Infantile esotropia: ALISON Y. FIRTH evidence for conservative management in the visually immature where follow-up treatment is unavailable or limited

The article in this issue of Eye by Calcutt and By comparison with previously published Murrayl reports the prevalence of, and factors literature on the prevalence of amblyopia in involved in, the development of amblyopia in a essential infantile esotropia, the authors series of 113 untreated essential infantile conclude that there is a reduced tendency to esotropes. The authors define amblyopia as a amblyopia in untreated cases. The question is difference of 2 lines on the Snellen chart, but now posed as to whether early surgery in the consider 6/6 as normal visual acuity and hope of achieving some form of binocular vision therefore do not include subjects achieving 6/6 is justified if amblyopia may develop. The with their non-preferred eye, even if there was a authors state that where access to ongoing difference of 2 lines. Sixteen of their 113 cases therapy is not available, delaying surgery until fell into this category. In 10 of these visual adulthood means that there is a anisometropia (defined as 1 dioptre or more significant chance of retaining good visual difference in spherical equivalent) was present. acuity in both eyes. Presence of alternation and a larger angle of The dearth of literature on how the presence deviation were found to protect against of either amblyopia or a strabismus affects daily amblyopia. life has recently been highlighted.4 Which, if Since Zipe described fixation patterns in either, causes the greater disability? Whilst loss relation to strabismics, new methods of testing of stereopsis is problematic to those used to visual acuity in young patients have become normal binocular single vision, strabismics available, such as the Catford drum, preferential generally seem able to adapt. The question of looking acuity cards and Cardiff cards. what advantages a person with abnormal However, such tests have been shown to be less binocular single vision has in daily life than ideal in detecting amblyopia and compared with a person with no form of consequently (in addition to these visual acuity binocular single vision is unanswered. tests) a return to fixation preference in assessing In countries where eye care is readily interocular differences in infant vision has available we can strive for what we perceive as occurred. This can still be misleading and an ideal and discuss the benefits of abnormal Calcutt and Murray emphasise observation of binocular single vision in the prognosis of the point at which alternation occurs to help strabismus. (We must not forget, however, that reduce misdiagnosis of those amblyopes who whilst the follow-up care is available, some do cross-fixate, and acknowledge that fixation patients will not attend to take advantage of this preference alone is likely to overestimate the or comply with treatment.) In countries where presence of amblyopia? treatable conditions such as cataract and Anisometropia is identified as a factor in the trachoma result in blindness another aspect development of amblyopia. However, of 81 presents itself. Trauma is often the most non-amblyopes, 16 were anisometropic. Ten of important cause of unilateral loss of vision, UniverSity Department of these were among 20 patients who showed 1 particularly in developing countries; other Ophthalmology and Orthoptics line difference in visual acuity (not classified as causes include cataract, corneal scars of various Floor 0 amblyopes) and a further 3 did not achieve causes, phthisis bulbi, infections and Royal Hallamshire Hospital normal vision with either eye, demonstrating staphyloma.5-8 Thus the need for reasonable Glossop Road gross refractive errors (c. Calcutt, personal visual acuity in the 'reserve eye' may be more Sheffield S10 2JF, UK communication 1998). important than in developed countries. In cases Fax: +44 (0)114 2766381

Eye (1998) 12, 165-166 © 1998 Royal College of Ophthalmologists 165 where treatment is ongoing, amblyopia may not be a 4. Snowdon SK, Stewart-Brown S1. Preschool vision screening: problem following early surgery for infantile esotropia, results of a systematic review. York: NHS Centre for Reviews and Dissemination, University of York, 1997:21-6. but evidence does exist for a fixation preference and development of amblyopia post-operatively.9 5. Thylefors B. Epidemiological patterns of ocular trauma. Aust NZ J Ophthalmol 1992;20:95-8. The authors, in presenting these data, give an inherent warning to those who may be involved in patient 6. Whitfield R, Schwab L, Ross-Degnan D, Steinkuller P, Swartwood J. Blindness and eye disease in Kenya: ocular management where follow-up care is limited, to consider status survey results from the Kenya Rural Blindness their preferred outcome before suggesting early surgery Prevention project. Br J Ophthalmol 1990;74:333-40. for essential infantile esotropia. 7. Kortlang e, Koster Je, Coulibaly S, Dubbeldam RP. Prevalence of blindness and visual impairment in the region References of Segou, Mali: a baseline survey for a primary eye care 1. Calcutt e, Murray ADN. Untreated essential infantile programme. Trop Med Int Health ]996;]:314-9. esotropia: factors affecting the development of amblyopia. Eye 8. Alemayehu W, Tekle-Haimanot R, Forsgren L, Erkstedt J. 1998;12:167-72. Causes of visual impairment in central Ethopia. Ethiop Med J 2. Zipf RF. Binocular fixation pattern. Arch Ophthalmol 1995;33:163-74. ] 976;94:40] -5. 3. Calcutt C. Is fixation preference assessment an effective 9. Hoyt CS, Jastrzebski GB, Marg E. Amblyopia and congenital method of detecting strabismic amblyopia? Br Orthopt J esotropia: visual evoked potential measurements. Arch 1995;52:29-31. Ophthalmol 1984;102:58-61.

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