Eyeglass Lens Materials
The standard material for a long time, all the way back to the days of Benjamin Franklin, and beyond. Tempered glass lenses offer exceptional optics and are very scratch-resistant, but they are much heavier than modern materials. Also, they can break more easily, potentially causing grievous harm to your eyes. Still available, but very rarely used nowadays.
CR-39 aka “plastic”
Back in the 1940s, the Pittsburgh Plate and Glass Company (now PPG Industries) developed a number of different polymers for military and heavy industrial uses, including “Columbia Resin 39.” In 1947, the Armorlite Lens Company introduced CR-39 lenses – the first lightweight plastic eyeglass lens that had optics comparable to glass. This material replaced glass during the 1970s and was the industry standard for many years.
Polycarbonate aka “poly”
In the early 1970s, Gentex Corporation introduced the first polycarbonate lenses for safety glasses. Over the next few years, poly lenses became increasingly popular and remain so today. Poly lenses are lighter and thinner than equivalent CR-39 lenses and they also offer a measure of UV-protection and superior impact resistance. Poly replaced CR-39 as the new industry standard during the 2000s. Poly is the preferred choice for children due to its impact resistance.
As a byproduct of their work developing bullet-proof materials for the military, PPG Industries introduced a new material in 2001 with similar UV-blocking properties and impact resistance as polycarbonate, but with superior optics, superior strength, and lighter weight. These three improved performance properties are the “Tri” in Trivex.
One of the key factors that determine good optics for an ophthalmic lens is the material’s refractive index – this is a measure of how well the material bends light. As the strength of a prescription increases, lens thickness increases. For a given prescription, the higher the index, the less material is required. To avoid unnecessarily bulky and/or heavy glasses, as well as the dreaded “soda bottle” glasses look, Hi-Index plastics offer a thinner and lighter option. Hi-Index is available for all prescriptions; for very strong prescriptions, Hi-Index may be the only option.
What is covered by my Vision Insurance?
Most vision insurance policies have a material benefit – it could be a copay or a simple discount off the usual & customary cost. In addition to the material benefit, many policies will have a separate benefit for materials other than CR-39. For children 18 and under, many vision policies cover 100% of the cost of uncoated, single vision polycarbonate lenses. Details vary greatly – our opticians can help you interpret your specific vision benefits.
The other good news… whether you have vision insurance or not, most lenses come with some type of warranty for normal wear & tear.
NOTE! Running over your glasses with your car or a pet using your glasses as a chew toy is not normal wear & tear. All poly lenses come with a one-year/onetime replacement; basic AR coatings come with a one-year/one-time replacement; mid- and high level AR coatings come with a two-year/two-time replacement.
Our opticians will be able to provide specific details during your visit.