To compare the exodrift between unilateral lateral rectus (ULR) recession and observation groups in moderate angle intermittent exotropia (IXT).

A retrospective study was performed in 769 patients who were diagnosed with IXT from 2005 to 2015. Seventy-six patients were enrolled in this study that presented with IXT of 20 to 25 prism diopters (PD) on their first visit and were observed for more than 6 months without or after operation. The observation group (group 1) was composed of 29 patients who had regular examination without operation. The surgery group (group 2) was composed of 47 patients with ULR recession that were observed for deviation changes since surgery.

The mean age was 71.8 ± 22.0 months at first visit in group 1 and 91.1 ± 18.9 months before surgery in group 2 ( p < 0.01). The distant exodeviation was 22.9 ± 2.5 PD at first visit in group 1 and 22.9 ± 2.4 PD before surgery in group 2 ( p = 0.89). During follow-up, mean exodrift was 0.6 ± 9.0 PD in group 1 and 10.0 ± 7.4 PD in group 2 ( p < 0.01). Exodrift up to postoperative 6 months in group 2 was 3.2 ± 4.0 PD and exodrift from postoperative 6 months to 2 years in group 2 was 7.1 ± 6.9 PD. More exodrift was noticed after post-operative 6 months ( p = 0.04).

Comparing the exodrift between the groups in moderate angle IXT, patients in the observation group showed less exodrift. Patients who had a ULR recession presented more exodrift after postoperative 6 months. Even though they were orthotropic at postoperative 6 months when the operation was thought to be stabilized, an increase in exodrift after postoperative 6 months could not be excluded.