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What is color blindness?

Color blindness is the term used to describe an inability to distinguish between certain colors. Most cases of color blindness are partial; complete color blindness, which would apply to someone who sees only black, white, and gray, is extremely rare.

Most people who have a color vision deficiency are unable to distinguish between reds and greens, especially in their pastel tones in dim light. In normal light situations, they can see all

colors normally. The second most common type is inability to distinguish between reds and greens even in normal light situations. Less common is an inability to distinguish between blues and greens.

What causes colorblindness?

Lining the back of the eye is a thin, pinkish layer of tissue called the retina. It contains rod cells that perceive light and cone cells that

perceive light and color. All colors in the spectrum are made up of combinations of red, green, and blue in light rays that enter the eye. Similarly, there are three types of cone cells — one type for perceiving each of these colors — and all are needed in order to be able to see a full range of normal colors. Those people with a deficiency in color vision have a partial or complete defect in one or more of these types of cone cells, which results in not being able to distinguish colors or between different shades of the same color.

Most commonly, the inability to distinguish certain colors is inherited due to a defect carried on the X chromosome. The inherited deficiency is present at birth, but may not become apparent until the child learns to speak and identify colors. About 10 times as many men as women are affected by hereditary color blindness,

although women with normal vision may carry the problem gene and transmit it to their sons. In other people, color blindness develops later in life and indicates the presence of an eye disease. A red-green color deficiency may indicate nerve damage, excessive tobacco use, or some type of poisoning. Blue-yellow color deficiency is usually caused by such diseases as glaucoma, retinal detachment, diabetic or hypertensive retinal degeneration, methyl alcohol poisoning, or normal aging.

How is color blindness diagnosed and treated?

People with severe color blindness may realize it on their own. More subtle forms of color vision deficiency are usually diagnosed during an eye examination.

Professional evaluation of color vision tests is essential because people with normal vision have wide variations in their perception of color distinctions, and color blind people usually have some residual ability to distinguish the colors to which they are supposedly "blind."

What can I do myself?
Be aware of your own and your children's ability to discern color. Pay particular attention to any changes in your ability to distinguish colors, and to all aspects of vision. If you have difficulty distinguishing certain colors, such as reds and greens, it is important that you make a conscious effort to compensate for your visual impairment. This may entail relying on cues other than color alone, such as watching traffic flow in addition to the stop/go lights.

When should I see my doctor?
If you notice any difficulty in differentiating color, make an appointment to see an ophthalmologist promptly.

What will the doctor do?
Color vision screening is usually performed with pseudoisochromatic plates. They are filled with multicolored dots with numbers printed in dots of one color on a field of another color. Some of these plates allow a person with normal vision to see one number, while a person with color vision deficiency sees no number or a different number.

There is no cure for color blindness. A doctor may prescribe a colored contact lens for one eye to enhance a person's ability to see contrasts, but it won't actually affect the ability to differentiate between colors. Although a colored filter may be added to eyeglasses, instead of wearing a contact lens, this is usually a less desirable choice because the lens is worn over only one eye. It may also distort space perception.

In some cases, a vision rehabilitation therapist can train a color-blind person to distinguish colors.

The course of color blindness

The degree of color blindness present at birth normally does not change throughout life. When color vision deficiency is caused by disease later in life, treatment of the underlying illness usually halts its progression.

Is color blindness dangerous?
Color vision deficiency normally does not interfere with everyday life. However, severe red-green color blindness can make driving hazardous if a person cannot distinguish between the colors of traffic lights.