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Jalaiah P. Varikooty, Nancy J. Keir, Trefford L. Simpson; Estimating in-vivo Contact Lens Wettability Through Tear Film Hydrodynamics. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6098.
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The stability and ease of spread of the tear film over the lens surface may be an indicator of contact lens wettability. The present in-vivo methods of determining lens wettability are complex and do not predict the comfort of lens wear. We introduce a novel and objective way of determining in-vivo lens wettability.
20 videos from 10 participants who had worn the same type of silicone hydrogel lens for at least 8 hours were analysed. We imaged the spread of tear-film over the lens surface after a blink, in the morning after lens insertion and also after 8 hours of lens wear. Using a customized, calibrated ImageJ macro the velocity of reflective particles in the videos was determined. The results were analyzed using R and ProFit.
The upward particle velocity (UPV) was highest immediately after a blink and declined with time. We were able to establish that the spread of the tear film was different upon lens insertion than it was after 8 hours of lens wear by measuring UPV (p=0.001). The exponential time constants were 11.5±1.7 for lens insertion in the morning and 47.1 ± 28.0 after 8 hours of lens wear.
We have introduced a novel and non-invasive way to measure in-vivo wettability of the lens/tear-film interface. Additional studies are needed to understand if this simple measure is associated with other aspects of lens wettability or lens comfort.
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