ASK THE LABS

Dispensing Glass

Though not as popular as plastic and other lens materials, glass has a place at the dispensing table. Here’s what you should know….

a couple of months ago, this column addressed whether glass was still a viable lens material, and what type of Rx or patient would be a good fit for this sometimes forgotten lens. (Yes, its pristine optics makes it still a viable choice for many people, especially those who want a highly scratch-resistant lens and superior optics). But there was still more to talk about. We asked a couple of labs that process glass to weigh in on some more questions about when and how to best dispense these lenses.

Q: Are there restrictions on using glass lenses (other than safety and for children)?

a: Glass is usually not recommended for higher prescriptions due to the weight of the produced lenses. The stronger the prescription, the thicker the lens; and the thicker the lens, the heavier it’s going to be. While there are options for minus lenses, such as 1.70 or 1.80 index lenses, this tends not to be an option for higher plus lenses. Most of the higher-index materials tend only to be available in low base curves, making higher-plus prescriptions difficult to do in glass.

For similar reasons, larger frames in glass also tend to have the same problems. They usually create lenses that are fairly heavy.

There are a few areas where glass is used instead of plastic. These include special leaded 1.80 index glass used for radiology, or sodium-filtering lenses used in glass working and to improve contrast.

— Bill “Other Bill” Heffner, IV, vice president, FEA Industries, Morton, PA

a: In general, most people will benefit from the superior visual acuity provided by glass lenses. In higher prescriptions, the dispenser and customer must manage the frame dimensions. Glass lenses are usually contra-indicated for children, those patients participating in high-impact activities such as sports or work environments requiring safety glasses, or anyone who has limited vision in one eye.

— Mike Yager, vice president, sales, Vision Dynamics Lab, Louisville, KY

Q: Does dispensing glass lenses present any particular challenges in fitting or processing?

a: The challenge with glass lenses is that they require more care than plastic lenses, from the perspective of both the ECP and the optical lab.

ECPs have to make sure they communicate to their patient the benefits of glass, as well as making sure they know the drawbacks. It should be easy for them to position glass as a more premium option, since it does have better optics and superior scratch resistance to pretty much any other material available. They just have to make sure the patient is aware that glass is going to be heavier than plastic.

— Bill Heffner, FEA Industries

a: Processing glass lenses presents some interesting challenges for labs. As a glass lens processor, you must have specific equipment dedicated to only processing glass. The lab must also have people experienced in processing glass, which is quite different than plastic given the range of available indices up to 1.90. Each index has its own characteristics and nuances including how lenses are chem-hardened at the end of the process, as each glass lens must be individually dropped ball tested to meet FDA impact standards. Because of this, only a handful of labs are comfortable or skilled in processing glass.

— Mike Yager, Vision Dynamics Lab