Measurement of Fusion Control with Eye Tracking Device in Intermittent Exotropia

<b>Background/Objectives</b>: We wished to develop an automated method for quantifying fusion control in patients with intermittent exotropia (IXT) using an eye tracking device. <b>Methods</b>: Fifty subjects fixated on visual targets on an LCD monitor at a distance of 45 cm, consisting of dots moving horizontally and vertically and randomly appearing dots at fixed positions. The control group consisted of participants with less than 5 prism diopters (PD), and the IXT group consisted of IXT patients with 10 PD or more, excluding divergence excess types. Fixation disparity (FD) was measured using an eye tracking device, and the FD score was compared with the Newcastle Control Score (NCS) and the Mayo Clinic office-based scale (OCS) score. The subjects repeated the test twice, and the test-retest reliability was determined. <b>Results</b>: The fixation disparity scores of the IXT group during horizontal pursuit, vertical pursuit, and random dot fixation showed positive correlations with the NCS (r = 0.549, 0.583, and 0.481, respectively) and OCS score (r = 0.551, 0.570, and 0.505, respectively). The test-retest reliability of the FD scores of the IXT group using an eye tracking device was fair to good for each task (ICC = 0.633, 0.656, and 0.697, respectively). <b>Conclusions</b>: The eye tracking device developed for automated measurement of fusion control has the potential to assist in functional assessments of IXT.