The purpose of this study is to investigate the effect of unilateral medial rectus muscle resection (UMR) for the treatment of recurrent intermittent exotropia after bilateral lateral rectus muscle recession (BLR).

Medical records of 121 subjects who underwent UMR for the treatment of recurrent intermittent exotropia after BLR with more than six months of follow-up were reviewed. Patients were classified into two groups, the 4-mm group who underwent 4-mm UMR and the 5-mm group who underwent 5-mm UMR. Successful postoperative motor alignment was defined as within 10 prism diopters (PD) of exotropia and four PD of esotropia.

The mean time interval between the primary surgery and recurrence was 13.55 ± 20.78 months (1-120 months). Average follow-up period after secondary surgery was 27.42 ± 15.98 months (6-48 months). Cumulative success rate at six months after UMR was 87.1% in the 4-mm group and 88.2% in the 5-mm group, respectively, and that at 24 months was 72.7% in the 4-mm group and 50.0% in the 5-mm group ( p = 0.132). The average effect of resection was 4.87 ± 0.91 PD/mm in the 4-mm group and 4.73 ± 0.84 PD/mm in the 5-mm group ( p = 0.374).

Because of recurrent intermittent exotropia, less time is required for surgery in UMR after BLR, and patients and parents are more likely to accept a secondary surgery because of single muscle surgery. Therefore, UMR may be an effective surgical method for patients with 16-30 PD of recurrent intermittent exotropia.