Vision/ Glasses/ Lenses

Glasses, spectacles, or eyeglasses are frames bearing lenses worn below the forehead and in front of the human eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection or for protection from UV rays. more...

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Special glasses are used for viewing three-dimensional images from two-dimensional displays or experiencing virtual reality.

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Lenses were originally made from glass, but many are now made from various types of plastic, including CR-39 or polycarbonate.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 value 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.

History

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

Sunglasses were first used in China in the 12th century or possibly earlier. The "lenses" of these glasses were flat panes of smoky quartz, which offered no corrective powers but did protect the eyes from glare.

Glasses first began to appear in common use in northern Italy late in the 13th century; most likely in the late 1280s. It is not clear when the technology was invented. It has been said that Marco Polo reported seeing many pairs of glasses in China as early as 1275. In 1676, Franciscus Redi, a professor of medicine at the University of Pisa, wrote that he possessed a 1289 manuscript whose author complains that he would be unable to read or write were it not for the recent invention of glasses, and a record of a sermon given in 1305, in which the speaker, a Dominican monk named Fra Giordano da Rivalto, remarked that glasses had been invented less than twenty years previously, and that he had met the inventor. Based on this evidence, Redi credited another Dominican monk, Fra Alessandro da Spina of Pisa, with the re-invention of glasses after their original inventor kept them a secret, a claim contained in da Spina's obituary record.

Read more at Wikipedia.org