Clinical Characteristics of Patients with Intermittent Exotropia According to the Response to Short-term Prism Adaptation Test

Purpose: To evaluate the prevalence of the prism adaptation response in patients with intermittent exotropia (IXT) using theshort-term prism adaptation test (PAT) and to assess factors associated with prism adaptation response in IXT patients. Methods: A case-controlled retrospective analysis was performed on 113 patients with IXT without prior surgical treatment. Age, sex, visual acuity, refraction, stereoacuity, control scale, type of exotropia, history of occlusion, and presence of accompanyingvisual symptoms were recorded. Prism alternate cover test (PACT) was performed with fixation targets at 6 m and1/3 m. All patients underwent short-term PAT wearing prism glasses that offset the exodeviation previously measured byPACT. After 30 minutes, angle deviation was measured, and patients were classified into either an increase group, which hadan increase in deviation ≥5 prism diopters after short-term PAT, or a no-change group. Analysis was performed to investigatethe clinical factors influencing the increase in exodeviation after short-term PAT. Results: Fifty patients (44.2%) showed an increase ≥5 prism diopters during distance or near fixation after short-term PATcompared to the previous PACT: 12 patients (10.6%) showed an increment at distance fixation, and 45 patients (39.8%)showed an increase at near fixation. At distance fixation, the increase-group had a significantly smaller maximum anglemeasured by PACT. At near distance, age at PAT, maximum distance angle, minimum distance angle, maximum near angle,minimum near angle, angle fluctuation at near, and IXT type showed significant associations with positive short-term PATresponse. In the multivariate analysis, older age and smaller maximum near angle were significantly associated with positiveshort-term PAT response at near fixation. Conclusions: Short-term PAT could be helpful in older IXT patients with a small maximum angle of deviation at near fixationto mitigate the vergence aftereffect and show the maximum angle of deviation.