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Color blindness or color vision deficiency (CVD) is the decreased ability to see color or differences in
color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
. It can impair tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights. Color blindness may make some academic activities more difficult. However, issues are generally minor, and the colorblind automatically develop adaptations and coping mechanisms. People with total color blindness (achromatopsia) may also be uncomfortable in bright environments and have decreased visual acuity. The most common cause of color blindness is an inherited problem or variation in the functionality of one or more of the three classes of
cone cell Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cone ...
s in the retina, which mediate color vision. The most common form is caused by a genetic disorder called
congenital red–green color blindness Congenital red–green color blindness is an inherited condition that is the root cause of the majority of cases of color blindness. It has no significant symptoms aside from its minor to moderate effect on color vision. It is caused by vari ...
. Males are more likely to be color blind than females, because the
genes In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
responsible for the most common forms of color blindness are on the
X chromosome The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex-d ...
. Non-color-blind females can
carry Carry or carrying may refer to: People *Carry (name) Finance * Carried interest (or carry), the share of profits in an investment fund paid to the fund manager * Carry (investment), a financial term: the carry of an asset is the gain or cost of h ...
genes for color blindness and pass them on to their children. Color blindness can also result from physical or chemical damage to the eye, the
optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
, or parts of the
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
. Screening for color blindness is typically done with the
Ishihara color test The Ishihara test is a color vision test for detection of red-green color deficiencies. It was named after its designer, Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.S. Ishihara, Tests for colo ...
. There is no cure for color blindness. Diagnosis may allow an individual, or their parents/teachers to actively accommodate the condition. Special lenses such as ''
EnChroma EnChroma lenses are a brand of color correcting glasses designed to alleviate symptoms of red–green color blindness. Studies have shown that while the lenses alter the perception of already perceived colors, they do not restore normal color vis ...
'' glasses or ''X-chrom'' contact lenses may help people with red–green color blindness at some color tasks, but they do not grant the wearer "normal color vision".
Mobile apps A mobile application or app is a computer program or software application designed to run on a mobile device such as a phone, tablet, or watch. Mobile applications often stand in contrast to desktop applications which are designed to run on de ...
can help people identify colors. Red–green color blindness is the most common form, followed by blue–yellow color blindness and total color blindness. Red–green color blindness affects ''up to'' 1 in 12 males (8%) and 1 in 200 females (0.5%). The ability to see color also decreases in old age. In certain countries, color blindness may make people ineligible for certain jobs, such as those of
aircraft pilot An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators, because they a ...
s,
train driver A train driver, engine driver, engineman or locomotive driver, commonly known as an engineer or railroad engineer in the United States and Canada, and also as a locomotive handler, locomotive operator, train operator, or motorman, is a pers ...
s, crane operators, and people in the
armed forces A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...
. The effect of color blindness on artistic ability is controversial, but a number of famous artists are believed to have been color blind.


Effects

A colorblind subject will have decreased (or no) color discrimination along the red–green axis, blue–yellow axis, or both, though the vast majority of the colorblind are only affected on their red–green axis. The first indication of colorblindness generally consists of a person using the wrong color for an object, such as when painting, or calling a color by the wrong name. The colors that are confused are very consistent among people with the same type of color blindness. File:Вечір на "інтегралі" - річка Південний Буг.jpg, Normal sight File:Deuteranopia sight.jpg, Deuteranopia sight File:Tritanopia sight.jpg, Tritanopia sight File:Monochromacy sight.jpg, Monochromacy sight


Confusion colors

Confusion colors are pairs or groups of colors that will often be mistaken by the colorblind. Confusion colors for red–green color blindness include: * Cyan and Grey * Rose-Pink and Grey * Blue and Purple * Yellow and Neon Green * Red, Green, Orange, Brown Confusion colors for blue–yellow color blindness include: * Yellow and Grey * Blue and Green * Dark Blue/Violet and Black * Violet and Yellow-Green * Red and Rose-Pink These colors of confusion are defined quantitatively by straight confusion lines plotted in
CIEXYZ The CIE 1931 color spaces are the first defined quantitative links between distributions of wavelengths in the electromagnetic visible spectrum, and physiologically perceived colors in human color vision. The mathematical relationships that defin ...
, usually plotted on the corresponding
chromaticity diagram Chromaticity is an objective specification of the quality of a color regardless of its luminance. Chromaticity consists of two independent parameters, often specified as hue (h) and colorfulness (s), where the latter is alternatively called ...
. The lines all intersect at a ''copunctal point'', which varies with the type of color blindness. Chromaticities along a confusion line will appear
metameric In biology, metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions. In ...
to
dichromats Dichromacy (from Greek ''di'', meaning "two" and ''chromo'', meaning "color") is the state of having two types of functioning photoreceptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats require ...
of that type. Anomalous trichromats of that type will see the Chromaticities as metameric if they are
close enough ''Close Enough'' is an American animated sitcom created by J. G. Quintel. Originally intended to air on TBS in 2017, the project faced various delays and setbacks before eventually premiering on HBO Max on July 9, 2020. The series has received ...
, depending on the strength of their CVD. For two colors on a confusion line to be metameric, the Chromaticities first have to be made ''isoluminant'', i.e. to have the same
Lightness Lightness is a visual perception of the luminance (L) of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a stan ...
. Note also that colors that may be isoluminant to the standard observer (typical trichromat) may not be isoluminant to a dichromat.


Color tasks

Cole describes four color tasks, all of which are impeded to some degree by color blindness: * Comparative – When multiple colors must be compared, such as with mixing paint * Connotative – When colors are given an implicit meaning, such as red = stop * Denotative – When identifying colors, for example by name, such as "where is the yellow ball?" * Aesthetic – When colors look nice – or convey an emotional response – but don't carry explicit meaning The following sections describe specific color tasks with which the colorblind typically have difficulty.


Food

Colorblindness causes difficulty with the ''connotative'' color tasks associated with selecting or preparing food, for example: * Selecting food for ripeness can be difficult. The green–yellow transition of bananas is particularly hard to identify. * Detecting bruises, mold or rot on some foods * Determining when meat is done by color * Distinguishing some varietals, such as a
Braeburn The Braeburn is a cultivar of apple that is firm to the touch with a red/orange vertical streaky appearance on a yellow/green background. Its color intensity varies with different growing conditions. It was discovered as a chance seedling in 1 ...
from a
Granny Smith The Granny Smith, also known as a green apple or sour apple, is an apple cultivar which originated in Australia in 1868. It is named after Maria Ann Smith, who propagated the cultivar from a chance seedling. The tree is thought to be a hybrid ...
apple * Distinguishing colors associated with artificial flavors (e.g. jelly beans, sports drinks)


Skin color

Changes in skin color due to bruising, sunburn, rashes or even blushing are easily missed by those with red–green colorblindness. These discolorations are often linked to the blood oxygen saturation, which affects skin reflectance.


Traffic lights

The colors of
traffic light Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
s can be difficult for the red–green colorblind. This includes distinguishing: * red/amber lights from sodium street lamps; * green lights (closer to cyan) from normal white lights. * Red from amber lights, especially when there are no positional clues available (see image). The main coping mechanism to overcome these challenges is to memorize the position of lights. The order of the common triplet traffic light is standardized as red–amber–green from top to bottom or left to right. Cases that deviate from this standard are rare. One such case is a traffic light in Tipperary Hill in
Syracuse, New York Syracuse ( ) is a City (New York), city in and the county seat of Onondaga County, New York, Onondaga County, New York, United States. It is the fifth-most populous city in the state of New York following New York City, Buffalo, New York, Buffa ...
, which is upside-down (green–amber–red top to bottom) due to the sentiments of its
Irish American , image = Irish ancestry in the USA 2018; Where Irish eyes are Smiling.png , image_caption = Irish Americans, % of population by state , caption = Notable Irish Americans , population = 36,115,472 (10.9%) alone ...
community. However, it has been criticized due to the potential hazard it poses for color-blind drivers. There are several features of traffic lights available that help accommodate the colorblind: * British Rail signals use more easily identifiable colors: the red is blood red, the amber is yellow and the green is a bluish color. * The relative position of traffic lights is fixed internationally as red, amber, green from top to bottom. Horizontal lights will differ depending on the country, but right hand traffic typically follows a "red light always on the left" pattern. * Most British road traffic lights are mounted vertically on a black rectangle with a white border (forming a "sighting board") so drivers can more easily look for the position of the light. * In the eastern provinces of Canada, traffic lights are sometimes differentiated by shape in addition to color: square for red, diamond for yellow, and circle for green (see included image of horizontal traffic light from
Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...
).


Signal lights

Navigation light A navigation light, also known as a running or position light, is a source of illumination on a watercraft, aircraft or spacecraft, meant to give information on the craft's position, heading, or status. Some navigation lights are colour-coded r ...
s in marine and aviation settings employ red and green lights to signal the relative position of other ships or aircraft. Railway signal lights also rely heavily on red–green–yellow colors. In both cases, these color combinations can be difficult for the red–green colorblind. Lantern Tests are a common means of simulating these light sources to determine not necessarily whether someone is colorblind, but whether they can functionally distinguish these specific signal colors. Those who cannot pass this test are generally completely restricted from working on aircraft, ships or rail.


Fashion

Color analysis is the analysis of color in its use in fashion, to determine personal color combinations that are most aesthetically pleasing. Colors to combine can include clothing, accessories, makeup, hair color, skin color, eye color, etc. Color analysis involves many aesthetic and comparative color task that can be difficult for the color blind. Most colorblind individuals conservatively avoid brightly colored clothes to avoid combining colors that may be viewed as unaesthetic by people with normal color vision.


Art

Inability to distinguish color does not necessarily preclude the ability to become a celebrated artist. The 20th century expressionist painter
Clifton Pugh Clifton Ernest Pugh AO, (17 December 1924 – 14 October 1990) was an Australian artist and three-time winner of Australia's Archibald Prize. One of Australia's most renowned and successful painters, Pugh was strongly influenced by German Expr ...
, three-time winner of Australia's
Archibald Prize The Archibald Prize is an Australian portraiture art prize for painting, generally seen as the most prestigious portrait prize in Australia. It was first awarded in 1921 after the receipt of a bequest from J. F. Archibald, J. F. Archib ...
, on biographical, gene inheritance and other grounds has been identified as a protanope. 19th century French artist
Charles Méryon Charles Meryon (sometimes Méryon, 23 November 1821 – 14 February 1868) was a French artist who worked almost entirely in etching, as he had colour blindness. Although now little-known in the English-speaking world, he is generally recognise ...
became successful by concentrating on
etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types ...
rather than painting after he was diagnosed as having a red–green deficiency. Jin Kim's red–green color blindness did not stop him from becoming first an
animator An animator is an artist who creates multiple images, known as frames, which give an illusion of movement called animation when displayed in rapid sequence. Animators can work in a variety of fields including film, television, and video gam ...
and later a character designer with
Walt Disney Animation Studios Walt Disney Animation Studios (WDAS), sometimes shortened to Disney Animation, is an American animation studio that creates animated features and short films for The Walt Disney Company. The studio's current production logo features a scene fro ...
.


Advantages

People with deuteranomaly are better at distinguishing shades of
khaki The color khaki (, ) is a light shade of tan with a slight yellowish tinge. Khaki has been used by many armies around the world for uniforms and equipment, particularly in arid or desert regions, where it provides camouflage relative to sandy ...
, which may be advantageous when looking for predators, food, or camouflaged objects hidden among foliage. Dichromats tend to learn to use texture and shape clues and so may be able to penetrate camouflage that has been designed to deceive individuals with normal color vision. Some tentative evidence finds that color blind people are better at penetrating certain color camouflages. Such findings may give an evolutionary reason for the high rate of red–green color blindness. There is also a study suggesting that people with some types of color blindness can distinguish colors that people with normal color vision are not able to distinguish. In World War II, color blind observers were used to penetrate camouflage. In the presence of chromatic noise, the colorblind are more capable of seeing a luminous signal, as long as the chromatic noise appears
metameric In biology, metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions. In ...
to them. This is the effect behind most "reverse" Pseudoisochromatic plates (e.g. ''"hidden digit"''
Ishihara plate The Ishihara test is a color vision test for detection of red-green color deficiencies. It was named after its designer, Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.S. Ishihara, Tests for colo ...
s) that are discernible to the colorblind, but unreadable to color normals.


Digital design

Color code A color code is a system for displaying information by using different colors. The earliest examples of color codes in use are for long-distance communication by use of flags, as in semaphore communication. The United Kingdom adopted a color c ...
s are useful tools for designers to convey information. The interpretation of this information requires users to perform a variety of Color Tasks, usually comparative but also sometimes connotative or denotative. However, these tasks are often problematic for the colorblind when design of the color code has not followed best practices for accessibility. For example, one of the most ubiquitous
connotative A connotation is a commonly understood cultural or emotional association that any given word or phrase carries, in addition to its explicit or literal meaning, which is its denotation. A connotation is frequently described as either positive or ...
color codes is the "red means bad and green means good" or similar systems, based on the classic signal light colors. However, this color coding will almost always be undifferentiable to either Deutans or Protans and therefore should be avoided or supplemented with a parallel connotative system (
symbols A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
,
smiley A smiley, sometimes referred to as a smiley face, is a basic ideogram that represents a smiling face. Since the 1950s it has become part of popular culture worldwide, used either as a standalone ideogram, or as a form of communication, such a ...
s, etc.). Good practices to ensure design is accessible to the colorblind, include: * When possible (e.g. in simple video games or apps), allowing the user to choose their own colors is the most inclusive design practice. * Using other signals that are parallel to the color coding, such as patterns, shapes, size or order. This not only helps color blind people, but also aids understanding by normally sighted people by providing them with multiple reinforcing cues. * Using brightness contrast (different shades) in addition to color contrast (different hues) * To achieve good contrast, conventional wisdom suggests converting a (digital) design to grayscale to ensure there is sufficient brightness contrast between colors. However, this does not account for the different perceptions of brightness to different varieties of colorblindness, especially Protans, Tritans and Monochromats. * Viewing the design through a CVD Simulator to ensure the information carried by color is still sufficiently conveyed. At a minimum, the design should be visible for Deutans, the most common kind of colorblindness. * Maximizing the area of colors (e.g. increase size, thickness or boldness of colored element) makes the color easier to identify. Color contrast improves as the angle the color subtends on the retina increases. This applies to all types of color vision. * Maximizing brightness (value) and saturation (chroma) of the colors to maximize color contrast. * Converting connotative tasks to comparative tasks by including a
legend A legend is a Folklore genre, genre of folklore that consists of a narrative featuring human actions, believed or perceived, both by teller and listeners, to have taken place in human history. Narratives in this genre may demonstrate human valu ...
, even when the meaning is considered obvious (e.g. red means danger). * Avoiding denotative color tasks (
color naming A color term (or color name) is a word or phrase that refers to a specific color. The color term may refer to human perception of that color (which is affected by visual context) which is usually defined according to the Munsell color system, or t ...
) when possible. Some denotative tasks can be converted to comparative tasks by depicting the actual color whenever the color name is mentioned; for example, colored typography in "", or "purple ()". * For denotative tasks (
color naming A color term (or color name) is a word or phrase that refers to a specific color. The color term may refer to human perception of that color (which is affected by visual context) which is usually defined according to the Munsell color system, or t ...
), using the most common shades of colors. For example, green and yellow are colors of confusion in red–green CVD, but it is very common to mix forest green () with bright yellow (). Mistakes by the colorblind increase drastically when uncommon shades are used, e.g. neon green () with dark yellow (). * For denotative tasks, using colors that are classically associated with a color name. For example, use "firetruck" red () instead of
burgundy Burgundy (; french: link=no, Bourgogne ) is a historical territory and former administrative region and province of east-central France. The province was once home to the Dukes of Burgundy from the early 11th until the late 15th century. The c ...
() to represent the word "
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...
".


Unordered Information

A common task for designers is to select a subset of colors (''qualitative'' colormap) that are as mutually differentiable as possible ( salient). For example, player pieces in a
board game Board games are tabletop games that typically use . These pieces are moved or placed on a pre-marked board (playing surface) and often include elements of table, card, role-playing, and miniatures games as well. Many board games feature a comp ...
should be as different as possible. Classic advice suggests using Brewer palettes, but several of these are ''not'' actually colorblind-accessible. A recent, free, powerful tool that checks color contrast of a group of colors i
Adobe's Color Blind Safe Tool
Unfortunately, the colors with the greatest contrast to the red–green colorblind tend to be colors of confusion to the blue–yellow colorblind, and vice versa. However, since red–green is much more prevalent than blue–yellow CVD, design should generally prioritize those users ( Deutans, then Protans).


Ordered Information

A common task for data visualization is to represent a color scale, or ''sequential'' colormap, often in the form of a
heat map A heat map (or heatmap) is a data visualization technique that shows magnitude of a phenomenon as color in two dimensions. The variation in color may be by hue or intensity, giving obvious visual cues to the reader about how the phenomenon is c ...
or
choropleth A choropleth map () is a type of statistical thematic map that uses pseudocolor, i.e., color corresponding with an aggregate summary of a geographic characteristic within spatial enumeration units, such as population density or per-capita inc ...
. Several scales are designed with special consideration for the colorblind and are widespread in academia, including Cividis, Viridis and
Parula ''Parula'' was formerly a small genus of New World warblers which breed in North and South America. In 1758, Linnaeus classified the northern parula as a tit, ''Parus americanus'', and as taxonomy developed the genus name was modified first to ...

Matlab
. These comprise a light-to-dark scale superimposed on a yellow-to-blue scale, making them
monotonic In mathematics, a monotonic function (or monotone function) is a function between ordered sets that preserves or reverses the given order. This concept first arose in calculus, and was later generalized to the more abstract setting of order ...
and perceptually uniform to all forms of color vision.


Classification

Much terminology has existed and does exist for the classification of color blindness, but the typical classification for color blindness follows the von Kries classifications, which uses severity and affected cone for naming.


Based on severity

Based on clinical appearance, color blindness may be described as total or partial. Total color blindness (monochromacy) is much less common than partial color blindness. Partial colorblindness includes dichromacy and anomalous trichromacy, but is often clinically defined as mild, moderate or strong.


Monochromacy

Monochromacy is often called ''total color blindness'' since there is no ability to see color. Although the term may refer to acquired disorders such as
cerebral achromatopsia Cerebral achromatopsia is a type of color-blindness caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina. It is often confused with congenital achromatopsia but underlying physiological de ...
, it typically refers to congenital color vision disorders, namely
rod monochromacy Achromatopsia, also known as Rod monochromacy, is a medical syndrome that exhibits symptoms relating to five conditions, most notably monochromacy. Historically, the name referred to monochromacy in general, but now typically refers only to an au ...
and
blue cone monochromacy Blue-cone monochromacy (BCM) is an inherited eye disease that causes severe color blindness, poor visual acuity, nystagmus and photophobia due to the absence of functional red (L) and green (M) cone photoreceptor cells in the retina. BCM is a r ...
). In cerebral achromatopsia, a person cannot perceive colors even though the eyes are capable of distinguishing them. Some sources do not consider these to be true color blindness, because the failure is of perception, not of vision. They are forms of
visual agnosia Visual agnosia is an impairment in recognition of visually presented objects. It is not due to a deficit in vision (acuity, visual field, and scanning), language, memory, or intellect. While cortical blindness results from lesions to primary visual ...
.
Monochromacy Monochromacy (from Greek ''mono'', meaning "one" and ''chromo'', meaning "color") is the ability of organisms or machines to perceive only light intensity, without respect to spectral composition (color). Organisms with monochromacy are called ...
is the condition of possessing only a single channel for conveying information about color. Monochromats are unable to distinguish any colors and perceive only variations in brightness. Congenital monochromacy occurs in two primary forms: # Rod monochromacy, frequently called complete
achromatopsia Achromatopsia, also known as Rod monochromacy, is a medical syndrome that exhibits symptoms relating to five conditions, most notably monochromacy. Historically, the name referred to monochromacy in general, but now typically refers only to an au ...
, where the retina contains no cone cells, so that in addition to the absence of color discrimination, vision in lights of normal intensity is difficult. # Cone monochromacy is the condition of having only a single class of cone. A cone monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues. Cone monochromacy is divided into classes defined by the single remaining cone class. However, red and green cone monochromats have not been definitively described in the literature.
Blue cone monochromacy Blue-cone monochromacy (BCM) is an inherited eye disease that causes severe color blindness, poor visual acuity, nystagmus and photophobia due to the absence of functional red (L) and green (M) cone photoreceptor cells in the retina. BCM is a r ...
is caused by lack of functionality of L (red) and M (green) cones, and is therefore mediated by the same genes as red–green color blindness (on the X chromosome). Peak spectral sensitivities are in the blue region of the visible spectrum (near 440 nm). People with this condition generally show
nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. Infants can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision. Due to the invol ...
("jiggling eyes"),
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 ...
(light sensitivity), reduced
visual acuity Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal ...
, and
myopia 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 ...
(nearsightedness). Visual acuity usually falls to the 20/50 to 20/400 range.


Dichromacy

Dichromats can match any color they see with some mixture of just two
primary color A set (mathematics), set of primary colors or primary colours (see American and British English spelling differences#-our, -or, spelling differences) consists of colorants or colored lights that can be mixed in varying amounts to produce a gamu ...
s (in contrast to those with normal sight ( trichromats) who can distinguish three primary colors). Dichromats usually know they have a color vision problem, and it can affect their daily lives. Dichromacy in humans includes protanopia, deuteranopia, and tritanopia. Out of the male population, 2% have severe difficulties distinguishing between red, orange, yellow, and green. (Orange and yellow are different combinations of red and green light.) Colors in this range, which appear very different to a normal viewer, appear to a dichromat to be the same or a similar color. The terms protanopia, deuteranopia, and tritanopia come from Greek, and respectively mean "inability to see (''anopia'') with the first (''prot-''), second (''deuter-''), or third (''trit-'') one.


Anomalous trichromacy

Anomalous trichromacy is the mildest type of color deficiency, but the severity ranges from almost dichromacy (strong) to almost normal trichromacy (mild). In fact, many mild anomalous trichromats have very little difficulty carrying out tasks that require normal color vision and some may not even be aware that they have a color vision deficiency. The types of anomalous trichromacy include protanomaly, deuteranomaly and tritanomaly. It is approximately three times more common than
dichromacy Dichromacy (from Greek ''di'', meaning "two" and ''chromo'', meaning "color") is the state of having two types of functioning photoreceptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats require ...
. Anomalous trichromats exhibit
trichromacy Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal expla ...
, but the color matches they make differ from normal trichromats. In order to match a given spectral yellow light, protanomalous observers need more red light in a red/green mixture than a normal observer, and deuteranomalous observers need more green. This difference can be measured by an instrument called an Anomaloscope, where red and green lights are mixed by a subject to match a yellow light.


Based on affected cone

There are two major types of color blindness: difficulty distinguishing between red and green, and difficulty distinguishing between blue and yellow. These definitions are based on the
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
of the partial colorblindness. Clinically, it is more common to use a genotypical definition, which describes which
cone A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines con ...
/
opsin Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become Retinylidene proteins, but are usually still called opsins regardless. Most pro ...
is affected.


Red–green color blindness

Red–green color blindness includes protan and deutan CVD. Protan CVD is related to the L-cone and includes protanomaly (anomalous trichromacy) and protanopia (dichromacy). Deutan CVD is related to the M-cone and includes deuteranomaly (anomalous trichromacy) and deuteranopia (dichromacy). The phenotype (visual experience) of deutans and protans is quite similar. Common colors of confusion include red/brown/green/yellow as well as blue/purple. Both forms are almost always symptomatic of
congenital red–green color blindness Congenital red–green color blindness is an inherited condition that is the root cause of the majority of cases of color blindness. It has no significant symptoms aside from its minor to moderate effect on color vision. It is caused by vari ...
, so affects males disproportionately more than females. This form of colorblindness is sometimes referred to as ''daltonism'' after
John Dalton John Dalton (; 5 or 6 September 1766 – 27 July 1844) was an English chemist, physicist and meteorologist. He is best known for introducing the atomic theory into chemistry, and for his research into colour blindness, which he had. Colour b ...
, who had red–green dichromacy. In some languages, ''daltonism'' is still used to describe red–green color blindness. * Protan (2% of males): Lacking, or possessing anomalous L-opsins for long-wavelength sensitive cone cells. Protans have a neutral point at a
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK color ...
-like wavelength around 492 nm (see
spectral color A spectral color is a color that is evoked by ''monochromatic light'', i.e. either a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths (e.g. lasers). Every wavelength of visible light is percei ...
for comparison)—that is, they cannot discriminate light of this wavelength from
white White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White on ...
. For a protanope, the brightness of red, is much reduced compared to normal. This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. They may learn to distinguish reds from yellows primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference.
Violet Violet may refer to: Common meanings * Violet (color), a spectral color with wavelengths shorter than blue * One of a list of plants known as violet, particularly: ** ''Viola'' (plant), a genus of flowering plants Places United States * Viol ...
, lavender, and purple are indistinguishable from various
shades of blue Varieties of the color blue may differ in hue, chroma (also called saturation, intensity, or colorfulness), or lightness (or value, tone, or brightness), or in two or three of these qualities. Variations in value are also called tints and sha ...
. A very few people have been found who have one normal eye and one protanopic eye. These ''unilateral dichromats'' report that with only their protanopic eye open, they see wavelengths shorter than neutral point as blue and those longer than it as yellow. * Deutan (6% of males): Lacking, or possessing anomalous M-opsins for medium-wavelength sensitive cone cells. Their neutral point is at a slightly longer wavelength, 498 nm, a more greenish hue of cyan. Deutans have the same hue discrimination problems as protans, but without the dimming of long wavelengths. Deuteranopic unilateral dichromats report that with only their deuteranopic eye open, they see wavelengths shorter than neutral point as blue and longer than it as yellow.


Blue–yellow color blindness

Blue–yellow color blindness includes tritan CVD. Tritan CVD is related to the S-cone and includes tritanomaly (anomalous trichromacy) and tritanopia (dichromacy). Blue–yellow color blindness is much less common than red–green color blindness, and more often has acquired causes than genetic. Tritans have difficulty discerning between bluish and greenish hues. Tritans have a neutral point at 571 nm (yellowish). * Tritan (<0.01% of individuals): Lacking, or possessing anomalous S-opsins or short-wavelength sensitive cone cells. Tritans see short-wavelength colors (
blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when obs ...
,
indigo Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', m ...
and spectral
violet Violet may refer to: Common meanings * Violet (color), a spectral color with wavelengths shorter than blue * One of a list of plants known as violet, particularly: ** ''Viola'' (plant), a genus of flowering plants Places United States * Viol ...
) as greenish and drastically dimmed, some of these colors even as
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have o ...
. Yellow and orange are indistinguishable from
white White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White on ...
and
pink Pink is the color of a namesake flower that is a pale tint of red. It was first used as a color name in the late 17th century. According to surveys in Europe and the United States, pink is the color most often associated with charm, politeness, ...
respectively, and purple colors are perceived as various
shades of red Varieties of the color red may differ in hue, colorfulness, chroma (also called saturation, intensity, or colorfulness) or lightness (or value, tone, or brightness), or in two or three of these qualities. Variations in value are also called tints ...
. Unlike protans and deutans, the mutation for this color blindness is carried on chromosome 7. Therefore, it is not sex-linked (equally prevalent in both males and females). The OMIM gene code for this mutation is 304000 "Colorblindness, Partial Tritanomaly". * Tetartan is the "fourth type" of colorblindness, and a type of blue–yellow color blindness. However, its existence is hypothetical and given the molecular basis of human color vision, it is unlikely this type could exist.


Summary of cone complements

The below table shows the cone complements for different types of human color vision, including those considered color blindness, normal color vision and 'superior' color vision. The cone complement contains the types of cones (or their opsins) expressed by an individual.


Causes

Color blindness is any deviation of color vision from normal
trichromatic Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal expl ...
color vision (often as defined by the standard observer) that produces a reduced
gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
. Mechanisms for color blindness are related to the functionality of
cone cell Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cone ...
s, and often to the expression of
photopsin Vertebrate visual opsins are a subclass of ciliary opsins and mediate vision in vertebrates. They include the opsins in human rod and cone cells. They are often abbreviated to ''opsin'', as they were the first opsins discovered and are still th ...
s, the
photopigments Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore moiety of photosensitive chromoproteins, such as the pigments involved in photosynthesis and ...
that 'catch'
photons A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alway ...
and thereby convert light into chemical signals. Color vision deficiencies can be classified as inherited or acquired. * ''Inherited'': inherited or congenital/genetic color vision deficiencies are most commonly caused by mutations of the genes encoding opsin proteins. However, several other genes can also lead to less common and/or more severe forms of color blindness. * ''Acquired'': color blindness that is not present at birth, may be caused by chronic illness, accidents, medication, chemical exposure or simply normal aging processes.


Genetics

Color blindness is typically an inherited genetic disorder. The most common forms of colorblindness are associated with the
Photopsin Vertebrate visual opsins are a subclass of ciliary opsins and mediate vision in vertebrates. They include the opsins in human rod and cone cells. They are often abbreviated to ''opsin'', as they were the first opsins discovered and are still th ...
genes, but the mapping of the human genome has shown there are many causative mutations that don't directly affect the opsins. Mutations capable of causing color blindness originate from at least 19 different chromosomes and 56 different genes (as shown online at the
Online Mendelian Inheritance in Man Online Mendelian Inheritance in Man (OMIM) is a continuously updated catalog of human genes and genetic disorders and traits, with a particular focus on the gene-phenotype relationship. , approximately 9,000 of the over 25,000 entries in OMIM r ...
MIM.


Genetics of red–green color blindness

By far the most common form of colorblindness is
congenital red–green color blindness Congenital red–green color blindness is an inherited condition that is the root cause of the majority of cases of color blindness. It has no significant symptoms aside from its minor to moderate effect on color vision. It is caused by vari ...
(Daltonism), which includes protanopia/protanomaly and deuteranopia/deuteranomaly. These conditions are mediated by the
OPN1LW OPN1LW is a gene on the X chromosome that encodes for long wave sensitive (LWS) opsin, or red cone photopigment. It is responsible for perception of visible light in the yellow-green range on the visible spectrum (around 500-570nm). The gene conta ...
and
OPN1MW Green-sensitive opsin is a protein that in humans is encoded by the ''OPN1MW'' gene. OPN1MW2 OPN1MW2 is a duplication of the OPN1MW gene, which encodes the medium wavelength sensitive (MWS) photopsin. The gene duplication is present in about 50% ...
genes, respectively, both on the
X chromosome The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex-d ...
. An 'affected' gene is either missing (as in Protanopia and Deuteranopia -
Dichromacy Dichromacy (from Greek ''di'', meaning "two" and ''chromo'', meaning "color") is the state of having two types of functioning photoreceptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats require ...
) or is a
chimeric gene Chimeric genes (literally, made of parts from different sources) form through the combination of portions of two or more coding sequences to produce new genes. These mutations are distinct from fusion genes which merge whole gene sequences into ...
(as in Protanomaly and Deuteranomaly). Since the
OPN1LW OPN1LW is a gene on the X chromosome that encodes for long wave sensitive (LWS) opsin, or red cone photopigment. It is responsible for perception of visible light in the yellow-green range on the visible spectrum (around 500-570nm). The gene conta ...
and
OPN1MW Green-sensitive opsin is a protein that in humans is encoded by the ''OPN1MW'' gene. OPN1MW2 OPN1MW2 is a duplication of the OPN1MW gene, which encodes the medium wavelength sensitive (MWS) photopsin. The gene duplication is present in about 50% ...
genes are on the X chromosome, they are
sex-linked Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome ( autosome). In humans, these are termed X-linked recessive, ...
, and therefore affect males and females disproportionately. Because the colorblind 'affected'
alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
are recessive, color blindness specifically follows
X-linked recessive inheritance X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males (who are necessarily homozygous for the gene mutation because they have one X and one Y ...
. Males have only one X chromosome (XY), and females have two (XX); Because the male only has one of each gene, if it is affected, the male will be colorblind. Because a female has two alleles of each gene (one on each chromosome), if only one gene is affected, the dominant normal alleles will "override" the affected, recessive allele and the female will have normal color vision. However, if the female has two mutated alleles, she will still be colorblind. This is why there is a disproportionate prevalence of colorblindness, with ~8% of males exhibiting colorblindness and ~0.5% of females.


Genetics of blue–yellow color blindness

Blue–yellow color blindness is a rarer form of colorblindness including tritanopia/tritanomaly. These conditions are mediated by the
OPN1SW Blue-sensitive opsin is a protein that in humans is encoded by the ''OPN1SW'' gene. See also * Opsin Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When boun ...
gene on
Chromosome 7 Chromosome 7 is one of the 23 pairs of chromosomes in humans, who normally have two copies of this chromosome. Chromosome 7 spans about 159 million base pairs (the building material of DNA) and represents between 5 and 5.5 percent of the total D ...
.


Other genetic causes

Several inherited diseases are known to cause color blindness: *
achromatopsia Achromatopsia, also known as Rod monochromacy, is a medical syndrome that exhibits symptoms relating to five conditions, most notably monochromacy. Historically, the name referred to monochromacy in general, but now typically refers only to an au ...

(also called rod monochromatism, stationary cone dystrophy or cone dysfunction syndrome) *
cone dystrophy A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision. Presentation The most common symptoms of cone dystrophy are vision loss (age of onset r ...
*
cone-rod dystrophy A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision. Presentation The most common symptoms of cone dystrophy are vision loss (age of onset r ...
*
Leber's congenital amaurosis Leber congenital amaurosis (LCA) is a rare inherited eye disease that appears at birth or in the first few months of life. It affects about 1 in 40,000 newborns. LCA was first described by Theodor Leber in the 19th century. It should not be co ...
*
retinitis pigmentosa Retinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visual field). As peripheral vision worsens, people may ...

(initially affects rods but can later progress to cones and therefore color blindness). They can be congenital (from birth) or can commence in childhood or adulthood. They can be stationary, that is, remain the same throughout a person's lifetime, or progressive. As progressive phenotypes involve deterioration of the retina and other parts of the eye, many of the above forms of color blindness can progress to legal blindness, i.e. an acuity of 6/60 (20/200) or worse, and often leave a person with complete blindness.


Non-genetic causes

Physical trauma can cause color blindness, either neurologically – brain trauma which produces swelling of the brain in the
occipital lobe The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipital lobe is the vi ...
– or retinally, either acute (e.g. from laser exposure) or chronic (e.g. from
ultraviolet light 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 i ...
exposure). Color blindness may also present itself as a symptom of degenerative diseases of the eye, such as
cataract A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...
and age-related
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 ...
, and as part of the retinal damage caused by
diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...
.
Vitamin A Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...
deficiency may also cause color blindness. Color blindness may be a
side effect In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
of prescription drug use. For example, red–green color blindness can be caused by
ethambutol Ethambutol (EMB, E) is a medication primarily used to treat tuberculosis. It is usually given in combination with other tuberculosis medications, such as isoniazid, rifampicin and pyrazinamide. It may also be used to treat ''Mycobacterium avi ...
, a drug used in the treatment of
tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
. Blue–yellow color blindness can be caused by
sildenafil Sildenafil, sold under the brand name Viagra, among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. It is unclear if it is effective for treating sexual dysfunction in women. It is taken by ...
, an active component of
Viagra Sildenafil, sold under the brand name Viagra, among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. It is unclear if it is effective for treating sexual dysfunction in women. It is taken by ...
.
Hydroxychloroquine Hydroxychloroquine, sold under the brand name Plaquenil among others, is a medication used to prevent and treat malaria in areas where malaria remains sensitive to chloroquine. Other uses include treatment of rheumatoid arthritis, lupus, an ...
can also lead to hydroxychloroquine retinopathy, which includes various color defects. Exposure to chemicals such as styrene or organic solvents can also lead to color vision defects. Simple colored filters can also create mild color vision deficiencies. John Dalton's original hypothesis for his deuteranopia was actually that the
vitreous humor The vitreous body (''vitreous'' meaning "glass-like"; , ) is the clear gel that fills the space between the lens and the retina of the eyeball (the vitreous chamber) in humans and other vertebrates. It is often referred to as the vitreous humor ...
of his eye was discolored: An autopsy of his eye after his death in 1844 showed this to be definitively untrue, though other filters are possible. Actual physiological examples usually affect the blue–yellow opponent channel and are named
Cyanopsia ''Cyanopsia'' is a medical term for seeing everything tinted with blue. It is also referred to as ''blue vision''. Cyanopsia often occurs for a few days, weeks, or months after removal of a cataract from the eye. Cyanopsia also sometimes occurs a ...
and
Xanthopsia Xanthopsia is a color vision deficiency in which there is a dominantly yellow bias in vision due to a yellowing of the optical media of the eye. The most common causes are digoxin's inhibitory action on the sodium pump, and the development of catar ...
, and are most typically an effect of yellowing or removal of the
lens 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''), ...
. The opponent channels can also be affected by the prevalence of certain cones in the
retinal mosaic Retinal mosaic is the name given to the distribution of any particular type of neuron across any particular layer in the retina. Typically such distributions are somewhat regular; it is thought that this is so that each part of the retina is served ...
. The cones are not equally prevalent and not evenly distributed in the retina. When the number of one of these cone types is significantly reduced, this can also lead to or contribute to a color vision deficiency. This is one of the causes of tritanomaly.


Diagnosis


Color vision test

The main method for diagnosing a color vision deficiency is in testing the color vision directly. The
Ishihara color test The Ishihara test is a color vision test for detection of red-green color deficiencies. It was named after its designer, Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.S. Ishihara, Tests for colo ...
is the test most often used to detect red–green deficiencies and most often recognized by the public. Some tests are clinical in nature, designed to be fast, simple, and effective at identifying broad categories of color blindness. Others focus on precision and are generally available only in academic settings. * pseudoisochromatic plates, a classification which includes the
Ishihara color test The Ishihara test is a color vision test for detection of red-green color deficiencies. It was named after its designer, Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.S. Ishihara, Tests for colo ...
and HRR test, embed a figure in the plate as a number of spots surrounded by spots of a slightly different color. These colors must appear identical (
metameric In biology, metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions. In ...
) to the colorblind, but distinguishable to color normals. Pseudoisochromatic Plates are used as screening tools because they are cheap, fast and simple, but they do not provide precise diagnosis of CVD. * Lanterns, such as the
Farnsworth Lantern Test The Farnsworth Lantern Test, or FALANT, is a color vision test originally developed specifically to screen sailors for tasks requiring color vision, such as identifying signal lights at night. It screens for red-green deficiencies, but not the much ...
, project small colored lights to a subject, who is required to identify the color of the lights. The colors are those of typical signal lights, i.e. red, green and yellow, which also happen to be colors of confusion of red–green CVD. Lanterns do not diagnose colorblind, but they are occupational screening tests to ensure an applicant has sufficient color discrimination to be able to perform a job. * Arrangement tests can be used as screening or diagnostic tools. The Farnsworth–Munsell 100 hue test is very sensitive, but the Farnsworth D-15 is a simplified version used specifically for screening for CVD. In either case, the subject is asked to arrange a set of colored caps or chips to form a gradual transition of color between two anchor caps. * Anomaloscopes are typically designed to detect red–green deficiencies and are based on the Rayleigh match, which compares a mixture of red and green light in variable proportions to a fixed spectral yellow of variable luminosity. The subject must change the two variables until the colors appear to match. They are expensive and require expertise to administer, so are generally only used in academic settings.


Genetic testing

While genetic testing cannot directly evaluate a subject's color vision (
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
), most congenital color vision deficiencies are well-correlated with
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
. Therefore, the
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
can be directly evaluated and used to predict the
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
. This is especially useful for progressive forms that do not have a strongly color deficient phenotype at a young age. However, it can also be used to sequence the L- and M-Opsins on the X-Chromosome, since the most common
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
s of these two genes are known and have even been related to exact spectral sensitivities and peak wavelengths. A subject's color vision can therefore be classified through
genetic testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...
, but this is just a prediction of the phenotype, since color vision can be affected by countless non-genetic factors such as your
cone mosaic The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
.


Management

Despite much recent improvement in
gene therapy for color blindness Gene therapy for color blindness is an experimental gene therapy of the human retina aiming to grant typical trichromatic color vision to individuals with congenital color blindness by introducing typical alleles for opsin Animal opsins are G- ...
, there is currently no FDA approved treatment for any form of CVD, and otherwise no cure for CVD currently exists. Management of the condition by using lenses to alleviate symptoms or smartphone apps to aid with daily tasks is possible.


Lenses

There are several kinds of lenses that an individual can wear that can increase their accuracy in some color related tasks. However, none of these will "''fix''" color blindness or grant the wearer normal color vision. There are three kinds of lenses: * A red-tint contact lens worn over the non-dominant eye, will leverage
binocular disparity Binocular disparity refers to the difference in image location of an object seen by the left and right human eye, eyes, resulting from the eyes’ horizontal separation (parallax). The brain uses binocular disparity to extract depth information from ...
to improve discrimination of some colors. However, it can make other colors more difficult to distinguish. A 1981 review of various studies to evaluate the effect of the X-chrom (one brand) contact lens concluded that, while the lens may allow the wearer to achieve a better score on certain color vision tests, it did not correct color vision in the natural environment. A case history using the X-Chrom lens for a rod monochromat is reported and an X-Chrom manual is online. * Tinted glasses (e.g. Pilestone/Colorlite glasses) apply a tint (e.g. magenta) to incoming light that can distort colors in a way that makes some color tasks easier to complete. These glasses can circumvent many colorblind tests, though this is typically not allowed. * Glasses with a
notch filter In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the opposite of a band-pass filter. A notch filter is a ba ...
(e.g.
EnChroma EnChroma lenses are a brand of color correcting glasses designed to alleviate symptoms of red–green color blindness. Studies have shown that while the lenses alter the perception of already perceived colors, they do not restore normal color vis ...
glasses) filter a narrow band of light that excites both the L and M cones (yellow–green wavelengths). When combined with an additional stopband in the short wavelength (blue) region, these lenses ''may'' constitute a
neutral-density filter In photography and optics, a neutral-density filter, or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition. It can be a colorless (clear) or ...
(have no color tint). They improve on the other lens types by causing less distortion of colors and will essentially increase the saturation of some colors. They will only work on trichromats (anomalous or normal), and unlike the other types, do not have a significant effect on Dichromats. The glasses do not significantly increase one's ability on colorblind tests.


Aids

Many mobile and computer applications have been developed to aid color blind individuals in completing color tasks: * Some applications can identify a color—by name or RGB code—of a color on screen or the color of an object by using the device's camera. * Some applications will make images easier to interpret by the colorblind by enhancing color contrast in natural images and/or information graphics. These methods are generally called ''daltonization'' algorithms. * Some applications can simulate color blindness by applying a filter to an image or screen that reduces the gamut of an image to that of a specific type of color blindness. While they don't directly help colorblind people, they allow those with normal color vision to understand how people with color blindness see the world. Their use can help improve inclusive design by allowing designers to simulate their own images to ensure they are accessible to the colorblind. In 2003, a cybernetic device called
eyeborg An eyeborg or eye-borg is a body modification apparatus which fits on the wearer's head, and is designed to allow people to perceive color through sound waves. It works with a head-mounted antenna that senses the colors directly in front of a pers ...
was developed to allow the wearer to hear sounds representing different colors. Achromatopsic artist
Neil Harbisson Neil Harbisson (27 July 1982) is a Catalan-born British-Irish-American cyborg artist and activist for transpecies rights. He is best known for being the first person in the world with an antenna implanted in his skull. Since 2004, internation ...
was the first to use such a device in early 2004; the eyeborg allowed him to start painting in color by memorizing the sound corresponding to each color. In 2012, at a
TED Conference TED Conferences, LLC (Technology, Entertainment, Design) is an American-Canadian non-profit media organization that posts international talks online for free distribution under the slogan "ideas worth spreading". TED was founded by Richard Sau ...
, Harbisson explained how he could now perceive colors outside the ability of human vision.


Epidemiology

Color blindness affects a large number of individuals, with protans and deutans being the most common types. In individuals with Northern European ancestry, as many as 8 percent of men and 0.4 percent of women experience congenital color deficiency. Interestingly, even Dalton's very first paper already arrived upon this 8% number:


History

During the 17th and 18th century, several philosophers hypothesized that not all individuals perceived colors in the same way: The phenomenon only came to be scientifically studied in 1794, when English chemist
John Dalton John Dalton (; 5 or 6 September 1766 – 27 July 1844) was an English chemist, physicist and meteorologist. He is best known for introducing the atomic theory into chemistry, and for his research into colour blindness, which he had. Colour b ...
gave the first account of colour blindness in a paper to the
Manchester Literary and Philosophical Society The Manchester Literary and Philosophical Society, popularly known as the Lit. & Phil., is one of the oldest learned societies in the United Kingdom and second oldest provincial learned society (after the Spalding Gentlemen's Society). Promine ...
, which was published in 1798 as ''Extraordinary Facts relating to the Vision of Colours: With Observations''. Genetic analysis of Dalton's preserved eyeball confirmed him as having deuteranopia in 1995, some 150 years after his death. Influenced by Dalton, German writer
J. W. von Goethe Johann Wolfgang von Goethe (28 August 1749 – 22 March 1832) was a German poet, playwright, novelist, scientist, statesman, theatre director, and critic. His works include plays, poetry, literature, and aesthetic criticism, as well as treati ...
studied color vision abnormalities in 1798 by asking two young subjects to match pairs of colors. In 1875, the Lagerlunda train crash in Sweden brought color blindness to the forefront. Following the crash, Professor Alarik Frithiof Holmgren, a physiologist, investigated and concluded that the color blindness of the engineer (who had died) had caused the crash. Professor Holmgren then created the first test for color vision using multicolored skeins of wool to detect color blindness and thereby exclude the colorblind from jobs in the transportation industry requiring color vision to interpret safety signals. However, there is a claim that there is no firm evidence that color deficiency did cause the collision, or that it might have not been the sole cause. In 1920, Frederick William Edridge-Green devised an alternative theory of color vision and color blindness based on Newton's classification of 7 fundamental colors (
ROYGBIV ROYGBIV is an acronym for the sequence of hues commonly described as making up a rainbow: red, orange, yellow, green, blue, indigo, and violet. There are several mnemonics that can be used for remembering this color sequence, such as the ...
). Edridge-Green classified color vision based on how many distinct colors a subject could see in the spectrum. Normal subjects were termed ''hexachromic'' as they could not discern Indigo. Subjects with superior color vision, who could discern indigo, where ''heptachromic''. The colorblind were therefore ''dichromic'' (equivalent to dichromacy) or ''tri-'', ''tetra-'' or ''pentachromic'' (anomalous trichromacy).


Rights

In the United States, under federal anti-discrimination laws such as the
Americans with Disabilities Act The Americans with Disabilities Act of 1990 or ADA () is a civil rights law that prohibits discrimination based on disability. It affords similar protections against discrimination to Americans with disabilities as the Civil Rights Act of 1964 ...
, color vision deficiencies have not been found to constitute a disability that triggers protection from workplace discrimination. A Brazilian court ruled that people with color blindness are protected by the Inter-American Convention on the Elimination of All Forms of Discrimination against Person with Disabilities. At trial, it was decided that the carriers of color blindness have a right of access to wider knowledge, or the full enjoyment of their human condition.


Occupations

Color blindness may make it difficult or impossible for a person to engage in certain occupations. Persons with color blindness may be legally or practically barred from occupations in which color perception is an essential part of the job (''e.g.,'' mixing paint colors), or in which color perception is important for safety (''e.g.,'' operating vehicles in response to color-coded signals). This occupational safety principle originates from the aftermath of the 1875 Lagerlunda train crash, which Alarik Frithiof Holmgren blamed on the color blindness of the engineer and created the first occupational screening test against the colorblind. Color vision is important for occupations using telephone or computer networking cabling, as the individual wires inside the cables are color-coded using green, orange, brown, blue and white colors. Electronic wiring, transformers, resistors, and capacitors are color-coded as well, using black, brown, red, orange, yellow, green, blue, violet, gray, white, silver, gold.


Driving

Red–green colorblindness can make it difficult to drive, primarily due to the inability to differentiate red–amber–green
traffic lights Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic light ...
. Protans are further disadvantaged due to the darkened perception of reds, which can make it more difficult to quickly recognize brake lights. In response, some countries have refused to grant
driver's license 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 ...
s to individuals with color blindness: * In April 2003, Romania removed color blindness from its list of disqualifying conditions for learner driver's licenses. It is now qualified as a condition that could potentially compromise driver safety, therefore a driver may have to be evaluated by an authorized ophthalmologist to determine if they can drive safely. As of May 2008, there is an ongoing campaign to remove the legal restrictions that prohibit colorblind citizens from getting driver's licenses. * In June 2020, India relaxed its ban on driver's licenses for the colorblind to now only apply to those with strong CVD. While previously restricted, those who test as mild or moderate can now pass the medical requirements. * Australia instituted a tiered ban on the colorblind from obtaining commercial driver's licenses in 1994. This included a ban for all protans, and a stipulation that deutans must pass the
Farnsworth Lantern The Farnsworth Lantern Test, or FALANT, is a color vision test originally developed specifically to screen sailors for tasks requiring color vision, such as identifying signal lights at night. It screens for red-green deficiencies, but not the muc ...
. The stipulation on deutans was revoked in 1997 citing a lack of available test facilities, and the ban on protans was revoked in 2003. * All colorblind individuals are banned from obtaining a driver's license in China and since 2016 in Russia (2012 for dichromats).


Piloting aircraft

Although many aspects of aviation depend on color coding, only a few of them are critical enough to be interfered with by some milder types of color blindness. Some examples include color-gun signaling of aircraft that have lost radio communication, color-coded glide-path indications on runways, and the like. Some jurisdictions restrict the issuance of pilot credentials to persons with color blindness for this reason. Restrictions may be partial, allowing color-blind persons to obtain certification but with restrictions, or total, in which case color-blind persons are not permitted to obtain piloting credentials at all. In the United States, the
Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
requires that pilots be tested for normal color vision as part of their medical clearance in order to obtain the required medical certificate, a prerequisite to obtaining a pilot's certification. If testing reveals color blindness, the applicant may be issued a license with restrictions, such as no night flying and no flying by color signals—such a restriction effectively prevents a pilot from holding certain flying occupations, such as that of an airline pilot, although commercial pilot certification is still possible, and there are a few flying occupations that do not require night flight and thus are still available to those with restrictions due to color blindness (e.g., agricultural aviation). The government allows several types of tests, including medical standard tests (''e.g.,'' the Ishihara, Dvorine, and others) and specialized tests oriented specifically to the needs of aviation. If an applicant fails the standard tests, they will receive a restriction on their medical certificate that states: "Not valid for night flying or by color signal control". They may apply to the FAA to take a specialized test, administered by the FAA. Typically, this test is the "color vision light gun test". For this test an FAA inspector will meet the pilot at an airport with an operating control tower. The color signal light gun will be shone at the pilot from the tower, and they must identify the color. If they pass they may be issued a waiver, which states that the color vision test is no longer required during medical examinations. They will then receive a new medical certificate with the restriction removed. This was once a Statement of Demonstrated Ability (SODA), but the SODA was dropped, and converted to a simple waiver (letter) early in the 2000s. Research published in 2009 carried out by the
City University of London City, University of London, is a public research university in London, United Kingdom, and a member institution of the federal University of London. It was founded in 1894 as the Northampton Institute, and became a university when The City Univ ...
's Applied Vision Research Centre, sponsored by the UK's
Civil Aviation Authority A civil aviation authority (CAA) is a national or supranational statutory authority that oversees the regulation of civil aviation, including the maintenance of an aircraft register. Role Due to the inherent dangers in the use of flight vehicles, ...
and the U.S. Federal Aviation Administration, has established a more accurate assessment of color deficiencies in pilot applicants' red/green and yellow–blue color range which could lead to a 35% reduction in the number of prospective pilots who fail to meet the minimum medical threshold.


See also

*
List of people with color blindness This is a list of people with color blindness, meaning they have a decreased ability to see color or differences in color. A–Z References {{reflist, colwidth=30em People A person ( : people) is a being that has certain capacities ...
*
Motion blindness Akinetopsia (Greek: a for "without", kine for "to move" and opsia for "seeing"), also known as cerebral akinetopsia or motion blindness, is a term introduced by Semir Zeki to describe an extremely rare neuropsychological disorder, having only been ...
* Red–green color model - A color model that mimics tritan color blindness *
Tetrachromacy Tetrachromacy (from Greek language, Greek ''tetra'', meaning "four" and ''chromo'', meaning "color") is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cell in the eye. Org ...
* Color anomia - Ability to see colors, but inability to name colors. *
Color agnosia Cerebral achromatopsia is a type of color-blindness caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina. It is often confused with congenital achromatopsia but underlying physiological de ...
- Ability to see colors, but inability to recognize colors.


References


Further reading

* * * * * * * *


External links

*
"A Glossary of Color Science."
{{Authority control Color vision Genetic disorders by system Visual disturbances and blindness X-linked recessive disorders Wikipedia medicine articles ready to translate Agnosia Wikipedia neurology articles ready to translate