The Book Fiend Info Center

Glasses or specs, more formally known as eyeglasses or spectacles, are frames holding optical lenses worn in front of the eyes, usually for refractory correction, eye protection, or for shelter from damaging sun rays.

Current day Eyeglasses are usually supported by pads on the nasal bridge and by hooked arms placed over the ears. Former forms include the pince-nez, monocle, and lorgnette.

Eyeglass frames are usually created from metal or plastic. Lenses were in the beginning made with glass, but now, many are made from versatile forms of metal plastic, including CR-39 and polycarbonate. These materials lower the risk of breakage and weigh less than glass lenses. Some plastics also have more advantageous optic properties compared to glass, such as better transmission of visible light and greater absorption of ultraviolet light. Some plastics have a larger index of refraction compared with most forms of glass; this maybe helpful in the manufacturing of corrective lenses processed to correct various visual abnormalities such as nearsightedness, allowing thinner lenses for a given prescription. Newer plastic lenses, called izon, can also correct for the higher order distortions that naturally take place in the surface of the eye. These lenses create sharper vision and help with the halos, starbursts, and comet-tails often associated with night time driving glare. Wavefront guided LASIK surgery
may also correct for the higher order aberrations.

Scratch-resistant coats could be applied to almost all plastic lenses giving them corresponding scratch resistance to glass. Hydrophobic coatings designed to ease cleaning are also in stock, as are anti-reflective coatings designed to reduce glare, better night vision and make the wearer’s eyes more visible.

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