Measurement of the fracture toughness of some contact lens hydrogels.

The fracture toughness of three polymethacrylate contact lens hydrogel materials was measured using the method of Generalized Fracture Mechanics. One hydrogel (SNOFLEX S68) had a significantly higher fracture energy per unit area (Jc) than the others, probably because it undergoes plastic deformation at high strains. Differences in toughness imply differences in the mechanical durability of the contact lenses in normal use, which could not be so readily deduced from the results of tensile strength tests.