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Spectacles were originally made from glass, but many are now made from plastic due to the danger of breakage and the greater weight of glass lenses. Glass lenses, on the other hand, are much less prone to scratching.
Spectacles fitted with corrective lenses are a very common means of correcting focus problems such as myopia (commonly called nearsightedness or short-sightedness), and hyperopia[?] (commonly called farsightedness or long-sightedness). Myopic people cannot focus at long distances; people with hyperopia cannot focus at close distances. Astigmatism[?] is mismatched focussing horizontally and vertically. Presbyopia[?] is limited flexibility in focussing. None of these conditions are diseases.
Glasses can be very simple. Magnifying lenses for reading that are used to treat mild hyperopia and presbyopia that can be bought off the shelf, but most glasses are made to a particular prescription, based on degree of myopia or hyperopia combined with astigmatism. Lenses can be ground to specific eyes, but in most cases standard off-the-shelf prescriptions suffice, but require custom-fitting to particular frames.
Traditional multifocal lenses have two or three distinct viewing areas, each requiring a conscious effort of refocusing. These were originally separate lenses, as invented by Benjamin Franklin, an early eyeglass-wearing celebrity.
Some modern multifocal lenses give a smooth transition between these lenses, unnoticeable by most wearers. Other glasses wearers sometimes have lenses specifically intended for use with computer monitors at a fixed distance. On the other hand, many people simply have several pairs of glasses, one for each task or distance.
On the other hand, many people are attracted to people who wear glasses, and glasses are available in a very wide range of styles, materials, and even designer labels.
Spectacles can be a major part of personal expression, from the extravagance of Elton John and Dame Edna Everage[?], from Groucho Marx to John Denver all the way to the varied professional personas of eyeglass-wearing knowledge workers[?].
For some celebrities, glasses form part of the identity. American Sen. Barry Goldwater continued to wear lensless horn-rimmed spectacles after being fitted with contact lenses because he was not recognizable without his trademark glasses. British comedic actor Eric Sykes, who became profoundly deaf as an adult, wears spectacles that contain no lenses, but are in fact a bone-conducting hearing aid[?].
Halo effect[?] refers to the stereotype that the wearers of spectacles are intelligent or, especially in teen culture, even geeks. This is conception rooted in that the first people to wear glasses were those who did a lot of reading in an era when most people were illiterate.
Other kinds of spectacles include tinted protective lenses, ranging from sunglasses, which protect the eye from glare and ultraviolet radiation, to specialized units that protect against extreme brightness and are used for welding and viewing eclipses.
Prescription sunglasses, which combine protection from bright light with vision correction, have become fairly common. Some glasses have photo-sensitive lenses that darken as the light grows brighter. They are sunglasses and indoor glasses in one.
There are also simpler glasses which are made of rigid plastic and designed to protect the eyes from flying objects. Some of these, particularly goggles made for atheletes, may have a prescription as well.
Spectacles fitted with differently coloured or polarized lenses can be used to view three-dimensional images.