Color blindness in humans is the inability to perceive differences between some or all colors that other people can distinguish. It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or due to exposure to certain chemicals. The English chemist John Dalton in 1794 published the first scientific paper on the subject, "Extraordinary facts relating to the vision of colors", after the realization of his own color blindness; because of Dalton's work, the condition is sometimes called Daltonism, although this term is now used for a type of color blindness called deuteranopia (see below). Binomial name Homo sapiens Linnaeus, 1758 Subspecies Homo sapiens idaltu (extinct) Homo sapiens sapiens Human beings define themselves in biological, social, and spiritual terms. ... For alternative meanings, see color (disambiguation). ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... An eye is an organ that detects light. ... A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin. ... In the anatomy of animals, the brain, or encephalon, is the supervisory center of the nervous system. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... John Dalton John Dalton (September 6, 1766 – July 27, 1844) was a British chemist and physicist, born at Eaglesfield, near Cockermouth in Cumberland. ... 1794 was a common year starting on Wednesday (see link for calendar). ... // What is science? There are different theories of what science is. ...

Color blindness is usually classed as a disability; however, in select situations color blind people have advantages over people with normal color vision. Color blind hunters are better at picking out prey against a confusing background, and the military have found that color blind soldiers can sometimes see through camouflage that fools everyone else. Monochromats may have a minor advantage in dark vision, but only in the first five minutes of dark adaptation. The term disability, as it is applied to humans, refers to any condition that impedes the completion of daily tasks using traditional methods. ... This article is about the hunting of prey by human society. ... Anolis caroliensis showing blending camouflage and counter-shading. ...

Classification of color deficiencies

• Acquired
• Congenital

• Anomolous trichomacy

• Protanomaly
• Deuteranomaly
• Tritanomaly

• Dichromacy

• Protanopia
• Deuteranopia
• Tritanopia

• Monochromacy

• Rod monochromacy
• Achromatopsia

This is a sample image. Everyone should be able to see the number 83. The pictures below should look similar (containing just different numbers) to people with normal vision, but some of them will not be visible to people with a color vision deficiency. Note, however, that the contrast in these tests is much subtler than commonly seen in other similar tests.

3 + 80 File links The following pages link to this file: Color blindness Talk:Color blindness Categories: GFDL images ...

Simple test for color blindness

To the right are four pictures with 2-digit numbers designed to test for different kinds of color blindness. Note that monitor or lighting differences may affect whether or not the images can be seen.

Rates of occurrence

Color blindness affects a significant number of people, although exact proportions vary among groups. In Australia, for example, approximately 4% of the population suffers from some deficiency in color perception. Isolated communities with a restricted gene pool sometimes produce high proportions of color blindness, including the less usual types. Examples include rural Finland and some of the Scottish islands. Royal motto: Nemo me impune lacessit (Latin: No one provokes me with impunity) Scotlands location within the UK Languages with Official Status1 English Scottish Gaelic Capital Edinburgh Largest city Glasgow First Minister Jack McConnell Area - Total - % water Ranked 2nd UK 78,782 km² 1. ...

This image contains a two digit number similar to the sample above. Someone who is protanopic might not see this number.

This image shows the number 37 File links The following pages link to this file: Color blindness Talk:Color blindness Categories: GFDL images ...

Causes of color blindness

There are many types of color blindness. The most common varieties are hereditary (genetic) photoreceptor disorders, but it is also possible to acquire color blindness through damage to the retina, optic nerve, or higher brain areas. Higher brain areas implicated in color processing include the parvocellular pathway of the lateral geniculate nucleus of the thalamus, and visual area V4 of the visual cortex. Acquired color blindness is generally unlike the more typical genetic disorders. For example, it is possible to acquire color blindness only in a portion of the visual field but maintain normal color vision elsewhere. Some forms of acquired color blindness are reversible. Transient color blindness also occurs (very rarely) in the aura of some migraine sufferers. The lateral geniculate nucleus (LGN) of the thalamus is a part of the brain, which is the primary processor of visual information, received from the retina, in the CNS. Schematic diagram of the primate lateral geniculate nucleus. ... The thalamus is a part of the brain. ... Visual area V4 is an one of the visual areas in the extrastriate visual cortex of the macaque monkey. ... The visual cortex is the general term applied to both the primary visual cortex (also known as V1) and the visual association area (V2, V3, V4, V5). ... An aura is an optical effect wherein gas or dust surrounding an object luminesces or reflects light from the object. ...

Someone who is deuteranopic might not see this number. Please note that the second digit in this number may be difficult to discern even by those with normal vision.

The normal human retina contains two kinds of light sensitive cells: the rod cells (active in low light) and the cone cells (active in normal daylight). Normally, there are three kinds of cones, each containing a different pigment. The cones are activated when the pigments absorb light. The absorption spectra of the pigments differ; one is maximally sensitive to short wavelengths, one to medium wavelengths, and the third to long wavelengths (their peak sensitivities are in the blue, yellowish-green, and yellow regions of the spectrum, respectively). It is important to realize that the absorption spectra of all three systems cover much of the visible spectrum, so it is incorrect to refer to them as "blue", "green" and "red" receptors, especially because the "red" receptor actually has its peak sensitivity in the yellow. The sensitivity of normal color vision actually depends on the overlap between the absorption spectra of the three systems: different colors are recognized when the different types of cone are stimulated to different extents. For example, red light stimulates the long wavelength cones much more than either of the others, but the gradual change in hue seen as wavelength reduces is the result of the other two cone systems being increasingly stimulated as well. Insert non-formatted text hereThis image shows the number 49. ... Human eye cross-sectional view. ... Normalised absoption spectra of human rod (R) and cone (S,M,L) cells. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina which only function in relatively bright light. ... An absorption spectrum is a diagram depicting the wavelengths of electromagnetic radiation absorbed by a material. ... For other uses, see Blue (disambiguation) Blue is one of the three primary additive colors; blue light has the shortest wavelength range (about 420-490 nanometres) of the three primary colors. ... Look up Green on Wiktionary, the free dictionary Green is a color seen commonly in nature. ... Red is a color at the lowest frequencies of light discernible by the human eye. ... Yellow is a color with a wavelength 565-590 nanometers. ...

Someone who is tritanopic might not see this number.

The different kinds of color blindness result from one or more of the different cone systems either not functioning at all, or functioning in an unusual way. When one cone system is compromised, dichromacy results. The most frequent forms of human color blindness result from problems with either the middle or long wavelength sensitive cone systems, and involve difficulties in discriminating reds, yellows, and greens from one another. They are collectively referred to as "red-green color blindness", though the term is an over-simplification and somewhat misleading. Other forms of color blindness are much rarer. They include problems in discriminating blues from yellows, and the rarest forms of all, complete color blindness or monochromacy, where one cannot distinguish any color from grey, as in a black-and-white movie or photograph. This image shows the number 56, and can hardly be read by someone suffering Tritanopia (Blue-Blindness) File links The following pages link to this file: Color blindness Talk:Color blindness Categories: GFDL images ... A dichromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than two different pure spectral lights. ... A monochromat is an organism that is truly color blind. ... Gray or grey is a color seen commonly in nature. ... Black-and-white (or variations including Black and White) can refer to a general term used in photography, film, and other media (see black-and-white). ...

Red-green color blindness

Types of red-green color blindness

There are several types of red-green color blindness:

• Protanopia: Lacking the long-wavelength sensitive retinal cones, those with this condition are unable to distinguish between colors in the green-yellow-red section of the spectrum. They have a neutral point at a wavelength of 492 nm—that is, they cannot discriminate light of this wavelength from white. Their sensitivity to light in the orange and red part of the spectrum is also reduced. 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 below the neutral point as blue and those above it as yellow. This is a rare form of color blindness.
• Deuteranopia: Lacking the medium-wavelength cones, those affected are again unable to distinguish between colors in the green-yellow-red section of the spectrum. Their neutral point is at a slightly longer wavelength, 498 nm. This is one of the rarer forms of colorblindness making up about 1% of the male population, also known as Daltonism after Dalton. (Dalton's diagnosis was confirmed as deuteranopia in 1995, some 150 years after his death, by DNA analysis of his preserved eyeball.) Deuteranopic unilateral dichromats report that with only their deuteranopic eye open, they see wavelengths below the neutral point as blue and those above it as yellow.
• Protanomaly: Having a mutated form of the long-wavelength pigment, whose peak sensitivity is at a shorter wavelength than in the normal retina, protanomalous individuals are less sensitive to red light than normal. This means that they are less able to discriminate colors, and they do not see mixed lights as having the same colors as normal observers. They also suffer from a darkening of the red end of the spectrum. This causes reds to reduce in intensity to the point where they can be mistaken for black. Protanomaly is a fairly rare form of color blindness, making up about 1% of the male population.
• Deuteranomaly: Having a mutated form of the medium-wavelength pigment. The medium-wavelength pigment is shifted towards the red end of the spectrum resulting in a reduction in sensitivity to the green area of the spectrum. Unlike protanomaly the intensity of colors is unchanged. This is the most common form of color blindness, making up about 6% of the male population.

Ground or earth in a mains (AC power) electrical wiring system is a conductor that exists primarily to help protect against faults. ... A nanometre (American spelling: nanometer, symbol: nm) is 1. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ...

Dichromacy and anomalous trichromacy

Protanopes and deuteranopes are dichromats; that is, they can match any color they see with some mixture of just two spectral lights (whereas normally humans are trichromats and require three lights). Those having protanomaly or deuteranomaly are trichromats, but the color matches they make differ from the normal: 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. They are called anomalous trichromats. A trichromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than three different pure spectral lights. ...

Protanomaly and deuteranomaly can be readily observed using an instrument called an anomaloscope, which mixes spectral red and green lights in variable proportions, for comparison with a fixed spectral yellow. If this is done in front of a large audience of men, as the proportion of red is increased from a low value, first a small proportion of people will declare a match, while most of the audience are seeing the mixed light as greenish. These are the deuteranomalous observers. Next, as more red is added the majority will say that a match has been achieved. Finally, as yet more red is added, the remaining, protanomalous, observers will declare a match at a point were everyone else is seeing the mixed light as definitely reddish.

Genetics of red-green color blindness

Genetic red-green color blindness affects men much more often than women, because the genes for the red and green color receptors are located on the X chromosome, of which men have only one and women have two. Such a trait is called sex-linked. Genetic females (46, XX) are red-green color blind only if both their X chromosomes are defective with a similar deficiency, whereas genetic males (46, XY) are color blind if their only X chromosome is defective. This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... Figure 1: Chromosome. ... Sex-linked genes are those carried on the mammalian X chromosome but not the Y chromosome. ...

The gene for red-green color blindness is transmitted from a color blind male to all his daughters who are heterozygote carriers and are perceptually unaffected. In turn, a carrier woman passes on a mutated X chromosome region to only half her male offspring. The sons of an affected male will not inherit the trait, since they receive his Y chromosome and not his (defective) X chromosome. Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. ...

Because one X chromosome is inactivated at random in each cell during a woman's development, it is possible for her to have four different cone types, if, for example, a carrier of protanomaly has a child with a deuteranomalic man. The deficiencies can combine to form a fourth receptor whose absorption spectrum peaks in the yellow-green area. Denoting the normal vision alleles by P and D and the anomalous by p and d, the carrier is PD pD and the man is Pd. The daughter is either PD Pd or pD Pd. Suppose she is pD Pd. The cells in her body express her mother's chromosome pD and her father's Pd. Thus some of the cones are anomalous with both deficiencies and some are normal. As a result she has the normal short, medium and long wavelength-sensitive types of cone, with an additional category of receptor that combines the deficiencies. Such women are tetrachromats, since with their four-cone systems, they require a mixture of four spectral lights to match an arbitrary light. In those species in which sex is determined by the presence of the Y or W chromosome rather than the diploidy of the X or Z, a Barr body is the inactive X chromosome in a female cell, or the inactive Z in a male. ... A tetrachromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than four different pure spectral lights. ...

Blue-yellow color blindness

Color blindness involving the inactivation of the short-wavelength sensitive cone system (whose absorption spectrum peaks in the bluish-violet) is called tritanopia or, loosely, blue-yellow color blindness. Mutation of the short-wavelength sensitive cones is called tritanomaly. Tritanopia is equally distributed among males and females, because the gene coding for the short-wavelength receptor is located on chromosome 7 and therefore not sex-linked, but since mutations in both copies are required, it is less frequently apparent.

Monochromacy

Complete inability to distinguish any colors is called monochromacy. It occurs in two forms: cone monochromacy, where only a single cone system appears to be functioning, so that no colors can be distinguished, but vision is otherwise more or less normal; and achromatopsia or rod monochromacy, 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. A monochromat is an organism that is truly color blind. ... Maskun is a medical condition (also called achromatopsia) characterized by a low cone count or lack of function in cone cells; these are the light receptors responsible for colour perception. ...

While normally rare, achromatopsia is very common on the island of Pingelap, a part of the Pohnpei state, where it is called maskun: about 1/12 of the population there has it. The island was devastated by a storm in the eighteenth century, and one of the few male survivors carried a gene for achromatopsia; the population is now several thousand, of whom about 30% carry this gene. District center of Pohnpei Map of Pohnpei Pohnpei (also spelled Ponape and earlier Bonabee) is one of the islands in the Federated States of Micronesia (FSM), and is one of the Senyavin Islands. ...

Diagnosis

Color blindness is most often tested using the Ishihara color test, which consists of a series of pictures of colored spots. A figure (usually a number) is embedded in the picture as a number of spots in a slightly different color, and can be seen with normal color vision, but not with a particular color defect. The full set of tests has a variety of figure/background color combinations, and enable diagnosis of which particular visual defect is present. The anomaloscope, described above, is also used in diagnosing anomalous trichromacy. The Ishihara color test is a test for color blindness. ...

However, the Ishihara color test is criticized for containing only numbers and thus not being useful for young children. It is often stated that it is important to identify these problems as soon as possible and explain them to the children to prevent possible problems and psychological traumas ("Why did you color the sky purple, Johnny?!"). For this reason, alternative color vision tests were developed using only symbols (square, circle, car).

Most clinical tests are designed to be fast, simple, and effective at identifying broad categories of color blindness. In academic studies of color blindness, on the other hand, there is more interest in developing flexible tests ([1], for example) to collect thorough datasets, identify copunctal points, and measure just noticeable differences. In psychophysics, the just noticeable difference (usually abbreviated as jnd, using lowercase letters) is the smallest difference in a sensory input that is perceivable by a human being or other animal. ...

Design implications of color blindness

Color codes present particular problems for color blind people as they are often difficult or impossible for color blind people to understand. A color code is a system for displaying information by using different colors. ...

Good graphic design avoids using color coding or color contrasts alone to express information, as this not only helps color blind people, but also aids understanding by normally sighted people. The use of Cascading Style Sheets on the world wide web allows pages to be given an alternative color scheme for color-blind readers. This color scheme generator helps a graphic designer see color schemes as seen by eight types of color blindness. Graphic design is the applied art of arranging image and text to communicate a message. ... In computing, Cascading Style Sheets (CSS) is a stylesheet language used to describe the presentation of a document written in a markup language. ... Graphic representation of the World Wide Web around Wikipedia The World Wide Web (WWW, W3, or simply Web) is an information space in which the items of interest, referred to as resources, are identified by global identifiers called Uniform Resource Identifiers (URIs). ...

It is sometimes claimed that in extreme emergencies everyone is color blind. When the need to process visual information as rapidly as possible arises, for example in a train or aircraft crash, the visual system may operate only in shades of grey, with the extra information load in adding color being dropped. This is an important possibility to consider when designing, for example, emergency brake handles or emergency phones.

See also

• List of colors

The following is a partial list of colors with associated articles. ...

External links

• Congenital Colour Vision Deficiencies, description from the University of Calgary
• Color Vision Testing Made Easy, samples of this alternative test
• Attempts to simulate some rough features of color blind vision:
  • How do things look to colorblind people?, Causes of Color -- WebExhibits
  • How the world looks to a color blind person, example images drawn using distorted colors
  • VisCheck, demonstrations of color blindness and simulation software
  • ColorBlind Web Page Filter, shows how your web page looks under various forms of color blindness

The University of Calgary is a university of approximately 46,000 students located in the north-western part of Calgary, Alberta, Canada (pop. ...

Color vision is the capacity of an organism or machine to distinguish objects based on the wavelength of the light they reflect or emit. ... A monochromat is an organism that is truly color blind. ... A dichromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than two different pure spectral lights. ... A trichromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than three different pure spectral lights. ... A tetrachromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than four different pure spectral lights. ... A pentachromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than five different pure spectral lights. ...