Glasses Lenses

Eyeglass lenses are commonly made from plastic, including CR-39 and polycarbonate. These materials reduce the danger of breakage and weigh less than glass lenses. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light. Some plastics have a greater index of refraction than most types of glass; this is useful in the making of corrective lenses shaped to correct various vision abnormalities such as myopia, allowing thinner lenses for a given prescription. Newer plastic lenses, called iZon, can also correct for the symptoms of the higher order aberrations that naturally occur on a person's optical system (including retina, lens, and cornea). These lenses create sharper vision for people who have problems with blurry or dull vision, as well as help reduce the halos, starbursts, and comet-tails often associated with night time driving. Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Hydrophobic coatings designed to ease cleaning are also available, as are anti-reflective coatings intended to reduce glare, improve night vision and make the wearer's eyes more visible

What is CR-39 ?
CR-39, or allyl diglycol carbonate (ADC), is a plastic polymer commonly used in the manufacture of eyeglass lenses. The abbreviation stands for “Columbia Resin #39,” because it was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940. The first commercial use of CR-39 monomer was to help create glass-reinforced plastic fuel tanks for the B-17 bomber aircraft in World War II, reducing weight and increasing range of the bomber. After the War, the Armorlite Lens Company in California is credited with manufacturing the first CR-39 eyeglass lenses in 1947.