Color blindness is the inability to see certain colors in the usual way.

Color blindness occurs when there is a problem with the color-sensing materials (pigments) in certain nerve cells of the eye. These cells are called cones. They are found in the retina, the light-sensitive layer of tissue at the back of the inner eye.

If you are missing just one pigment, you might have trouble telling the difference between red and green. This is the most common type of color blindness. Other times, people have trouble seeing blue-yellow colors. People with blue-yellow color blindness almost always have problems identify reds and greens, too.

The most severe form of color blindness is achromatopsia. A person with this rare condition cannot see any color. Achromatopsia is often associated with lazy eye, nystagmus (small, jerky eye movements), severe light sensitivity, and extremely poor vision.

Most color blindness is due to a genetic problem. (See: X-linked recessive) About 1 in 10 men have some form of color blindness. Very few women are color blind.

The drug hydroxychloroquine (Plaquenil) can also cause color blindness. It is used to treat rheumatoid arthritis, among other conditions.

Symptoms vary from person to person, but may include:

• Trouble seeing colors and the brightness of colors in the usual way
• Inability to tell the difference between shades of the same or similar colors

Often, the symptoms may be so mild that some persons do not know they are color blind. A parent may notice signs of color blindness when a child is learning his or her colors.

Rapid, side-to-side eye movements and other symptoms may occur in severe cases.

Your doctor or eye specialist can check your color vision in several ways. Testing for color blindness is commonly done during an eye exam.

There is no known treatment.

Color blindness is a life-long condition. Most persons are able to adjust without difficulty or disability.

Those who are colorblind may not be able to get a job that requires color vision. For example, a pilot needs to be able to see colors.

Make an appointment with your health care provider or ophthalmologist if you think you (or your child) have color blindness.

Yanoff M, Duker JS, Augsburger JJ, et al. Ophthalmology. 2nd ed. St. Louis, Mo: Mosby; 2004:34.

Goldman L, Ausiello D. Cecil Textbook of Medicine, 22nd ed. Philadelphia, Pa: WB Saunders; 2004:2410.