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Michael Leonard Read, Chantal Coles-Brennan, Carole Maldonado-Codina, Philip Morgan; Assessment of contact lens wettability using the WAVE (Wettability Analysis in an in Vitro Environment) system. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3931.
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To evaluate saline film stability for a range of soft contact lenses over a succession of automated lens submersion/emersion cycles; each of which was triggered by automatic detection of saline film break-up using live image analysis.
The WAVE system (Figure 1) has been developed to assess saline film stability on a contact lens. A lens was placed on a mount within a saline bath (35°C). The saline level was varied using a computer-controlled pump to allow a thin saline film to be deposited on the lens during the emersion process. A dome-illuminator, digital camera and live image analysis were used to assess film stability. Following detection of film break-up, the lens was briefly resubmerged, depositing a new film on the lens surface in a cyclic manner. A laboratory study was undertaken to compare saline film stability for eight contact lens types (senofilcon A, etafilcon A, lotrafilcon A, lotrafilcon B, balafilcon A, comfilcon A and filcon group IV) over a 6-hour cycling period. Mean film break-up time (FBUT) and change in FBUT (Mean - Initial FBUT) through the 6-hour period were assessed with linear regression models. The distribution of break-up was assessed by averaging the break-up patterns across the cycles to generate a heat map for each lens (Figure 2).
Differences in mean FBUT were observed between lens types (p<0.0001), with values ranging between 25.4 seconds (filcon IV) and 161.8 seconds (etafilcon A). The change in FBUT through the 6-hour period differed between lens types (p=0.003), with all lens types showing a reduction in film break-up time through the cycling period. The location of film break-up was also observed to differ between lens types.
This study highlighted the ability of the WAVE system to characterize saline film stability during lens cycling. Differences in film stability were observed between lens types indicating the critical role material properties play in influencing lens-wetting properties. Repeated exposure of the lens to air was shown to reduce film stability for all lens types, highlighting the need to minimize air exposure during lens wear. The WAVE system appears able to mimic the film formation aspect of the blinking process, but further work is required to better model the biologically complex tear film and to understand whether findings on the WAVE system are predictive of clinical performance.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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