Health Library Color BlindnessFrom Healthwise

What is color blindness?

Color blindness results from an absence or malfunction of certain color-sensitive cells in the retina. The retina is the nerve layer at the back of the eye that converts light into nerve signals that are sent to the brain. A person with color blindness has trouble seeing red, green, blue, or mixtures of these colors.

Normally, the eye has three types of cone cells, which are light-sensitive cells that are located in the retina. Each type is sensitive to either red, green, or blue light. You see color when your cone cells sense different amounts of these three basic colors. When one or more of these types of cone cells is absent or fails to function properly, you may not see one of these three colors or you may see a variation of that color or a different color.

Cone cells are concentrated mostly in the central part of the retina (the macula) to provide clear, sharp color vision. They work best in relatively bright light, so it is difficult to see colors in dim light. See an picture of the eye that shows the retina and the macula.

The term “color vision problem” is often used instead of color blindness because most people with color blindness can see some color. Very few people with color blindness can see no color at all.

What causes color blindness?

Most color vision problems are inherited (genetic) and are present at birth. Other color vision problems are caused by aging, disease, injury to the eye (acquired color vision problems), optic nerve problems, or side effects of some medicines. Inherited color vision problems are more common than acquired problems and affect males far more often than females.

What are the symptoms?

The symptoms of color vision problems vary with the severity of the condition. In some people the problem is very minor, and they may not even be aware that they see color differently from people with normal color vision. In other people the color vision problem is severe, and they can distinguish only a few shades (a person with normal color vision can see many thousands of colors). In rare cases, a person cannot see color at all but sees only black, white, and gray.

How is color blindness diagnosed?

Tests are used to measure the ability to recognize different colors.

The most common test is the pseudoisochromatic plate test. In this test, you are asked to look at an arrangement of colored dots and identify a pattern, such as a letter or number. The type of color vision problem you have can often be determined by which patterns you can and can't see in the various plates used for the test.

For people with acquired color vision problems, an arrangement test is used. This test involves arranging colored chips in sequence according to hue (color) from a reference color. People who are color-blind cannot arrange the colored chips correctly.

How is it treated?

Inherited color vision problems cannot be treated or corrected. Some acquired color vision problems can be treated, depending on the cause. For example, if a cataract is causing a problem with color vision, surgery to remove the cataract may restore normal color vision.

A color vision problem can have a significant impact on a person's life. Color vision problems may affect learning abilities and reading development and may limit a person's career choices. However, children and adults with color vision problems can learn to compensate for their inability to see colors.

Frequently Asked Questions

Symptoms of color blindness can vary. Different people see different shades of colors. You may not be able to see red, green, and blue or variations of those colors. If the color vision problem is not severe, you may not realize that you are seeing something different than a person who has normal color vision.

People with less severe color vision problems see variations of colors. They may not be able to tell the difference between red and green but can see blue and yellow.

People with severe color vision problems cannot see color at all. They see only shades of gray, black, and white.

Inherited color vision problems affect both eyes equally; acquired color vision problems may occur in only one eye or may affect one eye more than the other. Inherited problems with color vision are usually present at birth and do not change. An acquired color vision problem may change over time as a person ages or during the course of the disease or injury that causes the problem.

Tests can detect color blindness by measuring the ability to recognize different colors.

A test that is used to check for inherited color vision problems is called a pseudoisochromatic plate test. For this test, you are asked to look at a square of colored dots and identify a pattern, such as a letter or number, within the colored dots. People who have normal color vision can see these patterns. People who have color vision problems can see only some of these patterns or cannot see the patterns at all. Often the type of color vision problem a person has can be determined from which patterns they can identify in the plate test.

An arrangement test is used to check for acquired color vision problems or check the severity of inherited color vision problems. This test involves arranging colored chips in sequence according to hue (color) from a reference color. People who have normal color vision can arrange the colored chips with similar color. People who have color vision problems cannot arrange the colored chips correctly.

For more information about vision tests, including tests used for color vision, see the topic Vision Tests.

Early detection

Because a color vision problem can have a significant impact on a person's life, it is important to detect it as early as possible. In children, color vision problems can affect learning abilities and reading development and may limit career choices. Most experts recommend eye exams for children between ages 3 and 5. Vision screening is recommended for all children at least once before entering school, preferably between the ages of 3 and 4.

There is no medical treatment for color blindness that is inherited. Some acquired color vision problems can be treated, depending on the cause.

Color blindness that is acquired may sometimes be improved by surgery. For example, if you are having trouble seeing colors because of cataracts, surgery to treat the cataracts may improve color vision. If the problem is caused by a side effect of medication, color vision may be improved when that medication is stopped.

There may be some things you can do to help compensate for a color vision problem.

• Specially tinted contact lenses and eyeglasses may help you see differences between colors. However, these lenses do not provide normal color vision and can distort objects.
• Glasses that block glare (with side shields or wide temples) are helpful because people with color vision problems can see differences between colors better when there is less glare and brightness. A person with color vision problems can actually see better when the lighting is not bright.
• If you do not see color at all and rely on rod cells for vision (rod monochromatism), you may need to wear tinted or dark glasses with side shields, because rod cells work better in dim light. You may also need corrective lenses (glasses or contact lenses) because vision using only the rod cells is less clear and sharp.

Color vision problems cannot be prevented.

Color blindness can have a significant impact on your life. Many common activities rely on signs or signals that are color-coded, such as traffic signs, signal lights, and maps. Choosing clothing with appropriate matching or complementary colors can also be more of a challenge.

In many cases, there are ways to help compensate for your inability to see or distinguish colors by the way you observe things or by watching other people's actions. You may rely on brightness or location rather than color to identify objects. For example, you can learn the order of the three colored lights on a traffic signal and know that if the bottom light is lit, it means that the light is green and it is safe to go.

Color vision problems can affect learning abilities and reading development. Children may try to hide the fact that they cannot see certain colors by watching other classmates or even copying their work. Not being able to tell the difference between colors can be a serious problem for children and can lead to poor class work and low self-esteem.

• Testing for color vision problems during routine vision screening may help a child avoid having trouble in school. If your child is having trouble in school, have his or her vision, including color vision, checked by an eye doctor.
• If your child has color vision problems, it is important that his or her teacher be aware of this. Even simple things like reading yellow chalk on a green board can be hard for a child with color vision problems.
• You may want to offer suggestions to your child's teacher about how to help your child see better. This can include using a different color chalk or seating your child where there is no glare from bright lights. You can test your child at home with different colors of chalk, pens, and paper to find out which colors are easiest for your child to see.

Color vision problems may limit career choices. For example, color photographers, interior and clothing designers, and painters need normal color vision. Laws prohibit people with severe color vision problems from holding certain jobs, such as airline pilot, police officer, and some positions in the military.

Organizations

• Eye Problems, Noninjury

Other Works Consulted

• Sieving PA (2004). Retinitis pigmentosa and related disorders. In M Yanoff, JS Duker, eds., Ophthalmology, 2nd ed., pp. 813–823. St. Louis: Mosby.

Author:	Robin Parks, MS	Last Updated: October 31, 2007
Medical Review:	Kathleen Romito, MD - Family Medicine Carol L. Karp, MD - Ophthalmology
© 1995-2008 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated. This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.