The Friction Coefficient of Commercially Available Contact Lenses at a Cornea-Contact Lens Biointerface

Abstract

Background: At the ocular surface, epithelial cells are subject to shear and frictionforces during blinking. This can lead to wear damage, especially when there isinadequate lubrication in the presence of a compromised tear film1. Contact lenses areassociated with increased lid wiper damage, epitheliopathy and tear film instability2caused by increased friction due to the lens material3. This may lead to dry eye disease.Due to this, lenses often include agents that attempt to improve surface properties.These properties, particularly friction, are therefore paramount to preventing ocularsurface damage and discomfort.Methods: A custom cornea-contact lens biomechanical friction test was used totest commercially available contact lenses (Air Optix Aqua, Acuvue Oasys, Acuvue2,and Acuvue TruEye Dailies) The contact lenses and human corneas (obtained fromLions Eye Bank, n=5) were articulated against each other in a saline bath at effectivesliding velocities between 0.3-30 mm/sec and under loads of approximately 12-32 kPa.Friction coefficients were calculated from the axial load and torque measured duringarticulation of the test surfaces.Results: Kinetic friction coefficients, <mkinetic, Neq>, in saline for each lens wasapproximately 0.080.02, 0.120.04, 0.150.05 and 0.090.02 for Acuvue2, Air Optix,TruEye and Oasys respectively (meansem). Values of <mkinetic, Neq> in TruEye weresignificantly greater than those in both AC2 and Oasys (p<0.05), which were not similarto each other and Air Optix Aqua (p>0.05).Conclusions: TruEye, a silicone hydrogel daily wear lens, had higher friction thanboth Oasys and Acuvue2, which were not significantly different from each other. Theseresults suggest that the unique wetting agent contained in Oasys and TruEye do notsignificantly affect in vitro friction measurements. Future experiments will examine ifadding ocular lubricants, such as hyaluronan and/or lubricin, can further reduce thefriction of these lenses and ultimately improve in vivo wear.