Eyeglasses

Eyeglasses (U.S),glasses or spectacles ( also more rarely cheaters) are pieces of glass or clear plastic, called lenses, that are held in front of a person's eyes by a frame made of metal or plastic. They can be used for many reasons. These include safety. fashion and to correct a person's vision.  The earliest known eyeglasses are in the thirteenth century in Italy.

Uses 
Corrective lenses let some people see or read better if they have problems seeing. If the someone is long-sighted (the light is focusses past the retina), they use a different type of glasses than someone who is short-sighted. Lenses can also correct Astigmatism. Contact lenses also help people see better. Corrective lenses usually are made by opticians following eyeglass prescription from an optometrist. It's also possible to get adjustable focus glasses where one can change the lens power.

Reading glasses that are sold over the counter may help those with presbyopia who only need to wear glasses occasionally. They typically come in lens powers from +0.25 to +4. 

3d glasses are used during 3d movies.

Glasses can also protect the eyes. Goggles and safety glasses are strong and protect the eyes from flying objects. Sunglasses (with dark tinted lenses) keep too much sunlight from getting in people's eyes. Some glasses are tinted for special applications, fashion and light sensitivity conditions. Some eyeglasses, often with yellow lenses, block blue light from a computer, game, tablet, smart phone or TV.

Styles 
Eyeglasses are made in many different styles. These may be worn for fashion or function. These styles include:
 Aviator glasses - Usually metal frames with a bar directly above the nose bridge.
 Wayfarer glasses - Eyeglasses or sunglasses with thicker plastic frames and small metal detailing on the front of the glasses.
 Wraparound glasses - Those where the lenses curve around the face offering a greater field of vision and more protection than "flat" glasses.
Wire-rim glasses - Glasses with thin !metal frames.
Horn-rimmed glasses - With thicker plastic frames.
 Windsor, granny or John Lennon glasses - with perfectly round lenses.
 Flip up glasses - Glasses with two pairs of lenses, the outer pair flips up and down as needed.
 Mountaineering glasses - Frames with fabric shields on the temples. Designed to protect the eyes at high altitudes.
 Semi-rimless glasses - With the lens rim only on top.
 Rimless glasses - Without eye rims.
 GI glasses or birth control glasses - Eyeglasses, usually considered ugly, issued by the United States Military to its soldiers at basic training.

Historical styles
 Rivet spectacles or scissors glasses - One of the oldest styles dating back to the medieval era and essentially consisting of two magnifying glasses attached at the handles with a rivet. These seem to have been invented in Florence around 1286. In a sermon from 1306, a Dominican friar wrote: “It is not yet twenty years since there was found the art of making eyeglasses, which make for good vision… And it is so short a time that this new art, never before extant, was discovered.”
 Pince-nez - Glasses without temple arms, popular during the 19th and early 20th centuries

Related pages 
 Myopia (nearsightedness)
Hyperopia (farsightedness)
Corrective lens
 Bifocals

References