COLOR BLINDNESS

A defect in the ability to discriminate between simple colors. John Dalton, the British chemist, who was himself color blind, gave the first accurate description of this disorder in 1794. For about a hundred years afterward it was known as Daltonism.Color blindness takes many forms, ranging from simple color weakness to the complete inability to detect color differences. Some people have normal color vision in one eye and have some form of defect in the other. These rare individuals are invaluable for scientific research since they can report and compare normal and defective color perception of the same object.There are three major categories of color blindness. In anomalous trichromatism the individual can respond to all three of the primary colors in the spectrum (red, blue, and yellow), but only if they are bright and vivid. However, he has trouble distinguishing pale colors such as tan, pink, and light green. This is a fairly common defect and many authorities describe it as color weakness rather than color blindness.In dichromatism the individual responds to only two of the primary colors. This defect takes two basic forms, red-green and blue-yellow blindness. In the red-green variety, red, green, blue, and violet are difficult to differentiate, and all colors are seen as the same shade of yellow or blue. Some people are more insensitive to red hues (protanopia), others to green hues (deu- teranopia). These are often called red blindness and green blindness respectively.Red-green color blindness is by far the most common form. Between 4 and 8 per cent of males are affected, but only about 0.5 per cent of females. The reason for the greater prevalence of this defect among males is that it is a sex-linked recessive trait, transmitted by the mother.In blue-yellow blindness all colors are seen as either red or green. This is a rare defect which is usually congenital but may also be due to a disease of the retina or optic nerve tract or both.In monochromatism, or achromatism, the individual is totally color blind and everything is seen in different shades of gray. This form of the defect is extremely rare, occurring once in about 40,000 persons. There seem to be two different causes. In the congenital variety the “cones,” or color-sensitive cells of the retina do not develop. Since these cells are the only kind found in the fovea of the eye, the person is blind in this area. In order to see at all, he must make jerky eye movements called “miner’s nystagmus.” Monochromatic individuals are extremely sensitive to light and often go about with halfclosed eyelids. The defect is most often found in albinism, an inherited condition in which there is an absence of pigment cells throughout the body.Color blindness can also be brought about as a result of injury or disease such as optic neuritis, lead poisoning, and carbon disulfide poisoning. Recovery is possible in these cases, but no adequate treatment for congenital color blindness has been found. There is no scientific justification for the claim that vitamin A cures the condition. It may, however, improve visual acuity to a point where a partially color-blind person can pass a color-vision test.Color-blind individuals are frequently unaware of the defect unless they are tested and informed of the results. They do not miss color simply because they have never experienced it. Moreover, if they become aware of the defect, they are often able to hide it by learning the colors of common objects from other people.There are various tests for color blindness. In one test (the Holmgren Test) a subject is required to sort strands of yam on the basis of color. Red- green blind individuals will sort red and green strands into the same pile. This test is open to question since the yams differ in both color and brightness and a person might sort them on the basis of brightness alone. The widely used Ishihara test consists of a series of cards containing dots of various colors. They are so arranged that numbers are formed by dots of a given color. People with normal color vision immediately see the numbers, but individuals with color defects are unable to read some or all of the numbers because the dots appear to be the same color as the background. This general principle is also used in more recently developed tests, such as the Dvorine Pseudo-Iso- chromatic Plates and the Hardy-Rand- Rittler Pseudo-Isochromatic Plates. The latter test employs colored triangles, circles, and squares instead of numbers so that it will be applicable to illiterate persons and children who have not yet learned to read.The short, quickly administered Farnsworth Dichotomous Test For Color Blindness is a particularly useful screening instrument for industry, military service and vocational guidance purposes. The subject arranges plastic caps in order according to color. Normal response patterns can be determined by immediate inspection, and errors can be quickly plotted on a diagnostic chart. The Farnsworth Munsell 100-Hue Test for Color Discrimination is widely used not only in measuring color discrimination of color blind persons, but also in carrying out research on vision, and in selecting color graders, dye and paint mixers, and inspectors for jobs requiring accurate color discrimination.Most color-blind people do not feel they are greatly handicapped. They learn to compensate by becoming more aware of brightness differences, and by remembering which articles of clothing go together. Color weakness can sometimes be remedied by wearing glasses with special filters, and even people who are red-green blind can read the traffic lights because the “go” is usually a blue green. Only a small number of occupations require keen color discrimination; John Dalton’s defect did not prevent him from becoming a renowned figure in the exacting science of chemistry.

Cite this page: N., Pam M.S., "COLOR BLINDNESS," in PsychologyDictionary.org, November 28, 2018, https://psychologydictionary.org/color-blindness/ (accessed December 5, 2020).
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