What is an Eyeglass?
Eyeglasses 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 temple arms placed over the ears.
Eyeglass lenses are commonly made from plastic, including CR-39 and 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. Newer plastic lenses, called iZon, can also correct for the symptoms of the higher order aberrations that naturally occur on a persons optical system (including retina, lens, and cornea). These lenses create sharper vision for people who have problems with blurry or dull vision, as well as help reduce the halos, starbursts, and comet-tails often associated with night time driving.