They may still call them “glasses” but more and more these days, eyewear and other ophthalmological devices are made of plastic. Here are some of the most common types:
Plastic CR-39 Lenses
Plastic CR-39 lenses are one of the most popular prescriptions owing to their economy, durability, comfort and impact resistance. Although these plastic lenses boast superb optics, they are typically used for only mild or minimal prescriptions.
Because CR-39 is often sold with no added features, it has no additional fees either, making it the most inexpensive option in lens-wear today. Compared to polycarbonate, CR-39 provides vastly better optics, rating just one notch below the material with the highest clarity value: glass itself.
It does have negatives, however: CR-39 is the thickest and heaviest lens material on the market. Its density makes it easy to shatter or crack so it is much less compatible with rimless or semi-rimless frames and not compatible at all with drill mount designs. If you opt for CR-39 lenses, be advised that UV-protection comes at an additional cost because, in contrast to polycarbonate, they aren’t inherently UV-protected. 
Polycarbonate Lenses
Lighter and thinner than most polymers, impact-resistant polycarbonate lenses are shatter-proof and provide 100% UV protection, making them an ideal choice for active adults and children. They’re also suited for strong prescriptions since they do not need thickness to do their job when correcting vision, minimizing any “Mr McGoo” — like distortions. Unfortunately, because polycarbonate lenses are so flexible and soft — which is what makes them incredibly impact-resistant — it also means they scratch easily.
However in recent years, scratch coatings have been developed that help immensely to keep polycarbonate competitive with other lens material options.
Trivex® Lenses
Like polycarbonate, Trivex eyeglass lenses are a urethane-based pre-polymer substance developed by a company named PPG Industries. Trivex was designed to provide exceptional strength, optical clarity, remarkable strength, and ultra-lightweight comfort. These lenses are impact-resistant, lightweight, thin and offer100% UV protection. Moreover, Trivex lenses offer better central and peripheral vision than polycarbonate lenses. Their only drawback is that they’re not as suitable for many lens types.
High-index Lenses
A high index lens is a lens that features a higher “index” of refraction. That translates into a greater ability to bend light rays to provide clear vision for people with stronger prescriptions. Why is that important for eyeglass wearers? Vision can be corrected with less material, making the lens much thinner, lighter, and more comfortable for long-term wear.
High index lenses are manufactured to be thinner at the edges of the lens and lighter in weight overall.
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