Development and Preliminary Evaluation of a Smartphone App for Measuring Eye Alignment

PURPOSE: We evaluate a smartphone application (app) performing an automated photographic Hirschberg test for measurement of eye deviations. METHODS: Three evaluation studies were conducted to measure eye deviations in the horizontal direction. First, gaze angles were measured with respect to the ground truth in nonstrabismic subjects (n = 25) as they fixated monocularly on targets of known eccentricity covering an angular range of approximately ±13°. Second, phoria measurements with the app at near fixation (distance = 40 cm) were compared with the modified Thorington (MT) test in normally-sighted subjects (n = 14). Third, eye deviations using the app were compared to a cover test with prism neutralization (CTPN; n = 66) and Synoptophore (n = 34) in strabismic subjects. Regression analyses were used to compare the app and clinical measurements of the magnitude and direction of eye deviations (prism diopters, Δ). RESULTS: The gaze angles measured by the app closely followed the ground truth (slope = 1.007, R(2) = 0.97, P < 0.001), with a root mean squared error (RMSE) of 2.4Δ. Phoria measurements with the app were consistent with MT (slope = 0.94, R(2) = 0.97, P < 0.001, RMSE = 1.7Δ). Overall, the strabismus measurements with the app were higher than with Synoptophore (slope = 1.15, R(2) = 0.91, P < 0.001), but consistent with CTPN (slope = 0.95, R(2) = 0.95, P < 0.001). After correction of CTPN values for near fixation, the consistency of the app measurements with CTPN was improved further (slope = 1.01). CONCLUSIONS: The app measurements of manifest and latent eye deviations were consistent with the comparator clinical methods. TRANSLATIONAL RELEVANCE: A smartphone app for measurement of eye alignment can be a convenient clinical tool and has potential to be beneficial in telemedicine.