Four of five prescription eyeglasses are not strong enough to withstand everyday hazards, such as getting hit with a tennis ball, even though they’re up to government standards.
Reliable data on how many people are injured each year by shattered eyeglasses are not available, but Dr. Paul F. Vinger of Tufts Medical School in Medford, Mass., says he bets “there are a couple thousand a year.”
Of the four materials commonly used for eyeglass lenses, only polycarbonate plastic has high-impact strength, Vinger found in a study published in today’s edition of The Journal of the American Medical Association.
Polycarbonate is used in an estimated 18 percent to 20 percent of prescription glasses.
The other common materials - allyl resin plastic, heat-tempered glass and chemically tempered glass - all shattered when Vinger and his fellow researchers struck them with baseballs, tennis balls, lacrosse balls, golf balls and air gun pellets.
“Why put something in front of your eye which, if it breaks, could hurt you?” he said.
The U.S. Eye Injury Registry recorded 8,200 serious eye injuries over the past few years, with 82 percent occurring when the victim was not wearing glasses. Dress glasses were worn in 3 percent of the cases and safety glasses in 2 percent. Type of eyewear was not known in the rest.
Dr. Stephen Miller, director of the American Optometric Association’s clinical center in St. Louis, said there’s no question that polycarbonate has more impact resistance.
“But I’m not sure there’s much of a problem,” he said. “For everyday use there’s probably no compelling reason to change the standards.”
He said polycarbonate has some drawbacks, including higher price and distortion around the edge of lenses in large frames.