The effect of lens wear on refractive index of conventional hydrogel and silicone-hydrogel contact lenses: a comparative study

Lira, M.; Santos, L.; Azeredo, J.; Yebra-Pimentel, E.; Real Oliveira, M.E.C.D.

Contact Lens and Anterior Eye the Journal of the British Contact Lens Association 31(2): 89-94


ISSN/ISBN: 1367-0484
PMID: 17964212
DOI: 10.1016/j.clae.2007.09.001
Accession: 056305632

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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). 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. 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). 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.