L&T: In the Lens Lab

Aug
2002

Hit or Miss

Hit or
Miss
Illustration by Jane Sanders

Addressing the FDA’s requirements
for impact-resistance testing.

By John Young

Back in the early 1970s, the U.S. Food and Drug Administration (FDA) enacted a regulation regarding the testing of glass lenses for strength and impact resistance. Glass was the prominent material at the time; conventional plastic was still in its relative infancy.

In fact, in those days, high-index plastic and polycarbonate lenses were not yet available for use in ophthalmic eyewear. In addition, there were no hard coatings or anti-reflective (A-R) coatings available on plastic lenses. When the FDA wrote the regulation (21 CFR Part 801.410) they simply were not aware of what was coming. As a result, since then, the agency has allowed manufacturers of plastic lenses to “batch test” the lenses they make each day to ensure they pass its “Drop Ball” test. Thus, optical labs and dispensers could use these lenses without worrying about testing them individually prior to dispensing; after all, testing lenses with a 5¼" steel ball would cause damage to the surface of each and every lens by leaving a small impression or dent.

The only problem is many of the A-R and hard coat treatments we use today affect the impact strength of the lenses dispensed. Based on the testing we have completed at COLTS, a hard coating will decrease plastic lens strength anywhere from 20 to 70 percent. A-R coatings, meanwhile, can reduce plastic lens strength 30 to 50 percent. A hard coating plus an A-R coating—the most popular combination today—can reduce plastic lens strength 40 to 80 percent.

Why? A plastic lens is prone to scratching because its surface is soft. A coating that is harder will likewise be more brittle than the lens. With plastic lenses, if the marriage between coating and lens is good—and bonds the coating permanently to the surface of the lens—then the lens also becomes more brittle. When a lab spin-coats a hard coat to the surface of a plastic lens, both the thickness and the age of the coating being applied can seriously affect the strength of the lens. Finishing, too, can have an impact on lens strength if there is too much force or the edger wheel is dull. Forcing a grooving machine to cut the lens or pushing a dull drill when creating mounting holes also significantly affects strength.

For these reasons, lens manufacturers have eliminated the warranties they have traditionally offered on their lenses based on their own daily “batch testing” (even thought they still conduct these tests). Now, it is up to each lab and dispenser location to complete impact/strength testing when they have finished processing a lens.

It is still possible to statistically “batch test” these lenses, as long as testers follow the FDA’s statistical program. Some suggest weekly “batch testing” (which is not specified in the FDA regulation). But, it should be noted that when a product fails testing, FDA regulations 21 CFR 820.80 and 820.160 state there must be a way to guarantee recall of all products processed during that period. It is for this reason daily testing is preferred. The OLA has issued an excellent methodology to help labs ensure they are testing all of the potentially dangerous lenses and treatments they may miss by some other methods. COLTS Laboratories and the OLA have also worked together to offer a low cost, no hassle method that is the only guaranteed solution available—other than testing every lens per FDA guidelines.

So there are options available to the retailer and the optical lab to comply with FDA requirements. What is not available is the option to ignore this law. Process variability alone can cause lenses that passed yesterday to fail today. We have been very fortunate in the ophthalmic industry to have a low level of wearer injury due, in no small part, to this FDA regulation. Diligence will maintain our good record and keep our liability down in these litigious times.

John Young is an ophthalmic lens expert with more than 25 years experience in the optical industry. He has worked for several lens manufacturers, including American Optical and Essilor, and is the former technical director of the Optical Industry Association. His company, COLTS Laboratories, is a Clearwater, Fla.-based independent lens testing facility designed to provide thorough and accurate quality and performance evaluations of spectacle lens products. His clients include lens manufacturers, wholesale labs, independent research organizations, large retailers and independent dispensers. The lab was the first U.S. ophthalmic testing laboratory accredited by the American Association for Laboratory Accreditation. It is also a Safety Equipment Institute-accredited eye protection/safety test lab. Young can be reached by phone at (727) 725-2323 and by email at john@colts-laboratories.com.

 

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