Influence of Day and Night Wear on Surface Properties of Silicone Hydrogel Contact Lenses and Bacterial Adhesion

Abstract

Abstract: : Purpose: The aim of this study is to determine the effect of continuous wear on physico–chemical surface properties of silicone hydrogel contact lenses and their susceptibility to bacterial adhesion. Methods: In this study volunteers wore two pairs of either "lotrafilcon A" or 'balafilcon A" silicone hydrogel lenses. The first pair was worn continuously for a week, the second pair for 4 weeks. One lens out of each pair was used for surface characterization, the other one for bacterial adhesion experiments. Lens surfaces were characterized by examinination of their wettablilty, roughness and elemental composition. Adhesion of the hydrophilic Staphylococcus aureus 835 and hydrophobic Pseudomonas aeruginosa #3 bacterial strains to a lens was studied using a parallel plate flow chamber. Results: Before use, the lotrafilcon A lens was rougher, was more wettable and had a higher susceptibility for S. aureus adhesion than the balafilcon A lens. After wear, both lens types became more and equally wettable, whereas the differences in elemental surface composition decreased as well. S. aureus adhered more on worn balafilcon A lenses, while the opposite was seen for P. aeruginosa. The initial deposition rates of both bacteria to lotrafilcon A lenses decreased by wearing and were found to correlate with the surface roughness of worn lenses. Conclusions: In this study the differences in surface properties between 2 types of silicone hydrogel lenses were found to change after 1 week of continuous wear. Generally, bacteria adhered in lower numbers and less tenaciously to worn lenses, except S. aureus, adhering in higher numbers to worn balafilcon A lenses.

Keywords: contact lens • microbial pathogenesis: experimental studies • keratitis