Fig. 7. Average impact energies fracturing 2-mm thick lenses as a function of projectile (steel-ball) diameter. Impact energy increases with both projectile size and projectile velocity. Z80.1 indicates the impact energy of the ANSI dress lens drop-ball test (B· ,-inch steel ball). (Modified from Davis JK: Perspectives on impact resistance and polycarbonate lenses. Int Ophthalmol Clin 28:215, 1988.)