|Mike Ritzinger says he’s “very into the Abbe factor.” But that’s only one reason why the optician and owner of Gregory Optical in Elk River, Minn. is a proponent of glass lenses, which, in general, have higher Abbe values than their plastic counterparts.|
“I was fortunate to grow up with a father who was an optician,” he explains. “I used to get quizzed on optics at the dinner table every night when I was a kid. He used to say things like, ‘In my day there was no such thing as plastic.’ To him, glass was the only lens option and the best lens option.”
Times have changed, of course, and glass now accounts for only about 10 percent of the lenses dispensed at Gregory Optical and 4.7 percent of the lenses dispensed among independents nationally, according to the 20/20 MarketPulse—Premium Lens Survey of Independents. But for Gregory, glass is an important niche, Ritzinger says. Of the dispensary’s glass sales, 80 percent fall into the photochromic category, with conventional glass as the base material.
“The stereotype still holds,” Ritzinger notes. “Construction workers, delivery people and farmers—people who spend a lot of time outdoors—love those lenses.” The remaining 20 percent, however, encompass what the dispenser refers to as the “most valuable lenses” he sells—high-index glass lenses. High-index glass lenses are some of the thinnest lenses available on the market. They are available with indexes of refraction in the 1.60 to 1.90 range, some higher—and thinner—than even the highest-index plastic lens to date (1.74).
“We sell these lenses primarily to professional people,” Ritzinger says. “How they look is important to them. They want the thinnest lens possible and, for them, money is no object. They’ll easily spend $500 to $600 on a pair of eyeglasses. The look is worth it to them.”
What they don’t always realize is they are also benefiting from the best optics spectacle lenses have to offer. The primary measure of optical quality—Abbe value—gauges the amount of chromatic aberration in a lens material. Chromatic aberration refers to the unwanted color eyeglass wearers can see around objects as a result of imperfections in the lens. The higher the value, the lower the amount of aberration (therefore, the better the overall optics).
Glass and high-index glass lenses have Abbe values in the upper 50s (60 is considered optimal). Conventional plastic lenses have an Abbe value of 58, but polycarbonate, Trivex, mid-index plastic and high-index plastic have Abbe values between 30 and 50.
“If patients are willing to be converted to glass after we’ve explained all the issues, we make sure they know exactly what they’re getting for their buck,” Ritzinger says. “When we deliver their new eyewear, we have them look through their new eyewear, then look through their old eyewear again so they can see the difference. They always say their vision seems much crisper.”
Typically, dispensers like Ritzinger say high-index glass customers fall into the upper income levels and favor high-end frames as well. They use their high-index glass eyewear as a “dressy” back-up pair or “for going out,” preferring them for cosmetic reasons to thicker high-index plastic product. The product allows dispensers to drastically reduce the edge and center thickness for their high-myopic customers, creating a unique cosmetic appeal for patients who might otherwise be fitted with thicker lenses.
Of course, with every benefit, there’s a cost and there are, as Ritzinger says, “issues” with glass lenses. Many of the thinner, high-index (i.e., more cosmetically appealing) glass lenses do not meet U.S. Food and Drug Administration requirements for impact resistance, meaning they do not pass the “drop-ball” test. Dispensers fitting these lenses usually ask patients to sign a waiver acknowledging they’ve been told of and understand the potential safety issues of wearing high-index glass lenses.
But while glass lenses aren’t as impact-resistant as their plastic counterparts, they are more impervious to scratching. They also retain lens treatments and coatings (such as anti-reflective coatings and cosmetic tints) more effectively.
“Glass lenses can last 30 years,” Ritzinger claims.
Dispensers, though, do have to be careful about the types and styles of frames they use with high-index glass. Unless high-index glass is fit into a smaller frame, the size of the lens could lead to a weight problem and offset the benefits of the thinner product. Plastic frames offer better support for high-index glass than wire and rimless frames because exposed glass edges can chip easily.
Dispensers also suggest staying away from high-index glass bifocals. Because the high-index glass bifocal segments are fused together (rather than molded into the lens as they are in plastic bifocals), dispensers say there is “too much of an image jump” between the visual fields. They suggest dispensing a separate pair of plastic progressives, multifocals or clip-ons for presbyopes.
And there are other issues. Though Ritzinger, who finishes all his lens orders on-site, says that glass presents few if any problems in the lab, wholesale lab executives warn glass lenses do take longer to process in both the surfacing and finishing areas, and they are also a challenge to mount. This is of course due to the fact they are more prone to breakage than lenses made from other materials. In addition, many of today’s newer “dry-cut” edgers can not process glass lenses. Glass can only be edged by “wet-cut” edgers.
Also, glass lenses finished in-office usually don’t meet FDA standards for impact-resistance. Most dispensers do not have the facilities necessary to temper (either chemically or via heat) glass lenses and then test them for FDA compliance on-site. Chemical tempering, the preferred method, can take more than 12 hours.
But in the minds of dispensers like Ritzinger, the positives to dispensing high-index glass lenses far outweigh the particulars. He says he’s able to sell the lenses for as much as twice the price as conventional plastic lenses.
“They’re my favorite lenses to dispense,” he says.