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Glasses, also known as eyeglasses or spectacles, are
vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...
eyewear, with
lenses A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
(clear or tinted) mounted in a frame that holds them in front of a person's
eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and con ...
, typically utilizing a bridge over the nose and hinged arms (known as temples or temple pieces) that rest over the ears. Glasses are typically used for vision correction, such as with reading glasses and glasses used for
nearsightedness Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...
; however, without the specialized lenses, they are sometimes used for cosmetic purposes. Safety glasses provide
eye protection Eye protection is protective gear for the eyes, and sometimes face, designed to reduce the risk of injury. Examples of risks requiring eye protection can include: impact from particles or debris, light or radiation, wind blast, heat, sea sp ...
against flying debris for construction workers or lab technicians; these glasses may have protection for the sides of the eyes as well as in the lenses. Some types of safety glasses are used to protect against visible and near-visible light or radiation. Glasses are worn for eye protection in some sports, such as
squash Squash may refer to: Sports * Squash (sport), the high-speed racquet sport also known as squash racquets * Squash (professional wrestling), an extremely one-sided match in professional wrestling * Squash tennis, a game similar to squash but pla ...
. Glasses wearers may use a strap to prevent the glasses from falling off. Wearers of glasses that are used only part of the time may have the glasses attached to a cord that goes around their neck, to prevent the loss of the glasses and breaking. The loss of glasses would be detrimental to those working in these conditions. Sunglasses allow for better vision in bright daylight, and may protect one's eyes against damage from excessive levels of
ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
. Typical sunglasses lenses are tinted for protection against bright light or polarized to remove glare;
photochromic glasses A photochromic lens is an optical lens that darkens on exposure to light of sufficiently high frequency, most commonly ultraviolet (UV) radiation. In the absence of activating light, the lenses return to their clear state. Photochromic lenses may ...
are blacked out or lightly tinted in dark or indoor conditions, but turn into sunglasses when they come in contact with ultraviolet light. Most over-the-counter sunglasses do not have corrective power in the lenses; however, special prescription sunglasses can be made. People with conditions that have
photophobia Photophobia is a medical symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of ...
as a primary symptom (like certain migraine disorders or
Irlen syndrome Irlen syndrome, occasionally referred to as scotopic sensitivity syndrome (SSS) or Meares–Irlen syndrome, is a postulated disorder of vision or image-processing in the brain. Irlen syndrome is also sometimes referred to as asfedia or visual ...
) often wear sunglasses or precision tinted glasses, even indoors and at night. Specialized glasses may be used for viewing specific visual information, for example
3D glasses Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...
for 3D films ( stereoscopy). Sometimes glasses are worn purely for fashion or aesthetic purposes. Even with glasses used for vision correction, a wide range of fashions are available, using plastic, metal, wire, and other materials for frames.


Types

Glasses can be marked or found by their primary function, but also appear in combinations such as prescription sunglasses or safety glasses with enhanced magnification.


Corrective

Corrective lenses are used to correct
refractive error Refractive error, also known as refraction error, is a problem with focusing light accurately on the retina due to the shape of the eye and or cornea. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism ...
s by bending the light entering the eye in order to alleviate the effects of conditions such as nearsightedness (myopia), farsightedness (hypermetropia) or
astigmatism Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at n ...
. The ability of one's eyes to accommodate their focus to near and distant focus alters over time. A common condition in people over forty years old is
presbyopia Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
, which is caused by the eye's
crystalline lens The lens, or crystalline lens, is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it ca ...
losing elasticity, progressively reducing the ability of the lens to accommodate (i.e. to focus on objects close to the eye). Few people have a pair of eyes that show exactly equal refractive characteristics; one eye may need a "stronger" (i.e. more refracting) lens than the other. Corrective lenses bring the image back into focus on the retina. They are made to conform to the prescription of an ophthalmologist or optometrist. A
lensmeter A lensmeter or lensometer (sometimes even known as focimeter or vertometer), is an ophthalmic instrument. It is mainly used by optometrists and opticians to measure the back or front vertex power of a spectacle lens and verify the correct pres ...
can be used to verify the specifications of an existing pair of glasses. Corrective eyeglasses can significantly improve the
life quality Quality of life (QOL) is defined by the World Health Organization as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards ...
of the wearer. Not only do they enhance the wearer's visual experience, but can also reduce problems that result from eye strain, such as
headaches Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
or squinting. The most common type of corrective lens is "single vision", which has a uniform
refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...
. For people with
presbyopia Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
and
hyperopia Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, i ...
, bifocal and
trifocal Trifocals are eyeglasses with lenses that have three regions which correct for distance, intermediate (arm's length), and near vision. John Isaac Hawkins developed the trifocal lens in 1827. Trifocals are mostly used by people with advanced pres ...
glasses provide two or three different refractive indices, respectively, and progressive lenses have a continuous gradient. Lenses can also be manufactured with high refractive indices, which allow them to be more lightweight and thinner than their counterparts with "low" refractive indices. Reading glasses provide a separate set of glasses for focusing on close by objects. Reading glasses are available without prescription from
drugstore A pharmacy (also called "drugstore" in American English or "community pharmacy" or "chemist" in Commonwealth English, or rarely, apothecary) is a retail shop which provides pharmaceutical drugs, among other products. At the pharmacy, a pharmaci ...
s, and offer a cheap, practical solution, though these have a pair of simple lenses of equal power, and so will not correct refraction problems like
astigmatism Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at n ...
or refractive or prismatic variations between the left and right eye. For the total correction of the individual's sight, glasses complying to a recent ophthalmic prescription are required. People who need glasses to see often have corrective lens restrictions on their
driver's licenses A driver's license is a legal authorization, or the official document confirming such an authorization, for a specific individual to operate one or more types of motorized vehicles—such as motorcycles, cars, trucks, or buses—on a public r ...
that require them to wear their glasses every time they drive or risk fines or jail time. Some militaries issue prescription glasses to servicemen and women. These are typically
GI glasses GI glasses are eyeglasses issued by the American military to its service members. Dysphemisms for them include the most common "birth control glasses" (BCGs) and other variants. At one time, they were officially designated as regulation prescri ...
. Many state prisons in the United States issue glasses to inmates, often in the form of clear plastic aviators. Adjustable-focus eyeglasses might be used to replace bifocals or trifocals, or might be used to produce cheaper single-vision glasses (since they don't have to be custom-manufactured for every person).
Pinhole glasses Pinhole glasses, also known as stenopeic glasses, are glasses, eyeglasses with a series of pinhole-sized perforations filling an opaque sheet of plastic in place of each lens. Similar to the workings of a pinhole camera, each perforation allows on ...
are a type of corrective glasses that do not use a lens. Pinhole glasses do not actually refract the light or change focal length. Instead, they create a diffraction limited system, which has an increased depth of field, similar to using a small
aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...
in photography. This form of correction has many limitations that prevent it from gaining popularity in everyday use. Pinhole glasses can be made in a
DIY "Do it yourself" ("DIY") is the method of building, modifying, or repairing things by oneself without the direct aid of professionals or certified experts. Academic research has described DIY as behaviors where "individuals use raw and sem ...
fashion by making small holes in a piece of card which is then held in front of the eyes with a strap or cardboard arms.


Safety

Safety glasses are worn to protect the eyes in various situations. They are made with break-proof plastic lenses to protect the eye from flying debris or other matter. Construction workers, factory workers, machinists and lab technicians are often required to wear safety glasses to shield the eyes from flying debris or hazardous splatters such as blood or chemicals. As of 2017, dentists and surgeons in Canada and other countries are required to wear safety glasses to protect against infection from patients' blood or other body fluids. There are also safety glasses for
welding Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...
, which are styled like wraparound sunglasses, but with much darker lenses, for use in welding where a full-sized
welding helmet A welding helmet is a type of personal protective equipment used in performing certain types of welding to protect the eyes, face, and neck from flash burn, sparks, infrared and ultraviolet light, and intense heat. The modern welding helmet used to ...
is inconvenient or uncomfortable. These are often called "flash goggles" because they provide protection from welding flash.
Nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from pe ...
frames are usually used for protective eyewear for sports because of their lightweight and flexible properties. Unlike most regular glasses, safety glasses often include protection beside the eyes as well as in front of the eyes.


Sunglasses

Sunglasses provide more comfort and protection against bright
light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
and often against
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
(UV) light. To properly protect the eyes from the dangers of UV light, sunglasses should have UV-400 blocker to provide good coverage against the entire light spectrum that poses a danger. Light polarization is an added feature that can be applied to sunglass lenses. Polarization filters are positioned to remove horizontally polarized rays of light, which eliminates glare from horizontal surfaces (allowing wearers to see into water when reflected light would otherwise overwhelm the scene). Polarized sunglasses may present some difficulties for pilots since reflections from water and other structures often used to gauge altitude may be removed. Liquid-crystal displays emit polarized light, making them sometimes difficult to view with polarized sunglasses. Sunglasses may be worn for aesthetic purposes, or simply to hide the eyes. Examples of sunglasses that were popular for these reasons include tea shades and
mirrorshades ''Mirrorshades: The Cyberpunk Anthology'' (1986) is a cyberpunk short story collection, edited by American writer Bruce Sterling. Contents * "The Gernsback Continuum" by William Gibson * "Snake-Eyes" by Tom Maddox * "Rock On" by Pat Cadigan * "T ...
. Many blind people wear nearly opaque glasses to hide their eyes for cosmetic reasons. Many people with light sensitivity conditions wear sunglasses or other tinted glasses to make the light more tolerable. Sunglasses may also have corrective lenses, which requires a prescription. Clip-on sunglasses or sunglass clips can be attached to another pair of glasses. Some wrap-around sunglasses are large enough to be worn over another pair of glasses. Otherwise, many people opt to wear contact lenses to correct their vision so that standard sunglasses can be used.


Mixed doubleframe

The double frame uplifting glasses have one moving frame with one pair of lenses and the basic fixed frame with another pair of lenses (optional), that are connected by
four-bar linkage In the study of mechanisms, a four-bar linkage, also called a four-bar, is the simplest closed-chain movable linkage. It consists of four bodies, called ''bars'' or ''links'', connected in a loop by four joints. Generally, the joints are config ...
. For example, sun lenses could be easily lifted up and down while mixed with myopia lenses that always stay on.
Presbyopia Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
lenses could be also combined and easily removed from the field of view if needed without taking off glasses.


3D glasses

The illusion of three dimensions on a two-dimensional surface can be created by providing each eye with different visual information. 3D glasses create the illusion of three dimensions by filtering a signal containing information for both eyes. The signal, often light reflected off a movie screen or emitted from an electronic display, is filtered so that each eye receives a slightly different image. The filters only work for the type of signal they were designed for.
Anaglyph 3D Anaglyph 3D is the stereoscopic 3D effect achieved by means of encoding each eye's image using filters of different (usually chromatically opposite) colors, typically red and cyan. Anaglyph 3D images contain two differently filtered colored ...
glasses have a different colored filter for each eye, typically red and blue or red and green. A
polarized 3D system A polarized 3D system uses polarization glasses to create the illusion of three-dimensional images by restricting the light that reaches each eye (an example of stereoscopy). To present stereoscopic images and films, two images are projected s ...
on the other hand uses polarized filters. Polarized 3D glasses allow for color 3D, while the red-blue lenses produce an image with distorted coloration. An active shutter 3D system uses electronic shutters.
Head-mounted display A head-mounted display (HMD) is a display device, worn on the head or as part of a helmet (see Helmet-mounted display for aviation applications), that has a small display optic in front of one ( monocular HMD) or each eye ( binocular HMD). An ...
s can filter the signal electronically and then transmit light directly into the viewer's eyes. Anaglyph and polarized glasses are distributed to audiences at
3D movies 3D films are motion pictures made to give an illusion of three-dimensional solidity, usually with the help of special glasses worn by viewers. They have existed in some form since 1915, but had been largely relegated to a niche in the motion pict ...
. Polarized and active shutter glasses are used with many home theaters. Head-mounted displays are used by a single person, but the input signal can be shared between multiple units.


Magnification (bioptics)

Glasses can also provide magnification that is useful for people with vision impairments or specific occupational demands. An example would be '' bioptics'' or ''bioptic telescopes'' which have small
telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...
s mounted on, in, or behind their regular lenses. Newer designs use smaller lightweight telescopes, which can be embedded into the corrective glass and improve aesthetic appearance (mini telescopic spectacles). They may take the form of self-contained glasses that resemble
goggles Goggles, or safety glasses, are forms of protective eyewear that usually enclose or protect the area surrounding the eye in order to prevent particulates, water or chemicals from striking the eyes. They are used in chemistry laboratories and ...
or binoculars, or may be attached to existing glasses.


Yellow-tinted computer/gaming glasses

Yellow-tinted glasses are a type of glasses with a minor yellow tint. They perform minor color correction, on top of reducing eyestrain from lack of blinking. They may also be considered minor corrective non-prescription glasses. Depending on the company, these computer or gaming glasses can also filter out high energy blue and ultra-violet light from LCD screens,
fluorescent lighting A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet ligh ...
, and other sources of light. This allows for reduced eye-strain. These glasses can be ordered as standard or prescription lenses that fit into standard optical frames.


Blue-light blocking glasses

Eyeglasses that filter out blue light from computers, smartphones and tablets are becoming increasingly popular in response to concerns about problems caused by blue light overexposure. The problems claimed range from
dry eyes Dry eye syndrome (DES), also known as keratoconjunctivitis sicca (KCS), is the condition of having dry eyes. Other associated symptoms include irritation, redness, discharge, and easily fatigued eyes. Blurred vision may also occur. Symptoms rang ...
to eye strain,
sleep cycle The sleep cycle is an oscillation between the slow-wave and REM (paradoxical) phases of sleep. It is sometimes called the ultradian sleep cycle, sleep–dream cycle, or REM-NREM cycle, to distinguish it from the circadian alternation between sle ...
disruption, up to
macular degeneration Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, som ...
which can cause partial blindness. However, there is no measurable ultraviolet radiation from computer monitors. Long hours of computer use may cause eye strain, not blue light. Many eye symptoms caused by computer use will lessen after the usage of the computer is stopped. Decreasing evening screen time and setting devices to night mode will improve sleep. Several studies have shown that blue light from computers does not lead to eye diseases, including macular degeneration. The American Academy of Ophthalmology (AAO) does not recommend special eyewear for computer use, although it recommends using prescription glasses measured specifically for computer screen distance (depending on individuals, but possibly 20-26 inches from the face), which are not the same as "blue-light blocking" glasses. The position of the College of Optometrists (UK) is "the best scientific evidence currently available does not support the use of blue-blocking spectacle lenses in the general population to improve visual performance, alleviate the symptoms of eye fatigue or visual discomfort, improve sleep quality or conserve macula health."


Frames

The ophthalmic frame is the part of a pair of glasses that is designed to hold the lenses in the proper position. Ophthalmic frames come in a variety of styles, sizes, materials, shapes, and colors.


Parts

* pair of eye wires or rims surrounding and holding the lenses in place * bridge which connects the two eye wires * chassis, the combination of the eye wires and the bridge * top bar or brow bar, a bar just above the bridge providing structural support and/or style enhancement (country/Grandpa style). The addition of a top bar makes a pair of glasses aviator eyeglasses * pair of brows or caps, plastic or metal caps which fit over the top of the eye wires for style enhancement and to provide additional support for the lenses. The addition of brows makes a pair of glasses
browline glasses Browline glasses are a style of eyeglass frames where the "bold" upper part holding the lenses resembles eyebrows framing the eyes. They were very popular during the 1950s and 1960s, especially in the United States of America. The glasses were ...
* pair of nose pads that allows a comfortable resting of the eye wires on the nose * pair of pad arms connect the nose pads to the eye wires * pair of temples (earpieces) on either side of the skull * pair of temple tips at the ends of the temples * pair of end pieces connect the eye wires via the hinges to the temples * pair of frame-front end pieces * pair of hinges connect the end pieces to the temples, allowing a swivel movement. Spring-loaded flex hinges are a variant that is equipped with a small spring that affords the temples a greater range of movement and does not limit them to the traditional, 90-degree angle.


Temple types

* Skull temples: bend down behind the ears, follow the contour of the skull and rest evenly against the skull * Library temples: generally straight and do not bend down behind the ears. Hold the glasses primarily through light pressure against the side of the skull * Convertible temples: used either as library or skull temples depending on the bent * Riding bow temples: curve around the ear and extend down to the level of the ear lobe. Used mostly on athletic, children's, and industrial safety frames; * Comfort cable temples: similar to the riding bow, but made from a springy cable of coiled metal, sometimes inside a plastic or silicone sleeve. The tightness of the curl can be adjusted along its whole length, allowing the back to fit the wearer's ear curve perfectly. Used for physically active wearers, children, and people with high prescriptions (heavy lenses). See the image of 1920s frames above.


Materials


Plastic and polymer

*
Cellulose acetate In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and ...
* Optyl, a type of
hypoallergenic Hypoallergenic, meaning "below average" or "slightly" allergenic, is a term meaning that something (usually cosmetics, pets, textiles, food, etc.) causes fewer allergic reactions. The term was first used in 1953 in an advertising campaign for cos ...
material made especially for eyeglass frames. It features a type of elasticity that returns the material to its original shape. * Cellulose propionate, a molded, durable plastic *
3D-printed 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
plastic using super-fine polyamide powder and Selective laser sintering processes – see Mykita Mylon (The frames can be 3-D printed by Fused Filament Fabrication for pennies of Acrylonitrile butadiene styrene, ABS, Polylactic acid, PLA or nylon) *
Nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from pe ...


Metal

Various metals and alloys may be used to make glasses, such as gold, silver, aluminum, beryllium, stainless steel, titanium, monel and nickel titanium.


Natural material

Natural materials such as wood, bone, ivory, leather and semi-precious or precious stones may also be used.


Corrective lens shape

Corrective lenses can be produced in many different shapes from a circular lens called a lens blank. Lens blanks are cut to fit the shape of the frame that will hold them. Frame styles vary and fashion trends change over time, resulting in a multitude of lens shapes. For lower power lenses, there are few restrictions, allowing for many trendy and fashionable shapes. Higher power lenses can distort peripheral vision and may become thick and heavy if a large lens shape is used. However, if the lens is too small, it can drastically reduce the field of view. Bifocals, Bifocal, Trifocal lenses, trifocal, and progressive lenses generally require a taller lens shape to leave room for the different segments while preserving an adequate field of view through each segment. Frames with rounded edges are the most efficient for correcting myopia, myopic prescriptions, with perfectly round frames being the most efficient. Before the advent of eyeglasses as a fashion item, when frames were constructed with only functionality in mind, virtually all eyeglasses were either round, oval, rectangular or curved octagons. It was not until glasses began to be seen as an accessory that different shapes were introduced to be more aesthetically pleasing than functional.


History


Precursors

Scattered evidence exists for use of visual aid devices in Greek and Roman times, most prominently the use of an emerald by Nero, Emperor Nero as mentioned by Pliny the Elder. The use of a Lens (optics), convex lens to form an enlarged/magnified image was most likely described in Ptolemy's ''Optics (Ptolemy), Optics'' (which survives only in a poor Arabic translation). Ptolemy's description of lenses was commented upon and improved by Ibn Sahl (mathematician), Ibn Sahl (10th century) and most notably by Ibn al-Haytham, Alhazen (''Book of Optics'', c. 1021). Latin translations of the 12th century, Latin translations of Ptolemy's ''Optics'' and of Alhazen became available in Europe in the 12th century, coinciding with the development of "reading stones". Robert Grosseteste's treatise ''De iride'' (''On the Rainbow''), written between 1220 and 1235, mentions using optics to "read the smallest letters at incredible distances". A few years later in 1262, Roger Bacon is also known to have written on the magnifying properties of lenses. The development of the first eyeglasses took place in northern Italy in the second half of the 13th century. Independently of the development of optical lenses, some cultures developed "sunglasses" for eye protection, without any corrective properties. For example, flat panes of smoky quartz were used in 12th-century China, and the Inuit have used Inuit snow goggles, snow goggles for eye protection.


Invention

The earliest recorded comment on the use of lenses for optical purposes was made in 1268 by Roger Bacon. The first eyeglasses were estimated to have been made in central Italy, most likely in Pisa, by about 1290: In a sermon delivered on 23 February 1306, the Dominican Order, Dominican friar Jordan of Pisa, Giordano da Pisa (–1311) wrote "It is not yet twenty years since there was found the art of making eyeglasses, which make for good vision ... And it is so short a time that this new art, never before extant, was discovered. ... I saw the one who first discovered and practiced it, and I talked to him." Giordano's colleague Friar Alessandro della Spina of Pisa (d. 1313) was soon making eyeglasses. The ''Ancient Chronicle of the Dominican Monastery of St. Catherine in Pisa'' records: "Eyeglasses, having first been made by someone else, who was unwilling to share them, he [Spina] made them and shared them with everyone with a cheerful and willing heart." Venice quickly became an important center of manufacture, especially due to using the high-quality glass made at Murano. By 1301, there were guild regulations in Venice governing the sale of eyeglasses. and a separate guild of Venetian spectacle makers was formed in 1320. In the fourteenth century they were very common objects: Francesco Petrarca says in one of his Epistolae familiares, letters that, until he was 60, he didn't need glasses, and Franco Sacchetti mentions them often in his Trecentonovelle. The earliest pictorial evidence for the use of eyeglasses is Tommaso da Modena's 1352 portrait of the cardinal Hugh de Provence reading in a scriptorium. Another early example would be a depiction of eyeglasses found north of the Alps in an altarpiece of the church of Bad Wildungen, Germany, in 1403. These early glasses had convex lenses that could correct both
hyperopia Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, i ...
(farsightedness), and the
presbyopia Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
that commonly develops as a symptom of aging. Although concave lenses for myopia (near-sightedness) had made their first appearance in the mid-15th century, it was not until 1604 that Johannes Kepler published the first correct explanation as to why convex and concave lenses could correct presbyopia and myopia. Early frames for glasses consisted of two magnifying glasses riveted together by the handles so that they could grip the nose. These are referred to as "rivet spectacles". The earliest surviving examples were found under the floorboards at Kloster Wienhausen, a convent near Celle in Germany; they have been dated to ''circa'' 1400. The world's first Optician, spectacle specialist shop opened in Strasbourg (then Holy Roman Empire, now France) in 1466.


Other claims

The 17th century claim by Francesco Redi that Salvino degli Armati of Florence invented eyeglasses in the 13th century has been exposed as erroneous. Marco Polo is mistakenly claimed to have encountered eyeglasses during his travels in China in the 13th century. However, no such evidence appears in his accounts. Section (History of Eyeglasses) From pp. 266–267 (translated): "3. Do the Europeans have the Chinese to thank for eyeglasses? ... Messrs. Scrini and Fortin in Paris have asserted this recently with the words: 'One knows, on the other hand, that when Marco Polo went to China, he learned that for a very long time already, the inhabitants had been using eyeglasses.' This assertion lacked any substantiation. So I have closely perused the German translation of 'the books of Marco Polo' (2nd ed., Leipzig 1855) once again as well as carefully compared [that book] to the original text (the book of Marco Polo by Pauthier, Paris 1865, 2 volumes): not a syllable about eyeglasses in China is found therein. Our highly esteemed Sinologist, Prof. Graube, had the kindness to peruse also the English edition (by Yule, London 1875), with the same negative result. Thus the sentence of Messrs. Scrini and Fortin is to be crossed out; this error may not be the only one to have infiltrated the literature." Indeed, the earliest mentions of eyeglasses in China occur in the 15th century and those Chinese sources state that eyeglasses were imported. In 1907 Professor Berthold Laufer speculated, in his history of glasses, that for glasses to be mentioned in the literature of China and Europe at approximately the same time it was probable that they were not invented independently, and after ruling out the Turks, proposed India as a location. However, Joseph Needham speculated that the mention of glasses in the Chinese manuscript Laufer used "in part" to credit the prior invention of them in Asia did not exist in older versions of that manuscript, and the reference to them in later versions was added during the Ming dynasty. In 1971 Rishi Agarwal, in an article in the ''British Journal of Ophthalmology'', states that Vyasatirtha was observed in possession of a pair of glasses in the 1520s, he argues that it "is, therefore, most likely that the use of lenses reached Europe via the Arabs, as did Hindu mathematics and the ophthalmological works of the ancient Hindu surgeon Sushruta", but all dates are given well after the existence of eyeglasses in Italy was established, and there had been significant shipments of eyeglasses from Italy to the Middle East, with one shipment as large as 24,000 glasses.


Later developments

The American scientist Benjamin Franklin, who had both myopia and
presbyopia Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
, invented bifocals. Historians have from time to time produced evidence to suggest that others may have preceded him in the invention; however, a correspondence between George Whatley and John Fenno, editor of ''The Gazette of the United States'', suggested that Franklin had indeed invented bifocals, and perhaps 50 years earlier than had been originally thought. The first lenses for correcting
astigmatism Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at n ...
were designed by the British astronomer George Airy in 1825. Over time, the construction of frames for glasses 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 sometime before 1727, possibly 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 were also fashionable from the second half of the 18th century and into the early 19th century. In the early 20th century, Moritz von Rohr and Carl Zeiss AG, Zeiss (with the assistance of H. Boegehold and A. Sonnefeld) developed the Zeiss Punktal spherical point-focus lenses that dominated the eyeglass lens field for many years. In 2008, Joshua Silver designed eyewear with adjustable corrective glasses. They work by using a built-in syringe to pump a silicone solution into a flexible lens. Despite the increasing popularity of contact lenses and laser Refractive surgery, corrective eye surgery, glasses remain very common, as their technology has improved. 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 offer dramatically better ability to withstand the stresses of daily wear and the occasional accident. Modern frames are also often made from strong, lightweight materials such as titanium alloys, which were not available in earlier times.


In fashion

FIle:Woman in Eyeglasses - Marcelo Chagas.jpg, 250px, Woman wearing eyewear with non-prescription lenses in a fashion photo shoot. In the 1930s, "spectacles" were described as "medical appliances". Wearing spectacles was sometimes considered socially humiliating. In the 1970s, fashionable glasses started to become available through manufacturers, and governments also recognized the demand for stylized eyewear. Graham Pullin describes how devices for disability, like glasses, have traditionally been designed to camouflage against the skin and restore ability without being visible. In the past, design for disability has "been less about projecting a positive image as about trying not to project an image at all". Pullin uses the example of spectacles, traditionally categorized as a medical device for "patients", and outlines how they are now described as eyewear: a fashionable accessory. Much like other fashion designs and accessories, eyewear is created by designers, has reputable labels, and comes in collections, by season and designer. In recent years it has become more common for consumers to purchase eyewear with non-prescription lenses as a fashion accessory.


Society and culture


Market

The market for spectacles has been characterized as having highly inelastic demand. Advertising restrictions in the United States, for example, have correlated with higher prices, suggesting that adverts make the spectacles market more Price competition, price-competitive. It has also been claimed to be monopolistically competitive, as in the case of Luxottica. There are claims that insufficiently free market competition inflates the prices of frames, which cost an average of $25–$50 U.S. to make, to an average retail price of $300 in the United States. This claim is disputed by some in the industry.


Redistribution

Some organizations like Lions Clubs International, Unite For Sight, ReSpectacle, and New Eyes for the Needy provide a way to donate glasses and sunglasses to people on low incomes or no income. Unite For Sight has redistributed more than 200,000 pairs.


Fashion

Many people require glasses for the reasons listed above. There are many shapes, colors, and materials that can be used when designing frames and lenses that can be utilized in various combinations. Oftentimes, the selection of a frame is made based on how it will affect the appearance of the wearer. Some people with good natural eyesight like to wear eyeglasses as a style accessory. In Japan, some companies ban women from wearing glasses.


Personal image

For most of their history, eyeglasses were seen as unfashionable, and carried several potentially negative connotations: wearing glasses caused individuals to be stigmatized and stereotyped as pious clergymen, as those in religious vocation were the most likely to be literate and therefore the most likely to need reading glasses, elderly, or physically weak and passive. The Social stigma, stigma began to fall away in the U.S. in the early 1900s when the popular Theodore Roosevelt was regularly photographed wearing eyeglasses, and in the 1910s when popular comedian Harold Lloyd wore a pair of horn-rimmed glasses as the "Glasses" character in his films. In the United Kingdom, wearing glasses was characterised in the nineteenth century as "a sure sign of the weakling and the mollycoddle", according to Neville Cardus, writing in 1928. Ernest Killick, "Tim" Killick was the first professional cricketer to play while wearing glasses "continuously", after his vision deteriorated in 1897. "With their aid he placed himself in the forefront among English professionals of all-round abilities." Since eyeglasses have become an acceptable fashion item and often act as a key component in individuals' personal image. Musicians Buddy Holly and John Lennon became synonymous with the styles of eye-glasses they wore to the point that thick, black horn-rimmed glasses are often called "Buddy Holly glasses" and perfectly round metal eyeglass frames called "John Lennon glasses" (or, more recently, "Harry Potter (character), Harry Potter glasses"). British comedic actor Eric Sykes was known in the United Kingdom for wearing thick, square, horn-rimmed glasses, which were in fact a sophisticated hearing aid that alleviated his deafness by allowing him to "hear" vibrations. Some celebrities have become so associated with their eyeglasses that they continued to wear them even after taking other measures against vision problems: U.S. Senator Barry Goldwater and comedian Drew Carey continued to wear non-prescription glasses after being fitted for contacts and getting LASIK, laser eye surgery, respectively. Other celebrities have used glasses to differentiate themselves from the characters they play, such as Anne Kirkbride, who wore oversized 1980s-style round horn-rimmed glasses as Deirdre Barlow in the soap opera ''Coronation Street''; and Masaharu Morimoto, who wears glasses to separate his professional persona as a chef from his stage persona as Iron Chef Japanese. In 2012, some NBA players wore lensless glasses with thick plastic frames like horn-rimmed glasses during Post-game show, post-game interviews - geek chic that draws comparisons to actor Jaleel White's infamous styling as TV character Steve Urkel. In superhero fiction, eyeglasses have become a standard component of various heroes' disguises as masks, allowing them to adopt a nondescript demeanor when they are not in their superhero personae: Superman is well known for wearing 1950s-style horn-rimmed glasses as Clark Kent, while Wonder Woman wears either round, Harold Lloyd-style glasses or 1970s-style bug-eye glasses as Diana Prince. An example of the halo effect is seen in the stereotype that those who wear glasses are intelligent. This belief can have positive consequences for people who wear glasses, for example in elections. Studies show that wearing glasses increases politicians' electoral success, at least in Western cultures.


Styles

In the 20th century, eyeglasses came to be considered a component of fashion; as such, various different styles have come in and out of popularity. Most are still in regular use, albeit with varying degrees of frequency. * Aviator sunglasses * Browline glasses * Bug-eye glasses * Cat eye glasses *
GI glasses GI glasses are eyeglasses issued by the American military to its service members. Dysphemisms for them include the most common "birth control glasses" (BCGs) and other variants. At one time, they were officially designated as regulation prescri ...
* Goggles * Horn-rimmed glasses * Lensless glasses * Monocle * Pince-nez * Rimless glasses * Sunglasses * Ray-Ban Wayfarer, Wayfarer sunglasses * Windsor glasses


See also

* Adjustable-focus eyeglasses * Baden-Powell's unilens * Eye examination * Eyeglass prescription * History of optics * X-ray vision * Plurale tantum


Notes


References


General bibliography

* . * .


External links


Spectacles Gallery
at the British Optical Association Museum * . * , on eyes and how eyeglasses correct vision (page 120).
"Common Spectacles Styles before, during and after the Civil War"
(2012 article) via the Internet Archive; Antique Eyeglasses in America. {{Authority control Corrective lenses Eyewear Italian inventions Ophthalmology Protective gear Sports equipment