Fracture Characteristics of Ophthalmic Lenses

A variety of methods were used to apply strain to ophthalmic lenses, both glass and plastic. Some lenses were supported by a neoprene ring as required in the Food and Drug Administration (FDA) test procedure; others were inserted in a spectacle form and placed on a humanoid head form. Steel balls, aluminum cylinders, and pine boards were used to strike the lenses at defined velocities. Fractures of chemtempered glass lenses occurred in the range of 3800 to 20,000 microstrain. Plastic CR‐39 lenses survived 4000 to 5000 microstrain but failed beyond this range. A computer program was designed to simulate the experimental results and can be used to predict results when the conditions are altered.