muscle is innervated by the VI
nerve, which enters the muscle on its bulbar side. Its function is abduction of the
eye (Fig. 1.4).

Superior rectus muscle
This muscle arises from the superior portion of the Annulus of Zinn and courses
forward for approximately 42 mm along the dorsal aspect of the globe forming an angle of 23◦ with the sagittal axis of the globe. Superiorly, it is in close
contact with the levator muscle. It penetrates Tenon’s capsule at roughly 15 mm
from the insertion and the last few mms of the muscle are in contact with the
eye. The insertion is at 7.7 mm from the limbus with a width of 11 mm. The
muscle is innervated by the superior division of the III nerve, which enters the muscle on its bulbar side. Its functions are elevation, intorsion and adduction of the
eye (Fig. 1.5).

Inferior rectus muscle
This muscle arises from the inferior portion of the Annulus of Zinn and courses
forward for approximately 42 mm along the ventral aspect of the globe forming
an angle of 23◦ with the sagittal axis. It penetrates Tenon’s capsule roughly 15 mm
from the insertion and the last few millimetres of the muscle are in contact with the
eye as it arcs to insert at 6.5 mm from the limbus. The width of insertion is 10 mm.
The muscle is innervated by the inferior division of the III nerve, which enters the
muscle on its bulbar side. Its functions are depression, extorsion and adduction of
the eye (Fig. 1.6).

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Extraocular Muscle Anatomy and Innervation

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Figure 1.5 Superior rectus action. The course of the superior rectus is at an angle of 23◦ to
the medial wall of the orbit. Actions in adduction are principally intorsion and adduction; in the
primary position, actions are elevation, intorsion and adduction; action in abduction is
principally elevation.

Superior oblique muscle
This muscle originates from the orbital apex from the periosteum of the body
of the sphenoid bone, medial and superior to the optic foramen. It courses forward for approximately 40 mm along the medial wall of the orbit to the trochlea

Figure 1.6 Inferior rectus action. The course of the inferior rectus is at an angle of 23◦ to the
medial wall of the orbit. In adduction, the actions are principally extorsion and adduction; in
the primary position, actions are depression, extorsion and adduction; action in abduction is
principally depression.

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Clinical Orthoptics

Figure 1.7 Superior oblique action. The course of the superior oblique tendon is at an angle
of 51◦ to the medial wall of the orbit. Action in adduction is depression; in the primary
position, actions are depression, intorsion and abduction; in abduction, action is intorsion.

(a V-shaped fibrocartilage that is attached to the frontal bone). The trochlear region
is described by Helveston et al. (1982).
The muscle becomes tendonous roughly 10 mm posterior to the trochlea and is
encased in a synovial sheath through the trochlea. From the trochlea, it courses
posteriorly, laterally and downwards forming an angle of 51◦ with the visual axis
of the eye in the primary position. It passes beneath the superior rectus and inserts
on the upper temporal quadrant of the globe ventral to the superior rectus. Its
insertion is fanned out in a curved line 10–12 mm in length. The muscle is innervated by the IV nerve that enters the muscle on its upper surface roughly 12 mm
from its origin. Its functions are intorsion, depression and abduction of the eye

(Fig. 1.7).

Inferior oblique muscle
This muscle arises from the floor of the orbit from the periosteum covering the
anteromedial portion of the maxilla bone. It courses laterally and posteriorly for
approximately 37 mm, forming an angle of 51◦ with the visual axis. It penetrates
Tenon’s capsule near the posterior ventral surface of the inferior rectus, crosses
the inferior rectus and curves upwards around the globe to insert under the lateral
rectus just anterior to the macular area. The muscle is innervated by the inferior
division of the III nerve that enters the muscle on its bulbar surface. Its functions
are extorsion, elevation and abduction of the eye (Fig. 1.8).
Figure 1.9 illustrates the muscle insertions in relation to the anterior segment
of the eye. Figure 1.10 illustrates the positions of main action of each extraocular
muscle and Table 1.1 illustrates all primary, secondary and tertiary muscle actions.


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Figure 1.8 Inferior oblique action. The course of the inferior oblique is at an angle of 51◦ to
the medial wall of the orbit. Action in adduction is elevation; actions in the primary position

are elevation, extorsion and abduction; in abduction, action is extorsion.

Figure 1.9 Extraocular muscle insertions. SR, superior rectus; MR, medial rectus;
LR, lateral rectus; IR, inferior rectus.
SR

LR

RIGHT

IR

IO

IO

MR

MR

SO

SO

SR

LEFT

LR

IR

SR

Superior rectus

IR

Inferior rectus

LR

Lateral rectus

MR

Medial rectus

IO

Inferior oblique

SO

Superior oblique

Figure 1.10 Cardinal positions of gaze – position of main action of extraocular muscles.

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