Quantity and Conformation of Lysozyme Deposited on Conventional and Silicone Hydrogel Contact Lens Materials Using an In Vitro Model

Abstract

Purpose. To determine the activity of hen egg lysozyme (HEL) deposited on conventional and silicone hydrogel contact lens materials by using an in vitro model. Methods. ACUVUE 2 (etafilcon A), PureVision (balafilcon A), ACUVUE Advance (galyfilcon A), Focus NIGHT & DAY (lotrafilcon A), O2 Optix (lotrafilcon B), Proclear (omafilcon A), and ACUVUE OASYS (senofilcon A) contact lenses were deposited in vitro in a phosphate-buffered solution (PBS) containing 2 mg/mL HEL. Lenses were briefly rinsed in PBS to remove unbound material and extracted in a mixture of acetonitrile and trifluoroacetic acid. After lyophilization, extracts were examined for lysozyme activity by micrococcal assay and total protein by Western blot. Results. In terms of total protein accumulation, ACUVUE 2 showed the most, with 1,800 μg per lens. Proclear was next, with 68 μg per lens, and Focus NIGHT & DAY showed the least, with 2 μg per lens. ACUVUE Advance, ACUVUE OASYS, and O2 Optix accumulated similar amounts of lysozyme, at approximately 6 μg per lens. Lysozyme deposited on ACUVUE 2 showed the greatest activity (91% ± 5%), and this result was statistically different from all other lens types (P<0.001). Lysozyme deposited on Focus NIGHT & DAY (24% ± 5%) and O2 Optix (23% ± 11%) showed the lowest activity. Lysozyme deposits on other lens materials showed intermediate activity (ACUVUE Advance, 60% ± 15%; ACUVUE OASYS, 51% ± 9%; PureVision, 58% ± 8%; and Proclear, 38% ± 3%). Conclusions. Silicone hydrogel lenses acquire less lysozyme deposit than conventional group II (Proclear) or group IV (ACUVUE 2) lenses do, and the levels of activity of the lysozyme are highly variable between materials.