Assessment of pre-lens tear film particle velocity measurements in participants wearing daily disposable silicone hydrogel lenses

Abstract

Purpose: Themeasurement of the free upward flow of particles that occur naturally in the tear-film is an in-vivo and non-invasive way to assess tear-film spread and stability after a blink, where faster movement suggests enhanced contact lens surface wettability. Method: In a double-masked, randomized, contralateral-eye design, 40 videos from 20 participants wearing stenfilcon A (SA; CooperVision) in one eye and delefilcon A (DA; Alcon) in the other for at least six-hours were analyzed. Tear-film spread over the lens surface was imaged in the morning, approximately five minutes post lens-insertion, and again after six hours of lens wear. Using a customized calibrated ImageJmacro, the upward particle velocities (UPV) of multiple reflective particles from each video were determined and averaged. The UPV is reported as Mean± SD (mm/s). Wilcoxon matched-pairs signed-ranks test was used to compare the average UPV between the two lenses at each time-point. Results: Themean participant agewas 31.9±12.3 years (19–60 years). The SA lens exhibited greater UPV than the DA lens postinsertion (2.50±0.98 vs 2.16±0.70; p=0.035). After six hours of lenswear therewere no differences in UPV between the lenses (SA: 2.23±0.58 vs DA: 2.12±0.52; p=0.218). There was a strong correlation between the post-insertion UPV of both lenses (Spearman’s rho correlation coefficient =0.83). The average UPV measurement period, across all observations, was 1.45 s, with no difference between SA and DA lenses (p=0.191). Conclusions: The higher UPV of the SA lens post-insertion is suggestive of enhanced lens surface wetting immediately following insertion. However, there was no statistical difference when UPV was measured after six hours of lens wear. The link between comfort and UPV is worthy of further study. Jalaiah Varikooty is a Clinical Scientist at the Centre for Contact Lens Research, School of Optometry and Vision Science, University of Waterloo. His research interests focus on the tear film and the ocular surface. He is currently developing novel methods to objectively measure interactions between contact lens wettability, the tear-film, ocular surface signs, and ocular discomfort.