Effect of vertical transposition of the medial rectus muscle on primary position alignment in infantile esotropia with 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 34(Delta) at distance and 40(Delta) at near. The surgical dose-response relationship was significantly greater (at both distance and near) in the A pattern group (2.43(Delta)/mm, distance [p = 0.005]; 2.76(Delta)/mm, near [p = 0.04]) than in the simple group (1.566(Delta)/mm, distance; 2.03(Delta)/mm, near). The surgical response in the V pattern group (1.96(Delta)/mm, distance [p = 0.34]; 2.03(Delta)/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. (J AAPOS 2011;15:14-16)