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Color Blindness

Color blindness

Definition

Color blindness is an abnormal condition characterized by the inability to clearly distinguish different colors of the spectrum. The difficulties can range from mild to severe. It is a misleading term because people with color blindness are not blind. Rather, they tend to see colors in a limited range of hues; a rare few may not see colors at all.

Description

Normal color vision requires the use of specialized receptor cells called cones, which are located in the retina of the eye. There are three types of cones, red, blue, and green, which enable people to see a wide spectrum of colors. An abnormality, or deficiency, of any of the types of cones will result in abnormal color vision.

There are three basic variants of color blindness. Red/green color blindness is the most common deficiency, affecting 8 percent of Caucasian males and 0.5 percent of Caucasian females. The prevalence varies with culture.

Blue color blindness is an inability to distinguish both blue and yellow, which are seen as white or gray. It is quite rare and has equal prevalence in males and females. It is common for young children to have blue/green confusion that becomes less pronounced in adulthood. Blue color deficiency often appears in people who have physical disorders such as liver disease or diabetes mellitus .

A total inability to distinguish colors (achromatopsia) is exceedingly rare. These affected individuals view the world in shades of gray. They frequently have poor visual acuity and are extremely sensitive to light (photophobia), which causes them to squint in ordinary light.

Demographics

Researchers studying red/green color blindness in the United Kingdom reported an average prevalence of only 4.7 percent in one group. Only 1 percent of Eskimo males are color blind. Approximately 2.9 percent of boys from Saudi Arabia and 3.7 percent from India were found to have deficient color vision. Red/green color blindness may slightly increase an affected person's chances of contracting leprosy. Pre-term infants exhibit an increased prevalence of blue color blindness. Achromatopsia has a prevalence of about one in 33,000 in the United States and affects males and females equally.

Causes and symptoms

Red/green and blue color blindness appear to be located on at least two different gene locations. The majority of affected individuals are males. Females are carriers but are not normally affected. This indicates that the X chromosome is one of the locations for color blindness. Male offspring of females who carry the altered gene have a 50 percent chance of being color-blind. The rare female that has red/green color blindness, or rarer still, blue color blindness, indicates there is an involvement of another gene. As of 2004, the location of this gene was not yet identified.

Achromatopsia, the complete inability to distinguish color, is an autosomal recessive disease of the retina. Thus, both parents have one copy of the altered gene but do not have the disease. Each of their children has a 25 percent chance of not having the gene, a 50 percent chance of having one altered gene (and, like the parents, being unaffected), and a 25 percent risk of having both the altered gene and the condition. In 1997, the achromatopsia gene was discovered to reside on chromosome 2.

The inability to correctly identify colors is the only sign of color blindness. It is important to note that people with red/green or blue varieties of color blindness use other cues such as color saturation and object shape or location to distinguish colors. They can often distinguish red or green if they can visually compare the colors. However, most have difficulty accurately identifying colors without any other references. Most people with any impairment in color vision learn colors, as do other young children. These individuals often reach adolescence before their visual deficiency is identified.

Color blindness is sometimes acquired. Chronic illnesses that can lead to color blindness include Alzheimer's disease, diabetes mellitus, glaucoma, leukemia, liver disease, chronic alcoholism , macular degeneration, multiple sclerosis, Parkinson's disease, sickle cell anemia , and retinitis pigmentosa. Accidents or strokes that damage the retina or affect particular areas of the brain eye can lead to color blindness. Some medications such as antibiotics , barbiturates, anti-tuberculosis drugs, high blood pressure medications, and several medications used to treat nervous disorders and psychological problems may cause color blindness. Industrial or environmental chemicals such as carbon monoxide, carbon disulfide, fertilizers, styrene, and some containing lead can cause loss of color vision. Occasionally, changes can occur in the affected person's capacity to see colors after age 60.

When to call the doctor

An ophthalmologist should be consulted at the time color blindness is first suspected.

Diagnosis

There are several tests available to identify problems associated with color vision. The most commonly used is the American Optical/Hardy, Rand, and Ritter Pseudoisochromatic Test. It is composed of several discs filled with colored dots of different sizes and colors. A person with normal color vision looking at a test item sees a number that is clearly located somewhere in the center of a circle of variously colored dots. A color-blind person is not able to distinguish the number.

The Ishihara Test is comprised of eight plates that are similar to the American Optical Pseudoisochromatic Test plates. The individual being tested looks for numbers among the various colored dots on each test plate. Some plates distinguish between red/green and blue color blindness. Individuals with normal color vision perceive one number. Those with red/green color deficiency see a different number. Those with blue color vision see yet a different number.

A third analytical tool is the Titmus II Vision Tester Color Perception Test. The subject looks into a stereoscopic machine. The test stimulus most often used in professional offices contains six different designs or numbers on a black background, framed in a yellow border. Titmus II can test one eye at a time. However, its value is limited because it can only identify red/green deficiencies and is not highly accurate.

Treatment

As of 2004 there is no treatment or cure for color blindness. Most color vision deficient persons compensate well for their abnormality and usually rely on color cues and details that are not consciously evident to persons with typical color vision.

Inherited color blindness cannot be prevented. In the case of some types of acquired color deficiency, if the cause of the problem is removed, the condition may improve with time. But for most people with acquired color blindness, the damage is usually permanent.

Prognosis

Color blindness that is inherited is present in both eyes and remains constant over an individual's entire life. Some cases of acquired color vision loss are not severe, may appear in only one eye, and last for only a short time. Other cases tend to become worse with time.

Prevention

There is no way to prevent genetic color blindness. There is no way to prevent acquired color blindness that is associated with Alzheimer's disease, diabetes mellitus, leukemia, liver disease, macular degeneration, multiple sclerosis, Parkinson's disease, sickle cell anemia, and retinitis pigmentosa.

Some forms of acquired color blindness may be prevented. Limiting use of alcohol and drugs such as antibiotics, barbiturates, anti-tuberculosis drugs, high blood pressure medications, and several medications used to treat nervous disorders and psychological problems to levels that are required for therapeutic benefit may limit acquired color blindness.

Parental concerns

Parents can inquire about other family members who have experienced color blindness. If such family members exist, parents can have their children tested for color perception at an early age. Screening for color perception is usually performed in grade school.

KEY TERMS

Achromatopsia The inability to distinguish any colors.

Cones Receptor cells, located in the retina of the eye, that allow the perception of colors.

Photophobia An extreme sensitivity to light.

Retina The inner, light-sensitive layer of the eye containing rods and cones. The retina transforms the image it receives into electrical signals that are sent to the brain via the optic nerve.

Rods Photoreceptors, located in the retina of the eye, that are highly sensitive to low levels of light.

Resources

BOOKS

Color Blindness: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet Resources. San Diego, CA: Icon Group International, 2003.

Fay, Aaron, and Frederick A. Jokobiec. "Diseases of the Visual System." In Cecil Textbook of Medicine, 22nd ed. Edited by Lee Goldman, et al. Philadelphia: Saunders, 2003, pp. 240619.

Olitsky, Scott, and Leonard B. Nelson. "Disorders of Vision." In Nelson Textbook of Pediatrics, 17th ed. Edited by Richard E. Behrman, et al. Philadelphia: Saunders, 2003, pp. 20879.

Wiggs, Janey L. "Color Vision." In Ophthalmology, edited by Myron Yanoff and Jay S. Duker. St. Louis, MO: Mosby, 2000.

PERIODICALS

Abadi, R. V. "Effects of Color Blindness." Ophthalmic and Physiological Optics 24, no. 3 (2004): 25257.

Atchison, D. A., et al. "Traffic Signal Color Recognition Is a Problem for Both Protan and Deutan Color-vision Deficients." Human Factors 45, no. 3 (2003): 495503.

Dick, F., et al. "Is Color Vision Impairment Associated with Cognitive Impairment in Solvent Exposed Workers?" Occupational and Environmental Medicine 61, no. 1 (2004): 7678.

Tagarelli, A., et al. "Color Blindness in Everyday Life and Car Driving." Acta Ophthalmology Scandinavia 52, no. 4 (2004): 43642.

ORGANIZATIONS

American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 662112672. Web site: <www.aafp.org/>.

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 600071098. Web site: <www.aap.org/default.htm>.

WEB SITES

"Color Blindness: More Prevalent Among Males." Howard Hughes Medical Institute. Available online at <www.hhmi.org/senses/b130.html> (accessed November 16, 2004).

Rutherford, Kim. "What Is Color Blindness?" KidsHealth for Kids. Available online at <http://kidshealth.org/kid/talk/qa/color_blind.html>(accessed November 16, 2004).

Waggoner, Terrace L. Ishihara Test for Color Blindness. Available online at <www.toledo-bend.com/colorblind/Ishihara.html>(accessed November 16, 2004).

L. Fleming Fallon Jr., MD, DrPH

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"Color Blindness." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Encyclopedia.com. 22 May. 2017 <http://www.encyclopedia.com>.

"Color Blindness." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Encyclopedia.com. (May 22, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/color-blindness

"Color Blindness." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Retrieved May 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/color-blindness

Color Blindness

Color Blindness

Definition

Color blindness is an abnormal condition characterized by the inability to clearly distinguish different colors of the spectrum. The difficulties can be mild to severe. It is a misleading term because people with color blindness are not blind. Rather, they tend to see colors in a limited range of hues; a rare few may not see colors at all.

Description

Normal color vision requires the use of specialized receptor cells called cones, which are located in the retina of the eye. There are three types of cones, termed red, blue, and green, which enable people to see a wide spectrum of colors. An abnormality, or deficiency, of any of the types of cones will result in abnormal color vision.

There are three basic variants of color blindness. Red/green color blindness is the most common deficiency, affecting 8% of Caucasian males and 0.5% of Caucasian females. The prevalence varies with culture.

Blue color blindness is an inability to distinguish both blue and yellow, which are seen as white or gray. It is quite rare and has equal prevalence in males and females. It is common for young children to have blue/green confusion that becomes less pronounced in adulthood. Blue color deficiency often appears in people who have physical disorders such as liver disease or diabetes mellitus.

A total inability to distinguish colors (achromatopsia) is exceedingly rare. These affected individuals view the world in shades of gray. They frequently have poor visual acuity and are extremely sensitive to light (photophobia), which causes them to squint in ordinary light.

Researchers studying red/green color blindness in the United Kingdom reported an average prevalence of only 4.7% in one group. Only 1% of Eskimo males are color blind. Approximately 2.9% of boys from Saudi Arabia and 3.7% from India were found to have deficient color vision. Red/green color blindness may slightly increase an affected person's chances of contracting leprosy. Pre-term infants exhibit an increased prevalence of blue color blindness. Achromatopsia has a prevalence of about 1 in 33,000 in the United States and affects males and females equally.

Causes and symptoms

Red/green and blue color blindness appear to be located on at least two different gene locations. The majority of affected individuals are males. Females are carriers, but are not normally affected. This indicates that the X chromosome is one of the locations for color blindness. Male offspring of females who carry the altered gene have a 50-50 chance of being colorblind. The rare female that has red/green color blindness, or rarer still, blue color blindness, indicates there is an involvement of another gene. As of 2001, the location of this gene has not been identified.

Achromatopsia, the complete inability to distinguish color, is an autosomal recessive disease of the retina. This means that both parents have one copy of the altered gene but do not have the disease. Each of their children has a 25% chance of not having the gene, a 50% chance of having one altered gene (and, like the parents, being unaffected), and a 25% risk of having both the altered gene and the condition. In 1997, the achromatopsia gene was located on chromosome 2.

The inability to correctly identify colors is the only sign of color blindness. It is important to note that people with red/green or blue varieties of color blindness use other cues such as color saturation and object shape or location to distinguish colors. They can often distinguish red or green if they can visually compare the colors. However, most have difficulty accurately identifying colors without any other references. Most people with any impairment in color vision learn colors, as do other young children. These individuals often reach adolescence before their visual deficiency is identified.

Color blindness is sometimes acquired. Chronic illnesses that can lead to color blindness include Alzheimer's disease, diabetes mellitus, glaucoma, leukemia, liver disease, chronic alcoholism, macular degeneration, multiple sclerosis, Parkinson's disease, sickle cell anemia, and retinitis pigmentosa. Accidents or strokes that damage the retina or affect particular areas of the brain eye can lead to color blindness. Some medications such as antibiotics, barbiturates, anti-tuberculosis drugs, high blood pressure medications, and several medications used to treat nervous disorders and psychological problems may cause color blindness. Industrial or environmental chemicals such as carbon monoxide, carbon disulfide, fertilizers, styrene, and some containing lead can cause loss of color vision. Occasionally, changes can occur in the affected person's capacity to see colors after age 60.

Diagnosis

There are several tests available to identify problems associated with color vision. The most commonly used is the American Optical/Hardy, Rand, and Ritter Pseudoisochromatic test. It is composed of several discs filled with colored dots of different sizes and colors. A person with normal color vision looking at a test item sees a number that is clearly located somewhere in the center of a circle of variously colored dots. A color-blind person is not able to distinguish the number.

The Ishihara test is comprised of eight plates that are similar to the American Optical Pseudoisochromatic test plates. The individual being tested looks for numbers among the various colored dots on each test plate. Some plates distinguish between red/green and blue color blindness. Individuals with normal color vision perceive one number. Those with red/green color deficiency see a different number. Those with blue color vision see yet a different number.

A third analytical tool is the Titmus II Vision Tester Color Perception test. The subject looks into a stereoscopic machine. The test stimulus most often used in professional offices contains six different designs or numbers on a black background, framed in a yellow border. Titmus II can test one eye at a time. However, its value is limited because it can only identify red/green deficiencies and is not highly accurate.

Treatment

There is no treatment or cure for color blindness. Most color vision deficient persons compensate well for their abnormality and usually rely on color cues and details that are not consciously evident to persons with typical color vision.

Inherited color blindness cannot be prevented. In the case of some types of acquired color deficiency, if the cause of the problem is removed, the condition may improve with time. But for most people with acquired color blindness, the damage is usually permanent.

Prognosis

Color blindness that is inherited is present in both eyes and remains constant over an individual's entire life. Some cases of acquired color vision loss are not severe, may appear in only one eye, and last for only a short time. Other cases tend to be progressive, becoming worse with time.

Resources

BOOKS

Wiggs, Janey L. "Color Vision." In Ophthalmology, edited by Myron Yanoff and Jay S. Duker. St. Louis: Mosby, 2000.

ORGANIZATIONS

Achromatopsia Network. c/o Frances Futterman, PO Box 214, Berkeley, CA 94701-0214. http://www.achromat.org/how_to_join.html.

American Academy of Ophthalmology. PO Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. http://www.eyenet.org.

International Colour Vision Society: Forschungsstelle fuer Experimentelle Ophthalmologie. Roentgenweg 11, Tuebingen, D-72076. Germany http://orlab.optom.unsw.edu.au/ICVS.

National Society to Prevent Blindness. 500 East Remington Rd., Schaumburg, IL 60173. (708) 843-2020 or (800) 331-2020. http://www.preventblindness.org.

OTHER

"Breaking the Code of Color." Seeing, Hearing and Smelling the World. http://www.hhmi.org/senses/b/b130.htm.

"Color Blindness." Geocities. http://www.geocities.com/Heartland/8833/coloreye.html.

"Medical Encyclopedia: Colorblind." MEDLINEplus. http://medlineplus.adam.com/ency/article/001002sym.htm.

University of Manchester. http://www.umist.ac.uk/UMIST_OVS/welcome.html.

University of Nevada-Reno. http://www.delamare.unr.edu/cb/.

KEY TERMS

Achromatopsia The inability to distinguish any colors.

Cones Receptor cells that allow the perception of colors.

Photophobia An extreme sensitivity to light.

Retina The light-sensitive layer of tissue in the back of the eye that receives and transmits visual signals to the brain through the optic nerve.

Rod Photoreceptor that is highly sensitive to low levels of light and transmits images in shades of gray.

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color blindness

color blindness, visual defect resulting in the inability to distinguish colors. About 8% of men and 0.5% of women experience some difficulty in color perception. Color blindness is usually an inherited sex-linked characteristic, transmitted through, but recessive in, females. Acquired color blindness results from certain degenerative diseases of the eyes. Most of those with defective color vision are only partially color-blind to red and green, i.e., they have a limited ability to distinguish reddish and greenish shades. Those who are completely color-blind to red and green see both colors as a shade of yellow. Completely color-blind individuals can recognize only black, white, and shades of gray. Color blindness is usually not related to visual acuity; it is significant, therefore, only when persons who suffer from it seek employment in occupations where color recognition is important, such as airline pilots, railroad engineers, and others who must recognize red and green traffic signals. Tests for color blindness include identifying partially concealed figures or patterns from a mass of colored dots and matching skeins of wool or enameled chips of various colors.

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Color Blindness

COLOR BLINDNESS

DEFINITION


Color blindness is a condition in which people have mild to severe difficulty identifying colors. Color blind people may not be able to recognize various shades of colors and, in some cases, cannot recognize colors at all.

DESCRIPTION


Normal color vision requires the use of special cells in the retina (the innermost lining) of the eye called cones. There are three types of conesblue, green, and redwhich allow an individual to recognize a large spectrum of colors. Cones sometimes do not function normally. When that happens, a person has trouble recognizing colors.

Color Blindness: Words to Know

Cone cells:
Cone cells are special cells in the retina and are responsible for color vision.
Retina:
The retina is the innermost lining of the eye, containing light sensitive nerve tissue composed of rod and cone cells.

The three basic types of color blindness are as follows:

  • Red/green color blindness. Red/green color blindness is the most common form of the disorder. It affects about 8 percent of all Caucasian (white) males and 0.5 percent of all Caucasian females. People with this disorder can distinguish red from green if the two colors are next to each other, but they cannot identify red or green by itself. For example, they can pick out red or green from a package of colored pencils, but if handed a red pencil, they could not identify that the pencil was red.
  • Blue color blindness. Blue color blindness is rare. People with this disorder cannot distinguish blue or yellow. Both colors are seen as white or gray. The disorder occurs with equal frequency in men and women and usually accompanies certain other physical disorders, such as liver disease or diabetes (see diabetes mellitus entry).
  • Total color blindness. Total color blindness is called achromatopsia (pronounced a-KRO-muh-tope-see-uh). This disorder is the rarest of all forms of color blindness. People with this disorder see everything as white, black, or some shade of gray. The disorder affects about 1 person in 33,000 in the United States. It is caused by hereditary factors. Achromatopsia is usually accompanied by other vision problems, such as extreme sensitivity to light.

CAUSES


Most cases of color blindness are inherited, with males being affected far more often than females. Color blindness can also be acquired in other ways. These include:

  • Chronic (long-term) illnesses, such as Alzheimer's disease (see Alzheimer's disease entry), diabetes, glaucoma (see glaucoma entry), leukemia (see leukemia entry), liver disease, chronic alcoholism (see alcoholism entry), multiple sclerosis (see multiple sclerosis entry), and retinitis pigmentosa, a disease of the retina.
  • Traumas, such as those caused by accidents or strokes (see stroke entry).
  • Medications, such as antibiotics and drugs used to treat tuberculosis (see tuberculosis entry), high blood pressure, and nervous disorders.
  • Industrial toxins (poisons), including carbon monoxide, carbon disulfide, fertilizers, and chemicals that include lead.
  • Aging, people are at higher risk after the age of sixty.

SYMPTOMS


The symptom of color blindness is the long-term inability to distinguish colors or to see colors at all.

DIAGNOSIS


A variety of tests can be used to diagnose color blindness. The most common of these tests is the American Optical/Hardy, Rand, and Ritter (AO/H.R.R.) Pseudoisochromatic (pronounced SOO-doe-I-so-kro-MAT-ik) Test. This test includes the use of a plate covered with spots of one color (green or red, for example). In the middle of the plate is a figure, such as a number or letter, made of spots of a different color. A person with normal color vision can see the figure against the background. A color blind person cannot.

A similar test, the Ishihara test, uses eight test plates similar to those used in the AO/H.R.R. test. The person looks for numbers made up of dots of various colors on each plate.

A third test is the Titmus II Vision Tester Color Perception Test. In this test, a person looks into a viewing device at a series of figures on a black background framed by a yellow border. The test can easily be performed in a doctor's office. It is not considered to be a very accurate test, however, and can only test for red/green color blindness.

JOHN DALTON AND DALTONISM

The first person to describe color blindness was the English chemist and physicist John Dalton (17661844). Dalton is famous because he was the first modern scientist to develop the atomic theory. However, Dalton was interested in many topics besides atoms. For example, he was keenly interested in meteorology (the study of the weather) and kept daily weather records for fifty-seven years. His records, published as Meteorological Observations and Essays, are among the most complete in all of scientific history. The first scientific paper Dalton ever wrote was about color blindness. He probably became interested in the subject because he, as well as his brother, was color blind. In honor of his research, the condition of color blindness is still sometimes called daltonism.

TREATMENT


There is no cure or treatment for color blindness. Most people with the disorder learn to live with the problem and learn how to adjust to it.

PROGNOSIS


Hereditary forms of color blindness do not change during a person's lifetime. In cases where color blindness was not inherited, the disorder may gradually become more or less severe over time.

PREVENTION


Hereditary color blindness cannot be prevented. Acquired color blindness can be prevented if all possible causes of the disorder can be avoided.

FOR MORE INFORMATION


Books

D'Alonzo, T. L. Your Eyes! A Comprehensive Look at the Understanding and Treatment of Vision Problems. Clifton Heights, PA: Avanti, 1992.

Rosenthal, Odeda, and Robert H. Phillips. Coping with Color-Blindness. Garden City Park, NY: Avery Publishing Group, 1997.

Organizations

Achromatopsia Network. c/o Frances Futterman, PO Box 214, Berkeley, CA 947010214. http://www.achromat.org.

Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (847) 8432020; (800) 3312020. http://www.preventblindness.org.

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Color Blindness

Color Blindness

How Does Color Blindness Happen?

How Is Color Blindness Diagnosed and Treated?

Resource

Color blindness is a condition in which a person has a defect in the eye that causes an inability to identify various colors and shades.

KEYWORDS

for searching the Internet and other reference sources

Chroma

Color saturation

Hue

Ophthalmology

Vision

Red means stop. Green means go. It is one of the earliest lessons a child learns. But for more than 10 million people in the United States, this is not as simple as it sounds. These people usually are called color blind, although it is more accurate to say that they have poor color vision.

How Does Color Blindness Happen?

Color blindness almost always is inherited from the mothers genes. It affects boys most often, as girls usually have additional genetic material that overrides the vision problem. About 1 in 12 males has some degree of color blindness, whereas only about 1 in 100 females has it. People with color blindness often have no other vision problems, but color blindness is sometimes a result of other eye diseases and vision problems.

Eight million colors

The human eye can identify more than 8 million shades of colors. But the ability to distinguish among the colors begins with the three primary colors* of light: red, green, and blue. Just as a person can mix the color brown by coloring the same area with red and green crayons, the eye sees various colors by combining primary colors.

* primary colors
are sets of colors that can be mixed to create all other colors. There are two kinds of primary colors: subtractive or colorant primaries (red, blue, and yellow), which refer to pigments like crayons; and additive or light primaries (red, blue, and green), which refer to light.

As light passes through the eye, it focuses the image on the retina. The retina contains layers of cells at the inside rear of the eyeball and acts a little like the photographic film in a camera. The retina contains millions of receptors called rods that help see light and cones that help see light and colors. When light strikes the rods and cones, chemicals are released.

Red and green

People with poor color vision have cones that do not function properly, because they do not release some of the chemicals when they are struck by light. As a result, these people see only certain colors and shades. The most common form of color blindness is difficulty in seeing the colors red and green properly, or the same way most people see them. The condition can range from mild to severe. Sometimes a person simply cannot see the colors as vividly as a person who has normal color vision. Other times, there are areas that seem to lack color and to appear in shades of gray. Rarely does color blindness mean that people see everything in shades of gray, as in black-and-white photographs, movies, or television shows.

How Is Color Blindness Diagnosed and Treated?

The first signs of poor color vision may be noticed in school, when a child starts to learn to identify colors. A simple vision test can determine if the problem is color blindness. An image made up of dots is shown to the child. It may be a number (4, for example, as in the illustration at right) made up of green dots on a background of yellow and orange dots. If the child cannot see the green numeral 4 distinctly because it appears to blend in with the background, he may have color blindness.

There is no treatment or cure for color blindness. People are often taught to recognize colors in other ways. For example, traffic lights usually have the red light on top and green on the bottom.

See also

Blindness

Resource

Lighthouse International, 111 East 59 Street, New York, NY 10022. The Lighthouse International website posts fact sheets about vision problems, color contrast, and partial sight.

Telephone 800-829-0500 or 212-821-9713 (TTY)
http://www.lighthouse.org/color_contrast.htm

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