Changes in Exodeviation after the Monocular Occlusion Test in Adult Patients with Intermittent Exotropia and Its Association with the Level of Control

PURPOSE: We investigated the changes in ocular deviation after the monocular occlusion test in adults with intermittent exotropia and evaluated its association with the level of control. METHODS: We retrospectively enrolled adults (aged ≥18 years) with intermittent exotropia who visited our clinic between September 2015 and May 2019. Patients with basic intermittent exotropia with a distant deviation within 10 prism diopters (PD) of the near deviation were included. The largest ocular deviations obtained before and after 1 hour of monocular occlusion were compared. The level of control was measured using the LACTOSE (Look and Cover, then Ten seconds of Observation Scale for Exotropia) control scoring system. RESULTS: Forty-six consecutive adult patients (28 males, 18 females; mean age, 34.3 years) were enrolled. The mean ocular deviation was 36.3 PD (range, 18 to 5 PD) at distant fixation and 38.5 PD (range, 18 to 80 PD) at near fixation, which increased significantly to 38.5 PD (p = 0.043) and 41.1 PD (p = 0.011), respectively, after monocular occlusion. The mean ocular deviation increased ≥5 PD in 14 (30.4%) and 15 (32.6%) patients at distant and near fixation, respectively. The level of control was measured in 30 patients. A higher degree of near control was significantly associated with an increase of ≥5 PD in near fixation after the test (p = 0.009 for a near control score ≤2). CONCLUSIONS: The monocular occlusion test may help to determine the largest ocular deviation in adults with intermittent exotropia. Approximately one-third of patients exhibited an increase in ocular deviation ≥5 PD. Patients exhibiting good control were more likely to manifest an increase in the ocular deviation.