Chapter 17: Exodeviations

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Exodeviations 359on having been involved in the screening of populationsin other parts of the world, that exodeviationsoccur more commonly in the Middle East,subequatorial Africa, and the Orient than in theUnited States. They appear to occur least commonlyin central Europe. On the other hand, Chewand coworkers 43 reported no difference in the frequencyof exodeviations in white and African-American children in the United States.In comparing the prevalences reported fromdifferent countries, Jenkins 94 made the interestingobservation that the nearer a country is to theequator, the higher the prevalence of exodeviations.A comprehensive epidemiologic study inwhich ethnic population differences 87 and evenclimatic and heliotropic 54 factors are considered isneeded to explore the significance of these observations.The implication of a recent report that theprevalence of systemic and ocular disease ishigher during the first year of life in children withexotropia than in those with esotropia 82 is not atonce obvious.AGE OF ONSET AND NATURAL HISTORY. Contraryto common belief, onset of the majority ofexodeviations is shortly after birth. In Costenbader’s44, p. 353 series of 472 patients with intermittentexotropia of the divergence excess type, the deviationwas present at birth in 204 and appeared in16 at 6 months of age and in 72 between 6 and12 months of age. In only 24 of his patients didexotropia develop after 5 years of age. Krzystkowaand Pajakowa 105 reported the age of onsetto be before 2 years of age in 34.5% of theirpatients; Hall, 70 in 37%; and Holland, 80 in 70%.In a more recent study, the mean age at diagnosiswas 7.8 months. 16It is not always possible to ascertain by historyalone whether a constant exotropia was present atbirth or occurred shortly thereafter or was precededby a period of intermittency. Yet such informationwould be important in assessing the prognosis.In the latter instance the chances forrestoring normal binocular functions are betterthan in the former. Moore and Cohen 128 reportedthat fusion was unattainable after surgical alignmentin patients with a genuine ‘‘congenital’’ exotropia.Jampolsky 91 made the point that, with rare exceptions,exodeviations begin as an exophoria thatmay deteriorate into intermittent and constant exotropiaas suppression develops. He considered suppressionto be the key that unlocks the fusionmechanism. Such deviations usually occur first atdistance and later at near fixation. Obviously, theprognosis for recovery of normal binocular functionis infinitely better in patients who experiencea long phase of intermittency than in those with amanifest deviation since early childhood.Factors that may influence progression are thedecrease in tonic convergence with advancing age,development of suppression, gradual lessening ofaccommodative power, and increased divergenceof the orbits with advancing age. Progression maytake several forms. The deviation may increase at97, 130near or at distance fixation, exophoria maybecome intermittent or change to manifest exotropia,or suppression may develop.Burian 27 observed that the divergence excesstype of deviation tends to remain more or lessstable, whereas with simulated divergence excessthe near deviation tends to increase. In patientswith the convergence insufficiency type of deviation,binocular function degenerates rapidly andprogressively, and in those with a basic exotropiathere is a tendency for the deviation to increase orfor secondary convergence insufficiency to develop.The generally progressive nature of the diseasehas important therapeutic implications in regard toindications for and timing of surgery. At this point,therefore, it is necessary to emphasize that not allexodeviations are progressive and that some remainunchanged over many years of observation;57, 78in fact, some improve without therapy. VonNoorden 135 followed for an average of 3.5 years51 patients ranging from 5 to 10 years of agewith intermittent exotropia who, for one reason oranother, were not operated on. One or more signsof progression, as defined above, were present in75%, no change occurred in 9%, and 16% improvedwithout therapy. From these studies, itfollows that patients with intermittent exodeviationsneed to be evaluated over a period of timeto ascertain whether progression is taking placeand surgery is warranted, particularly those inwhom a constant deviation is present less than50% of the time.Constant, infantile exotropia with an onsetshortly after birth and with a large angle deviationthat does not change at near and distance fixationmay also occur and its clinical characteristics aresaid to be similar to those in infantile esotropia. 158An association between early-onset exotropia witha large angle and delayed visual maturation hasbeen reported. 184
360 Clinical Characteristics of Neuromuscular Anomalies of the EyeSEX DISTRIBUTION. Several authors have commentedon the preponderance of women in a populationof patients with exodeviations. Cass 37 reporteda prevalence of 62 (70%) women in 88patients; Gregersen, 67 61% women in 231 patients;and Krzystkowa and Pajakowa, 105 67% women in620 patients with exodeviations.REFRACTIVE ERRORS. The prevalence of refractiveerrors associated with exodeviations variesaccording to different investigators. Donders 48found 70% of ‘‘comparatively high’’ myopes in agroup of 100 patients with exotropia and concludedthat reduction of accommodation in suchpatients is pivotal in the etiology of exodeviations.28, 67, 105, 161From more recent studies, it appears,however, that distribution of refractive errors inexotropes resembles that in the nonstrabismic populationand that the etiology usually is unrelatedto the underlying refractive error.SIGNS AND SYMPTOMS. Generally, signs andsymptoms of exodeviations are no different fromthose observed in patients with other forms ofstrabismus, as discussed in Chapter 10. Patientswith exophoria commonly complain of eyestrain,blurring of vision, difficulties with prolonged periodsof reading, headaches, and diplopia. Childrenwith intermittent or constant exodeviations are lessfrequently symptomatic because, unless the deviationis of recent onset, a well-developed suppressionmechanism eliminates diplopia. 95 On theother hand, adults with intermittent exotropia arecommonly symptomatic, and their complaints arenot different from those with inadequately compensatedexophorias.PHOTOPHOBIA. One symptom that deservesspecial comment is photophobia, for it occurscommonly in association with intermittent exodeviations.In spite of the frequency of its occurrence,81, p. 219; 100, p. 234; 113; 146 little if any attempt hasbeen made in the literature to satisfactorily explainphotophobia in connection with exodeviations. Ithas been assumed that when a child is outdoorsand looking at infinity, there are no near cluesto stimulate convergence and that bright sunlightdazzles the retinas so that fusion is somehowdisrupted, causing the deviation to become manifest.118 These explanations imply that one eye isclosed to avoid diplopia and visual confusion.This view is held, for instance, by Wang andChryssanthou, 75 who found that patients withanomalous retinal correspondence are less apt tocomplain about photophobia than those with normalcorrespondence. Jampolsky 89 assumes that theintermittent exotrope shuts one eye in bright lightto avoid the many perceptual visual field changesthat take place in bright light diffusion, whichin turn may trigger the ‘‘hemiretinal suppressionmechanism’’ (see pp. 218, 365).Wirtschafter and von Noorden 183 demonstratedthat bright light adversely affects the amplitude offusional convergence in patients who maintain adelicate balance between exophoria and intermittentexotropia (see also Campos and Cipolli 36 ).Orthophoric patients, those with exophoria andadequate fusional amplitudes, and those with wellestablishedintermittent exotropia were not affectedin this manner. Eustace and coworkers 54also noted that bright light causes exophoria tobecome manifest and suggested the use of photochromaticlenses to relieve photophobia in suchpatients. Graefe 65 reported an increase in the deviationat near fixation under the influence of brightlight in patients with exophoria.It is a common misconception that habitualmonocular eye closure in bright sunlight is limitedto intermittent exotropes and that eye closure istriggered by diplopia. Wiggins and von Noorden 180observed photophobia predominantly in intermittentexotropes but also in constant exotropia, esotropia,and normal subjects. None of the subjectswas aware of diplopia before closing one eye orunder any other circumstances. The common factorin these patients was a significantly decreasedbinocular photophobia threshold, which was measuredby exposure to an intense artificial illumination.This finding was unrelated to the presence orabsence of anomalous correspondence as proposedby Wang and Chryssanthou. 175 The significance ofthese results and the reason for the highest incidenceof photophobia in the intermittent esotropiagroup remains elusive at this time.MICROPSIA. Another less well-known symptomof intermittent exodeviations is micropsia. Wehave seen several patients with this anomaly sincewe first became aware of it through the patient inCase 17–1.CASE 17–1This 21-year-old woman has had intermittent exotropiasince childhood. Her right eye had been operatedon by another ophthalmologist. She described hercurrent problem as follows: ‘‘When I look in thedistance, things go in and out of focus and then get
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Chapter 17: Exodeviations

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