Q -

It's rather difficult now to get "real glass" in eyeglasses in the US. I belive it still can be done, and glass has advantages for some people. Except in "optical aids" such as loupes and such, most lenses that are easily available probably will be plastic.

Several kinds of plastics are used, mainly because the plastics can be easily molded instead of spending hours grinding and polishing as with glass.

I haven't kept up on any recent changes in new plastics for lenses, but I believe a common material for plastics was in the polymethylmethacrylate family. The name may be off a bit, but these materials have high refractive index, great clarity, and allow making very lightweight lenses, especially when a large amount of correction is needed. They are, however, relatively soft, and usually are offered with scratch-resistant coatings. The last time I tried them, the anti-scratch coatings helped some, but they were still not as resistant to scratching, with the coatings, as the harder materials were without one. (That was several years ago (actually "decades" ago) so newer coatings may be available now.)

The polycarbonate lenses often are slightly heavier for the same amount of correction, but have good hardness and "toughness," so this material is generally used for "safety" glasses. If properly processessed, the polycarbonate lenses are quite hard, and scratch-resistant coatings are not generally needed or of any benefit. Unless something's changed since I last dug into the details, it would be rare to find an anti-scratch coating offered with polycarbonate lenses.

Since most eyeglass sellers use lens blanks from one or the other mass manufacturers, and since a trade-name can be ™ or © while the material name is already probably ®, many of the eyeglass sellers don't appear to know the chemical name/class of what they're using. They just use the sales literature that the lens manufacturer gives them, including the "lens name™" that the mfr tells them to. For the user, if an eyeglass provider offers an anti-scratch coating, it's probably safe to assume their material is a soft one; and I go look for a seller who doesn't suggest that it's needed - who probably is using polycarbonate. It can be hard for most consumers to determine what actually is being used though.

Especially in eyeglasses, it often is a compromise between the best durability and best optical properties. The available optical plastics are supposedly good enough optically that I'm told that some very good camera lenses now use mostly plastic lens elements.

John