L&T: In the Lens Lab

Oct
2002

A-R: Anti-Reflective or Awful Results?

Anti-reflective (A-R) coatings have had a troubled history since their introduction a decade or two ago. Initially, because of insufficient processing procedures and technology, the coatings weren’t very scratch resistant and they were prone to crazing or delaminating (from the lens surface). During the 1980s, A-R coated eyeglass wearers often complained about the difficulty in keeping coated lenses clean. (Thankfully, in the 1990s, hydrophobic coatings came to the rescue.)
Not surprisingly, these issues had a serious affect on repeat sales of A-R coated eyewear. The labs equipped with in-house coating systems—and the manufacturers producing these systems—have been working diligently over the years to correct these problems. In their defense, thin-film application to plastic is an extremely high-tech process. It’s only been through recent enhancements to computerized processing technology that some of these problems have been resolved.
The A-R Council—an industry group of coating manufacturers, distributors and, most recently, retailers—began the process of assessing what benefits an A-R coating brings to the consumer in general during the early 1990s.

A study by Ross and Bradley, at the Indiana University School of Optometry, completed the first study commissioned by the A-R Council. Their work has likely been the most significant to date because it proves that visual performance is reduced when looking through standard, uncoated lenses, particularly when driving at night. Those over 40—the age when night blindness begins to take its toll—benefit significantly from the use of an A-R coating. In fact, I received a call recently from an 83-year-old Florida man who told me his wife had begun allowing him to drive a car at night again because of the improved acuity his A-R coated lenses gave him. He was elated, proving that A-R coatings have opened a new benefit for retailers/opticians and their sales people to bring to patients’ attention.
With significant progress made in terms of performance, the A-R Council has turned its attention to problems with crazing and adhesion, some of which relate to processing issues. In the early- to mid-1990s, the organization initiated the process of establishing standards for testing that could identify coating problems before the lenses are sent out to the public. This has taken many years but the standards are nearly all complete and available. In fact, some of these standards are used here at COLTS Laboratories when testing A-R coatings.

At the same time, manufacturers of A-R coating machines have been busy finding new technology for coating the various lenses available in the marketplace (some call this “substrate matching,” an issue given all of the new lens materials and designs on the market today). Some have had great success in the improvement of the “stay-ability” or retention of an A-R coating.

At COLTS, we use a test we call “Real Life Simulation.” The test was devised about four years ago after we received a request from a retail organization. It has been compared to a one-year, 244-person clinical study/wearer test and found to directly correlate to actual wear. Using this test, we have seen a dramatic improvement in the capability of some A-R coating equipment to produce product that is defect free after three years of wear (see chart on previous page).
This is a significant step in the process and progress of improved A-R coatings. Based on what we’ve seen at COLTS, I am sure this trend will continue in the years to come as the product continues to add yet another dimension to the benefits of quality eyewear.

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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