Wright handbook of pediatric strabismus and amblyopia pdf download

Handbook of Pediatric Strabismus and Amblyopia

Handbook of Pediatric Strabismus and Amblyopia Edited by

Kenneth W. Wright, MD Director, Wright Foundation for Pediatric Ophthalmology Director, Pediatric Ophthalmology, Cedars-Sinai Medical Center, Clinical Professor of Ophthalmology, University of Southern California—Keck School of Medicine, Los Angeles, California

Peter H. Spiegel, MD Focus On You, Inc., Palm Desert, California Inland Eye Clinic, Murrieta, California Children’s Eye Institute, Upland, California

Lisa S. Thompson, MD Attending Physician, Stroger Hospital of Cook County, Chicago, Illinois

Illustrators Timothy C. Hengst, CMI Susan Gilbert, CMI Faith Cogswell

Kenneth W. Wright, MD Director, Wright Foundation for Pediatric Ophthalmology Director, Pediatric Ophthalmology, Cedars-Sinai Medical Center, Clinical Professor of Ophthalmology, University of Southern California—Keck School of Medicine Los Angeles, CA USA

Peter H. Spiegel, MD Focus On You, Inc. Palm Desert, CA Inland Eye Clinic, Murrieta, CA Children’s Eye Institute Upland, CA USA

Lisa S. Thompson, MD Attending Physician Stroger Hospital of Cook County Chicago, IL USA

Library of Congress Control Number: 2005932932 ISBN 10: 0-387-27924-5 ISBN 13: 978-0387-27924-4

e-ISBN 0-387-27925-4

Printed on acid-free paper. © 2006 Springer Science+Business Media, Inc. Reprinted from Wright and Spiegel: Pediatric Ophthalmology and Strabismus, second edition, 2003 Springer Science+Business Media. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, Inc., 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed in the United States of America. 987654321 springer.com

(BS/EB)

Preface

The Handbook of Pediatric Strabismus and Amblyopia is a practical, easy-to-understand resource on the diagnosis and management of both common and the more esoteric forms of strabismus. Emphasis is placed on the understanding of the basis of the strabismus, not rote memorization of strabismus patterns. Concepts regarding sensory adaptations and sensory testing are described in a simple way to elucidate rather than confuse the reader. An in-depth chapter on visual development and the pathophysiology of amblyopia is included. The goal of the Handbook of Pediatric Strabismus and Amblyopia is to make this often confusing subject simple and easy to understand. This book should make an excellent resource for board review. Chapters are reader friendly. They are organized with clear sub-headings that allow the readers to quickly find their area of interest. Diagrams and drawings are prevalent throughout the book to help illustrate otherwise difficult or complex concepts. Composite strabismus photographs are included to demonstrate the strabismus as it actually appears in the clinical setting and to help with pattern recognition. These composite strabismus photographs are very useful for board review. Each chapter is fully referenced to provide evidence-based practice guidelines and further in-depth reading. An important use of the handbook is patient and family education. Families are rightfully concerned about the strabismus and they have often been told conflicting and confusing information about it. Information, including diagrams and photographs from the handbook, can be shared with the families to clarify their specific type of strabismus. This important information is often lacking in general texts on ophthalmology. v

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preface

I hope you will find the Handbook of Strabismus and Amblyopia to be an invaluable adjunct to your practice and for board review. Kenneth W. Wright, MD

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

v ix

1 Pediatric Eye Examination . . . . . . . . . . . . . . . . . . Ann U. Stout

1

2 Anatomy and Physiology of Eye Movements . . . . Kenneth W. Wright

24

3 Binocular Vision and Introduction to Strabismus . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kenneth W. Wright

70

4 Visual Development and Amblyopia . . . . . . . . . . . Kenneth W. Wright

103

5 The Ocular Motor Examination . . . . . . . . . . . . . . Kenneth W. Wright

138

6 Sensory Aspects of Strabismus . . . . . . . . . . . . . . . Kenneth W. Wright

174

7 Esodeviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kenneth W. Wright

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8 Exotropia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kenneth W. Wright

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9 Alphabet Patterns and Oblique Muscle Dysfunctions . . . . . . . . . . . . . . . . . . . . . . Kenneth W. Wright

284

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contents

10 Complex Strabismus: Restriction, Paresis, Dissociated Strabismus, and Torticollis . . . . . . . . Kenneth W. Wright

323

11 Strabismus Surgery . . . . . . . . . . . . . . . . . . . . . . . . Kenneth W. Wright and Pauline Hong

388

12 Ocular Motility Disorders . . . . . . . . . . . . . . . . . . Mitra Maybodi, Richard W. Hertle, and Brian N. Bachynski

423

13 Optical Pearls and Pitfalls . . . . . . . . . . . . . . . . . . David L. Guyton, Joseph M. Miller, and Constance E. West

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Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

531

Contributors

Brian N. Bachynski, MD David L. Guyton, MD Richard W. Hertle, MD, FACS Pauline Hong, MD Mitra Maybodi, MD Joseph M. Miller, MD Ann U. Stout, MD Constance E. West, MD Kenneth W. Wright, MD

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1 Pediatric Eye Examination Ann U. Stout

THE HISTORY AND PHYSICAL EXAMINATION In the nonpediatric eye clinic, the physician often views the presence of a small child in an examining lane with some anxiety, if not dread. Examination of a child is quite different from that of the adult. The history is largely from a source other than the patient, and the examination requires patience and talent. There are several tricks to make the visit go as smoothly and efficiently as possible (see the box on the following page).

HISTORY Although ancillary personnel are often relied on to take the history, this is best obtained by the physician who knows how to direct the line of questioning to the most useful information. The old adage that “the patient is always right” is especially true in the case of parents’ observations about their children. Most of the history is obtained from the parents or the referring physician, but any input from the child is equally important. Many children will not complain of blurry vision or diplopia, but should they describe these symptoms one must be very alert to an acute process. This is also an invaluable time to observe the child in an unobtrusive fashion and preliminarily assess head position, eye alignment, and overall appearance. Often this may be the extent of the physical examination that one can obtain; once children realize that attention is focused on them, they may become very uncooperative. The problem precipitating the visit should be stated in the parents’ or child’s own words and then elaborated. Requisite 1

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questioning for all pediatric eye problems should clarify whether the problem is congenital or acquired and should specify the age of onset in the latter case. If the chief complaint is a visual problem, it is helpful for the parents to specify what the child can or cannot see; that is, does the child respond to lights, faces, toys near or far, very small items? In cases of strabismus, the frequency and stability of the deviation and any associated head posture are important. Precipitating factors may include fatigue, illness, sunlight, and close or distance work. For nystagmus, medications and the past medical history may be pertinent. With cataracts, any history of trauma, medications, or associated medical conditions is important, as well as the family history. Tearing patients need to be questioned about any redness, photophobia, or crusting of the lashes. In ptosis, the stability or variability is important, as is any associated chin elevation or general neuromuscular problems. For difficulties in school, it is helpful to determine if the problem is only visual or is related to a particular subject area (reading, spelling, writing, or math) and if there are any stress factors in the child’s extracurricular life. Important aspects of past history include prenatal and perinatal problems, birth weight, gestational age, and mode of delivery. Any medical problems should be elicited, as well as current medication and allergies. Early development should be assessed by asking about specific developmental milestones, such as rolling over, sitting up, and walking. The Denver Developmental Scale is a good reference for developmental norms.10 Later development can be ascertained by asking about scholastic level and performance. The family history is very important because often the young child does not have enough past history to be useful. The focus should be on the presence of strabismus, poor vision, and neurological problems. In the case of possible genetic disorders, the number and sex of siblings, possible consanguinity, and the number and gestational age of any miscarriages should be documented.

PHYSICAL EXAMINATION Establishing Rapport If you approach the examination with dread, the child will sense your personal tension and become uneasy. Children can be unpredictable, noncommunicative, and uncooperative, which

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may make the examination both time consuming and frustrating for a busy practitioner. However, if extra time is taken initially to gain the trust of the child, the rest of the exam will go much more easily. This “friendship” is often first established in the waiting room, where toys, appropriate books, and even small furniture should be made available. In a general practice seeing children on a fairly regular basis, at least one exam room should be outfitted to make a child feel relaxed and make the exam go more smoothly. A 20-foot lane is best because of the frequent use of single Allen cards and the need for distance measurements in strabismus. Attention-getting distance targets may include a remote control cartoon movie or a motorized animal. Near targets should have variety and appeal, as one frequently finds that “one toy–one look” is the rule. Approach young children as though you had come to play with and entertain them, and you will receive a lot of useful information in the process. Find out what they like to be called and use their name frequently, but speak softly and keep a respectful physical distance from them until they warm up to you. Also, find out from parents their favorite imaginary or cartoon characters and refer to these during your exam. Make a game of the exam; play peek-a-boo with cover testing, swoop near targets around like an airplane to evaluate the range of motility, refer to glasses and lenses used as “magic” or “funny

Useful Items for Pediatric Eye Exams Allen cards (single and linear) Wright figures (single and linear) Tumbling E (single and linear) Eye patches Interesting distance and near fixation targets Accommodative near targets (finger puppets, wiggle pictures) Portable slit lamp Papoose board Wire lid speculums (infant and child size) Loose retinoscopy lenses Loose prisms Fusional tests (Worth 4-Dot, Titmus or Randot, Bagolini lenses) 28-diopter lens Handheld tonometer (Perkins or Tonopen) Calipers

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sunglasses,” make funny sounds to get their attention. Do the noncontact things first: cover testing, fixation testing, pupillary and red reflex exam. Many small children object to physical contact by a stranger and once they are upset it is usually the end of the exam for the day. Sometimes they will more readily tolerate their parents placing glasses or a patch than a strange doctor. Remember, if you find yourself getting frustrated or impatient with a child in one area, stop and go on to some other aspect of the exam. With older children, asking direct questions about their hobbies, school, and family shows an interest in them and often distracts them from the anxiety of the exam. They often appreciate a handshake or pat on the knee. Explain to them what you are doing before you do it and be honest; avoid talking down to them. If they ask, do not tell them the mydriatic drops will not hurt, but explain that they will only sting for a minute, like swimming in a pool with chlorine.

Examination of the Uncooperative Child Sometimes, despite the best efforts, a child simply will not cooperate, and urgency of the problem or the need for further information may require physically restraining or sedating the child. A papoose board can be used to control a child up to around 5 years of age, depending on their size and strength. A lid speculum can then be used with a topical anesthetic to force the eyes open, although Bell’s phenomenon of the eyes often makes a thorough examination difficult, and crying can affect intraocular pressure measurements.

SEDATION For the child in whom relaxation is important, or when physical restraint seems too psychologically traumatic, as in older children, sedation should be used. The common modes of outpatient sedation include chloral hydrate (oral or suppository), Propofol infusion, or a combination injection of Demerol, Phenergan, and Thorazine (DPT). The first has the advantage of good sedation with a low level of respiratory depression and no effect on intraocular pressure (IOP). The latter two have analgesic as well as sedative properties, which may be useful in painful procedures, but there is slightly more respiratory depression and Propofol will lower IOP.24,37

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Although chloral hydrate is often not effective if the children are more than 2.5 years old, Propofol and DPT can be used in older children. Whenever sedatives are given, the child’s vital signs including pulse oximetry must be monitored until awake, ventilatory equipment must be available, and appropriately trained personnel should be in attendance. Any sedative may have a greater effect in children with underlying neurological abnormalities.

CHLORAL HYDRATE The minimal effective dose of chloral hydrate is 50 mg/kg, but often 80 to 100 mg/kg is needed if manipulation of the eyes is anticipated or if prolonged sedation is needed for electrophysiological testing.9,45,46 Half the initial dose can be repeated up to a maximum of 3 g if the child is not sedated in 30 min.22 Any sedative is best given on an empty stomach (4 h since eating) to increase absorption and decrease the risk of aspiration.

DPT DPT is given in a dose of 2 : 1 : 1 mg/kg, not to exceed 50 : 25 : 25. Because of the better analgesic effects, this is probably a better choice for painful procedures (laceration repairs, chalazion excisions, cryotherapy). Potential complications include respiratory depression, apnea, dystonic reactions, hypotension, seizures, and cardiac arrest.37 This mode of sedation should only be used when the child is under the supervision of a physician with appropriate training to manage complications, as in the emergency room.

EXAMINATION UNDER ANESTHESIA If it is impractical to sedate the child in the office, or if surgery is anticipated based on the exam findings, than examination under anesthesia should be arranged in the operating room. Modern anesthetic practices make general anesthesia a very safe procedure, even when done repeatedly. A disadvantage of general anesthesia is the purported intraocular pressure-lowering effects of inhalational anesthetics. Pressures taken under inhalational anesthetics have been lower than those measured in awake children, but this is probably a result of increased overall relaxation.13 Propofol has a similar effect on IOP.25 The pressure may actually increase several points after intubation.40 Use of laryngeal mask airways may eliminate this transient pressure rise.43 It is probably best to record the pressure both before and after intubation.

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External Examination The child’s overall appearance and level of alertness can be judged during the history taking. Head posture may also be noted then, as well as gross ocular alignment. The history or appearance may warrant more detailed examination of overall neuromuscular tone, cranial nerves, head circumference, extremities, or skin. The head may be assessed for symmetry, preauricular skin tags, ear position, and shape. The orbits should be appraised for ptosis, abnormalities in fissure size or shape, and orbital depth. Many of these findings do not require a systematic search but rather an overall heightened awareness of what is normal versus abnormal. The general assessment of a dysmorphic child should push the physician to more precisely define what abnormalities lead to that impression.

Visual Acuity Assessment: Preverbal To judge vision in the preverbal child, one must rely on the smallest age-appropriate target that will hold attention and on the difference, if any, between the two eyes. An appropriate target for a 1-year-old child may be a small finger puppet; but a 1-month-old may fixate only on a human face and do that rather unsteadily. Infants are unable to pursue targets smoothly until 6 to 8 weeks of age but instead will track using hypometric saccades.5 Targets with fine detail that require accommodation and focused attention are best for children over age 1, for even though accommodation is appropriate to target distance by age 3 to 4 months, the macula is still immature even at the age of 15 months.6 Children who have developed a pincer grasp can be asked to pick up small particles from the palm of your hand. Often cake sprinkles are useful because they are edible and such a target often ends up in the mouth.

FIXATION There are two types of fixation testing: monocular and binocular. In monocular fixation testing one assesses whether the patient fixes with the fovea (centrally) and the quality of fixation. Each eye should be occluded in turn and the smallest possible target that elicits a fixation response should be used. Monocular fixation should be assessed for three separate factors: quality and accuracy (good, fair, poor), location (central versus eccentric), and duration (maintained versus sporadic). Clinically, abbreviations

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are often used to describe fixation including GCM for good, central, and maintained, CSM for central, steady, and maintained, or FF for fix and follow. Eccentric fixation is an important sign as this shows that the patient is not fixing with the fovea and vision is in the range of 20/200 or worse. It is important to remember, when testing monocular fixation, that the fixation target should be slowly moved through the visual field to assess the quality of fixation. The target size and distance should be estimated and documented in the chart. It is important to be aware of the normal timetable for visual maturation, although this may vary widely with individuals. The newborn has only sporadic saccadic eye movements with very poor fix and follow; by 6 weeks, most infants will show some smooth pursuit and central fixation, and by 8 weeks the vast majority of infants will have central fixation with accurate smooth pursuit and easily demonstrate optokinetic drum responses.6 Smooth pursuit is asymmetrical until age 6 months of age, with monocular temporal to nasal pursuit being better than nasal to temporal pursuit. Tables 1-1 and 1-2 outline normal visual development. One should remember that there is a subgroup of patients who are otherwise normal yet show delayed visual maturation. However, even this group of patients should show improvement of visual function and should have central fix and follow by at least 6 months, with occasional delays up to 12 months of age. Binocular fixation preference compares the vision of one eye to the other. This test presumes that strong fixation preference in patients with strabismus indicates organic visual loss or

TABLE 1-1. Normal Visual Development. Pupillary light reaction present: 30 weeks gestation Blink response to visual threat: 2–5 months Fixation well developed: 2 months Smooth pursuit well developed: 6–8 weeks Saccades well developed (not hypometric): 1–3 months Optokinetic nystagmus (OKN) 1. Present at birth but with restricted slow-phase velocity. 2. Temporal to nasal monocular response better than nasal to temporal until 2–4 months. Accommodation appropriate to target: 4 months Stereopsis well developed: 3–7 months Contrast sensitivity function well developed: 7 months Ocular alignment stabilized: 1 month Foveal maturation complete: 4 months Optic nerve myelination complete: 7 months to 2 years

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TABLE 1-2. Age-Related Visual Acuity Estimates by Test Method. Technique

Birth

2 months

4 months

6 months

1 year

Age for 20/20 (months)

OKN FPL VEP

20/400 20/400 20/800

20/400 20/400 20/150

20/200 20/200 20/600

20/100 20/150 20/400

20/60 20/50 20/20

20–30 18–24 6–12

OKN, optokinetic nystagmus; FPL, forced-choice preferential looking; VEP, visual evoked potential.

amblyopia in the nonpreferred eye.12,48 Binocular testing has an advantage over monocular testing, because vision can be very poor (20/100 to 20/200) and the patient will still show essentially normal monocular fixation. Binocular fixation preference testing, however, will identify even mild amblyopia (two lines of Snellen acuity difference).44,47 It is important to assess monocular fixation before fixation preference testing to rule out the possibility of bilateral symmetrical visual loss in preverbal children. Fixation preference testing is very accurate for diagnosing amblyopia in children with large-angle strabismus.48 In patients with straight eyes or microtropias, binocular fixation preference testing can be done using the vertical prism test or induced tropia test.47 In patients with straight eyes, one does not know which eye is fixing; therefore, it is impossible to determine fixation preference. The vertical prism test induces a vertical deviation and therefore allows assessment of fixation preference. In patients with small-angle strabismus (less than 10–15 prism diopters), the induced vertical tropia dissociates peripheral fusion and eliminates any facultative suppression scotoma associated with the patient’s baseline ocular alignment. In turn, this eliminates the problem of overdiagnosis of amblyopia, previously described by Zipf.48 Fixation preference testing is a quick and accurate way of diagnosing amblyopia in clinical conditions such as anisometropic amblyopia, unilateral ptosis, postoperative congenital esotropia, and other conditions that could cause unilateral amblyopia.

OPTOKINETIC NYSTAGMUS Children with poor fixation to any targets as a result of either poor vision or central nervous system problems can be evaluated for the presence of optokinetic nystagmus (OKN) so long as they are able to generate saccades. Optokinetic nystagmus is an involuntary pursuit response to moving stripes filling up

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most of the visual field, so a response may be seen in infants who are merely uninterested in other targets. Response to a standard OKN drum implies vision of finger counting at 3 to 5 feet.16,17 One can also assess the damping of the induced vestibulo-ocular reflex. By spinning the child around, either in your arms or on a swivel chair, a vestibular nystagmus will be induced, despite the level of vision. If there is visual input once the spinning is stopped, the nystagmus should damp in 30 to 60 s due to the fixation reflex.

OTHER TESTS Many ingenious tests have been devised to try to better correlate the vision to a linear acuity and detect amblyopia. The most popular are forced-choice preferential looking (FPL) and pattern visual evoked potentials (PVEP). The preferential looking test using Teller acuity cards assesses grating acuity by presenting the child with high-contrast gratings of various spatial frequencies along with a paired blank card. Infants will naturally prefer to look at patterns if they can be seen, and the examiner assesses whether the child fixates on the pattern or not.36 This test reliably measures grating acuity, but it may take 20 to 30 min to perform and may be difficult to perform monocularly in children younger than 2 years old33 (Fig. 1-1). Although useful in the assessment of anisometropic or deprivation amblyopia, this test

FIGURE 1-1. Teller acuity preferential looking apparatus.

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FIGURE 1-2. Two Polaroid photogrpahs from MTI PhotoScreener, taken by a rotating flash. The white crescent in the pupils denotes a refractive error. The size and location of the crescent in each photo indicate the type and example of the problem. Findings: hyperopia,
2.00 D; astigmatism, 1.00 D. The displaced corneal light reflex demonstrates esotropia.

may underestimate strabismic amblyopia or decreased acuity secondary to macular disease, in which grating acuity may be much less affected than vernier and Snellen acuity. Therefore, although a detected difference confirms amblyopia, a normal test result does not rule out amblyopia.26 Fixation preference testing is more reliable in detecting strabismic amblyopia. PVEP measures the summed occipital cortical response to a pattern stimulus (Fig. 1-2). This method reflects the activity from the central retina and is therefore a good assessment of macular function.32 The resulting cortical potential can be evaluated by a trained electrophysiologist and Snellen acuity can be roughly estimated. The important parameters of the PVEP waveform are the amplitude and the latency of the spikes. The first major large positive deflection is the P1 spike, with a normal latency of 100 ms. Amblyopia diminishes the amplitude, as do uncorrected refractive error or organic problems. The difficulty in the test lies in the need for specially trained personnel to administer and interpret the test and the frequent need for seda-

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tion to get good results. Although the test can be administered while the child is awake, poor fixation may give artificially low results. In the sedated child (chloral hydrate), cycloplegia and appropriate refractive correction are necessary because retinal blur also affects test results.45,46 Despite these drawbacks, the test is often useful to monitor the progress of amblyopia therapy and to diagnose amblyopia in preverbal children.

Visual Acuity Assessment: Verbal OPTOTYPE Older children who are able to identify character shapes can be assessed with Allen cards, Wright figures, or Lea symbols.18 Often, a child who is not quite verbal, or is too shy to talk, can be asked to match a sheet of pictured figures to the displayed cards. The single cards are most useful in the beginning, because often the child does not attend well to distance targets such as projected figures. The child can also take a photocopy of the cards home to practice as a game with parents. It is best to start close to the child and work backward. In young children, the endpoint is more often demonstrated by a loss of attention than by an incorrect response. The disadvantage of single cards is that they cannot detect the crowding response that is so often seen in amblyopia. A child may test equally on single optotypes but show a marked discrepancy with linear optotypes.34 Once equal acuity is obtained on single cards, it is important to move to linear testing to confirm the findings. Both single and linear figures test only to the level of 20/30, which is adequate for children under the age of 3 years. The next step in preliterate testing is use of the tumbling E, Wright figures, or HOTV.18 With the “E game,” the child is asked to point his fingers in the direction of the “legs on the table.” Often, vertical orientations are more readily confused by children than horizontal directions, and this should be taken into account when determining the endpoint.39 The HOTV letters can be easily identified even if the full alphabet is not known. Again, single cards or linear projection can be used, the latter being best for amblyopia. These tests go to the 20/20 level and are slightly more challenging than picture cards. Once the child is literate, traditional Snellen letters can be used. For most children, this occurs around age 5 to 6, but do not confuse knowing the alphabet with being able to distinguish

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random letters. If in doubt about the reliability of letter testing, return to an easier test.

Visual Fields As soon as a child is able to fix steadily on a target, a rough estimate of visual fields can be obtained. Even if the child will not tolerate a patch, binocular fields can be checked for homonymous or bitemporal defects. Infants with good fixation will usually move to an interesting peripheral target once it comes into view as a result of the fixation reflex. The examiner captures the attention with a central target and then slowly brings in a peripheral target, watching for the first jump to the peripheral target. In this manner all four quadrants of the peripheral field can be tested. Patients with posterior optic pathway lesions that respect the vertical meridian will often ignore a peripherally advancing target until it crosses the midline and then suddenly move and pursue it. A slightly older child of 3 or 4 years may be able to respond accurately to finger counting by making a game of copying the examiner’s actions. Formal visual field testing such as Goldmann perimetry can sometimes be performed in preschool children. It is important to have a good idea of the suspected field loss and concentrate on these areas first. Usually the largest brightest target (V4e) is best, but smaller targets should be used if the child is capable of cooperating. Automated fields require prolonged concentration and steady fixation and are usually not reliable in children less than 9 to 10 years old. Some newer user-friendly programs are being developed that shorten testing time enough to make them more applicable for children (Welch Allyn; frequency doubling technology or FDT). The tangent screen is also not useful until reliable verbal responses can be made because it is difficult to monitor fixation.

Assessment of Color Vision in Children Although color vision testing is not often done in children, it helps in the diagnosis of decreased acuity of uncertain etiology and monitors progression in cases of macular degenerations or progressive optic neuropathies. Children on retinal toxic drugs also need to be evaluated. Congenital red-green color defects are often detected first by the pediatric ophthalmologist as an incidental finding. Screening questions are often useful in detecting

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these cases, which occur in 8% to 10% of the male population. The child may confuse green with brown crayons and purple with blue crayons; he may confuse yellow and red traffic lights or green and red lines on a paper. Often he will have no trouble accurately naming colors of large objects but will mistake smaller colored objects subtending less than 2°.5 The easiest way to screen for color vision defects is with color plates. There are two popular types of plates, which are each useful in specific situations. The Ishihara pseudoisochromatic color plates work on the principle of color confusion, which is common with dichromats and anomalous trichromats. These plates are extremely sensitive for red-green defects, which are usually congenital. Most acquired color defects show some loss in the blue-yellow range, and the Ishihara plates will miss these patients unless the loss has extended into the red-green range. The advantage of these plates is that they come in an illiterate form with geometric shapes that can be traced with a finger. This design is useful for children who do not know numbers but still requires the comprehension and fine motor skills of a 3- to 4-year-old. The Richmond pseudoisochromatic plates, formerly called American Optical Hardy-Rand-Rittler (AO-HRR) plates, work on color saturation and can detect both red-green and blue-yellow defects, making them more useful in acquired defects; unfortunately, these do not come in an illiterate format. Both tests use many two-digit numbers, which can intimidate young children, and often their responses are better if they are asked to name each digit separately. Another good test for children is the City University Color Vision Test (TCU test); this uses the colors in the Farnsworth D-15 in a book format, so that manipulation of the color discs is not necessary. Unfortunately, it is not the best test for screening, as 20% of color defectives will pass the test. In general, optic nerve disease is more likely to affect red-green perceptions, whereas retinal disease affects blue-yellow discrimination, although there are many exceptions to this rule.16,17

Assessment of Contrast Sensitivity Contrast sensitivity represents the minimal amount of contrast required to resolve various-sized objects from the background. As such, it is perhaps a more sensitive test of visual function than Snellen acuity, which only assesses high-contrast resolution. The contrast sensitivity threshold is the minimal amount

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of contrast required to detect sinusoidal gratings of different spatial frequencies. The contrast sensitivity function (CSF) is the curve obtained by plotting contrast sensitivity against spatial frequency. The peak of the curve is usually at three to four cycles per degree, although the maximal contrast sensitivity for each spatial frequency increases with age to stabilize in adolescence. Contrast sensitivity may show decrements in many disease processes despite a normal Snellen acuity, including cerebral lesions and multiple sclerosis.4 Amblyopes demonstrate a reduction in the CSF curve that may occur only at the peak (highfrequency loss) or throughout the curve (high- and low-frequency loss).20 This difference persists after Snellen acuity returns to normal and may be useful in detecting a continued need for amblyopia therapy.31A Occlusion therapy for amblyopia has also been shown to reduce contrast sensitivity in the dominant eye, even without decreased acuity, a type of mild occlusion amblyopia.24 Although testing previously required fairly complex equipment and was not suitable for young children, contrast sensitivity function can now be reliably measured on children over 4 years using the Vistech wall chart. The chart presents eight levels of contrast sensitivity (horizontal axis) for each of five levels of spatial frequency (vertical axis). The gratings are oriented in one of three directions,
15, 0, or 15, and the child imitates grating orientation with his hand as in the “E game.” The minimum contrast detectable at each spatial frequency is recorded and used to plot a contrast sensitivity function curve.

Red Reflex Evaluation of the red reflex is often forgone in adults because of the better sensitivity of other available tests; that is, visual acuity and high-power biomicroscopy of the anterior segment, lens and vitreous. In children, these tests may not be applicable for reasons of youth or lack of cooperation. Evaluation of and especially binocular comparison of the red reflex are invaluable in assessing media opacities or refractive aberrancies. The red reflex is best tested by staying far enough away from the child to illuminate both pupils with the same direct ophthalmoscope beam and comparing the quality and intensity of the reflexes between the two eyes. The exam should be done in dim illumination, to encourage pupil dilatation, and with the child’s attention focused in the distance, to avoid a near response. If the direct ophthalmoscope beam is too strong, the pupils will con-

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strict and the child will react to the brightness by blinking or turning away. It is important to assess the reflex both before and after dilation, especially if there is a visually significant opacity, to see how much of the undilated pupillary space is obscured. Dimming of the red reflex is also an important sign in early endophthalmitis after cataract or strabismus surgery. Bruckner described a useful test for strabismus using the red reflex from the direct ophthalmoscope. In the presence of strabismus, the red reflex will be brighter and the pupil will appear slightly larger in the deviated eye as the patient fixates on the light. This test can detect deviations as small as three prism diopters and is especially useful in evaluating postoperative alignment.38 The test can be carried a step further to evaluate amblyopia by narrowing the light beam and illuminating one eye at a time. Fixation with each eye should be steady on the light; if amblyopia is present, fixation may waver or the eye may remain deviated in the presence of strabismus. Photoscreening is a sophisticated application of the red reflex test. The MTI photoscreener creates a Polaroid picture of the red reflex that allows assessment of media opacities and refractive errors (see Fig. 1-2). Although not as sensitive as a traditional eye examination, it is a useful screening tool for general practitioners.29,30

Pupillary Examination Normal pupil size varies with age. The newborn has small, miotic pupils that increase to an average diameter of 7 mm by age 12 to 13 and then gradually decrease again throughout life. Reaction to light in infants is often difficult to assess due to the natural miosis and uncontrolled near response to the examination light. With careful observation, a small light response can be seen in addition to the near response, but care must be taken to not mistake one for the other. Older children should have the near response controlled as much as possible by a distance fixation target. If the examination light is too bright, the child will close his eyes; when necessary, they must be held open to get an adequate exam. It is important to rule out an afferent pupillary defect, especially with unilateral visual loss or strabismus. The swinging flashlight test is routinely used, as in adults, but care must be taken to aim the light directly into the pupil, especially in strabismus, or an artificial afferent defect may be produced because of incomplete retinal stimulation. It is important

16

handbook of pediatric strabismus and amblyopia

to remember that only dense amblyopia can produce an afferent defect and that even then it is barely detectable.31 Any afferent defect of significance in a patient with presumed amblyopia must be investigated further.

Slit Lamp Examination Although most young children who cannot cooperate with a slit lamp examination can be adequately evaluated with a muscle light, at times more detailed examination is mandatory. There are several handheld slit lamps, which have the advantage of being portable and useful in examining supine patients. The disadvantages are their cost and somewhat limited resolution. They are not very good for assessing mild intraocular inflammation or subtle corneal abnormalities, but they are the best alternative. There are several other more readily available magnifiers such as the direct and indirect ophthalmoscope, both of which can be focused on the anterior segment. Whichever source is used, the exam is still limited by the child’s resistance and movement, even while restrained. At times, sedation is required to obtain the necessary information. Often a child of 1 or 2 years will allow a quick look at the standard slit lamp; the key is to keep the light as dim as possible, have in mind what you most want to see, and look at that first.

Intraocular Pressure Measurements Certain children are more prone to develop elevated intraocular pressure, and these patients must have accurate measurements. Such patients include aphakes, those with any anterior segment anomaly, those with orbital vascular lesions, or those on steroids. Most children under 3 years will not cooperate with routine applanation tonometry and they must be supine (sedated or restrained). There are several useful handheld tonometers. The original Schiotz tonometer is easy to use and read but often is too large for the infant eye. It has the advantage of being less sensitive to pressures induced by lids or extraocular muscles but is more affected by ocular rigidity, which tends to be lower in infants. The Perkins tonometer is an applanation device using fluorescein and a split prism to assess the pressure. It is highly accurate at all ranges of pressure but requires some experience on the part of the examiner to read and is unreliable with an abnormal corneal surface. Contact must also be made directly

chapter 1: pediatric eye examination

17

on the cornea, which is often difficult in a struggling child with a good Bell’s phenomenon. The Tonopen is easier to use and can obtain approximate readings off the sclera or an irregular cornea, but it is not accurate at high or low pressures, and it is difficult to hear the tones that signal endpoint when the child is crying.23 The pneumotonometer is easy to use and does not require corneal contact, but the equipment is less portable than the other two. Struggling and crying both cause swings in the intraocular pressure, which must be taken into account, and pressures taken with a calm child are more accurate. Small infants who are drowsy will sometimes allow tonometry, especially if they are held in their mother’s arms and given a bottle or pacifier. Sedation may be necessary for truly accurate readings. Chloral hydrate has the advantage of not lowering the pressure, whereas inhalation anesthetics and Propofol can.3,25 If an exam under anesthesia is done, the pressure should be measured as soon as safely possible after induction because it will become artificially lower with time.13

Keratometry Assessment of corneal shape can be done qualitatively or quantitatively. Several conditions predispose to corneal astigmatism, which may be amblyogenic or require contact lens correction. Children with limbal dermoids or corneal scars may have poor retinoscopy reflexes, which make accurate assessment of astigmatism difficult. Placido’s disc is a keratoscope that images a series of concentric light rings on the cornea. The reflected image can be used to assess the axis of astigmatism and corneal regularity. It is handheld and nonthreatening to most children but only gives a rough qualitative assessment. More accurate measurements must be obtained with a keratometer; this may require a sleeping or sedated infant to get accurate readings, and the standard keratometer can be mounted on a special bar to use with supine infants.35 Such measurements are helpful for contact lens fitting. Alcon Corporation has produced a handheld keratometer that has been very helpful in the pediatric age group.

Dilatation and Cycloplegia Cycloplegia is essential to eliminate uncontrolled accommodation and adequately assess the refractive error in children. Several agents are available, but the adequacy of cycloplegia, not

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handbook of pediatric strabismus and amblyopia

the maximal pupil dilatation, is most important. Tropicamide is not a strong enough cycloplegic for young children; instead, cyclopentolate, homatropine, or atropine should be used. Cyclopentolate has the most rapid onset and shortest duration and thus lends itself to clinic use. For most children, one drop each of cyclopentolate 1% in combination with phenylephrine 2.5% is adequate.2 Lighter pigmented eyes may only require one or two applications, whereas darkly pigmented eyes may require more than three. For children less than 6 months old, it is safer to use diluted drops such as Cyclomidril (cyclopentolate 0.2% and phenylephrine 1%). Homatropine 5% is another choice used for clinic dilation, especially in darkly pigmented patients, but this drop lasts up to 3 days. Both cyclopentolate and homatropine produce maximal cycloplegia within 30 min to 1 h, but the former recovers within 1 day. Table 1-3 lists the various agents available and their effects. If cycloplegia seems inadequate, based on either pupil size or changing retinoscopy streak, it is best to use atropine; this is usually given to the parents to take home and administer. To avoid toxicity of frequently administered atropine, the drops are given twice a day for 3 days prior to the visit.15 For infants and very young children, the drops should be given only once a day to each eye, with one eye receiving one drop in the morning and the other eye receiving one drop at night. As an alternative, atropine 0.5% could be used. Atropine should not be given to children with possible heart defects or reactive airways. Punctal occlusion can be performed for 1 min after the drops to decrease systemic absorption. Parents should be alerted to discontinue the drops if signs of toxicity or allergy develop (flushing, tachycardia, fever, delirium, lid edema, redness of the eyes). Most cases of toxicity respond to discontinuation of the drops, but more severe cases can require treatment with subcutaneous physostigmine (Eserine), 0.25 mg every 15 min, until improvement occurs. This treatment is useful for toxicity with any of the antimuscarinic agents. The phenylephrine drops will occasionally cause blanching of the periocular skin, especially where the drop contacts the skin either by tears or a tissue; this is seen most often in infants and does not require treatment or discontinuation of the drops. For examination of premature babies, dilate with cyclomidril (combination of cyclopentolate and phenylephrine) and tropicamide 0.5%. Refraction is always an art, especially in a preverbal child. Care must be taken to control the working distance and the

0.5, 1, 2

2, 5

0.5, 1

Homatropine

Atropine

0.5, 1

Tropicamide

Cyclopentolate

2.5

Phenylephrine

Agent

Strength (%)

30–60

40–90

30–60

20–40

20

Maximum (min)

Mydriasis

7–14 days

1–3 days

6–24 h

2–6 h

2–3 h

Recovery time

TABLE 1-3. Cycloplegic/Mydriatic Agents in Children.

60–180

30–60

25–75

30

None

3–12 days

1–3 days

6–24 h

2–6 h

Recovery time

Cycloplegia Maximum (min)

Side effects

Flushing tachycardia, fever, delirium

Ataxia

Psychosis, seizure

Tachycardia, hypertension

chapter 1: pediatric eye examination

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handbook of pediatric strabismus and amblyopia

visual axis, or inaccurate readings will be taken. Expertise with loose trial lenses or a skiascopy rack is important as the phoropter is useless in small children. If the endpoint is unclear, it is best to get a second or even third reading, either by repeat refraction on another visit or by a second refractionist. There are several handheld autorefractors on the market now that show promise in pediatric application (Nikon Retinomax, Welch Allyn Suresight).1,8,42 Cycloplegia may still be necessary to optimize results.

Fundus Examination An adequate fundus examination is imperative for all children who present to the ophthalmologist. The extent of the fundus exam necessary will vary widely depending on the patient. For most patients visualization of the posterior pole (optic nerve and macula) is adequate; this is done quickly and easily in most children by keeping the indirect light low and not touching the child. A brief look may be all that is obtainable by this technique, but this is often adequate. The optic nerve can be examined in more detail with the direct ophthalmoscope if the examiner is unhurried and stays several inches away from the child. By staying focused on the retinal vessels, the observer can see the nerve as it wanders into view while the child is busy watching a distant target (moving targets, especially videos, work best for this). For more detailed fundus examination or examination of the periphery, sedation or restraints are usually needed because most children will not tolerate the examining light for extended periods of time. As fundus examination comes at the end of the clinic visit, the child may be sleeping, especially if they have taken a bottle after the eyedrops, and this makes the examination much easier. Children less than 2 years old can usually be restrained adequately to allow a thorough fundus examination, even to the periphery, whereas older children require examination under anesthesia if uncooperative.

References 1. Adams RJ, et al. Noncycloplegic autorefraction in infants and young children (ARVO abstract 2108). Investig Ophthalmol Vis Sci 2001; 42. 2. Altman B. Drugs in pediatric ophthalmology. In: Harley RD (ed) Pediatric ophthalmology. Philadelphia: Saunders, 1983.

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3. Ausinsch B, Graves SA, Munson ES, Levy NS. Intraocular pressures in children during isoflurane and halothane anesthesia. Anesthesiology 1975;42:167. 4. Beazley ID, Illingworth DF, Jahn A, Greer DV. Contrast sensitivity in children and adults. Br J Ophthalmol 1980;64:863. 5. Birch J, Chisholm IA, Kimear P, et al. Clincal testing methods. In: Pokorney J, Smith VC, Verriest G, Pinckers AJLG (eds) Congenital and acquired color vision defects. New York: Grune & Stratton, 1979. 6. Boothe RG, Dobson V, Teller DY. Postnatal development of vision in human and nonhuman primates. Annu Rev Neurosci 1985;8:495. 7. Breton ME, Nelson LB. What do color blind children really see? Guidelines for clinical prescreening based on recent findings. Surv Ophthalmol 1983;27:306. 8. el-Defrawy S, Clarke WN, Belec F, Pham B. Evaluation of a handheld autorefractor in children younger than 6. J Pediatr Ophthalmol Strabismus 1998;5:107. 9. Fox et al. Use of high dose chloral hydrate for ophthalmic exams in children: a retrospective review of 302 cases. J Pediatr Ophthalmol Strabismus 1990;27:242. 10. Frankenburg WK, Dodds JB. The Denver developmental screening test. J Pediatr 1967;71:181. 11. Fulton AB, Hansen RM, Manning KA. Measuring visual acuity in infants. Surv Ophthalmol 1981;25:352. 12. Dickey CF, Metz HS, Stewart SA, Scott WE. The diagnosis of amblyopia in cross-fixation. J Pediatr Ophthalmol Strabismus 1991;28:171. 13. Dominguez A, Banos MS, Alvarez G, et al. Intraocular pressure measurement in infants under general anesthesia. Am J Ophthalmol 1974; 78:10. 14. Dobson V, Teller DA. Visual acuity in human infants: a review and comparison of behavioral and electrophysiologic studies. Vision Res 1978;18:1469. 15. Gilman AG, Goodman LS, Gilman A. The pharmacological basis of therapeutics, 6th edn, 1980:11. 16. Glaser JS. Neuro-ophthalmologic examination: general considerations and special techniques. In: Glaser JS (ed) NeuroOphthalmology. Philadelphia: Lippincott, 1990. 17. Glaser JS. In: Glaser JS (ed) Neuro-Ophthalmology. Philadelphia: Lippincott, 1990. 18. Graf MH, Becker R, Kaufmann H. Lea Symbols: visual acuity assessment and detection of amblyopia. Graefe’s Arch Clin Exp Ophthalmol 2000;238:53. 19. Hered RW, Murphy S, Clanay M. Comparison of the HOTV and Lea Symbols chart for preschool vision screening. J Pediatr Ophthalmol Strabismus 1997;34:24. 20. Hess RF, Howell ER. The threshold contrast sensitivity function in strabismic amblyopia: evidence for a two type classification. Vision Res 1977;17:1049.

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21. Hoyt CS, Nickel BL, Billson FA. Ophthalmological examination of the infant. Dev Aspects Surv Ophthalmol 1982;26:177. 22. Judisch GF, Anderson S, Bell WE. Chloral hydrate sedation as a substitute for examination under anesthesia in pediatric ophthalmology. Am J Ophthalmol 1980;89:560. 23. Kao SF, Lichter PR, Bergstrom TJ, et al. Clinical comparison of the oculab tonopen to the Goldmann applanation tonometer. Ophthalmology 1987;94:1541. 24. Koskela PU, Hyvarinen L. Contrast sensitivity in amblyopia. III. Effect of occlusion. Acta Ophthalmol 1986;64:386. 25. Laurelti GR, Laurelti CR, Laurelti-Filho A. Propofol decreases ocular pressure in outpatients undergoing trabeculectomy. J Clin Anesth 1997;9:289. 26. Mayer DL, Fulton AB, Rodier D. Grating and recognition acuities of pediatric patients. Ophthalmology 1984;91:947. 27. McDonald MA. Assessment of visual acuity in toddlers. Surv Ophthalmol 1986;31:189. 28. McMillan F, Forster RK. Comparison of MacKay-Marg, Goldmann, and Perkins tonometers in abnormal corneas. Arch Ophthalmol 1975;93:420. 29. Oher WL, Scolt WE, Holgado SI. Photoscreening for amblyogenic factors. J Pediatr Ophthamol Strabismus 1995;32:289. 30. Simons BD, Siathowski RM, Schiffmen JC, Berry BE, Flynn JJ. Pedatric photoscreening for strabismus and refractive errors and a highrisk population. Ophthalmology 1999;106:1073. 31. Portnoy JZ, Thompson HS, Lennarson L, Corbett JJ. Pupillary defects in amblyopia. Am J Ophthalmol 1983;96:609. 31a. Rogers GL, Bremer DL, Leguire LE. The contrast sensitivity function and childhood amblyopia. Am J Ophthalmol 1987;104:64. 32. Sokol S. Visually evoked potentials: theory, techniques and clinical applications. Surv Ophthalmol 1976;21:18. 33. Sokol S, Hansen VC, Moskowitz A, et al. Evoked potential and preferential looking estimates of visual acuity in pedatric patients. Ophthalmology 1983;90:552. 34. Stuart JQ, Burian HM. A study of separation difficulty: its relationship to visual acuity in normal and amblyopic eyes. Am J Ophthalmol 1962;53:471. 35. Szirth B, Matsumoto E, Murphree AL, Wright KW. Attachment for the Bausch and Lomb keratometer in pediatry. J Pediatr Ophthalmol Strabismus 1987;24:186. 36. Teller DY, Morse R, Borton R, Regan D. Visual acuity for vertical and diagonal gratings in human infants. Vision Res 1974;14:1433. 37. Terndrup TE, Cantor RM, Madden MD. Intramuscular meperidine, promethazine, and chlorpromazine: analysis of use and complications in 487 pediatric emergency department patients. Ann Emerg Med 1989;18:528. 38. Tongue AC, Cibis GW. Bruckner test. Ophthalmology 1981;88: 1041.

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39. von Noorden GK. Symptoms in heterophoria and heterotropia and psychologic effects of strabismus. In: Klein EA (ed) Binocular vision and ocular motility. St. Louis: Mosby, 1990. 40. Watcha MF, Chu FC, Stevens JL, Forestner JE. Effects of halothane on intraocular pressure in anesthetized children. Anesth Analg 1990; 71:181. 41. Weiner N. Atropine, scopolamine, and related antimuscarinic drugs. In: Gilman AG, Goodman LS, Gilman A (eds) The pharmacological basis of therapeutics, 6th edn. New York: Macmillan, 1980. 42. Wesemann W, Dick B. Accuracy and accommodation capability of a handheld autorefractor. J Cataract Refract Surg 2000;26:62. 43. Whitford AM, Hone SW, O’Hare B, Magner J, Eustace P. Intraocular pressure changes following laryngeal mask airway insertion: a comparative study. Anesthesia 1997;52:794. 44. Wright KW, Edelman PM, Walonker F, Yiu S. Reliability of fixation preference testing in diagnosing amblyopia. Arch Ophthalmol 1986; 104:549–553. 45. Wright KW, Eriksen J, Shors TJ. Detection of amblyopia with P-VEP during chloral hydrate sedation. J Pediatr Ophthalmol Strabismus 1987;24:170–175. 46. Wright KW, Eriksen J, Shors TJ, Ary JP. Recording pattern visual evoked potentials under chloral hydrate sedation. Arch Ophthalmol 1986;104:718. 47. Wright KW, Walonker F, Edelman P. 10-diopter fixation test for amblyopia. Arch Ophthalmol 1981;99:1242. 48. Zipf RF. Binocular fixation pattern. Arch Ophthalmol 1976;94:401– 405.

2 Anatomy and Physiology of Eye Movements Kenneth W. Wright

OCULAR POSITION Within the orbit, the eye is suspended by six extraocular muscles (four rectus muscles and two oblique muscles), suspensory ligaments, and surrounding orbital fat (Fig. 2-1). A tug-of-war exists between the rectus and oblique muscles. The four rectus muscles insert anterior to the equator, and pull the eye posteriorly, while the two oblique muscles insert posterior to the equator providing anterior counterforces. Posterior orbital fat also pushes the eye forward. If rectus muscle tension increases, the eye will be pulled back causing enophthalmos and lid fissure narrowing. Simultaneous cocontraction of the horizontal rectus muscles in Duane’s syndrome, for example, can cause significant lid fissure narrowing and enophthalmos. In contrast, decreased rectus muscle tone causes proptosis and lid fissure widening. Conditions such as muscle palsies or a detached rectus muscle allow the eye to move forward and result in lid fissure widening. Rectus muscle tightening procedures such as resections tend to cause lid fissure narrowing whereas loosening procedures such as rectus recessions induce lid fissure widening. When the eye is looking straight ahead with the visual axis parallel to the sagittal plane of the head, the eye is in primary position. The vertical rectus muscles follow the orbits and diverge from the central sagittal plane of the head by 23°. Thus, the visual axis in primary position is 23° nasal to the muscle axis of the vertical rectus muscles (Fig. 2-2). This discrepancy between the vertical rectus muscle axis and the visual axis of the eye explains the secondary and tertiary functions of the vertical rectus muscles (see muscle functions, following). 24

Whitnall's lig. Superior oblique m. Levator palpebrae Müller's m. Superior rectus m. Intraconal fat

Lateral rectus m. Inferior rectus m.

Lockwood's lig. Extraconal fat

Inferior oblique m.

FIGURE 2-1. Side view of extraocular muscles. Note that the rectus muscles pull the eye posteriorly while the oblique muscles pull the eye anteriorly.

FIGURE 2-2. Diagram shows visual axis versus muscle/orbital axis. Note that the visual axes parallel the central sagittal plane, while the orbital axis of each eye diverges 23° from the visual axis.

25

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handbook of pediatric strabismus and amblyopia

The term position of rest refers to the position of the eyes when all the extraocular muscles are relaxed or paralyzed. Normally, the position of rest is divergent (i.e., exotropic), with the visual axis in line with the orbital axis. The eyes of a patient under general anesthesia are usually deviated in a divergent position.

OCULAR MOVEMENTS Ductions The term ductions is used to describe monocular eye movements without regard for the movement of the fellow eye (Fig. 2-3). Ductions result from an extraocular muscle contraction

A

B

E

C

F

D

G

FIGURE 2-3A–G. Diagram of ductions, which are monocular eye movements.

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chapter 2: anatomy and physiology of eye movements

TABLE 2-1. Extraocular Muscles.

Muscle Medial rectus Lateral rectus Superior rectus

Approximate muscle length (mm) Origin 40 40 40

Annulus of Zinn Annulus of Zinn Annulus of Zinn

Anatomic insertion (mm)

Tendon Arc of length contact (mm) (mm)

Action from primary position

5.5

4

6

Adduction

7.0

8

10

Abduction

8.0

6

6.5

6.5

7

7

26

12

1

15

Inferior rectus

40

Annulus of Zinn

Superior oblique

32

Inferior oblique

37

Orbit apex From above temporal annulus pole of of Zinn superior rectus to within 6.5 mm of optic nerve Lacrimal Macular fossa area

Elevation Adduction Intorsion Depression Adduction Extorsion Intorsion Depression Abduction

Extorsion Elevation Abduction

that pulls the scleral insertion site toward the muscle’s origin while the opposing extraocular muscle simultaneously relaxes. The contracting muscle is referred to as the agonist and the relaxing muscle as the antagonist. An upward movement of an eye is referred to as supraduction or sursumduction, a downward movement is termed infraduction or dorsumduction, a nasal-ward movement is termed adduction, and a temporal movement is termed abduction. Torsional rotations (twisting movements) are known as cycloductions, with incycloduction (intorsion) referring to a nasal rotation of the 12 o’clock position of the cornea and excycloduction (extorsion) referring to a temporal rotation of the 12 o’clock position.

Muscle Action Versus Field of Action The terms “muscle action” and the “field of action” are often confused. Muscle action refers to the effect of muscle contraction on the rotation of the eye when the eye starts in primary position. Table 2-1 lists the muscle actions of each extraocular muscle. Horizontal rectus muscles have but one action: horizontal rotation of the eye. Vertical rectus and oblique muscles,

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handbook of pediatric strabismus and amblyopia

however, have three actions: vertical, horizontal, and torsional. The most robust action is termed the primary action, followed by the less obvious secondary and tertiary actions. It is important to remember the classic descriptions of primary, secondary and tertiary muscle actions as they relate to the eye when it is in primary position. In contrast, the field of action of a muscle is the position of gaze when an individual muscle is the primary mover of the eye. Granted, virtually all eye movements are the result of combined contraction and relaxation of multiple muscles, but there are eight positions of gaze where one muscle provides the dominant force (Fig. 2-4). For example, when one looks up, the brain recruits both the superior rectus and the inferior oblique muscles. Looking up and nasal, however, is the primary function of the inferior oblique muscle, so this is the field of action of the inferior oblique muscle. A muscle’s function is best evaluated by having the patient look into the field of action of the

FIGURE 2-4. Diagram of the field of action of the extraocular muscles. Arrows point to the quadrant where the specified muscle is the major mover of the eye. SR, superior rectus; IR, inferior oblique; MR, medial rectus; SO, superior oblique; IO, inferior oblique; IR, inferior rectus; LR, lateral rectus.

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muscle. Thus, even though the secondary action of the inferior oblique muscle is abduction, evaluate inferior oblique function by having the patient look “up and nasal.” A patient with an inferior oblique palsy will show limitation of eye movement up and nasal. Note, for straight upgaze, the superior rectus muscle is the major elevator, and for straight down-gaze the inferior rectus is the major depressor, with the oblique muscles contributing little.

Smooth Pursuit Versus Saccadic Eye Movements There are two basic forms of eye movements: smooth pursuit and saccadic. Smooth pursuit eye movements are generated in the occipital parietal temporal cortex, with the right cortex controlling movements to the right and the left cortex controlling movements to the left. In humans, smooth pursuit first occurs at 4 to 6 weeks of age. These are slow accurate eye movements requiring visual feedback from central foveal fixation. Smooth pursuit eye movements can follow visual targets moving at velocities up to 30° per second (30°/s). Clinically, accurate smooth pursuit indicates central fixation and in preverbal children is an indication of good vision. Saccadic movements are rapid eye movements with velocities usually ranging from 200° to 700°/s, but saccades have been recorded up to 1000°/s. The peak velocity increases as the amplitude of the movement increases, and this relationship is termed the main sequence. Saccades are movements used to keep up with targets moving too fast for smooth pursuit and for quick refixation from one target to another. Saccadic eye movements develop before smooth pursuits, occurring as early as 1 week of age. Saccadic eye movements are generated in the frontal lobes and are under contralateral control; that is, right frontal lobe stimulation will result in a saccadic eye movement to the left. Saccadic movements can be voluntarily initiated, but they are not voluntarily controlled, and there is no significant visual feedback to adjust the amount of movement. It is thought that the amplitude of a saccadic movement is preprogrammed based on the degree of retinal eccentricity of the target; this is why saccadic movements are termed ballistic, analogous to the ballistic trajectory of a cannon ball. The neuronal signal that initiates a saccade consists of a burst of high-frequency discharge or pulse to the agonist and inhibition of the antagonist. Because all neurons available are activated for eye movements greater than

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handbook of pediatric strabismus and amblyopia

5°, the magnitude of a saccade is determined by the duration of the pulse. At the end of a saccade, tonic neuronal firing of the agonist and antagonist muscles occurs to hold the eye position referred to as the step. Vision during a saccadic eye movement is suspended or suppressed. Some have used the term saccadic omission for the process of cortical suppression.1 A tremendous force is required to produce a saccadic eye movement; therefore, the presence of saccadic eye movements indicates “good” muscle function. Only rectus muscles generate saccadic eye movements. When evaluating a patient with limited ductions, look for the presence of a normal saccadic eye movement into the field of limited ductions. If there is a brisk saccade in the direction of the limitation, this indicates good muscle function and suggests the limited movement is caused by restriction, not a muscle paresis. Optokinetic nystagmus (OKN) can be generated by a slowly rotating drum with stripes and used to evaluate smooth pursuit and saccadic eye movements. As the drum rotates toward the patient’s right, there is a smooth pursuit eye movement to the right to follow the stripe. As the end of the stripe passes, there is a fast saccadic movement to the left to refixate on the next stripe. At target velocities less than 30°/s, smooth pursuit keeps pace with the target. At velocities between 30° and 100°/s, smooth pursuit movements progressively lag behind the target. At velocities greater than 100°/s, OKN is not evoked. OKN can be used to evaluate saccadic and smooth pursuit eye movements. Look at the fast phase of OKN to evaluate saccadic movements and the slow phase to evaluate smooth pursuit.

ANATOMY OF THE EYE MUSCLES Rectus Muscles The four rectus muscles originate at the orbital apex at the annulus of Zinn and course anteriorly to insert on the anterior aspect of the globe. The “straight” course of the rectus muscles gives rise to the term rectus. The rectus muscle insertions form a progressive spiral termed the spiral of Tillaux around the corneal limbus. The medial rectus muscle is the closest to the limbus (5.5 mm), then the inferior rectus (at 6.5 mm), the lateral rectus (at 7.0 mm), and the superior rectus is the furthest from the limbus (8.0 mm). The muscle–scleral insertion line has

chapter 2: anatomy and physiology of eye movements

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FIGURE 2-5. Diagram of distance of the rectus muscle insertions from the limbus (in millimeters, mm). Note that the medial rectus muscle inserts closest to the limbus and the distances increase, going counterclockwise from the medial rectus toward the superior rectus, which inserts furthest from the limbus.

a horseshoe configuration with the rounded apex pointing toward the cornea (Fig. 2-5). One can remember this as the horseshoes are always galloping toward the cornea. The scleral thickness behind the rectus insertions is the thinnest of the eye, being only 0.3 mm thick. Hooking a rectus muscle requires passing the hook several millimeters behind the central muscle insertion to clear the posterior aspect of the horseshoe insertion. The widths of the insertions are all approximately 10 mm, and the distance between insertions or intermuscle spacing is only 6 to 8 mm. Because of the proximity of the rectus muscle insertions, it is easier than you might think to hook the wrong muscle during strabismus surgery. An important number to remember is the rectus muscle length, which is 40 mm for all rectus muscles and is also the length of the orbit. Rectus muscles are innervated from the intraconal side of the muscle belly at the junction of the anterior two-thirds and posterior one-third of the muscle.

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handbook of pediatric strabismus and amblyopia

HORIZONTAL RECTUS MUSCLES The horizontal rectus muscles consist of the medial and lateral rectus muscles. In primary position, each muscle has one action: the medial rectus is an adductor and the lateral rectus is an abductor (Fig. 2-6). When the eye elevates or depresses away from primary position, however, the horizontal rectus muscles take on secondary vertical functions. When the eye is “up,” the horizontal rectus muscles take on a secondary action of supraduction, and when the eye is “down,” the secondary action is infraduction (Fig. 2-7). In addition, if one surgically transposes a horizontal rectus muscle insertion up, the muscle becomes an elevator in addition to the horizontal function. Supraplacing the horizontal rectus insertions during strabismus surgery will induce a hyperdeviation whereas infraplacement induces a hypodeviation. Vertically displacing the medial and lateral rectus muscle insertion is an excellent way to correct small vertical deviations when performing a recession/resection procedure. In Duane’s syndrome, the common finding of upshoot and downshoot is probably caused by the secondary elevator and depressor actions of the cocontracting horizontal rectus

FIGURE 2-6. Diagram of simple function of the medial rectus (MR) and lateral rectus (LR) muscle with the eye in primary position.

chapter 2: anatomy and physiology of eye movements

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A

B

C FIGURE 2-7A–C. Diagram of secondary actions of the medial rectus when the eye rotates up or down. These secondary actions also relate to the lateral rectus. (A) Globe rotated superiorly; now the medial rectus acts as an elevator in addition to its adduction or horizontal function. (B) In the center part of the figure, the medial rectus is a pure adductor. (C) Globe rotated down; in this position, the medial rectus acts as a depressor and an adductor.

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handbook of pediatric strabismus and amblyopia

muscles. Remember, the secondary vertical functions of the horizontal rectus muscles occur only when the eye is rotated vertically off primary position.

MEDIAL RECTUS MUSCLE The medial rectus muscle is innervated by the lower division of the oculomotor nerve (third cranial nerve) and, in primary position, is a pure adductor. The medial rectus is uniquely diminutive. It has the shortest arc of scleral contact (6 mm) and the shortest tendon length of the rectus muscles (4 mm). The inferior oblique muscle actually has the shortest tendon (1 mm) of the extraocular muscles, but it is not a rectus muscle. (Be careful; this could be the basis of a trick question.) Of the extraocular muscles, the medial rectus inserts closest to the limbus and is therefore susceptible to insult during anterior segment surgical procedures. Inadvertent removal of the medial rectus muscle is a well-known complication of pterygium removal. The medial rectus is also unique, as it is the only rectus muscle without fascial connections to an adjacent oblique muscle. This lack of oblique muscle connection makes the medial rectus the most difficult to surgically retrieve if lost. Once disinserted, the medial rectus is free to retract completely off the globe into the orbital fat, making retrieval extremely difficult and, in some cases, almost impossible.

LATERAL RECTUS MUSCLE The lateral rectus muscle is innervated by the sixth cranial nerve and is a pure abductor. In direct contrast to the medial rectus muscle, the lateral rectus has the longest tendon (8 mm) and the longest arc of scleral contact (10 mm) of the rectus muscles. Be careful, the “longest” cited above refers to only rectus muscles, as the superior oblique tendon has the longest arc of contact and tendon length of all the extraocular muscles. (This could be the source of another trick question.) The long arc of contact occurs because the lateral rectus muscle initially has a divergent course following the lateral wall of the orbit. Then, in the anterior orbit, it turns nasally, wrapping around the globe to its scleral insertion point (see Fig. 2-6). This temporal to nasal wrap around the globe accounts for the long arc of contact. The inferior border of the lateral rectus muscle courses above the inferior oblique insertion, and there are connective tissue bands connecting the lateral rectus muscle to the inferior oblique muscle.13 This is an important anatomic relationship, because a lost lateral rectus

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muscle will come to rest at the insertion of the inferior oblique muscle. The surgeon can often find a lost lateral rectus muscle by tracing the inferior oblique muscle back to its insertion.

VERTICAL RECTUS MUSCLES

EA XIS

VISUAL AXIS

The superior and inferior rectus muscles are the vertical rectus muscles and are the major elevators and depressors of the eye, respectively. The vertical rectus muscles have secondary and tertiary actions because, in primary position, the muscle axis is 23° temporal to the visual axis of the eye (Figs. 2-2, 2-8A).

MU

SC L

23°

TEMPORAL VI MUSUA SC L & LE A

XIS

NASAL

MU SC LE

AX IS

A

B

VISUAL AXIS

C FIGURE 2-8A–C. Functions of the vertical rectus muscles with the eye in various positions of gaze. (A) The eye is in primary position with the visual axis 23° nasal to the muscle axis. (B) The eye is abducted 23° from the primary position, and the visual axis is in line with the muscle axis. (C) The eye is abducted more than 23° from the primary position, and the visual axis is now temporal to the muscle axis.

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handbook of pediatric strabismus and amblyopia

Their secondary action is adduction, and it occurs because the vertical rectus muscles pull the front of the eye nasal to the visual axis. Tertiary actions are torsional, consisting of intorsion for the superior rectus muscle and extorsion for the inferior rectus muscle. These secondary and tertiary muscle actions are dependent on eye position. If the eye is abducted 23°, for example, the muscle and visual axes will be in line, and the vertical rectus muscles lose their secondary and tertiary actions, leaving only their vertical actions (Fig. 2-8B). In this position of 23° abduction, the superior rectus acts purely as an elevator, and the inferior rectus purely as a depressor. With further abduction past 23°, the secondary and tertiary actions of the vertical rectus muscles return, but they are different. The secondary action for both vertical rectus muscles becomes abduction, and the tertiary functions reverse, becoming extorsion for the superior rectus and intorsion for the inferior rectus muscle (Fig. 2-8C).

SUPERIOR RECTUS MUSCLE The upper division of the oculomotor nerve innervates the superior rectus muscle. It is the major elevator of the eye, and its actions include supraduction (primary), adduction (secondary), and intorsion (tertiary). The superior rectus muscle overlies the superior oblique tendon and has connective tissue connections to the superior oblique tendon below and the levator palpebrae muscle above (Fig. 2-9). This anatomic relationship to the levator palpebrae is important because a large superior rectus recession can cause upper lid retraction and lid fissure widening. On the other hand, a superior rectus resection pulls the upper lid down, resulting in lid fissure narrowing. Lid fissure changes associated with superior rectus surgery can be minimized by surgically removing the fascial connections between the levator and the superior rectus muscles.

INFERIOR RECTUS MUSCLE The inferior rectus muscle is innervated by the lower division of the oculomotor nerve and is the principal depressor of the eye. Actions of the inferior rectus muscle include infraduction (primary), adduction (secondary), and extorsion (tertiary). The inferior rectus is sandwiched between the inferior oblique below

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FIGURE 2-9. Diagram of the eye and orbit from a top view looking down on the superior rectus (SR) muscle. Note that the superior rectus muscle overlies the superior oblique (SO). T, temporal; N, nasal.

and the sclera above (Fig. 2-10). The fascial connection between the inferior rectus muscle, the inferior oblique muscle, and the lower lid retractors (capsulopalpebral fascia) is termed Lockwood’s ligament (Fig. 2-11).17 These fascial connections are responsible for the eyelid changes that often occur after inferior rectus surgery. An inferior rectus recession results in lower lid retraction with lid fissure widening, and a resection causes lid advancement with lid fissure narrowing. If the inferior rectus is inadvertently disinserted or lost during surgery, these connections will hold the inferior rectus to the inferior oblique and keep it from retracting posteriorly. The surgeon who is in search of a lost inferior rectus muscle can usually find it lying between the inferior oblique and sclera.

FIGURE 2-10. Diagram of the eye and orbit viewed from below. Note that the inferior oblique (IO) underlies the inferior rectus (IR) muscle.

Conjunctiva Tarsus

Fornix Tenon's capsule

Orbicularis m.

Inf. rectus m.

ITM CPF Orbital septum CPH Lockwood's lig. Inf. oblique m.

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FIGURE 2-12. Diagram of the superior oblique (SO) muscle and tendon. The functional muscle axis extends from the trochlea to the superior oblique insertion. The muscle axis is 54° nasal to the visual axis.

OBLIQUE MUSCLES Like the vertical rectus muscles, the oblique muscles have primary, secondary and tertiary actions. In the case of the oblique muscles, this is because the functional muscle axis is approximately 50° nasal to the visual axis, and the insertion extends posterior to the equator of the eye (Figs. 2-12, 2-13). By

FIGURE 2-11. Diagram of the relationship between the inferior rectus, inferior oblique, lower lid retractors, and Lockwood’s ligament. The inferior tarsal muscle (ITM) courses from the posterior border of the tarsus toward the inferior oblique muscle. It then passes between the inferior oblique muscle and the inferior rectus muscle to insert at the capsulopalpebral head (CPH). The CPH extends posteriorly to connect the inferior oblique to the inferior rectus muscle. The capsulopalpebral fascia (CPF) is the anterior extension of the CPH and courses from the inferior oblique anteriorly to the tarsus along with the ITM. “Lockwood’s ligament” (Lockwood’s lig.) consists of these fascial attachments that connect the lower lid, inferior rectus, and inferior oblique muscles.

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handbook of pediatric strabismus and amblyopia

FIGURE 2-13. Diagram of the inferior oblique (IO) from a view from below. The inferior oblique muscle axis is 51° nasal to the visual axis.

comparing Figures 2-12 and 2-13, one can see that the oblique muscles have an almost identical functional course with both muscle axes at approximately 50°. The posterior muscle–scleral insertion gives the oblique muscles their seemingly paradoxical vertical functions, with the superior oblique being a depressor and the inferior oblique an elevator. The oblique muscles have no anterior ciliary blood supply, and they do not contribute to the anterior segment circulation. Remember that the “oblique muscles always course below the corresponding vertical rectus muscle” (Fig. 2-14).

SUPERIOR OBLIQUE MUSCLE The primary action of the superior oblique muscle is intorsion, but it also acts as a depressor (secondary) and an abductor (tertiary). Depression and abduction occur as the back of the eye is pulled up and in toward the trochlea. The superior oblique

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muscle originates at the orbital apex just above the annulus of Zinn and gradually becomes tendon at the trochlea (see Fig. 2-12). After passing through the trochlea, the superior oblique tendon reverses course and turns in a posterior temporal direction to pass under the superior rectus muscle to insert on sclera along the temporal border of the superior rectus muscle (Fig. 2-14). Even though the anatomic origin is at the apex of the orbit, the functional origin of the superior oblique is at the trochlea. This tendon is the longest tendon of the extraocular muscles, 26 mm in length. The tendon insertion fans out broadly under the superior rectus muscle, extending from the temporal pole of the superior rectus muscle to 6.5 mm from the optic nerve.13 Fascial attachments connect the superior oblique tendon to the superior rectus muscle above and to the sclera below.13 The tendon insertion can be functionally divided into two basic parts: the anterior one-third and the posterior two-thirds. Posterior fibers are responsible for depression and abduction whereas tendon fibers anterior to the equator are devoted to intorsion. This distinction between anterior and posterior superior oblique tendon fibers is important because one can

FIGURE 2-14. Diagram of posterior anatomy of the eye and muscles. Note the proximity of the inferior oblique to the macula and vortex veins (vv). The posterior aspect of the superior oblique insertion is in proximity to the superior temporal vortex vein and is approximately 6 to 8 mm from the optic nerve.

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handbook of pediatric strabismus and amblyopia

manipulate these functions surgically to correct specific motility disorders. The Harada–Ito procedure, for example, involves tightening the anterior fibers of the superior oblique tendon. Because the anterior tendon fibers intort the eye, the Harada–Ito procedure can be used to treat extorsion associated with superior oblique palsy. The trochlear nerve innervates the superior oblique muscle at its midpoint from outside the muscle cone. The superior oblique muscle is, in fact, the only eye muscle innervated on the outer surface of the muscle belly. This unique innervation explains why a retrobulbar anesthetic block results in akinesia of all the eye muscles except the superior oblique muscle.

TROCHLEA The trochlea (Latin for pulley) is a cartilaginous U-shaped structure attached to the periosteum that overlies the trochlear fossa of the frontal bone in the superior nasal quadrant of the orbit. It has been taught that the superior oblique tendon moves through the trochlea much like a rope through a pulley. Anatomic studies have shown, however, that tendon movement is not that simple. Within the trochlea is a connective tissue capsule with connective tissue bands that unite the superior oblique tendon to the surrounding trochlea (Fig. 2-15).46 Some of the tendon slackening distal to the trochlea may come from a telescoping elongation of the central tendon (Fig. 2-16).19 This telescoping elongation of the tendon appears to be caused by movement of the central tendon fibers that have scant interfiber connections. Thus, the mechanism for tendon movement is complex, with at least two mechanisms: (1) tendon movement through the trochlea (pulley and a rope) and (2) tendon elongation (telescoping).

INFERIOR OBLIQUE MUSCLE It is the principal extortor of the eye; however, other actions include elevation (secondary) and abduction (tertiary). The inferior oblique muscle originates at the lacrimal fossa located at the anterior aspect of the inferior nasal quadrant of the orbit (see Fig. 2-13). Starting at the lacrimal fossa, the inferior oblique muscle courses posteriorly and temporally underneath the inferior rectus muscle to its scleral insertion, which is adjacent to the inferior border of the lateral rectus muscle (see Fig. 2-14). The inferior oblique muscle has fascial connections to the lower

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A

B FIGURE 2-15A–B. Histology of the trochlea. (A) Low-magnification cross section of midtrochlea. H&E stain. Note horseshoe shape of cartilaginous tissue and the fibrous connective tissue ring that surrounds the superior oblique muscle. At this cross section, the superior oblique is two-thirds muscle and one-third tendon. (B) High-magnification cross section of superior oblique muscle in midtrochlea shows fibrous connective tissue ring connecting to muscle via fine fascial septae.

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C

D FIGURE 2-15C–D. (C) Low-magnification cross section of superior oblique tendon exiting the trochlea. Note small area of cartilage and larger ring of fibrous connective tissue that surrounds the superior oblique tendon as the tendon capsule. At this section, the superior oblique is onethird muscle and two-thirds tendon. (D) High magnification of the superior oblique tendon exiting the trochlea. Note the superior oblique tendon capsule consists of circumferential onionskin layers of fibrous connective tissue. The tendon capsule is attached to the superior oblique tendon capsule by circumferential connective tissue fibers. (From Wright et al., Ref. 46, with permission.)

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FIGURE 2-16. Diagram of anatomy of the trochlea. Note the central fibers of the tendon expand and retract more than the peripheral tendon fibers. (From Ref. 19, with permission.)

border of the lateral rectus muscle and to the overlying inferior rectus muscle via Lockwood’s ligament (see Fig. 2-11). When the inferior oblique muscle contracts, it pulls the back of the eye down and in toward the insertion at the lacrimal fossa. This action produces elevation, abduction, and extorsion (Fig. 2-14). Important structures near the inferior oblique insertion include the macula and inferior temporal vortex vein (Fig. 2-14). The inferior oblique muscle has only 1 mm of tendon at its insertion. The inferior oblique muscle is innervated by the inferior branch of the third nerve at a point just lateral to the inferior rectus muscle. Innervation occurs at the posterior aspect of the inferior oblique muscle belly, and the nerve is accompanied by blood vessels forming a neurovascular bundle. This neurovascular bundle is surrounded by an inelastic capsule of collagen tissue that protects the inferior oblique nerve from damage caused by stretching.39 The neurovascular bundle with its insertion into the posterior aspect of the muscle is an important structure in regard to inferior oblique surgery. Anterior transposition of the inferior oblique muscle is an effective surgical

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procedure used to treat inferior oblique muscle overaction; however, the complication of postoperative limited elevation has been reported.5,25,26,47 This complication is caused by anteriorizing the posterior muscle fibers at, or anterior to, the inferior rectus muscle insertion, because this tightens the inelastic neurovascular bundle.38 The tight neurovascular bundle acts as the functional origin of the inferior oblique muscle and changes the action of the inferior oblique muscle from an elevator to a depressor (Fig. 2-17A).16 This author has coined the term J-deformity for this acute bend of the anteriorized inferior oblique.47 When the patient looks up, the inferior oblique muscle contracts along with the superior rectus muscle, but the anteri-

Inferior oblique muscle

Neurofibrovascular bundle

Maxillary bone

Inferior rectus muscle

FIGURE 2-17A,B. (A) Diagram of inferior oblique muscle anteriorization with “J-deformity.” The J-deformity is caused by anterior placement of the posterior inferior oblique muscle fibers to the level of the inferior rectus muscle insertion. Because the neurovascular bundle of the inferior oblique muscle inserts in the posterior muscle belly, anteriorization of the posterior muscle fibers produces a tight neurovascular bundle; this causes limited elevation of the eye as active contraction of the anteriorized inferior oblique muscle pulls against the tight neurovascular bundle.16

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Vortex vein Inferior oblique muscle

Inferior rectus muscle

FIGURE 2-17A,B. (B) Diagram of the “graded anteriorization” technique described by Guemes and Wright that is effective in reducing inferior oblique overaction but avoids the postoperative complication of limited elevation.16 The new inferior oblique muscle insertion is shown being placed 1 mm behind the inferior rectus muscle insertion, and the posterior muscle fibers are placed an additional 4 to 5 mm further posterior, and parallel to the inferior rectus muscle axis. Note that the posterior placement of the posterior muscle fibers avoids the J-deformity. By keeping the posterior muscle fibers posterior to the anterior fibers and avoiding the J-deformity, the neurovascular bundle remains loose, preventing postoperative limitation of elevation.

orized inferior oblique muscle now depresses the eye and limits elevation; this is an active leash caused by inferior oblique contraction, and forced ductions on patients with this complication of limited elevation often show only slight restriction to supraduction. The complication of limited elevation can be avoided while maintaining excellent results by anterior transposition of the anterior muscle fibers at, or a millimeter or two behind, the inferior rectus insertion. Be sure to keep the posterior fibers back, behind the anterior fibers. Placing the posterior muscle fibers several millimeters posterior to the inferior rectus insertion and in line with the inferior rectus muscle prevents the J-deformity (Fig. 2-17B).16,47

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handbook of pediatric strabismus and amblyopia