Modern glasses are typically supported by pads on the bridge of the nose and by temples placed over the ears. Historical types include the pince-nez, monocle, and lorgnette.
Lenses were originally made from glass, but many are now made from various types of plastic, including CR-39 or polycarbonate. These materials reduce the danger of breakage and the greater weight of 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 vision abnormalities such as myopia, allowing thinner lenses for a given prescription. 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 improve night vision and make the wearer's eyes more visible.
Polycarbonate lenses are the lightest and most shatterproof, making them the best for impact protection. Polycarbonate lenses offer poor optics because of a low Abbe number of 31. CR-39 lenses are the most common plastic lenses, due to their low weight, high scratch resistance and low transparency for ultra violet and infared radiation.
Some glasses are not designed for vision correction. Safety glasses are a kind of eye protection against flying debris or against visible and near visible light or radiation. Sunglasses allow better vision in bright daylight, and may protect against damage from high levels of ultraviolet light.
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