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Prescription glasses, also known as eyeglasses or spectacles, are devices consisting of glass or hard plastic lenses mounted in a frame that holds them in front of a person’s eyes, typically using a bridge over the nose and arms which rest over the ears. Glasses are typically used for vision correction, such as with reading glasses and glasses used for nearsightedness. Safety glasses provide eye protection against flying debris for construction workers or lab technicians; these glasses may have protection for the sides of the eyes as well as in the lenses. Some types of safety glasses are used to protect against visible and near-visible light or radiation. Glasses are worn for eye protection in some sports, such as squash. Prescription glasses wearers may use a strap to prevent the glasses from falling off during movement or sports. Wearers of glasses that are used only part of the time may have the glasses attached to a cord that goes around their neck, to prevent the loss of the glasses.
Sunglasses allow better vision in bright daylight, and may protect ones eyes against damage from high levels of ultraviolet light. Typical sunglasses are darkened for protection against bright light or glare; some specialized glasses are clear in dark or indoor conditions, but turn into sunglasses when in bright light. Most sunglasses do not have corrective power in the lenses; however, special prescription sunglasses can be ordered. Specialized glasses may be used for viewing three- dimensional movies. Sometimes glasses with no corrective power in the lenses are worn simply for aesthetic or fashion purposes. Even with prescription glasses used for vision correction, a wide range of designs are available for fashion purposes, using plastic, wire, and other materials.
The number of Americans who are nearsighted has doubled since the 1970s and almost 3/4 of the US population wear prescription glasses. People are more likely to need glasses the older they get with 93% of people between the age of 65-75 wearing corrective lenses.
HISTORY:
The use of a convex lens to form an enlarged/magnified image is discussed In Alhazen’s book of optics. It’s from Arabic in the 12th century was instrumental to the invention of prescription eyeglasses in the 13th century Italy. English Robert Grosseteste’s treatise De iride written between 1220 and 1235, mentions using optics to read the smallest letters at incredible distances. A few years later in 1262, Roger Bacon is also known to have written on the magnifying properties of lenses.
Sunglasses, in the form of flat panes of smoky quartz, were used in china during the 12th century. Similarly, the intuit have used snow googles for eye protection. while they did not offer any corrective benefits they did improve visual acuity via the pinhole effect. In India, an indigenous form of eyeglasses were thought to have been invented independently. Agrawal noted in the British Journal of Ophthalmology that the account of Devanarayan, the use of spectacles by Vyasaraya the indigenous manufacture of spectacle lenses in South India, the different terms used for spectacles in the North and South Indian languages, and other historical facts all indicate that spectacles were invented in India, in all probability by the Kannada speaking Hindus. It is therefore most likely that the use of lenses reached Europe via the Arabs, as did Hindu mathematics and the ophthalmological works of the ancient Hindu surgeon.
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