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D.L. Meadows, H. Ketelson, N. McQueen, R. Stone; Dynamic Wetting Behavior of pHEMA–MAA and Silicone Hydrogel Contact Lenses . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1553.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Utilize a new technique to measure dynamic contact angle as an indicator of contact lens wettability for pHEMA–MAA (Group IV) and surface modified silicone hydrogel lenses. Methods: A sessile water drop technique was used in conjunction with high speed video equipment to measure advancing dynamic contact angles for unworn and patient worn contact lenses. The curved profile of the lens surface was analyzed using a fitting algorithm to calculate the contact angles. The lenses were cycled through buffered saline and air exposures to simulate exaggerated blinking conditions. Measurements were made in the presence of various non–ionic surfactants and disinfection products. Results: The contact angles of the pHEMA–MAA lenses increased from approximately 20° to 100° after 9–10 cycles and they were independent of the lens water content. This trend was consistent with historical data using pHEMA–MAA type hydrogel materials. The observed trend of increasing contact angles observed to plateau and remained relatively constant after 10 cycles. The change from the hydrophilic to hydrophobic (i.e., dewetted) lens surface could not be reversed when the dewetted lens was repeatedly soaked in buffered saline solution. For silicone hydrogel lens the initial contact angles were higher than those observed for the pHEMA–MAA lens. Dewetting kinetics were much slower in the case of the silicone hydrogel lens. The influence of surfactant pre–treatment on the wettability of the pHEMA–MAA lens showed Tetronic® 1304 gave excellent wettability. Comparatively, the lens pre–soaked in Tetronic® 1107 solution showed rapid dewetting surface properties following the early cycling stages. This lens wettability change from a hydrophilic to hydrophobic state followed the same trend observed using the lens that was not pre–soaked with surfactant, indicating low retention of the Tetronic® 1107. These same trends were observed for commercial disinfection products containing these surfactants. Conclusions: The pHEMA–MAA lenses showed significant dewetting properties when the lenses were cycled through saline solution–air exposures and the lens dewetting kinetics were dependent on the air exposure times used in the cycling procedure. The dewetting effects of the silicone hydrogel lenses were significantly different compared to the pHEMA–MAA lens. There was a strong lens wetting dependency on the type of surfactant used in the pre–soaking solution and subsequent substantivity of the surfactant. The different surface chemistries of the pHEMA–MAA and silicone hydrogel lenses appeared to play a key role in the observed lens dewetting phenomena.
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