Compression Testing of Three Soft Lens Polymers with a Simulated Fingernail

Abstract

An analysis of the mechanical proper­ties of finished lenses utilizing com­pression testing identifies factors contributing to soft lens damage. Sauflon 70, Snoflex 50, and Toyo 515 PolyHEMA lenses, all of plano power and equal thicknesses were com­pressed within the optical zone by loads exerted by a simulated fingernail made of guitar pick material. Six lenses of each polymer were used for each of three tests. It was found that Toyo 515 PolyHEMA had a relatively lower compressive strength than the other two non-HEMA materials; that the Sauflon 70 had the least ability to recover once compressed; and that all three polymers did not appear to recover their previous compression strength after undergoing a dehydra­tion/rehydration cycle. In the case of the Toyo 515 lenses, this last result was confirmed statistically.