Plastic vs Glass lenses
Although there are a variety of lenses out there on the market, the most obvious choice is between glass and plastic lenses. Glass lenses are the traditional ones, having been used for some time now, while plastic lenses are relatively newer. Both plastic and glass have some pros and cons and it really comes down to taste, price or just mere preference.
To start with, plastic being a lighter material makes plastic lenses much lighter than glass and therefore they are less likely to cause indentations. Also, heavier prescriptions of glass lenses have a tendency of slipping down the nose and breaking. This is the reason many places that prescribe glass lenses also have compulsory waivers that their clients must sign protecting them from any responsibility of damages.
On the upside, glass’ optical clarity is the best and as such glass lenses will have little to no distortion. Adding to that, it is the most scratch resistant optical material. This makes it the material of choice for a number of prominent manufacturers of lenses. However, glass will almost certainly shatter on impact, with the lenses splitting into smaller pieces. This is the reason glass is not recommended for active sports eyewear due to the risk of injuries to the eyes. Its weight also means that glass lenses cannot be worn over a long period of time.
Plastic lenses are mainly made from polycarbonate and CR-39 plastic material. Polycarbonate is popular for lenses because of its high resistance to impact. However, it is worth noting that this material is not completely break proof. It is very popular today especially for sunglasses and sports eyewear. Polycarbonate is the strongest plastic material, as well as the thinnest and the lightest. For all the material’s strengths, polycarbonate lenses also have the highest distortion compared to any other material.
CR-9 is another type of optical plastic. It has little distortion compared to polycarbonate. It is thinner and lighter than glass too. Although it is much more resistant to impact compared to glass, it may still break and shatter on impact thus is not so good for active sports. It is also more scratch resistant compared to polycarbonate.
Summary
Glass lenses are heavier than plastic lenses thus cannot be worn for a long time.
Glass is much more scratch resistant than any type of optical plastic.
Glass is the least resistant to impact compared to all optical plastics.
Glass lenses have the least amount of distortion compared to all plastic types.