   #copyright

Glasses

2007 Schools Wikipedia Selection. Related subjects: Engineering

   A pair of modern glasses
   Enlarge
   A pair of modern glasses
   A pair of more traditional glasses
   Enlarge
   A pair of more traditional glasses

   Glasses, spectacles, or eyeglasses are frames bearing lenses worn below
   the forehead and in front of the human eyes, sometimes for purely
   aesthetic reasons but normally for vision correction or eye protection
   or for protection from UV rays. Special glasses are used for viewing
   three-dimensional images from two-dimensional displays or experiencing
   virtual reality.

   Modern glasses are typically supported by pads on the bridge of the
   nose and by temples placed over the ears. Historical types include the
   pince-nez, monocle, and lorgnette.

   Lenses were originally made from glass, but many are now made from
   various types of plastic, including CR-39 or polycarbonate. These
   materials reduce the danger of breakage and the greater weight of 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 vision abnormalities such as
   myopia, allowing thinner lenses for a given prescription.
   Scratch-resistant coatings can be applied to most plastic lenses giving
   them similar scratch resistance to glass. Hydrophobic coatings designed
   to ease cleaning are also available, as are anti-reflective coatings
   intended to improve night vision and make the wearer's eyes more
   visible.

   Polycarbonate lenses are the lightest and most shatterproof, making
   them the best for impact protection. Polycarbonate lenses offer poor
   optics because of a low Abbe value of 31. CR-39 lenses are the most
   common plastic lenses, due to their low weight, high scratch resistance
   and low transparency for ultra violet and infared radiation.

   Some glasses are not designed for vision correction. Safety glasses are
   a kind of eye protection against flying debris or against visible and
   near visible light or radiation. Sunglasses allow better vision in
   bright daylight, and may protect against damage from high levels of
   ultraviolet light.

History

   Detail of a portrait of Hugh de Provence, painted by Tomasso da Modena
   in 1352
   Detail of a portrait of Hugh de Provence, painted by Tomasso da Modena
   in 1352

   The first recorded use of a corrective lens was by the emperor Nero,
   who was known to watch the gladiatorial games using an emerald.

   Sunglasses were first used in China in the 12th century or possibly
   earlier. The "lenses" of these glasses were flat panes of smoky quartz,
   which offered no corrective powers but did protect the eyes from glare.

   Glasses first began to appear in common use in northern Italy late in
   the 13th century; most likely in the late 1280s. It is not clear when
   the technology was invented. It has been said that Marco Polo reported
   seeing many pairs of glasses in China as early as 1275. In 1676,
   Franciscus Redi, a professor of medicine at the University of Pisa,
   wrote that he possessed a 1289 manuscript whose author complains that
   he would be unable to read or write were it not for the recent
   invention of glasses, and a record of a sermon given in 1305, in which
   the speaker, a Dominican monk named Fra Giordano da Rivalto, remarked
   that glasses had been invented less than twenty years previously, and
   that he had met the inventor. Based on this evidence, Redi credited
   another Dominican monk, Fra Alessandro da Spina of Pisa, with the
   re-invention of glasses after their original inventor kept them a
   secret, a claim contained in da Spina's obituary record.
   A scholar with glasses in Das Narrenschiff (1494)
   Enlarge
   A scholar with glasses in Das Narrenschiff (1494)

   In 1738, a Florentine historian named Domenico Manni reported that a
   tombstone in Florence credited one Salvino d'Armato (died 1317) with
   the invention of glasses. Other stories, possibly legendary, credit
   Roger Bacon with the invention. Bacon's published writings describe the
   magnifying glass (which he did not invent), but make no mention of
   glasses. His treatise De iride ("On the Rainbow"), which was written
   while he was a student of Robert Grosseteste, no later than 1235,
   mentions using optics to "read the smallest letters at incredible
   distances".

   These early spectacles had convex lenses that could correct the
   presbyopia (farsightedness) that commonly develops as a symptom of
   aging. Nicholas of Cusa is believed to have discovered the benefits of
   concave lens in the treatment of myopia (nearsightedness). However, it
   was not until 1604 that Johannes Kepler published in his treatise on
   optics and astronomy, the first correct explanation as to why convex
   and concave lenses could correct presbyopia and myopia.
   A portrait of Francisco de Quevedo y Villegas
   Enlarge
   A portrait of Francisco de Quevedo y Villegas

   The American scientist Benjamin Franklin, who suffered from both myopia
   and presbyopia, invented bifocals in 1784 to avoid having to regularly
   switch between two pairs of glasses. The first lenses for correcting
   astigmatism were constructed by the British astronomer George Airy in
   1827.

   Over time, the construction of spectacle frames also evolved. Early
   eyepieces were designed to be either held in place by hand or by
   exerting pressure on the nose (pince-nez). Girolamo Savonarola
   suggested that eyepieces could be held in place by a ribbon passed over
   the wearer's head, this in turn secured by the weight of a hat. The
   modern style of glasses, held by temples passing over the ears, was
   developed in 1727 by the British optician Edward Scarlett. These
   designs were not immediately successful, however, and various styles
   with attached handles such as scissors glasses and lorgnettes remained
   fashionable throughout the 18th and into the early 19th century.

   In the early 20th century, Moritz von Rohr at Zeiss (with the
   assistance of H. Boegehold and A. Sonnefeld ), developed the Zeiss
   Punktal® spherical point-focus lenses that dominated the eyeglass lens
   field for many years.

   Despite the increasing popularity of contact lenses and laser
   corrective eye surgery, glasses remain very common and their technology
   has not stood still. For instance, it is now possible to purchase
   frames made of special memory metal alloys that return to their correct
   shape after being bent. Other frames have spring-loaded hinges. Either
   of these designs offers dramatically better ability to withstand the
   stresses of daily wear and the occasional accident. Modern frames are
   also often made from strong, light-weight materials such as titanium
   alloys, which were not available in earlier times.

Types

Corrective

   Corrective lenses modify the focal length of the eye to alleviate the
   effects of nearsightedness (myopia), farsightedness (hyperopia) or
   astigmatism. As people age the eye's crystalline lens loses elasticity
   resulting in presbyopia, which limits their ability to change focus.

   The power of a lens is generally measured in diopters. Over-the-counter
   reading glasses are typically rated at +1.00 to +3.00 diopters. Glasses
   correcting for myopia will have negative diopter strengths. Lenses made
   to conform to the prescription of an ophthalmologist or optometrist are
   called prescription lenses and are used to make prescription glasses.

Safety

   Safety glasses with side shields
   Enlarge
   Safety glasses with side shields

   Safety glasses are usually made with shatter-resistant plastic lenses
   to protect the eye from flying debris. Although safety lenses may be
   constructed from a variety of materials that vary in impact resistance,
   certain standards suggest that they maintain a minimum 1 millimeter
   thickness at the thinnest point, regardless of material. Safety glasses
   can vary in the level of protection they provide. For example, those
   used in medicine may be expected to protect against blood splatter
   while safety glasses in a factory might have stronger lenses and a
   stronger frame with additional shields at the temples. The lenses of
   safety glasses can also be shaped for correction.
   Wraparound safety glasses
   Enlarge
   Wraparound safety glasses

   Some safety glasses are designed to fit over corrective glasses or
   sunglasses. They may provide less eye protection than goggles, face
   shields or other forms of eye protection, but their light weight
   increases the likelihood that they will actually be used. Recent safety
   glasses have tended to be given a more stylish design, in order to
   encourage their use. The pictured wraparound safety glasses are
   evidence of this style change with the close fitting nature of the
   wraparound dispensing with the need for side shields. Corrective
   glasses with plastic lenses can be used in the place of safety glasses
   in many environments; this is one advantage that they have over contact
   lenses.

   There are also safety glasses for welding, which are styled like
   wraparound sunglasses, but with much darker lenses, for use in welding
   where a full sized welding helmet is inconvenient or uncomfortable.
   These are often called "flash goggles", because they provide protection
   from welding flash).

   Nylon frames are usually used for protection eyewear for sports
   beacause of their lightweight and flexible properties. They are able to
   bend slightly and return to their original shape instead of breaking
   when pressure is applied to them. Nylon frames can become very brittle
   with age and they can be difficult to adjust.

Sunglasses

   Scratch-resistant sunglasses made using a NASA developed coating
   Enlarge
   Scratch-resistant sunglasses made using a NASA developed coating

   Sunglasses may be made with either prescription or non-prescription
   lenses that are darkened to provide protection against bright visible
   light. Good sunglasses should also protect against ultraviolet light.
   Because of changes in the atmosphere, ultraviolet levels are much
   higher than in the past and ultraviolet protection for eyes and skin is
   even more important. It is possible to have lenses that look very dark
   and yet offer little ultraviolet protection. Sunglasses vary greatly
   and many offer more style than protection.

   Glasses with photosensitive lenses, called photochromic lenses, become
   darker in the presence of UV light. Unfortunately, many car windshields
   protect the passengers from UV light while not shielding from bright
   visible light, making photochromic lenses ineffective where they are
   most needed. Still, they offer the convenience of not having to carry
   both clear glasses and sunglasses to those who frequently go indoors
   and outdoors during the course of a day.

   Light polarization is an added feature that can be applied to sunglass
   lenses. Polarization filters remove horizontal rays of light, which can
   cause glare. Popular among fishermen and hunters, polarized sunglasses
   allow wearers to see into water when normally glare or reflected light
   would be seen. Polarized sunglasses may present some difficulties for
   pilots since reflections from water and other structures often used to
   gauge altitude may be removed, or instrument readings on liquid crystal
   displays may be blocked.

   Yellow lenses are commonly used by golfers and shooters for its
   contrast enhancement and depth perception properties. Brown lenses are
   also common among golfers, but cause colour distortion. Blue, purple,
   and green lenses offer no real benefits to vision enhancement and are
   mainly cosmetic. Some sunglasses with interchangeable lenses have
   optional clear lenses to protect the eyes during low light or night
   time activities and a colored lense with UV protection for times where
   sun protection is needed. Debate exists as to whether "blue blocking"
   or amber tinted lenses have a protective effect.

   Sunglasses are often worn just for aesthetic purposes, or simply to
   hide the eyes. Examples of sunglasses that were popular for these
   reasons include teashades and mirrorshades.

Special

   The illusion of three dimensions on a two dimensional surface can be
   created by providing each eye with different visual information.
   Classic 3D glasses create the illusion of three dimensions when viewing
   specially prepared images. The classic 3D glasses have one red lens and
   one blue lens. 3D glasses made of cardboard and plastic are distributed
   at 3D movies. Another kind of 3D glasses uses polarized filters, with
   one lens polarized vertically and the other horizontally, with the two
   images required for stereo vision polarized the same way. The polarized
   3D specs allow for colour 3D, while the red-blue lenses produce a dull
   black-and-white picture with red and blue fringes.

   One kind of electronic 3D spectacles uses electronic shutters.

   Virtual reality glasses and helmets have separate video screens for
   each eye and a method for determining the direction the head is turned.

Variations

   Glasses can be very simple. Magnifying lenses for reading that are used
   to treat mild hypermetropia and presbyopia can be bought off the shelf,
   but most glasses are made to a particular prescription, based on degree
   of myopia or hypermetropia 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.

   As people age, their ability to focus is lessened and many decide to
   use multiple-focus lenses, bifocal or even trifocal to cover all the
   situations in which they use their sight. 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.

   Some modern multifocal lenses give a smooth transition between these
   lenses, unnoticeable by most wearers. Others have lenses specifically
   intended for use with computer monitors at a fixed distance. Many
   people have several pairs of glasses, one for each task or distance,
   with specific glasses for reading, computer use, television watching,
   and writing.

Fashion

   United States senator Barry Goldwater in horn-rimmed glasses.
   Enlarge
   United States senator Barry Goldwater in horn-rimmed glasses.

   Glasses are often regarded as unattractive, and many people prefer to
   wear contact lenses for that reason. Contact lenses also provide much
   improved peripheral vision.

   On the other hand, many people are attracted to people who wear
   glasses, and glasses are available in a wide range of styles,
   materials, and even designer labels.

   Glasses can be a major part of personal expression, from the
   extravagance of Elton John and Dame Edna Everage, from Groucho Marx to
   Woody Allen to John Denver to Drew Carey to Lisa Loeb all the way to
   the varied professional personas of eyeglass-wearing knowledge workers.

   For some celebrities, glasses form part of their identity. American
   Senator 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 soap star Anne
   Kirkbride had the same problem: her character on Coronation Street,
   Deirdre Barlow, became so well-known for her big frames that she was
   expected to wear them at social gatherings and in international tours,
   even though Kirkbride has always worn contact lenses. Drew Carey
   continued to wear glasses for the same reason after getting corrective
   laser eye surgery. British comedic actor Eric Sykes, who became
   profoundly deaf as an adult, wears glasses that contain no lenses; they
   are actually a bone-conducting hearing aid. Masaharu Morimoto wears
   glasses to separate his professional persona as a chef from his stage
   persona as Iron Chef Japanese. John Lennon wore his round "granny
   glasses" from some of his time with the Beatles to his assassination in
   1980.

   In popular culture, glasses were all the disguise Superman and Wonder
   Woman needed to hide in plain view as alter egos Clark Kent and Diana
   Prince, respectively. An example of halo effect is seen in the
   stereotype that those who wear glasses are intelligent or, especially
   in teen culture, even geeks and nerds. Some people who find that
   wearing glasses may look nerdy turn to contact lenses instead,
   especially under peer pressure.

   Another unpopular aspect of glasses is their inconvenience. Even
   through the creation of light frames, such as those made of titanium,
   very flexible frames, and new lens materials and optical coatings,
   glasses can still cause problems during rigorous sports. The lenses can
   become greasy or trap vapour when eating hot food, swimming, walking in
   rain or rapid temperature changes (such as walking into a warm building
   from cold temperatures outside), reducing visibility significantly.
   Scraping, fracturing, or breakage of the lenses require time-consuming
   and costly professional repair, though modern plastic lenses are almost
   indestructible and very scratch-resistant.

Other names

     * Pair of glasses (or just glasses) is commonly used in Britain and
       in North America. Compare with other meanings of the word glass.
     * Spectacles is widely used in Britain and occasionally in the U.S.,
       in addition to use by professional opticians. Also in frequent use
       is the shortened form, specs.
     * Eye glasses or eyeglasses is a word used in North American English.
       In contrast, glass eye refers to a cosmetic prosthetic artificial
       eye that replaces a missing eye.
     * Frames is sometimes used to refer to framed eyepieces, although it
       is not common.
     * Lenses is also sometimes used to refer to framed eyepieces,
       although it is not common.
     * Cheaters is used in the hipster argot. Eyeglasses were a common
       part of the hipster persona, for example Dizzy Gillespie.

   Retrieved from " http://en.wikipedia.org/wiki/Glasses"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
