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Glasses were originally made from glass, but many are now made from plastic (often polycarbonate or CR-39) due to the danger of breakage and the greater weight of glass lenses.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

This page about Glasses includes information from a Wikipedia article.
Additional articles about Glasses
News stories about Glasses
External links for Glasses
Videos for Glasses
Wikis about Glasses
Discussion Groups about Glasses
Blogs about Glasses
Images of Glasses

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. Leghemoglobin: In leguminous plants, such as alfalfa or soybeans, the nitrogen fixing bacteria in the roots are protected from oxygen by this iron heme containing, oxygen binding protein. The lenses themselves can also become greasy or trap vapour when eating hot food or swimming or walking in rain, reducing visibility significantly. Brown manganese-based porphyrin protein. 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. Pinnaglobin: Only seen in the mollusk Pinna squamosa. Another unpopular aspect of glasses is their inconvenience. Giant free-floating blood protein, contains many dozens even hundreds of Iron heme containing protein subunits bound together into a single protein complex with a molecular masses greater than 3.5 million daltons.

Some people who find that wearing glasses may look nerdy turn to contact lenses instead, especially under peer pressure. Erythrocruorin: found in many annelids, including earthworms. 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. Vanabins: also known as Vanadium Chromagen are found in the blood of Sea squirt and are hypothesised to use the rare metal Vanadium as its oxygen binding prosthetic group, but this hypothesis is unconfirmed. 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. Appears pink/violet when oxygenated, clear when not. 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. Hemerythrin: Some marine invertebrates and a few species of annelid use this iron containing non-heme protein to carry oxygen in their blood.

And of course John Lennon wore his round "granny glasses" from some of his time with the Beatles to his assassination in 1980. Uses copper prosthetic group instead of iron heme groups and is blue in color when oxygenated. Masaharu Morimoto wears glasses to separate his professional persona as a chef from his stage persona as Iron Chef Japanese. Found in the blood of many arthropods and molluscs. 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. Hemocyanin: Second most common oxygen transporting protein found in nature. Drew Carey continued to wear glasses for the same reason after getting corrective laser eye surgery. Is very similar to hemoglobin in structure and sequence, but is not arranged in tetramers, it is a monomer and lacks cooperative binding and is used to store oxygen rather than transport it.

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. Myoglobin: Found in the muscle tissue of many vertebrates including humans (gives muscle tissue a distinct red or dark gray color). 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. Other organisms including bacteria, protozoans and fungi all have hemoglobin-like proteins whose known and predicted roles include the reversible binding of gaseous ligands. For some celebrities, glasses form part of their identity. Hemoglobin is by no means unique; there are a variety of oxygen transport and binding proteins throughout the animal (and plant) kingdom. 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. It measures the degree of glycation (glucose binding) to albumin, the most common blood protein, and reflects average blood glucose levels over the previous 18-21 days, which is the half-life of albumin molecules in the circulation.

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. In these individuals an alternative test called "fructosamine level" can be used. Contact lenses also provide much improved peripheral vision. In individuals with abnormal RBCs, whether due to abnormal hemoglobin molecules (such as Hemoglobin S in Sickle Cell Anemia) or RBC membrane defects - or other problems, the RBC half-life is frequently shortened. Glasses are often regarded as unattractive, and many people prefer to wear contact lenses for that reason.
This Hb A1c level is only useful in individuals who have red blood cells (RBCs) with normal survivals (i.e., normal half-life). Many people have several pairs of glasses, one for each task or distance, with specific glasses for reading, computer use, and television watching. This test is especially useful for diabetics.

Others have lenses specifically intended for use with computer monitors at a fixed distance. Hb A1c values which are more than 7.0% are elevated. Some modern multifocal lenses give a smooth transition between these lenses, unnoticeable by most wearers. People whose Hb A1c runs 6.0% or less show good longer-term glucose control. These were originally separate lenses, as invented by Benjamin Franklin. For this reason a blood sample may be analyzed for Hb A1c level, which is more representative of glucose control averaged over a longer time period (determined by the half-life of the individual's red blood cells, which is typically 50-55 days). Traditional multifocal lenses have two or three distinct viewing areas, each requiring a conscious effort of refocusing.
Glucose levels in blood can vary widely each hour, so one or only a few samples from a patient analyzed for glucose may not be representative of glucose control in the long run.

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. For conversion, 1 g/dl is 0.62 mmol/L. Lenses can be ground to specific eyes, but in most cases standard off-the-shelf prescriptions suffice, but require custom-fitting to particular frames. Results are reported in g/L, g/dl or mmol/L. 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. Hemoglobin levels are amongst the most commonly performed blood tests, usually as part of a full blood count or complete blood count. Glasses can be very simple. Because of the slow rate of Hb A combination with glucose, the Hb A1c percentage is representative of glucose level in the blood averaged over a longer time (the half-life of red blood cells, which is typically 50-55 days).

None of these conditions is considered a disease. In diabetics whose glucose usually runs high, the percent Hb A1c also runs high. As most people age the crystalline lens of the eye loses elasticity resulting in presbyopia, which limits their ability to focus on nearby objects. As the concentration of glucose in the blood increases, the percentage of Hb A that turns into Hb A1c increases. 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. The resulting molecule is often referred to as Hb A1c. Hyperopia is a condition in which parallel rays of light entering the eye do not converge prior to reaching the retina. To a small extent, hemoglobin A slowly combines with glucose at a certain location in the molecule.

Myopia is a condition in which parallel rays of light entering the eye converge before reaching to retina. King George III of the United Kingdom was probably the most famous porphyria sufferer. Emmetropia, the condition of ideal focus is described as two parallel rays of light entering the eye and converging on or at the retina. There is a group of genetic disorders, known as the porphyrias that are characterized by errors in metabolic pathways of heme synthesis. Glasses fitted with corrective lenses are a common means of correcting focus problems such as myopia (nearsightedness, short-sightedness) and hyperopia (farsightedness, long-sightedness). Mutations in the globin chain are associated with the haemoglobinopathies, such as sickle-cell disease and thalassemia. Virtual reality glasses and helmets have separate video screens for each eye and a method for determining the direction the head is turned. In hemolysis (accelerated breakdown of red blood cells), associated jaundice is caused by the hemoglobin metabolite bilirubin, and the circulating hemoglobin can cause renal failure.

One kind of electronic 3D spectacles uses electronic shutters. Other anemias are rarer. Another kind of 3D glasses uses polarized filters. As absence of iron decreases heme synthesis, red blood cells in iron deficiency anemia are hypochromic (lacking the red hemoglobin pigment) and microcytic (smaller than normal). 3D glasses made of cardboard and plastic are distributed at 3D movies. Anemia has many different causes, although iron deficiency and its resultant iron deficiency anemia are the most common causes in the Western world. The classic 3D glasses have one red lens and one blue lens. Decreased levels of hemoglobin, with or without an absolute decrease of red blood cells, leads to symptoms of anemia.

Classic 3D glasses create the illusion of three dimensions when viewing specially prepared images. Improperly degraded haemoglobin protein or haemoglobin that has been released from the blood cells can clog small blood vessels especially the delicate blood filtering vessels of the kidneys, causing kidney damage. The illusion of three dimensions on a two dimensional surface can be created by providing each eye with different visual information. Increased levels of this chemical are detected in the blood if red cells are being destroyed more rapidly than usual. 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. The major final product of haem degradation is bilirubin. Popular among fishermen and hunters, polarized sunglasses allow wearers to see into water when normally glare or reflected light would be seen. When the porphyrin ring is broken up, the fragments are normally secreted in the bile by the liver.

Polarization filters remove horizontal rays of light, which can cause glare. When red cells reach the end of their life due to aging or defects, they are broken down, and the haemoglobin molecule broken up and the iron recycled. Light polarization is an added feature that can be applied to sunglass lenses. As a result, fetal blood in the placenta is able to take oxygen from maternal blood. 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. This means that the oxygen binding curve for fetal hemoglobin is left-shifted (i.e., a higher percentage of hemoglobin has oxygen bound to it at lower oxygen tension), in comparison to that of adult hemoglobin. 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. A variant hemoglobin, called fetal hemoglobin (Hb F, α2γ2), is found in the developing fetus, and binds oxygen with greater affinity than adult hemoglobin.

Glasses with photosensitive lenses, called photochromic lenses, become darker in the presence of UV light. This phenomenon, where molecule Y affects the binding of molecule X to a transport molecule Z, is called a heterotropic allosteric effect. Sunglasses vary greatly and many offer more style than protection. In people acclimated to high altitudes, the concentration of 2,3-diphosphoglycerate (2,3-DPG) in the blood is increased, which allows these individuals to deliver a larger amount of oxygen to tissues under conditions of lower oxygen tension. It is possible to have lenses that look very dark and yet offer little ultraviolet protection. Nitrogen dioxide and nitrous oxide are capable of converting hemoglobin to methemoglobin. 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. Oxidation to Fe+3 state converts hemoglobin into hemiglobin or methemoglobin which cannot bind oxygen.

Good sunglasses should also protect against ultraviolet light. The iron atom in the heme group must be in the Fe+2 oxidation state to support oxygen transport. plano) lenses that are darkened to provide protection against bright visible light. Hemoglobin also has competitive binding affinity for sulfur monoxide (SO), nitrogen dioxide (NO2) and hydrogen sulfide (H2S). Sunglasses may be made with either prescription or non-prescription (i.e. In heavy smokers, up to 20% of the oxygen-active sites can be blocked by CO. Main article: Sunglasses. When inspired air contains CO levels as low as 0.02% headache and nausea occur; if the CO concentration is increased to 0.1%, unconsciousness will follow.

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. When hemoglobin combines with CO, it forms a very bright-red compound called carboxyhemoglobin. 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. Hemoglobin binding affinity for CO is 200 times greater than its affinity for oxygen, meaning that small amounts of CO dramatically reduces hemoglobin’s ability to transport oxygen. Recent safety glasses have tended to be given a more stylish design, in order to encourage their use. CO competes with oxygen at the heme binding site. 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. The binding of oxygen is affected by molecules such as carbon monoxide (CO) (for example from tobacco smoking, cars and furnaces).

Some safety glasses are designed to fit over corrective glasses or sunglasses. This control of hemoglobin's affinity for oxygen by the binding and release of carbon dioxide is known as the Bohr effect. The lenses of safety glasses can also be shaped for correction. Conversely, when the carbon dioxide levels in the blood decrease (i.e., around the lungs), carbon dioxide is released, increasing the oxygen affinity of the protein. 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. Protons bind at various places along the protein and carbon dioxide binds at the alpha-amino group forming carbamate. Safety glasses can vary in the level of protection they provide. Hemoglobin can bind protons and carbon dioxide which causes a conformational change in the protein and facilitates the release of oxygen.

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. So blood with high carbon dioxide levels is also lower in pH (more acidic). Safety glasses are usually made with shatter-resistant plastic lenses to protect the eye from flying debris. Carbon dioxide reacts with water to give bicarbonate, carbonic acid freed protons via the reaction, which is catalyzed by carbonic anhydrase:. Lenses made to conform to the prescription of an ophthalmologist or optometrist are called prescription lenses and are used to make prescription glasses. Carbon dioxide occupies a different binding site on the hemoglobin. Glasses correcting for myopia will have negative diopter strengths. Hemoglobin's affinity for oxygen is decreased in the presence of carbon monoxide because both gases compete for the same binding sites on hemoglobin, carbon monoxide binding preferentially to oxygen.

Over-the-counter reading glasses are typically rated at +1.00 to +3.00 diopters. This positive cooperative binding is achieved through steric conformational changes of the hemoglobin protein complex: When one subunit protein in hemoglobin becomes oxygenated, it induces a confirmation or structural arrangement change in the whole complex causing the other 3 subunits to gain an increased affinity for oxygen. The power of a lens is generally measured in diopters. As a consequence, the oxygen binding curve of hemoglobin is sigmoidal, or 'S'-shape, as opposed to the normal hyperbolic (noncooperative) curve. Corrective lenses modify the focal length of the eye to alleviate the effects of shortsightedness (myopia), longsightedness (hyperopia) or astigmatism. The binding affinity of hemoglobin for oxygen is increased by the oxygen saturation of the molecule. Either of these designs offers dramatically better ability to withstand the stresses of daily wear and the occasional accident. In the tetrameric form of normal adult hemoglobin, the binding of oxygen is a cooperative process.

Other frames have spring-loaded hinges. In adults:. For instance, it is now possible to purchase frames made of special memory metal alloys that return to their correct shape after being bent. In the fetus:. Despite the increasing popularity of contact lenses and laser corrective eye surgery, glasses remain very common and their technology has not stood still. In the embryo:. 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. There are two kinds of contacts between the α and β chains: α1β1 and α1β2.

The modern style of glasses, held by temples passing over the ears, was developed in 1727 by the British optician Edward Scarlett. The four polypeptide chains are bound to each other by salt bridges, hydrogen bonds and hydrophobic interaction. 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. Haemoglobin A is the most intensively studied of the haemoglobin molecules. Early eyepieces were designed to be either held in place by hand or by exerting pressure on the nose (pince-nez). Each subunit has a molecular weight of about 16,000 daltons, for a total molecular weight of the tetramer of about 64,000 daltons. Over time, the construction of spectacle frames also evolved. The subunits are structurally similar and about the same size.

The first lenses for correcting astigmatism were constructed by the British astronomer George Airy in 1827. This is denoted as α2β2. 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. In adult humans, the most common haemoglobin type is a tetramer (which contains 4 subunit proteins) called haemoglobin A, consisting of two α and two β subunits non-covalently bound. 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 iron atom can either be in the Fe2+ or Fe3+ state, but ferrihaemoglobin (Methaemoglobin) (Fe3+) cannot bind oxygen. Nicholas of Cusa is believed to have discovered the benefits of concave lens in the treatment of myopia (nearsightedness). Two additional bonds perpendicular to the plane on each side can be formed with the iron to form the fifth and sixth positions, one connected strongly to the protein, the other available for binding of oxygen.

These early spectacles had convex lenses that could correct the farsightedness (presbyopia) that commonly develops as a symptom of aging. The iron atom is bonded equally to all four nitrogens in the center of the ring, which lie in one plane. Bacon's published writings describe the magnifying glass (which he did not invent), but make no mention of glasses. This iron atom is the site of oxygen binding. Other stories, possibly legendary, credit Roger Bacon with the invention. A heme group consists of an iron atom held in a heterocyclic ring, known as a porphyrin. 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. This folding pattern contains a pocket which is suitable to strongly bind the heme group.

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. Each individual protein chain arranges in a set of alpha-helix structural segments connected together in a "myoglobin fold" arrangment, so called because this arrangment is the same folding motif used in the heme/globin proteins. 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. Each subunit is composed of a protein chain tightly associated with a non-protein heme group. 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. The Haemoglobin molecule is an assembly of four globular protein subunits. Glasses were possibly invented in northern Italy, most likely in the late 1280s. .

. Mutations in the gene for the haemoglobin protein result in a group of hereditary diseases termed the hemoglobinopathies, the most common members of which are sickle-cell disease and thalassemia. Sunglasses protect against high levels of visible and ultraviolet light. The most common types of hemoglobin contains four such subunits. Safety glasses are a kind of eye protection against flying debris or visible and near visible light or radiation. The name hemoglobin is the concatenation of heme and globin, reflecting the fact that each subunit of hemoglobin is a globular protein with an embedded heme (or haem) group; each heme group contains an iron atom, and this is responsible for the binding of oxygen. Corrective spectacles have lenses shaped to correct vision abnormalities, such as myopia. Hemoglobin transports oxygen from the lungs to the rest of the body, such as to the muscles, where it releases the oxygen load.

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. Hemoglobin or haemoglobin (frequently abbreviated as Hb) is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Haemoglobin F (α2γ2) - In adults Haemoglobin F is restricted to a limited population of red cells called F cells. Some plastics have a greater index of refraction than most types of glass, allowing thinner lenses for a given prescription. Haemaglobin A22δ2) - δ chain synthesis begins late in the third trimester and in adults, it has a normal level of 2.5%. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light. Haemoglobin A (α2β2) (PDB 1BZ0) - The most common type.

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. Haemoglobin F (α2γ2) (PDB 1FDH). In hipster slang they are cheaters. Haemoglobin Portland (ξ2γ2). Spectacles is often shortened to specs. Gower 2 (α2ε2) (PDB 1A9W). Glasses are more often called eyeglasses in North American English, occasionally spectacles in British English, and (rarely) frames or lenses. Gower 1 (ξ2ε2).

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.

10-24-14 FTPPro Support FTPPro looks and feels just like Windows Explorer Contact FTPPro FTPPro Help Topics FTPPro Terms Of Use ftppro.com/1stzip.php ftppro.com/zip ftppro.com/browse2000.php PAD File Directory Business Search Directory Real Estate Database FunWebsites.org PressArchive.net WebExposure.us Display all your websites in one place HereIam.tv Celebrity Homepages Charity Directory Google+ Directory Move your favorite Unsigned Artist to the Top of the List