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S. Pineles, A. L. Rosenbaum, J. L. Demer; Should Pattern Exotropia Be Initially Overcorrected?. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2843.
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Although early post-surgical over-correction for exotropia is widely advised, post-operative drift has not been well quantified in concomitant exotropia, and has not been described with A and V patterns. The goal of this study is to further define the post-operative behavior of both of these patient populations.
We prospectively performed Hess screen analysis in 22 exotropic patients (mean age 42±16 yrs) before and two to six times after strabismus surgery, with post-operative follow-up two to 108 weeks. Primary surgery cases included medial rectus resection (2) and lateral rectus recession (10), combined resection/recession (8), and superior oblique tenectomy (2). Alignment trends in primary and secondary gazes were analyzed for concomitant, pattern, and re-operated subgroups. Results were also analyzed by type of surgery performed.
Mean pre-operative central gaze exotropia was 9.1±7.0 prism diopters. Thirteen cases were concomitant, while 8 exhibited A or V patterns. Fourteen cases were re-operations. In initial surgery for concomitant exotropia, there was a well-defined exotropic drift of approximately 5 prism diopters by 60 weeks post-operatively (linear regression, r=0.25); there was similar exo drift in reoperations. However, in pattern exotropia, post-operative drift was more variable, with mean esotropic drift of approximately 5 prism diopters (r=0.18). For all patients, final post-operative central gaze exotropia was 1.8±5.8 prism diopters, with significant pattern collapse (p<0.01).
Postoperative exo-shift of about 5 prism diopters occurs in initial and re-operated concomitant exotropia. However, in A and V patterns, there is more commonly esotropic post-operative drift, suggesting a different strabismus mechanism Initial over-correction of about 5 prism diopters is advisable for concomitant exotropia, but should be avoided in A and V patterns.
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