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.[4] 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.