Assessment of friction in aged soft contact lenses by an innovative method

Abstract

In the present research work, we intend to evaluate the effect of aging of CL (contact lenses) on friction and, in case there are alterations in the value of the coefficient of friction after aging, to understand which modifications in the material incite these variations. For this, a simulation of the aging process to which the CL are subject in vivo is carried out and the friction and stiffness of the CL are characterized, before and after aging. The aging procedure of SCLs (soft contact lenses) was simulated by a cycling process considering that the main parameter influencing the material surface is the transition between the closed and open eye and the exposure to environmental aggressions, particularly ultraviolet radiation. The values of the coefficient of friction and elastic modulus before and after the aging process were compared and was verified the increase of both parameters for all contact lenses. The hydrogel lens was the least affected by aging and the silicone - hydrogel lens based on delefilcon A was the one that showed the least stability of properties.

Keywords: Aging; Biotribology; Friction; Hertzian contact; SCLs (Soft contact lenses).