Changes in Distance Ocular Deviation After Smartphone Viewing in Young Adults Without Manifest Strabismus

Background: This prospective observational study assessed acute changes in distance ocular deviation after brief smartphone viewing in young adults without manifest strabismus and identified factors associated with the magnitude of change. Methods: Fifty-nine healthy young adults without strabismus (aged 20–30 years; mean ± standard deviation, 23.2 ± 2.5 years) wore a head-mounted eye-tracking system and viewed a smartphone for 30 min. Ocular deviation angles at near and distance fixation were measured immediately before and after smartphone viewing. During smartphone viewing, eye-movement parameters and smartphone distance were continuously recorded. Results: Before smartphone viewing, the mean deviation angles were −6.2 ± 6.8Δ and −2.0 ± 2.8Δ at near and distance fixation, respectively (negative values indicate exodeviation). After smartphone viewing, deviation angles shifted toward less exodeviation, measuring −4.3 ± 6.6Δ and −1.1 ± 2.4Δ at near and distance fixation, respectively. The magnitude of exodeviation reduction was negatively correlated with baseline ocular deviation, indicating that individuals with larger pre-viewing exodeviation exhibited greater alignment shifts after smartphone viewing. Eye-movement analysis revealed that gaze movements of <30°/s accounted for 57.8% of detected gaze-movement events. Conclusions: Thirty minutes of smartphone viewing was followed by a reduction in exodeviation at near and distance fixation in young adults without manifest strabismus. Greater baseline exodeviation was associated with a larger reduction, and low-velocity gaze movements predominated.