Insights into Tear Viscosity: A Study of 240 Volunteers

Tear viscosity is known to influence the flow resistance and stability of the tear film, making it a relevant parameter for the assessment of tear quality. However, limited information is available in the literature regarding its reference values. This study aimed to establish a baseline for tear viscosity in a cohort without a reported diagnosis of dry eye disease and to explore potential demographic and clinical factors that may influence it, using a prototype viscometer based on quartz crystal microbalance (QCM) technology.

In this exploratory study, a total of 240 volunteers (170 women and 70 men, aged 18-76 years) without a diagnosis of dry eye syndrome or active ocular infection or inflammation were included. Each participant completed a questionnaire based on the Women's Health Study, and tears were collected using a capillary for analysis with the QCM. The viscosity data were analyzed statistically for distribution fitting and correlations with QCM frequency and dissipation.

The raw viscosity data showed a right-skewed distribution (median = 7.0 cP, IQR = 24 cP). A log-normal distribution provided the best fit. No association was found between tear viscosity and QCM frequency or dissipation. Median tear viscosity values across demographic and clinical groups ranged from 3.8 to 16.1 cP, but these differences were not statistically significant (p > 0.05).

A preliminary reference estimate for tear viscosity in a population without a reported diagnosis of dry eye disease was established, providing a fundamental baseline for future research on viscosity as a potential biomarker for ocular diseases such as dry eye syndrome.