SHATTER RESISTANCE OF SPECTACLE LENSES

Objective.-To evaluate the relative strength and shatter resistance of spectacle tenses currently used in sunglasses and dress, sports, and industrial eyewear. Design.-Seven lenses that met the US American Nati onal Standards institute (ANSI) Z80 standards for dress glasses (made of high-index plastic, allyl resin plastic, heat tempered glass, chemi cally tempered glass, and polycarbonate, and with center thickness ran ging from 1 mm to 2.2 mm) and 4 lenses that met ANSI Z87 standards for industrial safety eyewear (allyl resin plastic, heat-tempered glass, chemically tempered glass, and polycarbonate, all with 3.0-mm center t hickness) were tested for impact resistance to 5 projectiles (air gun pellets, golf bails, tennis balls, lacrosse balls, and baseballs). Mai n Outcome Measures.-Impact energy required to shatter spectacle lenses . Results.-Based on 348 lens impacts, dress and industrial lenses made from glass, allyl resin plastic, and high-index plastic shattered at impact energies less than those expected to be encountered from the te st projectiles during their routine use. Polycarbonate lenses demonstr ated resistance to impact for all tested projectiles exceeding the imp act potential expected during routine use.Conclusions.-Under the test conditions of this study, polycarbonate lenses demonstrated greater im pact resistance than other commonly used spectacle lenses that conform to prevailing eyewear standards. These findings suggest that current ANSI Z80 and ANSI Z87 standards should be reevaluated.