The distance angle to target in surgery for intermittent exotropia

Patients with intermittent exotropia may have an increase in their angle of strabismus in the distance when the angle is measured either after 1 hour of monocular occlusion or while the patients fixate on a distant target outdoors. The hypothesis that surgery should be performed for this larger deviation has been suggested but not tested.

To test the hypothesis that surgery should be performed for the increased angle of strabismus in the distance in patients with intermittent exotropia and to investigate the factors that influence the angle of misalignment.

A prospective, clinical trial was conducted of patients with intermittent exotropia in whom the angle of misalignment in the distance increased after 1 hour of monocular occlusion or while the patients fixated on an outdoor target. The study group underwent surgery for the largest deviation measured; the control group underwent surgery for the initial angle measured at 6 m. All patients in whom the angle of misalignment increased while the patients were looking at an outdoor target were additionally measured in indoor illumination at 24 m and also at 6 m under floodlights that simulated outdoor illumination. Ninety patients undergoing surgery were randomized.

Forty-three (86.0%) of the 50 patients undergoing surgery for the largest angle measured had a satisfactory outcome vs 25 (62.5%) of the 40 patients in the control group (P<.001). The mechanism for the increase in exotropia while fixating on an outdoor target was studied in 76 patients, and the results were variable.

The angle of strabismus in patients with intermittent exotropia undergoing surgery should be measured while the patients fixate on an outdoor target and after 1 hour of monocular occlusion. Surgery should be performed for the largest angle measured.