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T. F. Svitova, T. Leung, M. C. Lin; Dynamics of Contact Lens-Surface Wettability in vitro: Effect of Dehydration-Rehydration Cycles. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3427. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of dehydration on soft contact lens surface wettability in vitro.
Wettability of contact lenses immersed in surfactant-free lens-care solution was evaluated in a dynamic-cycling regime using a modified captive bubble apparatus. The advancing and receding angles were measured concurrently with surface tension. Conventional pHEMA-based lenses (Accuvue2 (AV2), BioMedics55 (BM55), Proclear (PC), Extreme H2O), and silicone hydrogel (SiH) lenses (AirOptics N&D (AOND), PureVision (PV), Biofinity, Accuvue Oasys) were examined. The wettability measurements of pristine lenses were made in 20 ml of surfactant-free solution. After contact angle (CA) measurements, each lens was dried in a low-humidity environment for 1 hour, immersed in fresh solution and rehydrated for 30 min. CA and surface tension (ST) were then measured. The same lenses were dried overnight and rehydrated for 30 minutes; the measurements of CA and ST were repeated. ST of blister-pack solutions was measured by pendant drop method.
ST of blister-pack solutions ranged from 38 (Extreme H2O) to 68 mN/m (AOND). For all lenses, ST was lower than that of a surfactant-free solution (71.4±0.5 mN/m). Conventional lens surface wettability, gauged by aqueous adhesion energy (Eadh), was lowest for pristine BM55 lenses (34±1.2 mN/m) and similar for the remaining lenses (44.9±2 mN/m). For BM55 and AV2 lenses, dehydration for 1-hour or prolonged overnight dehydration followed by rehydration did not cause significant changes in lens surface wettability (p >0.05). For PC and Extreme H2O lenses, prolonged dehydration reduced Eadh by 10±3.5 mN/m and 7.1±2.3 mN/m, correspondingly, and the changes were statistically significant (p < 0.01). For SiH-lenses, overnight drying followed by rehydration changed Eadh within only ±5 mN/m, which was not statistically significant (p > 0.05).
The surface-active ingredients of blister solutions or built-in lens matrixes affect wetting properties of all studied SCLs. We hypothesize that these surfactants accumulate at the dry lens surface and facilitate lens rehydration after complete dehydration, and thus help to maintain lens-surface wettability. Consequently, none of the studied lenses became irreversibly hydrophobic after dehydration - rehydration cycles.
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