Measurement of Hourly Tear Volume Variation using Smartphone Meniscometer: A 24-Hour Pilot Study

This pilot study examines the tear volume dynamics in human subjects using a smartphone-based meniscometer (SPM) being developed, which enables non-invasive measurements in non-clinical settings. The diurnal tear volume variation for five healthy male volunteers was obtained by measuring tear meniscus radius (TMR) every one hour for a period of 24 hours. The results were found to be consistent with the reported data in the literature showing highest TMR in the early morning (8:00-10:00 AM) which gradually decreased till noon and remained stable. In contrast to previous studies that typically collected data every 3-4 hours during the day with limited data points, the current study, which examined TMR variations every hour, captured subtle periodic fluctuations in TMR throughout both day and night, highlighting individual variability. Each participant displayed unique TMR peaks and oscillations that may reflect their individual body constitution, hormonal rhythms, and homeostatic responses to environmental changes. These findings demonstrate the feasibility of SPM for continuous tear volume monitoring outside of clinical settings and provide new insights into the natural circadian variation of tear volume. Further studies with larger and more diverse samples are needed to validate these TMR patterns and their association with ocular symptoms and tear-related disorders, including dry eye disease.