In situ Activity of Lysozyme Deposited on Hydrogel Lenses

Abstract

Abstract: : Purpose: Deposition of lysozyme on hydrogel contact lenses is known to involve both adsorption and absorption. The overall deposition is dependent upon characteristics of the lens such as hydrophobicity, surface charge and water content. Lysozyme deposition on the HEMA–type etafilcon A lens (58% water content) is reported to be significantly greater than that to a silicone hydrogel lens (36% water content). Deposited lysozyme upon extraction from a lens demonstrated activity with a micrococcyl assay, but the degree of activity in–situ is unclear. Herein we report the in–situ activity of lysozyme on various lens types. Methods:Unworn etafilcon A lenses (SureVue), balafilcon A silicone lenses (Pure Vision) and a rigid gas permeable lens were soaked in various concentrations of lysozyme (5 ml of 2 to 100 ug/ml) for time periods up to 22 h. In–situ activity and amount of lysozyme were determined with a direct (without extraction) micrococcyl assay and a micro–BCA assay. Results:Screening of concentrations of lysozyme between ∼ 2 to 100 ug/ml indicated that concentration of 2 or 20 ug/ml in 5 ml phosphate buffer were most suitable for the assay system for etafilcon A lens. The total concentration (extracted) was higher than the concentration detected on the surface of lens. With repeated rinses (2 h intervals) of the lens, the concentrations on the surface decreased slowly. Markedly lower levels of lysozyme were deposited on silicone vs. etafilcon A lens, and about 90% was removed with the first rinse. Deposition on the RGP lens was low and no lysozyme was detected upon subsequent rinsings. Conclusions:Concentrations of lysozyme deposited on etafilcon A lenses appeared mostly absorbed and inactive but capable of replenishing a stable surface activity after repeated rinses. Total lysozyme deposited on the balafilcon A silicone lens from initially comparable concentrations to those used for the etafilcon A lens were markedly reduced and mostly adsorbed.

Keywords: cornea: tears/tear film/dry eye • contact lens