QUANTITATION OF CONTACT LENS CONTAMINANTS

Abstract

An artificial tear (AT) preparation containing 6 proteins and 6 lipids was developed as a deposit model (DM) for contact lens contamination. Quantitation was achieved by labeling with 14C and 3H and measuring the amount bound to the lens. Comparisons were made between deposition from AT and simpler DMs. Lens types included rigid gas permeable (RGP) and the four FDA groups of hydrogel lenses. A simple DM with lysozyme, a major lens contaminant, as the only protein in an isotonic solution gave deposits of 2.5–4.5 μg on Group I, II, III, and RGP lenses (24 hr) but 125 μg on Group IV (ionic, high water content) lenses. From the more complex AT preparation, lysozyme deposition decreased except for Group IV which showed an increase to 256 μg. Thus interaction of substances in the deposit solution affect deposition of the individual components. Extraction of lenses with acidified aqueous acetonitrile removed >90% lysozyme, but for Group IV lenses 3X as much radioactivity was recovered as was detected by counting the lens directly. This finding was used to estimate that about 1/3 of the lysozyme was at the surface of the Group IV lens while the remainder penetrated the gel network. Deposition of cholesteryl oleate, dioleoyl phosphatidylcholine, and triolein was examined on hydrogel and RGP lenses. The deposit was always < 1 μg/lens. A limitation was the amount of lipid that could be incorporated into AT; e.g., as the concentration of triolein increased from 1.8 to 8.8 (ig/ml AT, deposits increased form 3 to 60 ng/lens. This radiochemical methodology has proved to be a highly sensitive way to measure binding to contact lenses.