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  • Why Glass? Why Not?

    This part one of a series on glass in today's market. The series will continue in LabTalk magazine throughout the year - This first article was originally printed in the Jan/Feb 2015 issue.

    Digital Glass

    Glass lenses appear to have received a bad reputation. People seem to believe that glass lenses are obsolete. With the latest digital technology, however, it's easy to bring glass back to the forefront of the optical world. I'm sure you are asking, “Why would you ever want to do such a thing?” While glass may seem an odd choice for a material, there's plenty of things about glass that can make it the better choice. When we compare to plastic, glass has improved optical quality, durability, and a much better value perception from the customer.

    I'm fairly sure that most people will agree that glass has the best optical properties out of any material currently used to make optical lenses. There is a reason most equipment, such as a phoropter, tends to have glass lenses instead of using a material like polycarbonate. Having a higher optical quality is important when you're measuring, and it should be important to the care of the patient as well. Some patients may not notice any difference, and some patients can tell right away. For the more discerning patients, the superior quality of glass is something that they may not want to do without once they try it.

    Scratch resistance is one of the most sought-after qualities in a lens, which is why so much effort has gone in to developing all kinds of scratch coatings for plastic lenses. All of this effort in coating development to simply try and get back to the natural scratch resistance of glass. There is still no other optical material that comes close to the punishment that you can inflict on a glass lens. There's a reason that cell phones have glass screens and not plastic screens. I'm fairly certain that I want my eye wear to be at least as durable as my phone.
    This is not just in terms of scratching, but chemical resistance as well. This makes glass perfect for harsh conditions where other materials wouldn't last. Take polycarbonate, for example. It performs very well on impact testing. When you look at scratch resistance, however, it often comes up lacking. It can also do especially poor in places with a lot of chemicals, paints, and solvents – especially things like acetone. While we like it when a patient buys a second pair, we usually don't want it to be because the lenses had a problem.

    Glass has a certain feel that other materials just can't come close to. It's not just their weight, but there's a mystique around glass lenses that just make it seem like it's worth more than plastic. This is a great thing for the Eyecare Professional, as it makes it easier to use glass to fill a role in high-end lenses. Having this as a high-end product for something like sunwear, for example, helps to give added value to the final product. This is an important part in selling glass – the idea that it's a super-premium product. Since usage of glass isn't as widespread as plastic, glass has the ability to command a higher price – as it should, given the benefits that it has over many other materials.

    The Bad Side
    There are, of course, some negative things that have become associated with glass. One of these things is that glass has a very limited availability. This is in terms of both material/color selection, as well as prescription range and lens size. The second concern over glass tends to be about its weight – that it's too heavy for people to want to use.
    Thankfully, full-backside freeform has the same benefits in both plastic and glass, and greatly helps our availability. Technological advances in glass also make it possible to have thinner, lighter glass than ever before.

    Glass progressives have traditionally had a fairly restrictive range in terms of their color and size availability. Free-form helps us to eliminate that problem, since it's now possible to use single vision lenses to make a progressive. Just like with plastic free-form, this greatly opens up the color and lens size options that can be used, as well as a much quicker turn-around. This means that a full range of fixed-tint lenses – including gray, green, brown, rose, and yellow - are now available as progressives. Full back-side progressives in glass also help to overcome the issue of cut-out. Since the progressive design can be decentered on the back of the lens, it makes it possible to put a progressive in a much larger frame than was previously possible. Free-form also helps with the prescription range, as it's possible to get a glass free-form lens up to a +4.50 add power.
    Beyond general availability, it's important to note that there are also several major free-form designers that are currently available in glass. Apart from simply offering a 'house brand' lens, its important to be able to use brand-name designs as well. So far, lens designs from the following companies can be found in glass: IOT, KODAK, and Shamir.

    One of the major drawbacks to glass, compared to plastic, is weight. Glass can be heavy, especially with a high prescription. For low or plano prescriptions, however, there's not much of a noticeable difference between the weight plastic and glass. For higher prescriptions, there are some other options. High index glass is one option, though this can sometimes be a problem as well. As you use higher index glass, lenses do become thinner, but they can also become more dense. A better option is by using a brand new product called Thin & Clear. This material has all of the same properties as regular glass, but Thin & Clear can be made 25% thinner while still passing drop-ball. This means Thin & Clear can have a 1.5mm thickness, while regular glass usually has a 2.0-2.2mm minimum thickness.

    I sometimes hear that people don't like glass because they think that it's easy to break it, or that it's going to shatter while someone is wearing it. Most glass (unless it's polarized) is either air- or chemically-tempered to strengthen it. This ensures the glass is extremely tough and impact-resistant and is able to pass the drop-ball test. To this point, it's important to note that there's no requirement for every individual plastic lens to undergo drop-ball testing. The FDA only requires that a 'statistically significant' portion of them are tested. Glass lenses, on the other hand, must undergo testing with each and every lens. This means you can be sure that every glass lens – safety or dress wear – has been tested and won't shatter from an impact. Some people think having to drop-ball every lens means glass isn't safe. I prefer to think that it ensures that you know that when a lens is sent out, that it's already been tested and there's nothing to worry about. When it comes to plastic lenses, however, we just assume that if it's at a certain minimum thickness that it's going to be okay. It's also important to note that should a lens shatter, that tempered glass will crumble into dull pieces, while plastic tends to splinter in shards that can often be sharp.

    The question then becomes – how do we bring up the subject of glass with both Eyecare Professionals and with the end wearer? As with all new developments, education is the most important thing here. Obviously, glass isn't the best material for everyone all the time. It is, however, important to know all the options available. In order to go over all of the areas of important, I'll be exploring a number of different topics of glass that in future articles that will detail specific areas where these products can be positioned. Over the course of the year, we'll address the following topics:

    • Innovations in Glass Technology

    Thinner, lighter, better

    • On-the-Job Uses for Glass

    Occupational designs, shop workers, mechanics

    • Sunwear

    Premium eyewear, color availability, durability

    • Premium Brand Names

    IOT, Shamir, KODAK

    • Specialty Applications

    X-Ray, Contrast Enhancement, Glass Blowing

    All of these articles will explore what glass has to offer in specific markets. This will, hopefully, make it easier for an Eyecare Professional to find the right product for their customer. It will also help to dispel some of the myths around glass, and help to show it as the premium product that it is.

    Bill Heffner (the other one)
    FEA Industries
    Comments 7 Comments
    1. kaledarkwind's Avatar
      kaledarkwind -
      I just want to say, I read this article last week, and yesterday I had a PT that had a TON of questions about glass lenses. He was looking for Transitions in a FT28 and the options we work with were Trivex and Glass. Glass ended up being not only the cheaper option but also better as he works around chemicals. So Thanks for the Information as it provided me talking points and all the answers to the questions the PT asked.
    1. eyeguy245's Avatar
      eyeguy245 -
      The reason there's such a mammoth variety of lenses available is that there are consumers willing to buy the one most approprite for their needs/wants. Glass is one of the niches that deserves greater - much greater - attention. Prospective glass users are being ignored by our collective mindset that 'glass is dead.'

      It's not 'dead' for me...under the right conditions, glass outperforms optically, not to mention that most ARs adhere better than all plastics.
    1. DanLiv's Avatar
      DanLiv -
      Thanks for the article, it's making me think about glass (which I haven't except for ABO review in 15 years!).

      A big hindrance to me is AR. I AR everything I can, but in my limited experience with glass applying AR cancels the durability of glass and the lens is only as tough as the AR, and the ARs compatible with glass seem poor to me. I've had glass AR wearers come back after a couple years with very scratched lenses, but it's pretty clearly the AR that's scuffed and worn. I bet the glass underneath was fine.

      Can one get ALL the benefits of glass without foregoing AR?
    1. Mactire's Avatar
      Mactire -
      Great article. I often (read: always) get angry faces when I mention glass as an option.
      With glass selection becoming smaller the price goes up.
      I can understand employers preferring to sell plastics as the profit margin is higher.
      However, when wanting to sell a good product glass can be the better choice.

      For example, for some people progressive lenses aren't possible. So they will have to resort to bifocals. Most turn down bifocals and opt for two pair of glasses because they don't like the rim. Bifocals in glass however look much nicer than plastic ones.
    1. CCGREEN's Avatar
      CCGREEN -
      Round segs in glass are just about undetectable when pt is wearing them, so now you would have a almost invisible add.
    1. LilyO's Avatar
      LilyO -
      Excellent read! Thank you!
    1. johann's Avatar
      johann -
      Thanks for the article, it's a great view and information for me!!