eyeglasses

Glasses, also called eyeglasses or spectacles, are frames, bearing lenses worn in front of the eyes normally for vision correction, eye protection, or for protection from UV rays. more...

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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.

Glasses frames are commonly made from metal, horn or plastic. Lenses were originally made from glass, but many are now made from various types of plastic, including CR-39 or polycarbonate.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 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. 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 shatter-resistant, making them the best for impact protection, yet offer poor optics due to 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.

Not all glasses are designed solely for vision correction, but rather for protection, or simply just for aesthetic or fashion values. 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.

History

Precursors

The first suspected recorded use of a corrective lens was by the emperor Nero, who was known to watch the gladiatorial games using an emerald.

Invention of eyeglasses

Around 1284 in Italy, Salvino D'Armate is credited with inventing the first wearable eye glasses. The earliest pictorial evidence for the use of eyeglasses, however, is Tomaso da Modena's 1352 portrait of the cardinal Hugh de Provence reading in a scriptorium. Another early example would be a depiction of eyeglasses found north of the Alpes in an altarpiece of the church of Bad Wildungen, Germany, in 1403.

Read more at Wikipedia.org