Outcomes and Dose-Response Ratio of Surgery on Three Muscles in Large-Angle Exotropia

PURPOSE: To evaluate the efficacy of three-muscle surgery for the treatment of large-angle exotropia with particular attention to the success rate and mean dose-response ratio. METHODS: In a retrospective study, medical records were reviewed for 48 patients with exodeviation between 50 and 80 prism diopter (PD) who underwent bilateral lateral rectus recession as well as one medial rectus resection. Sex, age at surgery, presence of amblyopia, amount of preoperative and postoperative deviation, total amount of recessed and resected muscles, dose-response ratio, and associated vertical deviations were analyzed. RESULTS: The mean age of patients at surgery was 25.4 ± 14.3 years old (range, 1–55). The mean preoperative deviation was measured 62.8 ± 7.5 PD (range, 50–80 PD). The mean amount of total recession and resection was 23 ± 1.3 mm. After a mean follow-up of 15 ± 25 months (range, 3–144), 85.4% of patients were within 10 PD of orthophoria. The mean postoperative deviation decreased to 3.8 ± 7.5 PD (range, 0–30 PD). A mean dose-response ratio of 2.5 ± 0.3 PD/mm (range, 0.9–3.1 PD/mm) was found. Of all patients, 14.6% demonstrated undercorrection. CONCLUSION: Simultaneous surgery on three muscles is an effective method in resolving large-angle exotropia and results in excellent outcomes with low risk of undercorrection.