Lysozyme sorption in hydrogel contact lenses

PURPOSE. To examine the processes involved in formation of protein deposits on hydrogel contact lenses. METHODS. The adsorption and/or penetration of lysozyme on or into three typ es of contact lenses, etafilcon A, vifilcon A, and tefilcon, were investiga ted in vitro using a radiolabel-tracer technique, x-ray photoelectron spect roscopy, and laser scanning confocal microscopy. RESULTS. Binding of lysozyme to high-water-content ionic contact lenses (et afilcon A and vifilcon A) was dominated by a penetration process. The exten t of this penetration was a function of charge density of the lenses, so th at there was a higher degree of penetration of lysozyme in etafilcon A than in vifilcon A lenses. In contrast, the binding of lysozyme to tefilcon len ses was a surface adsorption process. The adsorption and desorption kinetic s showed similar trends to those found in human serum albumin (HSA) adsorpt ion on lens surfaces. However, the extent of lysozyme adsorption on tefilco n is much higher than HSA adsorption, probably because of the self-associat ion of lysozyme on the tefilcon lens surface. Furthermore, either penetrati on or adsorption of lysozyme involved reversible and irreversible processes and were both time dependent. CONCLUSIONS. Binding of lysozyme to hydrogel lenses involves surface adsorp tion or matrix penetration. These processes may be reversible or irreversib le. The properties of the lens materials, such as charge density (ionicity) and porosity (water content) of the lenses, determine the type and rates o f these processes.