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P. Stauffer, R. Desousa, D. Meadows, H. Ketelson; Effect of Solution Parameters on Bulk Water in Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4872. doi: https://doi.org/.
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The main objectives of this study were to explain, through in-vitro tests, why lens dehydration occurs in vivo during wear. To answer this objective the effect of temperature and solution osmolality on the bulk water in different contact lenses was studied.
Acuvue Advance*(AA), O2Optix* (O2O), SofLens* (SL), PureVision* (PV) and Acuvue*2 (AV2) contact lenses were equilibrated in solutions of osmolality 90, 300 and 480 mOs/kg , at temperatures of 4, 23 and 40 ºC. The percent water content (WC), diameter and structure of the water in these contact lenses was determined under each of these conditions.
All the lenses showed changes in their WC and diameter under different equilibration conditions. The changes also depended on the lens type being studied. AV2 lenses showed large decreases in WC (~20%) with increasing osmolality (90 to 480 mOs/kg) while increasing the temperature from 4 to 40 ºC lowered their WC only around 5%. The PV, AA and O2O lenses and the SL lenses, all showed similar trends in their WC profiles with changing temperature and osmolality, which were different to those observed for AV2 lenses. The WC of the PV, AA, O2O and SL lenses was significantly lowered (~20%) with increasing temperature (4 to 40 ºC) while increasing the osmolality of the soaking solutions (90 to 480 mOs/kg) produced minor decreases in WC. PV, AA and SL showed a larger WC decrease when the temperature was increased from 23 to 40 ºC compared to the change from 4 to 23 ºC. This was not observed for the O2O and AV2 lenses. The water structure present in these lenses under the different conditions was investigated by DSC and showed differences among the lens types.
The diameter and water content of contact lenses depends strongly on the temperature and the osmolality of the equilibration solution. The degree of these effects varies with the different lens types especially in the case of the silicone hydrogel lens materials. Then data obtained in this study suggests that rather than undergoing in vivo evaporation, lenses merely reach equilibrium according to how each lens material reacts to its physical environment.
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