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  • Title: The effect of lens wear on refractive index of conventional hydrogel and silicone-hydrogel contact lenses: a comparative study.
    Author: Lira M, Santos L, Azeredo J, Yebra-Pimentel E, Real Oliveira ME.
    Journal: Cont Lens Anterior Eye; 2008 Apr; 31(2):89-94. PubMed ID: 17964212.
    Abstract:
    PURPOSE: The purpose of this work was to evaluate the ability of four silicone-hydrogel contact lenses (galyfilcon A, balafilcon A, lotrafilcon A and lotrafilcon B) to retain their equilibrium water content before and after wear, through measurements of refractive index and compare with that of a conventional disposable hydrogel contact lens (etafilcon A). METHODS: The refractive indices of 115 contact lenses were measured using an automated refractometer (CLR 12-70, Index Instruments, Cambridge, U.K.) before and after a schedule of daily wear by 58 patients for 30 days in the case of silicone-hydrogel lenses and 15 days for the conventional contact lenses. RESULTS: In the silicone-hydrogel contact lenses the changes on the refractive indices were not statistically significant, however after being worn the refractive index of the conventional etalfilcon A hydrogel contact lens increased significantly (p<0.001). CONCLUSION: The results presented here show that after being worn the silicone-hydrogel contact lens, show more capacity to retain or to reach their initial equilibrium water content than conventional hydrogel contact lenses. This suggests that the silicone-hydrogel contact lenses are less susceptible to spoilation over time maintaining its biocompatibility and contributing to the clinical success of lens performance.
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