Distance alternate-letter suppression test for objective assessment of sensorial status in intermittent exotropia

PURPOSE. To investigate the value of distance alternate-letter suppression testing in the objective assessment of fusional control of intermittent exo tropia. METHODS. A total of 71 consecutive patients with intermittent exotropia (st udy group) and 112 normal subjects (control group) underwent a series of me asurements including distance alternate-letter suppression testing, Worth 4 Dot test at distance and near, and distance and near stereo acuity tests t o see whether sensorial behavior differed in the study and control groups. The distance alternate-letter suppression test and distance stereo acuity t ests were performed using the Mentor B-VAT II-SG Video Acuity Tester and Bi nocular Vision Testing System. The TNO test was used to measure near stereo acuity. RESULTS. Seventeen patients with intermittent exotropia (24%) presented sup pression with the distance alternate-letter suppression test, but none of t he normal subjects (p<0.001, chi(2) test). Only, three patients (4%) showed suppression on the Worth 4 Dot test at distance, and all had fusion on the Worth 4 Dot test near. Patients with intermittent exotropia had significan tly diminished distance stereo acuity compared to normal subjects (p<0.001) . Normal subjects and patients had good near stereo acuity (p>0.05). Patien ts with intermittent exotropia who had fusion with the distance alternate-l etter suppression test had significantly better distance stereo acuity than patients who had suppression (p<0.001). CONCLUSIONS. Distance alternate-letter suppression testing and distance ste reo acuity tests may be useful as objective measures for assessing sensory loss in patients with intermittent exotropia.