Impact resistance of ophthalmic lenses of various strengths and the influence of frame design.
Protection of the eyes by safety type spectacle, sunglass and goggle lenses has received considerable attention in recent years. Such protection can be enhanced by design of the frame. We report from 476 lenses mounted in 238 frames and subjected to 9,397 impacts. Maximum blows were delivered by a one inch diameter steel ball falling from a height of 122 inches. Results indicated that the force required to fracture lenses in plastic frame mountings was more than twice that required for fracture of identical strength lenses in wire rims. Minus cylindrical lenses were the most frangible. The lowest fracture and posterior dislocation rates were found in industrial plastic frames with a retaining lip. Greater energy attenuation can be induced in a heat tempered glass lens by even edge compression. Good lens and frame design, when properly correlated, should provide impact  attenuation distinctly exceeding conventional standards.
D005069:Evaluation Studies as Topic; D005135:Eye Protective Devices; D005139:Eyeglasses; D005898:Glass; D006245:Hardness Tests; D006257:Head; D006358:Hot Temperature; D006801:Humans; D008670:Metals; D008961:Models, Structural; D010969:Plastics; D011312:Pressure; D011482:Protective Devices
D008670:Metals; D010969:Plastics