What are glasses
2008-08-15

                                                                                                        What are glasses?

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. 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. Eyeglass 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 Lenses were originally made from glass, but many are now made from various types of plastic, including CR-39 or polycarbonate.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 high dispersion, and having a low Abe 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 infrared radiation. Not all glasses are designed solely for vision correction, but rather for protection, viewing visual information (such as stereoscopy) 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. The history of glasses A) Precursors The first suspected recorded use of a corrective lens may have been by the emperor Nero in the 1st century, who was known to watch the gladiatorial games using an emerald. Corrective lenses were said to be used by Abbes Bin Furnas in the 9th century. He had devised a way to finish sand into glass; which until this time was secret to the Egyptians. These glasses could be shaped and polished into round rocks used for viewing - known as reading stones. Sunglasses, in the form of flat panes of smoky quartz, protected the eyes from glare and were used in China in the 12th century or possibly earlier. However, they did not offer any corrective powers. B) Early Reports of the Invention and Use of Eyeglasses Most historians believe monks or craftsmen in Pisa (or perhaps Venice), Italy produced the first form of eyeglasses around 1285-1289. The magnifying lenses for reading were set into bone, metal, or leather mountings, shaped like two small magnifying glasses with the handles riveted together to form an inverted "V" shape that could be balanced on the Bridge of the nose. The first specific mention of eyeglasses is in a 1289 Italian manuscript written by a member of the doing Oppose family. The author wrote, "I am so debilitated by age that without the glasses known as spectacles, I would no longer be able to read or write." In 1306, Giordano ad Rialto - a monk in Pisa, Italy - remarked in a sermon, "it is not yet twenty years since the art of making spectacles, one of the most useful arts on earth, and was discovered. I myself have seen and conversed with the man who made them first." But the name of the inventor was never mentioned. Rialto coined the word chili (eyeglasses) and its use began to spread throughout Italy and Europe. Italian scholar Carlo Date (1619-76) reported many years later that he read an entry pertaining to the invention of eyeglasses in a Latin Chronicle written in 1313 in a monastery in Pisa. He described the passage in an essay presented to the Academia Della Crisco, a scholarly society in Florence: "Among the entries in this Chronicle, under the year 1313, it is recorded that in this monastery of St. Catherine there lived and died Friar Alessandro Spinal, a monk of most excellent character and most acute mind, who understood everything that he heard said or saw done. And when it happened that somebody else was the first to invent eyeglasses and was unwilling to communicate the invention to others, all by himself he made them and good-naturedly shared them with everybody." So perhaps it is Friar Alessandro Spinal of Pisa, Italy, whom we should thank for the gift of eyeglasses Other events in the History of Eyeglasses 1600's Spanish craftsmen create the first eyeglass frame temples. They attach ribbons of silk or strings to the frame and loop them over the wearer's ears. Spanish and Italian missionaries carry the new types of eyeglasses to China. The Chinese attach small metal weights to the strings instead of making loops. 1730 London Optician Edward Scarlett introduces rigid temples that rest atop the wearer's ears. 1752 London medical instruments designer James AmSouth designs spectacles with double-hinged temples, which become widely popular. He also introduces green and blue tinted lenses to reduce glare. 1784 American Benjamin Franklin invents Bifocal lenses. 1799 Scotsman John McAllister, Sr. opens the first optical shop in America in Philadelphia. 1800 The monocle (first called an eye ring) is introduced in England. Monocles remain popular in Europe among men in society's upper class throughout the 1800's. 1825 Englishman Sir George Airy designs the first lenses to correct astigmatism. 1826 Trifocal lenses are introduced by John Hawkins - inventor, musician, and engineer of London and Philadelphia. 1909 Dr. John Borsch, Jr. introduces fused bifocal lenses, making bifocals thinner and more attractive than Franklin-style bifocals. 1958 Sailor International of France introduces the first progressive multimodal lens, naming it various.