Shatter resistance of spectacle lenses
P. F. Vinger, L. Parver, D. V. Alfaro 3rd, T. Woods and B. S. Abrams
Tufts Medical School, Medford, Mass, USA.
OBJECTIVE: To evaluate the relative strength and shatter resistance of
spectacle lenses currently used in sunglasses and dress, sports, and
industrial eyewear. DESIGN: Seven lenses that met the US American National
Standards Institute (ANSI) Z80 standards for dress glasses (made of
high-index plastic, allyl resin plastic, heat tempered glass, chemically
tempered glass, and polycarbonate, and with center thickness ranging 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 thickness) were
tested for impact resistance to 5 projectiles (air gun pellets, golf balls,
tennis balls, lacrosse balls, and baseballs). MAIN 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 test projectiles during their routine
use. Polycarbonate lenses demonstrated resistance to impact for all tested
projectiles exceeding the impact potential expected during routine use.
CONCLUSIONS: Under the test conditions of this study, polycarbonate lenses
demonstrated greater impact 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.
