Vision Care Product News

MAY 2017

Product information for optical people.

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Page 54 of 83

VCPN IMPACT - RESISTANT LENSES: PAST, PRESENT AND FUTURE A RANGE OF DIFFERENT LENS MATERIALS MEET THE STANDARD, INDUSTRIAL SAFETY AND BALLISTIC LEVELS OF IMPACT RESISTANCE TO KEEP PATIENTS SAFE UNDER A VARIETY OF CONDITIONS By Ed De Gennaro, MEd, ABOM Requiring lens impact resistance in eyewear is a modern idea. From a durability perspective, eyeglasses have been viewed for the most part as delicate and even sometimes flimsy devices throughout history. Through the centuries, lenses were made of glass, and because of this, people accepted that their eyeglass lenses could scratch, chip and break. Back then, the only way to have made them stronger was to make them thicker, which would make them heavier, uncomfortable and poorly cosmetic. While the (U.S.) National Bureau of Standards published the Z2 Handbook H24 detail- ing the eye and face protection of industrial workers beginning in the 1930s, it wasn't until the 1960s that a dialogue began in America about protecting con- sumers from eye injuries through federal regulation. Supported by optical industry groups such as The Better Vision Institute and Prevent Blindness, the momen- tum for such regulation gained strength, and in 1971, the Federal Food and Drug Administration (FDA) established an impact resis- tance standard for eyeglass lens- es (Code of Federal Regulations CFR 801.410). The regulation prescribes a test that uses a stain- less steel ball dropped free-fall 50 inches onto the lens's front sur- face, which precipitated the rule's nickname of the "drop ball test." Understand that the discov- ery of glass dates back thou- sands of years. Contrast that with the implementation of a federal impact resistance regula- tion to protect consumers for eye injuries and you'll understand why eyeglass lens impact resis- tance for consumers is a mod- ern issue. That's not to say that impact resistance was completely ignored by the optical industry. Several manufacturers produced very capable safety eyewear using glass lenses. Yes, the lenses were thick and heavy, but they did the intended job. It was the advent of more capably impact-resis- tant plastic lens materials that spurred the industry to consider the impact resistance regulation. THE PRESENT For eyecare professionals, know- ing the exact impact resistance of a material is difficult for a few rea- sons. For starters, lenses break at different stress levels depend- ing on the type of object that strikes them. For example, a lens material may break at a lower impact with a large mass, slow moving projectile then it does with a small mass, high velocity projectile. For another material, it might be exactly the opposite. The shape of the lens material is a factor, as is the material's thickness. The size, shape and density of the projectile are all factors too. Life doesn't provide a single impact challenge to eye- glass wearers, which is the prob- lem with having a single impact test for the regulation. Lens materials manufactur- ers are more concerned with the overall performance of the materials they produce because they must perform well for Vision Care Technology May 2017 53 Courtesy COLTS Laboratories Courtesy Wiley X

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