Encyclopedia
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. 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.
Glasses are also known as eyeglasses , spectacles , and
frames or
lenses. See
Other names.
Glasses were originally made from
glass, but many are now made from
plastic because of 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.
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
The first recorded use of a corrective lens was by the emperor
Nero, who was known to watch the
gladiatorial games using an
emerald.
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.
In 1738, a
Florentine historian named Domenico Manni reported that a tombstone in Florence credited one Salvino d'Armato with the invention of glasses. Other stories, possibly legendary, credit
Roger Bacon with the invention. Bacon's published writings describe the
magnifying glass , but make no mention of glasses. His treatise
De iride , 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 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 . 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.
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 .
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 , 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 ,
farsightedness or astigmatism. As most people age the crystalline lens of the eye loses elasticity resulting in
presbyopia, which limits their ability to focus on nearby objects.
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 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.
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).
Sunglasses
Main article: SunglassesSunglasses 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.
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 color 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
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
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 is Britain [i]'s longest-running television soap opera [i] and its ...
,
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. This conception probably comes from an era when most people were
illiterate and the first people to wear glasses were those who did a lot of reading. 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 , 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 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
|Img = Dizzy Gillespie playing horn 1955.jpg
...
.
See also
References
External links
- , extensive history and pictures of spectacles.
