Novel Binocular Eye Alignment Monitor Device for Intermittent Exotropia: Objective Tool for Assessment of Rehabilitation

Significance: Intermittent exotropia exhibits inherent variability in the percentage of time the eye deviates and the amount of exodeviation; therefore, assessing the magnitude and duration of the eye's deviation is challenging. A portable monitoring device for longer assessments under natural viewing conditions can enhance evaluation and management, providing an objective tool for assessing therapeutic rehabilitative interventions. Purpose: The Binocular Eye Alignment Monitor (BEAM) was developed to evaluate eye alignment over an extended period objectively. This study aims to evaluate the BEAM by assessing its resolution, repeatability, and validity in differentiating individuals with intermittent exotropia from those with binocularly normal vision. Methods: Eye position was objectively recorded from 22 binocularly normal vision participants (average age of 15.6 years; 95% confidence interval (CI): 13.8-17.4 years), and 15 intermittent exotropia participants (average age of 12.5 years; 95%CI: 9.5-15.5 years). Participants watched an age-appropriate movie of their choice on a television located 6 meters away for 90 minutes after undergoing a strabismus evaluation in two test sessions, each occurring on a different day. The BEAM integrates a commercial eye tracker with custom hardware and software. Test and retest sessions were analyzed for the percentage of test time deviated, as well as the maximum, mean, and median deviation magnitudes. Reliability was assessed using the intraclass correlation coefficient and Bland-Altman plots. Results: The BEAM has a temporal resolution of 8 milliseconds and a spatial resolution of 2Δ. The intraclass correlation coefficient assessment of the test and retest sessions for the binocular normal vision group showed excellent reliability for percentage of time deviated and maximum deviation, and good reliability for mean and median deviation. A Mann-Whitney U-test revealed significant differences between groups for the percentage of time deviated and the maximum, mean, and median deviation (p<0.01). Bland-Altman plots indicated good repeatability and narrow limits of agreement in the binocular normal vision group, whereas the intermittent exotropia group showed greater variability. Conclusions: The results demonstrate that BEAM resolution is a reliable and valid system for quantifying intermittent exotropia metrics over extended periods.