Three-Muscle Surgery for Large- and Medium-Angle Intermittent Exotropia

To examine the success rate and the dose-response ratio of three-muscle compared to two-muscle surgery for the treatment of medium- and large-angle (20 to 45 prism diopters [PD]) intermittent exotropia.

Medical records of patients who underwent strabismus surgery for treatment of intermittent exotropia were reviewed. Patients with exodeviation of 20 to 45 PD who underwent either bilateral lateral rectus recession (BLRc; two-muscle group) or BLR recession and unilateral medial rectus resection (BLRc+UMR; three-muscle group) were selected. Preoperative and postoperative deviation and amount of recessed and resected muscles were assessed. Successful surgery was defined as postoperative deviation of 10 PD or less of orthophoria at the last visit. Dose-response ratio was analyzed.

Forty-four patients were included. The mean age of patients at surgery was 11.85 ± 10.82 years (range: 4 to 54 years) and was comparable in both groups. The mean far preoperative deviation was lower for the two-muscle than the three-muscle group, and measured 29.7 ± 5.9 and 34.4 ± 7.1 PD, respectively (P = .019). At the last follow-up, successful motor outcomes for both distance and near were achieved in 70.5% and 84.6% in the two-muscle and three-muscle group, respectively. At the last follow-up, mean dose-response ratio was significantly higher for the three-muscle group (1.82 ± 0.58 and 2.72 ± 0.72 PD/mm for the two-muscle and three-muscle group, respectively; P < .0001). Overcorrections were similar in both groups.

Primary repair surgery of intermittent exotropia with three-muscle surgery is an effective method of resolving 20 to 45 PD with excellent outcomes and a low risk of overcorrection.