Effect of vertical transposition of the medial rectus muscle on primary position alignment in infantile esotropia wuth A- or V- pattern strabismus.

PURPOSE: To determine the effect of vertical displacement of muscle insertions on the surgical dose-response relationship in patients undergoing bilateral medial rectus recessions. METHODS: Retrospective chart review of patients undergoing bilateral medial rectus recessions for correction of congenital esotropia with or without vertical displacement for A or V patterns. Patients were clustered into A pattern, V pattern, and "simple" (no pattern) groups. Strabismus angle at distance and near before and after surgery was recorded. Surgical dose-response relationships (in prism diopters/mm) were determined at the 6-month follow-up visit and compared. RESULTS: A total of 55 patients (28 male and 27 female patients; mean age, 6.9 years; range, 2-17 years) were included. Of these, 28 had either A pattern (18) or V pattern (10), and 27 were in the simple group. Mean preoperative angle of deviation was 34Δ at distance and 40Δ at near. The surgical dose-response relationship was significantly greater (at both distance and near) in the A pattern group (2.43Δ/mm, distance [p=0.005]; 2.76Δ/mm, near [p=0.04]) than in the simple group (1.56Δ/mm, distance; 2.03Δ/mm, near). The surgical response in the V pattern group (1.96Δ/mm, distance [p=0.34]; 2.03Δ/mm, near [p=0.94]) was not significantly different from the simple group. CONCLUSIONS: Upward displacement of the medial rectus muscles increased the surgical dose/response relationship in patients with A-pattern esotropia. A similar effect was not observed with downward displacement in patients with V-pattern strabismus. Surgeons should be aware of this enhanced response when planning surgery for A-pattern esotropia.