Depth Profile Assessment of the Early Phase Deposition of Lysozyme on Soft Contact Lens Materials Using a Novel In Vitro Eye Model

OBJECTIVE: To characterize the location of fluorescently labeled lysozyme on commercial contact lenses (CLs) using an in vitro eye model that simulates tear volume, tear flow, air exposure, and mechanical wear. METHODS: One commercially available conventional hydrogel CL material (etafilcon A) and three silicone hydrogel CL materials (balafilcon A, lotrafilcon B, and senofilcon A) were evaluated in this study. The CLs were mounted on the in vitro eye model and exposed to artificial tear fluid containing fluorescein isothiocyanate (FITC)-labeled lysozyme for 2 and 10 hrs. After these short incubation periods, circular discs were punched from the CLs at the center and periphery and were prepared for confocal laser scanning microscopy (CLSM). The CLSM captured a series of consecutive images spaced 5 μm apart, and the resulting images were rendered into two dimensional cross-sectional views of the CL. The mean fluorescence at each 5 μm slice was used to generate a histogram depicting the penetration of FITC-lysozyme into CLs. RESULTS: For both incubation periods, the CLSM images and histogram of etafilcon A showed that FITC-lysozyme is more concentrated at the lens surface, with a moderate amount of deposition in the lens matrix. For balafilcon A, FITC-lysozyme was evenly distributed throughout the lens. For lotrafilcon B, there was a greater amount of FITC-lysozyme deposition on the surfaces of the lens versus the matrix. Senofilcon A had differential FITC-lysozyme distribution profiles depending on the location of the lens. At the lens periphery, FITC-lysozyme primarily deposited on the surface, whereas FITC-lysozyme was uniformly distributed at the center of the lens. CONCLUSIONS: With the use of a sophisticated in vitro eye model, the study revealed a complex deposition pattern of FITC-labeled lysozyme on various CL materials after short periods of exposure. An understanding of the early deposition pattern of lysozyme on different CL material may elucidate new insights into the processes behind CL discomfort.