Ex vivo analysis of cholesterol deposition for commercially available silicone hydrogel contact lenses using a fluorometric enzymatic assay.

Abstract

Lipid deposition on silicone hydrogel (SiHy) lenses, which are believed to be caused by their hydrophobic surface, can lead to discomfort, reduced vision, and inflammatory reactions. This study used a highly specific and sensitive fluorometric enzymatic assay for ex vivo cholesterol analysis of seven types of SiHy lenses: balafilcon A, comfilcon A, enfilcon A, enhanced-lotrafilcon A, enhanced-lotrafilcon B, galyfilcon A, and senofilcon A. Cholesterol sorption was assessed in 140 previously worn SiHy lenses from 8 clinical trials conducted in the United States and Australia between 2006 and 2008. Patients wore the lenses for 2 to 4 weeks. Unworn negative control lenses for each lens material were obtained directly from the manufacturer. Lipids were isolated from the lenses using a two-step chloroform: methanol extraction method, and total cholesterol was quantified using a fluorometric enzymatic assay. Nonparametric Mann Whitney statistical analysis was performed to determine the differences in total cholesterol sorption between lens-specific data sets. Enhanced-lotrafilcon A and enhanced-lotrafilcon B contact lenses showed significantly lower median total cholesterol sorption (median±quartile, 0.30±0.2 μg/lens and 0.09±0.1 μg/lens, respectively) than all other types of lenses that were tested (P<0.0001). By contrast, enfilcon A (3.96±0.8 μg/lens) and galyfilcon A (3.75±1.1 μg/lens) showed the highest median total cholesterol sorption of all tested lenses. Cholesterol deposition in SiHy contact lenses seems to be lens polymer dependent. Enhanced-lotrafilcon A and enhanced-lotrafilcon B both sorbed the lowest amount of cholesterol compared with the other five types of SiHy lenses that were tested in this study.