Fig. 6. Average impact energies and range of impact energies that fracture 2-mm thick spectacle lenses. Projectiles were B· ,- or C· v-inch steel balls. Z80.1 indicates the impact energy of the ANSI dress lens drop-ball test, 0.2 J or 0.15 ft-lb. (Modified from Davis JK: Perspectives on impact resistance and polycarbonate lenses. Int Ophthalmol Clin 28:215, 1988.)