Distance Suppression as a Predictive Factor in Progression of Intermittent Exotropia

PURPOSE: To address the natural course of intermittent exotropia with small exodeviations (less than 20 prism diopters [PD]) according to the status of suppression, and to evaluate whether suppression testing at the initial visit can assist in predicting the progression of intermittent exotropia. METHODS: Clinical records of patients at the Korea University Anam Hospital, Seoul, Korea diagnosed between January 2014 and December 2018 with basic-type intermittent exotropia and initial distance deviations of less than 20 PD, older than four years of age and a minimum of three follow-up visits within a 6-month span were retrospectively reviewed. The participants were divided into two groups, the suppression group and the non-suppression group, based on the Vectogram results at the initial visit. Clinical characteristics, rate of surgery, and rate of progression were compared between the two groups. RESULTS: A total of 71 patients were included. Among them, 16 patients (22.5%) had visual suppression at the initial visit, while 55 patients (77.5%) had no suppression. At the initial visit, the mean distant angle of deviation was 13.7 ± 3.2 PD (range, 4 to 18 PD) in the suppression group and 12.7 ± 3.4 PD (range, 10 to 18 PD) in the non-suppression group. Ten patients (62.5%) underwent surgery in the suppression group and 12 patients (21.8%) underwent surgery in the non-suppression group (p < 0.01). Eleven patients (68.8%) in the suppression group and 13 (23.6%) in the non-suppression group developed progression (p < 0.01). CONCLUSIONS: Suppression testing was important to predict the progression of intermittent exotropia, in patients with exodeviation angles less than 20 PD at the initial visit.