Adhesion Measurements of Hydrogel Contact Lenses

Abstract

æAdhesion of hydrogel contact lenses is important for manufacturing considerations, user comfort, and conditions/complications to the health of the corneal epithelium of the user. One serious patho-physiology is corneal erosion, in which it is postulated that the hydrogel lens disrupts and damages sections of the corneal epithelium due to the hydrogels mechanical and adhesive properties. To this end, we quantitatively characterize the adhesion of contact lenses onto planar substrates. Using a Universal Testing Machine (UTM) we establish a protocol that compresses lenses of various brands against a planar substrate and consistently measures the applied force, F, approach distance, w0, contact radius, a, and the deformed lens profile w(r). From F(w0), the critical ñpull-offî and ñpull-inî forces are measured, which are used as a metric to deduce the overall lens adhesion energy using a linear elastic æshell model. Moreover, high speed imaging captures the delam-ination process as the substrate is pulled off of the sample lens surface, giving insights into the coupled mechanical and adhesion behavior for the first time.