Glasses

A pair of eyeglasses

Glasses, spectacles, or eyeglasses are frames bearing lenses worn 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 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 more often called eyeglasses in North American English, occasionally spectacles in British English, and (rarely) frames or lenses. Spectacles is often shortened to specs. In hipster slang they are cheaters.

Glasses were originally made from glass, but many are now made from plastic (often polycarbonate or CR-39) due to the danger of breakage and the greater weight of glass lenses.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, 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.

Corrective spectacles have lenses shaped to correct vision abnormalities, such as myopia.

Safety glasses are a kind of eye protection against flying debris or visible and near visible light or radiation.

Sunglasses protect against high levels of visible and ultraviolet light.

History

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

Glasses were possibly invented in northern Italy, most likely in the late 1280s. The identity of the original inventor is unknown, although a possible source is the Arabs, who may have had magnifying lenses in the 10th century. 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 (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.

These early spectacles had convex lenses that could correct the farsightedness (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 (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. 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.

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.

Corrective glasses

Corrective lenses modify the focal length of the eye to alleviate the effects of shortsightedness (myopia), longsightedness (hyperopia) or astigmatism. 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 glasses

Safety glasses with side shields Wraparound safety glasses

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 1mm thickness at the thinest 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 often be used in the place of safety glasses in many environments; this is one advantage that they have over contact lenses.

Sunglasses

Scratch-resistant sunglasses made using a NASA developed coating

Main article: Sunglasses

Sunglasses may be made with either prescription or non-prescription (i.e. plano) lenses that are darkened to provide protection against bright visible light. Good sunglasses should also protect against ultraviolet light. Due to 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 in that reflections from water and other structures often used to gauge altitude may be removed, or instrument readings on liquid crystal displays may be blocked.

Special glasses

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. 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.

Conditions glasses are used to correct

Glasses fitted with corrective lenses are a common means of correcting focus problems such as myopia (nearsightedness, short-sightedness) and hyperopia (farsightedness, long-sightedness). Emmetropia, the condition of ideal focus is described as two parallel rays of light entering the eye and converging on or at the retina. Myopia is a condition in which parallel rays of light entering the eye converge before reaching to retina. Hyperopia is a condition in which parallel rays of light entering the eye do not converge prior to reaching the retina. Some would say "the rays of light converge at an imaginary point behind the retina." Astigmatism is a condition in which parallel rays of light entering the eye converge at two separate locations, either before and/or after the retina. As most people age the crystalline lens of the eye loses elasticity resulting in presbyopia, which limits their ability to focus on nearby objects. None of these conditions is considered a disease.

Variation in glasses

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, and television watching.

Glasses as a fashion accessory

Buddy Holly's thick-rimmed glasses were part of his all-American image.

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 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, but are in fact 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. And of course 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 though the late-20th century saw 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 themselves can also become greasy or trap vapour when eating hot food or swimming or walking in rain, 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 for glasses

  • 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 US, 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.

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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. Perhaps the smallest hemispherical engine, the 4G12, a 1.2 L engine, was used in European and Middle Eastern Pony cars and pickups. The lenses themselves can also become greasy or trap vapour when eating hot food or swimming or walking in rain, reducing visibility significantly. They are I4, crossflow aluminum head, chaindriven 8 valve SOHC units. Even though the late-20th century saw 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 largest being the 4G16 makes 101 hp (75 kW) @6000 rpm and 110 ft·lbf (149 N·m) @ 4000 rpm. Another unpopular aspect of glasses is their inconvenience. The "hemi" was used in other Chrysler cars (presumably in early model Dodge Lancers) as well as several mitsubishi vehicles.

Some people who find that wearing glasses may look nerdy turn to contact lenses instead, especially under peer pressure. In 1974, 4G14 (1,436 cc, 89.8 in³) unit (indeed, its entire driveline) was used by Hyundai Motor Company to power the Pony, until 1983 when the 4G16 (1,597 cc, roughly 99 in³) was used in the Stellar, and in 1985 on the PonyII. 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. The spark plugs were not in the centre of the dome, but slightly off to the exhaust side. 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. Its displacement was very small, a 1.3 liter motor. 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. Beginning production circa 1969 was the 4G13, a prototype engine used in the first Mitsubishi Lancer.

And of course John Lennon wore his round "granny glasses" from some of his time with the Beatles to his assassination in 1980. The classic Hemi engines of the 1960s featured true hemispherical heads, and splayed (perpendicular) valves. Masaharu Morimoto wears glasses to separate his professional persona as a chef from his stage persona as Iron Chef Japanese. some notable engines designed and used by Porsche in both customer production car and Race cars:. British comedic actor Eric Sykes, who became profoundly deaf as an adult, wears glasses that contain no lenses, but are in fact a bone-conducting hearing aid. The basic design did not change much until 1996, when Porsche moved to water cooling. Drew Carey continued to wear glasses for the same reason after getting corrective laser eye surgery. When Porsche introduced the 911, it had a 2.0 L flat-6 engine, with hemispherical heads.

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. Also, at the 2005 SEMA show, Chrysler unvieled a 505-horsepower 6.4L HEMI which will be available as a crate engine and might find its way into production, perhaps with reduced horsepower. 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. Some versions of the 5.7L, including most 2006 production units, utilise a variable displacement technology called the Multi-Displacement System (MDS) to improve fuel economy. For some celebrities, glasses form part of their identity. It is available in two sizes; 5.7 and 6.1 liters. 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 Lisa Loeb all the way to the varied professional personas of eyeglass-wearing knowledge workers. This engine replaced Chrysler's large LA family of engines, particularly the Magnum 5.9, in the early 2000s.

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. This engine is not a true hemispherical head engine; it has a polyspherical combustion chamber, but retains the Hemi's traditional inline perpendicular valves. Contact lenses also provide much improved peripheral vision. Chrysler introduced a modern Hemi in 2002. Glasses are often regarded as unattractive, and many people prefer to wear contact lenses for that reason. Hemi.com provides information on three eras of Hemi power: 1951 to 1959, 1964 to 1971 and 2002 to current. Many people have several pairs of glasses, one for each task or distance, with specific glasses for reading, computer use, and television watching. Racers like "Big Daddy" Don Garlits have set many world records using Hemi power.

Others have lenses specifically intended for use with computer monitors at a fixed distance. The Hemi head design is so efficient and effective that it was, and is, a top performer in NHRA, IHRA, UDRA and other sanctioned drag racing events throughout the world. Some modern multifocal lenses give a smooth transition between these lenses, unnoticeable by most wearers. Hemi blocks were traditionally painted orange to distinguish them from other V8s. These were originally separate lenses, as invented by Benjamin Franklin. It was available in most Mopar muscle cars and pony cars of the period, although its high price and limited street tractability kept sales fairly low. Traditional multifocal lenses have two or three distinct viewing areas, each requiring a conscious effort of refocusing. The engine was available through 1971, and the DaimlerChrysler corporation still sells crate engines and parts.

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. It was based on the Chrysler RB engine big-block. Lenses can be ground to specific eyes, but in most cases standard off-the-shelf prescriptions suffice, but require custom-fitting to particular frames. In 1964, Chrysler introduced a new 426 in³ (7.0 L) Hemi, designed to win at NASCAR racing and sold to the public to meet homologation requirements and to enable the public to buy the winning engine. 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. This design, the Chrysler FirePower engine, was used until 1959. Glasses can be very simple. Experience with this engine led to Chrysler using the Hemi design for their first overhead valve V8 in 1951.

None of these conditions is considered a disease. Chrysler's first experience with the Hemi design was during World War 2, in which it developed an experimental 2500 hp (1864 kW) V16 engine for the P-47 Thunderbolt. As most people age the crystalline lens of the eye loses elasticity resulting in presbyopia, which limits their ability to focus on nearby objects. . Some would say "the rays of light converge at an imaginary point behind the retina." Astigmatism is a condition in which parallel rays of light entering the eye converge at two separate locations, either before and/or after the retina. Other manufacturers used the hemispherical design before World War II, including Daimler and Riley. Hyperopia is a condition in which parallel rays of light entering the eye do not converge prior to reaching the retina. Jaguar used this head design as well on the legendary XK engines, which powered cars ranging from the Le Mans winning D-Type to the XJ6 sedan.

Myopia is a condition in which parallel rays of light entering the eye converge before reaching to retina. Porsche has also been a notable user of the Hemi design, generating up to 86 hp per liter displacement on production cars (1973 2.4 L 911S), and even more on racing engines (906 Carrera engine). Emmetropia, the condition of ideal focus is described as two parallel rays of light entering the eye and converging on or at the retina. Chrysler has used the word "Hemi" extensively in its advertising, to the extent that the word is indelibly associated with Chrysler in North America. Glasses fitted with corrective lenses are a common means of correcting focus problems such as myopia (nearsightedness, short-sightedness) and hyperopia (farsightedness, long-sightedness). Perhaps the best-known proponent of the Hemi design has been the Chrysler Corporation, who have produced three generations of such engines: the first (the Chrysler FirePower engine) in the 1950s; the second (the 426 Hemi) from the mid 1960s through the mid 1970s; and finally in the early 2000s. Virtual reality glasses and helmets have separate video screens for each eye and a method for determining the direction the head is turned. Most applications have been in higher-priced luxury or sporting vehicles, because the hemi design is more expensive to build.

One kind of electronic 3D spectacles uses electronic shutters. Hemispherical cylinder heads have been used in some engines since they were first used by the Belgian car maker Pipe in 1905. Another kind of 3D glasses uses polarized filters. Placing the intake on the opposite side of the engine also reduces the air intake temperature and increases efficiency. 3D glasses made of cardboard and plastic are distributed at 3D movies. The hemispherical cylinder head increases the engine's efficiency through reduced thermal energy loss and increased airflow through the engine, but drawbacks such as increased production cost has meant that it has been a rare design. The classic 3D glasses have one red lens and one blue lens. These aspects help make the hemi-type engine more efficient and powerful, and less prone to engine knock.

Classic 3D glasses create the illusion of three dimensions when viewing specially prepared images. The spark plug in the center of the chamber makes for better ignition of the fuel/air mixture. The illusion of three dimensions on a two dimensional surface can be created by providing each eye with different visual information. The hemispherical combustion chamber design puts the intake/exhaust valves in-line, rather than side-by-side, allowing for better flow of air through the head (although the inlet and exhaust valves are not simultaneously open and there is no continuous flow). Polarized sunglasses may present some difficulties for pilots in that reflections from water and other structures often used to gauge altitude may be removed, or instrument readings on liquid crystal displays may be blocked. Chrysler's main innovation was to build them in such large numbers. Popular among fishermen and hunters, polarized sunglasses allow wearers to see into water when normally glare or reflected light would be seen. Stutz had built four valve engines, resembling modern car engines.

Polarization filters remove horizontal rays of light, which can cause glare. Harry Arminius Miller racing engines were more notable example. Light polarization is an added feature that can be applied to sunglass lenses. The BMW double push rod design, taken over by Bristol Cars, and the Peugeot 403 are other well known examples. 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. The term, "Hemi engine", is a trademark of Chrysler Corporation, though the concept is used by many manufacturers. 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. Hemi (from "hemisphere") or "crossflow cylinder head" is a design of internal-combustion engines in which the cylinder head's combustion chamber is of hemispherical form.

Glasses with photosensitive lenses, called photochromic lenses, become darker in the presence of UV light. Sunglasses vary greatly and many offer more style than protection. It is possible to have lenses that look very dark and yet offer little ultraviolet protection. Due to changes in the atmosphere, ultraviolet levels are much higher than in the past and ultraviolet protection for eyes and skin is even more important.

Good sunglasses should also protect against ultraviolet light. plano) lenses that are darkened to provide protection against bright visible light. Sunglasses may be made with either prescription or non-prescription (i.e. Main article: Sunglasses.

Corrective glasses with plastic lenses can often be used in the place of safety glasses in many environments; this is one advantage that they have over contact lenses. 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. Recent safety glasses have tended to be given a more stylish design, in order to encourage their use. 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.

Some safety glasses are designed to fit over corrective glasses or sunglasses. The lenses of safety glasses can also be shaped for correction. 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. Safety glasses can vary in the level of protection they provide.

Although safety lenses may be constructed from a variety of materials that vary in impact resistance, certain standards suggest that they maintain a minimum 1mm thickness at the thinest point regardless of material. Safety glasses are usually made with shatter-resistant plastic lenses to protect the eye from flying debris. Lenses made to conform to the prescription of an ophthalmologist or optometrist are called prescription lenses and are used to make prescription glasses. Glasses correcting for myopia will have negative diopter strengths.

Over-the-counter reading glasses are typically rated at +1.00 to +3.00 diopters. The power of a lens is generally measured in diopters. Corrective lenses modify the focal length of the eye to alleviate the effects of shortsightedness (myopia), longsightedness (hyperopia) or astigmatism. Either of these designs offers dramatically better ability to withstand the stresses of daily wear and the occasional accident.

Other frames have spring-loaded hinges. For instance, it is now possible to purchase frames made of special memory metal alloys that return to their correct shape after being bent. Despite the increasing popularity of contact lenses and laser corrective eye surgery, glasses remain very common and their technology has not stood still. 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.

The modern style of glasses, held by temples passing over the ears, was developed in 1727 by the British optician Edward Scarlett. 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. Early eyepieces were designed to be either held in place by hand or by exerting pressure on the nose (pince-nez). Over time, the construction of spectacle frames also evolved.

The first lenses for correcting astigmatism were constructed by the British astronomer George Airy in 1827. 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. 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. Nicholas of Cusa is believed to have discovered the benefits of concave lens in the treatment of myopia (nearsightedness).

These early spectacles had convex lenses that could correct the farsightedness (presbyopia) that commonly develops as a symptom of aging. Bacon's published writings describe the magnifying glass (which he did not invent), but make no mention of glasses. Other stories, possibly legendary, credit Roger Bacon with the invention. 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.

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 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. The identity of the original inventor is unknown, although a possible source is the Arabs, who may have had magnifying lenses in the 10th century. Glasses were possibly invented in northern Italy, most likely in the late 1280s.

. Sunglasses protect against high levels of visible and ultraviolet light. Safety glasses are a kind of eye protection against flying debris or visible and near visible light or radiation. Corrective spectacles have lenses shaped to correct vision abnormalities, such as myopia.

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. Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Some plastics have a greater index of refraction than most types of glass, allowing thinner lenses for a given prescription. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light.

Glasses were originally made from glass, but many are now made from plastic (often polycarbonate or CR-39) due to the danger of breakage and the greater weight of glass lenses. In hipster slang they are cheaters. Spectacles is often shortened to specs. Glasses are more often called eyeglasses in North American English, occasionally spectacles in British English, and (rarely) frames or lenses.

Historical types include the pince nez, monocle, and lorgnette. Modern glasses are typically supported by pads on the bridge of the nose and by temples placed over the ears. Special glasses are used for viewing three-dimensional images or experiencing virtual reality. Glasses, spectacles, or eyeglasses are frames bearing lenses worn in front of the human eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection.

Eyeglasses were a common part of the hipster persona, for example Dizzy Gillespie. Cheaters is used in the hipster argot. Lenses is also sometimes used to refer to framed eyepieces, although it is not common. Frames is sometimes used to refer to framed eyepieces, although it is not common.

In contrast, glass eye refers to a cosmetic prosthetic artificial eye that replaces a missing eye. Eye glasses or eyeglasses is a word used in North American English. Also in frequent use is the shortened form, specs. Spectacles is widely used in Britain and occasionally in the US, in addition to use by professional opticians.

Compare with other meanings of the word glass. Pair of glasses (or just glasses) is commonly used in Britain and in North America.

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