Dynamic Tear Film Stability Assessed via an Open-View Double-Pass Imaging System

PURPOSE: A novel dynamic optical metric derived from double-pass imaging called the Lacrima Stability Index (LaSI) was evaluated for the objective assessment of tear film stability. METHODS: Retinal point spread functions were recorded with an open-view double-pass system at 15.4 Hz with simultaneous pupil tracking. LaSI was defined as the central PSF energy normalised by the total light exiting the eye, and the time-to-90% decay (T90) was introduced as the time for LaSI to decline by 10%. RESULTS: In 39 eyes, LaSI traces remained stable in eyes with normal tear film stability but showed progressive decline in eyes with an unstable tear film. Using a 10-s cutoff to distinguish normal from reduced tear film stability subjects, T90 correctly classified 84.6% of eyes and showed a strong correlation with non-invasive break-up time (r = 0.76, p < 0.001). Agreement with the Ocular Surface Disease Index-6 scores was comparable for T90 and the non-invasive tear break-up time, although differences reflected the known dissociation between signs and symptoms. CONCLUSIONS: These findings suggest that LaSI provides a sensitive, time-resolved metric of tear film dynamics, with T90 serving as a clinically interpretable marker of tear film stability.