Purpose To compare 1-muscle vs 2-muscle surgery for moderate-angle hyperdeviations owing to presumed unilateral fourth nerve palsy. Design Retrospective chart review. Methods Seventy-three patients (aged 5–86 years) underwent either 1- or 2-muscle surgery at our institution for moderate hyperdeviation owing to presumed unilateral fourth nerve palsy, measuring 14–25 prism diopters (PD) in straight-ahead gaze at distance fixation. Six-week and 1-year motor success was defined as zero vertical deviation or 1–4 PD undercorrection at distance, overcorrection as any reversal of hypertropia, and undercorrection as >4 PD. Diplopia success was defined as no diplopia, or only rarely for distance straight ahead and reading. Results Twenty-eight patients underwent 1-muscle surgery, and 45 patients underwent 2-muscle surgery. Motor success was similar (64% vs 67%, P >.99 at 6 weeks; 47% vs 55%, P =.8 at 1 year, n = 46), but there were more undercorrections at 6 weeks with 1-muscle surgery (36% vs 16%, P =.09) and more overcorrections at 6 weeks with 2-muscle surgery (0% vs 18%, P =.02). Diplopia success was also somewhat similar between 1- and 2-muscle surgery at 6 weeks (73% vs 60%, P =.5) and 1 year (45% vs 59%, P =.5). Conclusion For moderate-angle hyperdeviations owing to presumed unilateral fourth nerve palsy, there appears no clear advantage of 2-muscle surgery for motor outcomes. Diplopia success was similar between 1- and 2-muscle surgery, owing to a greater number of less symptomatic undercorrections with 1-muscle surgery and a smaller number of more symptomatic overcorrections with 2-muscle surgery.
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