Diurnal Variation in Tear Film Lipid Layer Using Smartphone-based Interferometry

Tear film stability is essential for maintaining the health of the ocular surface. A tear film interferometer allows noninvasive observation of the dynamics of the tear film lipid layer, thereby enabling the evaluation of tear film stability. However, an interferometer is a medical device used only in clinical settings and is therefore not accessible to the general public. Self-checking of tear film stability in daily life may help prevent dry eye. This study investigates diurnal variation in the tear film lipid layer in daily life using a prototype smartphone-based interferometer. The system consists of a luminescent sheet attached to a smartphone camera, which allows the user to easily videorecord the dynamic behavior of the tear film lipid layer. Thirteen participants (5 with and 8 without contact lenses) were asked to record videos of their tear film five times per day. The diurnal variation of interference grade, spread grade, non-invasive break-up time, maximum blink interval, tear meniscus height, and dry-eye-related subjective symptoms evaluated using the visual analog scale were measured. The results revealed a significant decrease in mean tear meniscus height measured at 18:00 compared with 9:00 (P < 0.05) in participants without contact lenses. The mean interference grade at 15:00 and spread grade at 21:00 were significantly greater than those at 9:00 (P < 0.05) in participants with contact lenses. These results suggest that a smartphone-based interferometer is a potentially useful tool for evaluating tear film parameters in daily life.