Color blindness

"Colorblind" redirects here. For the disorder that causes most forms of color blindness, seeCongenital red–green color blindness.For other uses, seeColor blind (disambiguation).

Color blindness
Other names	Color vision deficiency, impaired color vision
Example of anIshihara color testplate. Viewers with normal color vision should clearly see the number "74".
Specialty	Ophthalmology
Symptoms	Decreased ability tosee colors
Duration	Long term
Causes	Genetic(inheritedusuallyX-linked)
Diagnostic method	Ishihara color test
Treatment	Adjustments to teaching methods,mobile apps
Frequency	Red–green: 8% males, 0.5% females (Northern European descent)

Color blindnessorcolor vision deficiency(CVD) is the decreased ability tosee coloror differences incolor.The severity of color blindness ranges from mostly unnoticeable to full absence of color perception. Color blindness is usually aninheritedproblem or variation in the functionality of one or more of the three classes ofcone cellsin the retina, which mediate color vision.The most common form is caused by a genetic condition calledcongenital red–green color blindness(including protan and deutan types), which affectsup to1 in 12 males (8%) and 1 in 200 females (0.5%).The condition is more prevalent in males, because theopsingenes responsible are located on theX chromosome.Rarer genetic conditions causing color blindness include congenital blue–yellow color blindness (tritan type),blue cone monochromacy,andachromatopsia.Color blindness can also result from physical or chemical damage to theeye,theoptic nerve,parts of thebrain,or from medication toxicity.Color vision also naturally degrades in old age.

Diagnosis of color blindness is usually done with acolor vision test,such as theIshihara test.There is no cure for most causes of color blindness, however there is ongoing research intogene therapyfor some severe conditions causing color blindness.Minor forms of color blindness do not significantly affect daily life and the color blind automatically develop adaptations and coping mechanisms to compensate for the deficiency.However, diagnosis may allow an individual, or their parents/teachers, to actively accommodate the condition.Color blind glasses(e.g.EnChroma) may help the red–green color blind at somecolor tasks,but they do not grant the wearer "normal color vision" or the ability to see "new" colors.Somemobile appscan use a device's camera to identify colors.

Depending on the jurisdiction, the color blind are ineligible for certain careers,such asaircraft pilots,train drivers,police officers,firefighters,and members of thearmed forces.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 color blind person will have decreased (or no) color discrimination along the red–green axis, blue–yellow axis, or both. However, the vast majority of the color blind are only affected on their red–green axis.

The first indication of color blindness 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.

• 
  Normal sight
• 
  Deuteranopic sight
• 
  Protanopic sight
• 
  Tritanopic sight
• 
  Monochromatic sight

Confusion colors

Confusion lines for the three types of dichromacy superimposed on CIEXYZ color space

Confusion colors are pairs or groups of colors that will often be mistaken by the color blind. Confusion colors for red–green color blindness include:

• cyan and grey
• rose-pinkand grey
• blue and purple
• yellow andneon green
• red, green, orange, brown

Confusion colors for tritan include:

• yellow and grey
• blue and green
• dark blue/violet and black
• violet and yellow-green
• red androse-pink

These colors of confusion are defined quantitatively by straight confusion lines plotted inCIEXYZ,usually plotted on the correspondingchromaticity diagram.The lines all intersect at acopunctal point,which varies with thetype of color blindness.Chromaticitiesalong a confusion line will appearmetamerictodichromatsof that type.Anomalous trichromatsof that type will see the chromaticities as metameric if they areclose enough,depending on the strength of their CVD. For two colors on a confusion line to be metameric, the chromaticities first have to be madeisoluminant,meaning equal inlightness.Also, colors that may be isoluminant to thestandard observermay not be isoluminant to a person with dichromacy.

Color tasks

Main article:Color task

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 do not carry explicit meaning

The following sections describe specific color tasks with which the color blind typically have difficulty.

Food

Simulation of the normal (above) and dichromatic (below) perception of red and green apples

Color blindness causes difficulty with theconnotativecolor tasks associated with selecting or preparing food. Selecting food for ripeness can be difficult; the green–yellow transition of bananas is particularly hard to identify. It can also be difficult to detect bruises, mold, or rot on some foods, to determine when meat is done by color, to distinguish some varietals, such as aBraeburnvs. aGranny Smithapple, or to distinguish colors associated with artificial flavors (e.g. jelly beans, sports drinks).

Skin color

Main article:Evolution of color vision in primates § Skin Tone

Changes in skin color due to bruising, sunburn, rashes or even blushing are easily missed by the red–green color blind.

Traffic lights

See also:§ Driving

The lack of standard positional clues makes this light difficult to interpret.

The colors oftraffic lightscan be difficult for the red–green color blindness. This difficulty includes distinguishing red/amber lights from sodium street lamps, distinguishing green lights (closer to cyan) from normal white lights, and distinguishing red from amber lights, especially when there are no positional clues available (see image).

The infamous inverted traffic light in Syracuse, New York

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 atraffic light in Tipperary HillinSyracuse, New York,which is upside-down (green–amber–red top to bottom) due to the sentiments of itsIrish Americancommunity.However, the light has been criticized due to the potential hazard it poses for color blind drivers.

Horizontal traffic light inHalifax, Nova Scotia,Canada

There are other several features of traffic lights available that help accommodate the color blind. British Rail signals use more easily identifiable colors: The red is blood red, the amber is yellow and the green is a bluish color.Most British road traffic lights are mounted vertically on a black rectangle with a white border (forming a "sighting board" ), so that drivers can more easily look for the position of the light. In theeastern 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 image).

Signal lights

See also:§ Occupations

Navigation lightsin marine and aviation settings employ red and green lights to signal the relative position of other ships or aircraft.Railway signal lightsalso rely heavily on red–green–yellow colors. In both cases, these color combinations can be difficult for the red–green color blind.Lantern Testsare a common means of simulating these light sources to determine not necessarily whether someone is color blind, 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, for example.

Fashion

See also:Color of clothing

Color analysisis 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 comparativecolor taskthat can be difficult for the color blind.

Art

Inability to distinguish color does not necessarily preclude the ability to become a celebrated artist. The 20th century expressionist painterClifton Pugh,three-time winner of Australia'sArchibald Prize,on biographical, gene inheritance and other grounds has been identified as a person with protanopia.19th century French artistCharles Méryonbecame successful by concentrating onetchingrather 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 ananimatorand later a character designer withWalt Disney Animation Studios.

Advantages

Deuteranomals are better at distinguishing shades ofkhaki,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 the color blind 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 color blind are more capable of seeing a luminous signal, as long as the chromatic noise appearsmetamericto them.This is the effect behind most "reverse"Pseudoisochromatic plates(e.g."hidden digit"Ishihara plates) that are discernible to the color blind but unreadable to people with typical color vision.

Digital design

See also:Color coding in data visualization

Testing the colors of a web chart,(center),to ensure that no information is lost to the various forms of color blindness

Color codesare useful tools for designers to convey information. The interpretation of this information requires users to perform a variety ofColor Tasks,usually comparative but also sometimes connotative or denotative. However, these tasks are often problematic for the color blind when design of the color code has not followed best practices for accessibility.For example, one of the most ubiquitousconnotativecolor codes is the "red means bad and green means good" or similar systems, based on the classicsignal light colors.However, this color coding will almost always beundifferentiabletodeutansorprotans,and therefore should be avoided or supplemented with a parallel connotative system (symbols,smileys,etc.).

Good practices to ensure design is accessible to the color blind include:

• When possible (e.g. in simple video games or apps), allowing the user to choose their own colors is themostinclusive design practice.
• Using other signals that are parallel to the color coding, such as patterns, shapes, size or order.This not only helps the color blind, 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 suggestsconverting a (digital) design to grayscaleto ensure there is sufficient brightness contrast between colors. However, this does not account for thedifferent perceptions of brightness to different varieties of color blindness,especiallyprotanCVD,tritanCVD andmonochromacy.
• Viewing the design through aCVD Simulatorto ensure the information carried by color is still sufficiently conveyed. At a minimum, the design should be tested fordeutanCVD, the most common kind of color blindness.
• 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 alegend,even when the meaning is considered obvious (e.g.red means danger).
• Avoiding denotative color tasks (color naming) 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 "purple",purpleor "purple ( ) ".
• For denotative tasks (color naming), using the most common shades of colors. For example, green and yellow are colors of confusion in red–green CVD, but it is not common to mix forest green ( ) with bright yellow ( ). Mistakes by the color blind 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 ofburgundy( ) to represent the word "red".

Unordered Information

Colors ofboard gamepieces must be carefully chosen to be accessible to the color blind.

A common task for designers is to select a subset of colors (qualitativecolormap) that are as mutually differentiable as possible (salient). For example, player pieces in aboard gameshould be as different as possible.

Classic advice suggests usingBrewer palettes,but several of these arenotactually accessible to the color blind.

Unfortunately, the colors with the greatestcontrastto thered–green color blindtend to becolors of confusionto theblue–yellow color blind,and vice versa. However, since red–green is muchmore prevalentthan blue–yellow CVD, design shouldgenerally prioritize those users (deutansthenprotans).

Ordered Information

Three sequential colormaps that have been designed to be accessible to the color blind

A common task for data visualization is to represent a color scale, orsequentialcolormap, often in the form of aheat maporchoropleth.Several scales are designed with special consideration for the color blind and are widespread in academia, including Cividis,ViridisandParula.These comprise a light-to-dark scale superimposed on a yellow-to-blue scale, making themmonotonicand perceptually uniform to all forms of color vision.

Classification

These color charts show how different color blind people see compared to a person with normal color vision.

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 color blindness includes dichromacy and anomalous trichromacy, but is often clinically defined as mild, moderate or strong.

Monochromacy

Main article:Monochromacy

Monochromacy is often calledtotal color blindnesssince there is no ability to see color. Although the term may refer to acquired disorders such ascerebral achromatopsia,it typically refers to congenital color vision disorders, namelyrod monochromacyandblue cone monochromacy).

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 ofvisual agnosia.

Monochromacyis 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:

1. Rod monochromacy, frequently called completeachromatopsia,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.
2. 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 monochromacyis 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 shownystagmus( "jiggling eyes" ),photophobia(light sensitivity), reducedvisual acuity,andmyopia(nearsightedness).Visual acuity usually falls to the 20/50 to 20/400 range.

Dichromacy

Main article:Dichromacy

Dichromats can match any color they see with some mixture of just twoprimary colors(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-) [cone] ".

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 thandichromacy.Anomalous trichromats exhibittrichromacy,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 anAnomaloscope,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 thephenotypeof the partial color blindness. Clinically, it is more common to use a genotypical definition, which describes whichcone/opsinis affected.

Red–green color blindness

Red–green color blindness includesprotananddeutanCVD. 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 ofcongenital red–green color blindness,so affects males disproportionately more than females.This form of color blindness is sometimes referred to asdaltonismafterJohn Dalton,who had red–green dichromacy. In some languages,daltonismis still used to describe red–green color blindness.

Illustration of the distribution of cone cells in thefoveaof an individual with normal color vision (left), and a color blind (protanopic) retina. The center of the fovea holds very few blue-sensitive cones.

• Protan(2% of males): Lacking, or possessing anomalousL-opsinsfor long-wavelength sensitive cone cells. Protans have a neutral point at acyan-like wavelength around 492 nm (seespectral colorfor comparison)—that is, they cannot discriminate light of this wavelength fromwhite.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,lavender, and purpleare indistinguishable from variousshades of blue.A very few people have been found who have one normal eye and one protanopic eye. Theseunilateral dichromatsreport 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 anomalousM-opsinsfor 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 includestritanCVD. 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 anomalousS-opsinsor short-wavelength sensitive cone cells. Tritans see short-wavelength colors (blue,indigoand spectralviolet) as greenish and drastically dimmed, some of these colors even asblack.Yellow and orange are indistinguishable fromwhiteandpinkrespectively, and purple colors are perceived as variousshades of red.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".

• Tetartanis the "fourth type" of color blindness, 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.

Cone system

Red

Green

Blue

N= normal A= anomalous

N

A

N

A

N

A

1

Normal vision

Trichromacy

Normal

2

Protanomaly

Anomalous trichromacy

Partial color blindness

Red– green

3

Protanopia

Dichromacy

4

Deuteranomaly

Anomalous trichromacy

5

Deuteranopia

Dichromacy

6

Tritanomaly

Anomalous trichromacy

Blue– yellow

7

Tritanopia

Dichromacy

8

Blue cone monochromacy

Monochromacy

Total color blindness

9

Achromatopsia

10

Tetrachromacy (carrier theory)

Tetrachromacy

'Superior'

Causes

See also:Trichromatic color visionandCongenital red–green color blindness § Mechanism

Color blindness is any deviation of color vision from normaltrichromaticcolor vision (often as defined by thestandard observer) that produces a reducedgamut.Mechanisms for color blindness are related to the functionality ofcone cells,and often to the expression ofphotopsins,thephotopigmentsthat 'catch'photonsand 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 color blindness are associated with thePhotopsingenes, but the mapping of the human genome has shown there are many causative mutations that do not 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 theOnline Mendelian Inheritance in Man[OMIM]).

Genetics of red–green color blindness

Main article:Congenital red–green color blindness § Genetics

Punnett squares for each combination of parents' color vision status giving probabilities of their offsprings' status; A superscript 'c' denotes a chromosome with an affected gene.

By far the most common form of color blindness iscongenital red–green color blindness(Daltonism), which includes protanopia/protanomaly and deuteranopia/deuteranomaly. These conditions are mediated by theOPN1LWandOPN1MWgenes, respectively, both on theX chromosome.An 'affected' gene is either missing (as in Protanopia and Deuteranopia -Dichromacy) or is achimeric gene(as in Protanomaly and Deuteranomaly).

Since theOPN1LWandOPN1MWgenes are on the X chromosome, they aresex-linked,and therefore affect males and females disproportionately. Because the color blind 'affected'allelesare recessive, color blindness specifically followsX-linked recessive inheritance.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 color blind. 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 color blind. This is why there is a disproportionate prevalence of color blindness, with ~8% of males exhibiting color blindness and ~0.5% of females.

Genetics of blue–yellow color blindness

Congenital blue–yellow color blindness is a much rarer form of color blindness including tritanopia/tritanomaly. These conditions are mediated by theOPN1SWgene onChromosome 7which encodes the S-opsin protein and follows autosomal dominant inheritance.The cause of blue–yellow color blindness is not analogous to the cause of red–green color blindness, i.e. the peak sensitivity of the S-opsin does not shift to longer wavelengths. Rather, there are 6 known point mutations of OPN1SW that degrade the performance of the S-cones.The OPN1SW gene is almost invariant in the human population. Congenital tritan defects are often progressive, with nearly normal trichromatic vision in childhood (e.g. mild tritanomaly) progressing to dichromacy (tritanopia) as the S-cones slowly die.Tritanomaly and tritanopia are therefore different penetrance of the same disease, and some sources have argued that tritanomaly therefore be referred to as incomplete tritanopia.

Other genetic causes

Several inherited diseases are known to cause color blindness, includingachromatopsia,cone dystrophy,Leber's congenital amaurosisandretinitis pigmentosa.These can becongenitalor commence in childhood or adulthood. They can be static/stationary orprogressive.Progressive diseases often involve deterioration of the retina and other parts of the eye, so often progress from color blindness to more severevisual impairments,up to and including total blindness.

Non-genetic causes

Physical trauma can cause color blindness, either neurologically – brain trauma which produces swelling of the brain in theoccipital lobe– or retinally, either acute (e.g. from laser exposure) or chronic (e.g. fromultraviolet lightexposure).

Color blindness may also present itself as a symptom of degenerative diseases of the eye, such ascataractand age-relatedmacular degeneration,and as part of the retinal damage caused bydiabetes.Vitamin Adeficiency may also cause color blindness.

Color blindness may be aside effectof prescription drug use. For example, red–green color blindness can be caused byethambutol,a drug used in the treatment oftuberculosis.Blue–yellow color blindness can be caused bysildenafil,an active component ofViagra.Hydroxychloroquinecan also lead to hydroxychloroquine retinopathy, which includes various color defects.Exposure to chemicals such as styreneor organic solventscan 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 thevitreous humorof his eye was discolored:

I was led to conjecture that one of the humours of my eye must be a transparent, but coloured, medium, so constituted as to absorb red and green rays principally... I suppose it must be the vitreous humor.

— John Dalton,Extraordinary facts relating to the vision of colours: with observations(1798)

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 namedCyanopsiaandXanthopsia,and are most typically an effect of yellowing or removal of thelens.

The opponent channels can also be affected by the prevalence of certain cones in theretinal mosaic.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 oftritanomaly.

Some people are also unable to distinct between blue and green, which appears to be a combination ofcultureand exposure to UV-light.

Diagnosis

Color vision test

Main article:Color vision test

An Ishihara test image as seen by subjects with normal color vision and by those with a variety of color deficiencies

The main method for diagnosing a color vision deficiency is in testing the color vision directly. TheIshihara color testis 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 theIshihara color testand 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) to the color blind 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 theFarnsworth Lantern Test,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 color blindness, but they are occupational screening tests to ensure an applicant has sufficient color discrimination to be able to perform a job.

A Farnsworth D-15 test

• Arrangement testscan be used as screening or diagnostic tools. TheFarnsworth–Munsell 100 hue testis very sensitive, but theFarnsworth D-15is 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.
• Anomaloscopesare typically designed to detect red–green deficiencies and are based on theRayleigh 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 they are generally only used in academic settings.

Genetic testing

While genetic testing cannot directly evaluate a subject's color vision (phenotype), most congenital color vision deficiencies are well-correlated withgenotype.Therefore, thegenotypecan be directly evaluated and used to predict thephenotype.This is especially useful forprogressiveforms 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 commonallelesof these two genes are known and have even been related to exactspectral sensitivitiesand peak wavelengths. A subject's color vision can therefore be classified throughgenetic testing,but this is just a prediction of the phenotype, since color vision can be affected by countless non-genetic factors such as yourcone mosaic.

Management

Despite much recent improvement ingene therapy for color blindness,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

Main article:Color blind glasses

There are three kinds of lenses that an individual can wear that can increase their accuracy in some color related tasks (although none of these will "fix"color blindness or grant the wearer normal color vision):

• A red-tint contact lens worn over the non-dominant eye will leveragebinocular disparityto 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 reportedand 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 manycolor vision tests,though this is typically not allowed.
• Glasses with anotch filter(e.g.EnChromaglasses) 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 lensesmayconstitute aneutral-density filter(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 color blind tests.

Aids

Many mobile and computer applications have been developed to aid color blind individuals in completing color tasks:

• Some applications (e.g.color pickers) can identify the name (or coordinates within acolor space) 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 color blind by enhancing color contrast in natural images and/or information graphics. These methods are generally calleddaltonizationalgorithms.
• 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 do not directly help color blind people, they allow those with normal color vision to understand how the color blind 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 color blind.

In 2003, a cybernetic device calledeyeborgwas developed to allow the wearer to hear sounds representing different colors.Achromatopsic artistNeil Harbissonwas 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 aTED Conference,Harbisson explained how he could now perceive colors outside the ability of human vision.

Epidemiology

Rates of color blindness

	Males	Females
Dichromacy	2.4%	0.03%
Protanopia	1.3%	0.02%
Deuteranopia	1.2%	0.01%
Tritanopia	0.008%	0.008%
Anomalous trichromacy	6.3%	0.37%
Protanomaly	1.3%	0.02%
Deuteranomaly	5.0%	0.35%
Tritanomaly	0.0001%	0.0001%

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 first paper already arrived upon this 8% number:

...it is remarkable that, out of 25 pupils I once had, to whom I explained this subject, 2 were found to agree with me...

— John Dalton,Extraordinary facts relating to the vision of colours: with observations(1798)

History

An 1895 illustration of normal vision and various kinds of color blindness

During the 17th and 18th century, several philosophers hypothesized that not all individuals perceived colors in the same way:

...there is no reason to suppose a perfect resemblance in the disposition of the Optic Nerve in all Men, since there is an infinite variety in every thing in Nature, and chiefly in those that are Material, 'tis therefore very probable that all Men see not the same Colours in the same Objects.

— Nicolas Malebranche,The search after truth(1674)

In the power of conceivingcolors,too, there are striking differences among individuals: and, indeed, I am inclined to suspect, that, in the greater number of instances, the supposed defects of sight in this respect ought to be ascribed rather to a defect in the power of conception.

— Dugald Stewart,Elements of the philosophy of the human mind(1792)

Gordon Lynn Wallsclaimsthat the first well-circulated case study of color blindness was published in a 1777 letter from Joseph Huddart toJoseph Priestley,which described "Harris the Shoemaker" and several of his brothers with what would later be described as protanopia. There appear to be no earlier surviving historical mentions of color blindness, despite its prevalence.

The phenomenon only came to be scientifically studied in 1794, when English chemistJohn Daltongave the first account of color blindness in a paper to theManchester Literary and Philosophical Society,which was published in 1798 asExtraordinary 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 writerJ. W. von Goethestudied color vision abnormalities in 1798 by asking two young subjects to match pairs of colors.

In 1837,August Seebeckfirst discriminated between protans and deutans (then as class I + II).He was also the first to develop an objective test method, where subjects sorted colored sheets of paper, and was the first to describe a female colorblind subject.

In 1875, theLagerlunda train crashin Sweden brought color blindness to the forefront. Following the crash, ProfessorAlarik 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 color blind from jobs in the transportation industryrequiring 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-Greendevised an alternative theory of color vision and color blindness based on Newton's classification of 7 fundamental colors (ROYGBIV). Edridge-Green classified color vision based on how many distinct colors a subject could see in the spectrum. Normal subjects were termedhexachromicas they could not discern Indigo. Subjects with superior color vision, who could discern indigo, wereheptachromic.The color blind were thereforedichromic(equivalent to dichromacy) ortri-,tetra-orpentachromic(anomalous trichromacy).

Rights

In the United States, under federal anti-discrimination laws such as theAmericans with Disabilities Act,color vision deficiencies have not been found to constitute a disability that triggers protection from workplace discrimination.

A Brazilian court ruled that the color blind 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 activities. 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 1875Lagerlunda train crash,whichAlarik Frithiof Holmgrenblamed on the color blindness of the engineer and created the first occupational screening test (Holmgren's wool test) against the color blind.

...I consider that to [Holmgren] above all others do we owe the present and future control of color-blindness on land and sea, by which life and property are safer, and the risks of travelling less.

— Benjamin Joy Jeffries,Color-blindness: Its Danger & Its Detection(1879)

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, and gold.

Participation, officiating and viewing sporting events can be impacted by color blindness. Professional football playersThomas DelaneyandFabio Carvalhohave discussed the difficulties when color clashes occur, and research undertaken by FIFA has shown that enjoyment and player progression can be hampered by issues distinguishing the difference between the pitch and training objects or field markings.SnookerWorld ChampionsMark WilliamsandPeter Ebdonsometimes need to ask the referee for help distinguishing between the red and brown balls due to their color blindness. Both have played foul shots on notable occasions bypottingthe wrong ball.

Driving

See also:§ Traffic lights

Red–green color blindness can make it difficult to drive, primarily due to the inability to differentiate red–amber–greentraffic lights.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 grantdriver's licensesto 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 color blind citizens from getting driver's licenses.
• In June 2020, India relaxed its ban on driver's licenses for the color blind 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 color blind from obtaining commercial driver's licenses in 1994. This included a ban for allprotans,and a stipulation thatdeutansmust pass theFarnsworth Lantern.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 color blind individuals are banned from obtaining a driver's license in Chinaand since 2016 in Russia (2012 for dichromats).

Piloting aircraft

See also:§ Signal lights

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 includecolor-gun signalingof aircraft that have lost radio communication, color-codedglide-path indicationson 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, theFederal Aviation Administrationrequires 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.,theIshihara,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 colorsignal light gunwill 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 theCity University of London's Applied Vision Research Centre, sponsored by the UK'sCivil Aviation Authorityand 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

• Color agnosia– Ability to see colors, but inability to recognize colors.
• Color anomia– Ability to see colors, but inability to name colors.
• List of people with color blindness
• Motion blindness
• Tetrachromacy

Further reading

• Kaiser PK, Boynton RM (1996).Human color vision.Washington, DC: Optical Society of America.ISBN978-1-55752-461-4.OCLC472932250.
• McIntyre D (2002).Colour blindness: causes and effects.Chester: Dalton Publishing.ISBN978-0-9541886-0-3.OCLC49204679.
• Rubin ML, Cassin B, Solomon S (1984).Dictionary of eye terminology.Gainesville, Fla: Triad Pub. Co.ISBN978-0-937404-07-2.OCLC10375427.
• Shevell SK (2003).The science of color.Amsterdam: Elsevier.ISBN978-0-444-51251-2.OCLC52271315.
• Hilbert D, Byrne A (1997).Readings on color.Cambridge, Mass: MIT Press.ISBN978-0-262-52231-1.OCLC35762680.
• Stiles WS, Wyszecki G (2000).Color science: concepts and methods, quantitative data and formulae.Chichester: John Wiley & Sons.ISBN978-0-471-39918-6.OCLC799532137.
• Kuchenbecker J, Broschmann D (2014).Plates for color vision testing.New York: Thieme.ISBN978-3-13-175481-3.
• Dalton J (1798). "Extraordinary facts relating to the vision of colours: with observations".Memoirs of the Literary and Philosophical Society of Manchester.5:28–45.OCLC9879327.

External links

• "A Glossary of Color Science."Archived4 October 2015 at theWayback Machine