Q. Do people who are color blind see everything in black and white?

"Color blindness" is the common term used to describe color vision deficiency. The term is misleading because total color blindness that turns the world into shades of gray is rare.

The most common type of color blindness makes it difficult for people to discriminate between red and green. The next most common form of the deficiency affects the perception of blues and yellows. Those with blue-yellow blindness almost always have red-green blindness, too.

Many people with color blindness don't know they have it. For example, they are taught at an early age that grass is green. They look at lawns and see yellow grass. Subsequently, if you ask them what color the grass is, they will tell you it's green.

Color blindness affects about 10 percent of men, but only one percent of women. Most people with color blindness inherited it. There is no treatment to correct inherited color blindness. However, there are specially-tinted eyeglasses that can help people with deficiencies to discriminate between colors.

Another cause of color blindness is aging, which gradually diminishes our ability to see colors.

Diseases can affect color vision, too. Usually, diseases affect the perception of blue and yellow. Some conditions that can cause color blindness are: diabetes, glaucoma, cataracts, macular degeneration, Alzheimer's disease, Parkinson's disease, leukemia and sickle cell anemia.

Some drugs can alter color perception, too. These include: drugs for heart problems, high blood pressure, rheumatoid arthritis, nervous disorders and psychological problems.

Exposure to certain chemicals can cause color blindness. These include: carbon disulfide, fertilizers, styrene and mercury.

The eye is like a camera. There's a lens in the front that focuses images on the retina in the back. The retina contains nerve cells that react to light and transmit information to your brain. If the cells responsible for color don't work properly, you suffer from color blindness.

If you think you are having a color-vision problem, see an eye doctor. You'll be asked to look at a book containing several multicolored dot patterns. If you have a color vision deficiency, you won't be able to pick out numbers and shapes from within the dot patterns.

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