Outcomes of Simultaneous Three- or Four-Horizontal Muscle Surgery for Very Large-Angle Convergence Insufficiency-Type and Basic-Type Exotropia.

Purpose: We investigated the outcomes of simultaneous three- or four-horizontal muscle surgery for very large-angle exotropia (> 60 prism diopters [Δ]). Subjects and Methods: This retrospective study included 24 patients (16 with convergence insufficiency-type and 8 with basic-type exotropia). The deviation angle was measured using the alternate prism and cover test, and stereopsis was evaluated. Patients were classified into three groups (F: ≤ 60 arcsec ("), C: 60"<, and N: nil stereoacuity). A successful motor outcome was defined as ≤ 10Δ of orthotropia. Pre- and postoperative results were compared. Results: Mean preoperative exodeviation at distance and near were 75.2 ± 13.0Δ and 89.2 ± 18.0Δ, respectively. Mean age at surgery was 47.8 ± 16.5 years, and mean follow-up period was 3.6 ± 4.2 years. Thirteen and 11 patients underwent four- and three-muscle surgeries, respectively. The mean distant and near deviations at 3 months postoperatively and at the final visit were 5.3 ± 10.4Δ and 8.4 ± 9.5Δ, 5.5 ± 8.6Δ and 9.4 ± 9.0Δ, respectively. No differences were found in the near and distant deviations between the two time points. The motor success rates at both time points were 63%. Stereopsis at the final visit improved significantly from F:4%, C:38%, and N:58% before surgery to F:38%, C:50% and N:13% at the final visit (P = 0.002, McNemar-Bowker test). Conclusions: Three- or four-horizontal muscle surgeries for very large-angle exotropia are effective in achieving favorable motor outcomes and stereopsis.