In vitro Uptake and Release Interactions of Benzylkonium Chloride (BAK) by Silicon–Containing and p–HEMA Hydrogel Contact Lens Materials

Abstract

Abstract: : Purpose: The in vitro uptake and release behavior of benzylkonium chloride (BAK) with silicon–containing (lotrafilcon and galyifilcon) and p–HEMA–containing (etafilcon and vifilcon) hydrogel contact lenses was studied via extract analysis with the Bovine Lens Assay and the Sodium Fluorescein Permeability Assay (SFPA). Methods: Contact lenses were soaked in a solution at varying concentrations of BAK (1%, 0.1%, 0.01%, and 0.001%) for more than 24 hours at room temperature. After exposure contact lenses were placed in a saline solution a total of 7 days at 37° C. Bovine lenses were exposed to the extract for 15 minutes, rinsed with saline and M199 and then incubated in culture medium at 37° C and 4–5% CO₂. The Bovine Lens Assay measures the potential for ophthalmic irritancy of an extract by evaluating its effect on the optical properties of the lens with a scanning laser system for 72 hours after exposure. With the SFPA, Mandin Darby Canine Kidney (MDCK) cells were grown to 80% confluence and were prepared for treatment in 24 well plate inserts. The SFPA evaluates cell membranes and tight junctions of a cultured MDCK monoloayer. Results are obtained spectrophotometrically. Results: The Bovine Lens Assay demonstrates that exposure to extracts obtained from silicon–containing lenses were significantly more damaging to the lens at higher concentrations then that obtained from the p–HEMA–containing contact lenses. Compared to controls (n=5, p<0.05) loss of sharp focus was evident with extract obtained from silicon–containing 1% BAK increasing from 0.29±0.03 mm (SEM) to 1.09±0.21 mm (SEM), whereas p–HEMA–containing at 1% BAK had no effect. Similar results were noted for SFPA. Conclusions: This experiment demonstrates that the Bovine Lens Assay and the SFPA can be used with extracts to determine the potential effects of an ophthalmic agent and its behavior with various contact lens polymers on the physiological and functional properties of the lens and on the integrity of an epithelium in culture.

Keywords: contact lens • ocular irritancy/toxicity testing • optical properties