Kinetics of in vitro Lysozyme Deposition on Silicone Hydrogel
L.N. Subbaraman1, M. Senchyna1, 2, L. Jones1 1School of Optometry, Centre for Contact Lens Research, University of Waterloo, Waterloo, ON, Canada, 2Alcon Research Ltd, Fort Worth, TX
PURPOSE: To determine lysozyme deposition as a function of time in group IV, group II and silicone hydrogel (SH) contact lens materials by artificially doping lenses with 125I labeled lysozyme.
METHODS: 4 individual Acuvue (AV; Gp IV), SofLens 66 (SL; Gp II) and SH lenses (Focus Night&Day (FND), PureVision (PV) and Acuvue Advance (AA)) were doped in 1mL of simple lysozyme solution (1.9 mg/ml) containing 125I labeled lysozyme. The lenses were doped for time periods ranging from 1 hr to 28 days at 37o C with constant shaking. Following the specified doping period, the lenses were rinsed briefly with phosphate buffered saline to remove unbound protein and were then placed in polypropylene tubes and counted in a Beckman Gamma Counter. The amount of protein adsorbed to the lenses was calculated by dividing the counts on the lenses by the specific activity of the protein.
RESULTS: Lysozyme accumulated rapidly on AV lenses (1 hr, 98±8 µg/lens), reached a maximum on the 7th day (1386±21 µg/lens) and then reached a plateau, with no further increase occurring (p=NS). Lysozyme accumulation on Gp II and SH lenses continued to increase across all time periods, with no plateau being observed (p<0.05). At 7 days, FND lenses deposited 1.8±0.4 µg of lysozyme per lens while PV and AA lenses deposited 5.9±2 and 3.6±1 µg of lysozyme respectively. After 28 days of doping, FND lenses deposited 4.2±1 µg of lysozyme per lens while PV and AA lenses deposited 19.4±3 and 16.8±4 µg of lysozyme respectively.
CONCLUSIONS: Radiochemical analysis is a sensitive and effective technique to determine the small quantities of lysozyme deposited on SH lenses. The kinetics of contact lens deposition depends on the chemical structure of lens material under consideration. Lysozyme deposition occurs rapidly with Gp IV materials before reaching a maximum, while SH and Gp II materials progressively accumulate lysozyme, with no plateau occurring.