SUMMARYIn this retrospective study based on 140 esotropic and 51 exotropic patients, the factors influencing successful outcome and response to strabismus surgery were investigated. Thirteen independent variables were chosen. The pre-operative deviation was found to be the only discriminant factor for early and late successful surgical outcomes in esotropic patients. For exotropic patients the visual acuity of the left eye was the discriminant factor for early successful surgical out come. In esotropic patients the response to surgery increased with increasing amounts of pre-operative deviation. It was lower for patients with older age of onset and larger amounts of medial rectus recession.For exotropic patients the response to surgery was higher for larger pre-operative deviations. Eliminating possible sources of error when determining the pre operative deviation will improve the predictability of the response to surgery and surgical outcome.The aim of strabismus surgery is to straighten the eyes in the primary position and to improve versions and the range of binocular single vision. The outcome of strabismus surgery shows great varia bility among patients. The determination of pre operative and intraoperative factors affecting suc cessful surgical outcome would help us to be more confident when planning a surgical intervention. The predictability of the surgical outcome also depends on the assessment of factors affecting the response to strabismus surgery. von Graefe l was the first to mention the dose-response relationship in strabis mus surgery in 1857 and von Pflugk 2 followed him using the degree/mm ratio (squint-angle reduction per millimetre of surgery). Many surgical formulas have been proposed, on the basis of both clinical experience and artificial eye models, to detect factors affecting the response to surgery and to improve the predictability of strabismus surgery ? � 8 Controversy

Results The mean pretreatment deviations were 38.6 ± 2.5 pd and 37.6 ± 1.9 pd for the ET and XT groups, respectively. After receiving

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