The natural history of surgically untreated intermittent exotropia-looking into the distant future

We studied patients with distance intermittent exotropia with at least 5 years follow-up before any surgical therapy, to determine how often amblyopia developed, whether there was progressive worsening in the angle or control of the exodeviation, whether there was deterioration in binocular vision, and other parameters.

Retrospective review of charts of patients with exodeviations examined consecutively over 17 years.

There were 109 patients followed for a mean of 9 years (range 5 to 25). Amblyopia was mild (20/25 in 33, 20/30 in 15, and 20/40 in 2). There was no significant change in the mean exoangle from initial to final visit (20.6 to 20.9 PD), but the initial to final exoangle decreased by more than 10 PD in 19%, remained stable in 58%, and increased by more than 10 PD in 23%. There was no statistically significant trend for worsening or improving when serial measurements were plotted and the aggregate slopes were analyzed. Change in control in the distance from initial to final visit was favorable in 26%, showed no change in 51%, and was unfavorable in 23%, with 17% deteriorating to a constant distance exotropia. Mean near stereoacuity at the final visit was 88 seconds of arc. Strabismus surgery was performed in 14% of patients from 5 to 18 years (mean 9) after their initial visit.

Visual acuity and near stereoacuity were generally good. There was little change in the mean angle of deviation from initial to final visit for the group, with a nearly chance occurrence for the distance deviation to progressively worsen or improve, perhaps explaining why strabismologists have had difficulty definitively prognosticating about the long-term stability of intermittent exotropia.