Lipid and protein deposition of N-vinyl pyrrolidone-containing group II and group IV frequent replacement contact lenses.
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PURPOSE: The purpose of this study was to investigate the degree of protein and lipid deposition that occurs on N-vinyl-2-pyrrolidone (NVP) containing group II (non-ionic, high water content) and NVP containing group IV (ionic, high water content) frequent replacement hydrogel contact lens materials. METHODS: Twenty subjects were fitted with Group II (Vasurfilcon A) and Group IV (Vifilcon A) contact lenses, which were replaced monthly. The lenses were worn as a contralateral pair for 3 consecutive monthly periods. At the end of each monthly period, the lenses were collected for analysis of protein and lipid deposits. Protein deposition (following extraction) was examined by transmission UV and lipoidal deposition was examined using fluorescence spectrophotofluorimetry. RESULTS: There was a significant difference in the lipid and protein deposition profiles between the two materials. The Group II lens deposited approximately 2x more lipid (38 versus 73 fluorescence units; P < 0.0001) and the Group IV lens deposited approximately 17x more protein (488 micrograms versus 28 micrograms; P < 0.0001). Whilst the mean results across months were not significantly different for either protein or lipid (P = NS), the results revealed significant inter- and intra-subject variation. CONCLUSIONS: Protein deposition was predominantly controlled by the ionic charge of the lens materials, whereas the lipid deposition was predominantly determined by the NVP content. This study demonstrates that inter-subject variation and material characteristics significantly influence the deposition profile of hydrogel contact lens materials.
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