You may have poor color vision and not know it. Some people figure out that they or their child has the condition when it causes confusion — such as when there are problems differentiating the colors in a traffic light or interpreting color-coded learning materials.

People affected by poor color vision may not be able to distinguish:

• Different shades of red and green
• Different shades of blue and yellow
• Any colors

The most common color deficiency is an inability to see some shades of red and green. Often, a person who is red-green or blue-yellow deficient isn't completely insensitive to both colors. Defects can be mild, moderate or severe.

Seeing colors across the light spectrum is a complex process that begins with your eyes' ability to respond to different wavelengths of light.

Light enters your eye through the cornea and passes through the lens and transparent, jelly-like tissue in your eye (vitreous body) to wavelength-sensitive cells (cones) at the back of your eye in the retina. The cones are sensitive to short (blue), medium (green) or long (red) wavelengths of light. Chemicals in the cones trigger a reaction and send the wavelength information through your optic nerve to your brain.

If your eyes are normal, you perceive color. But if your cones lack one or more wavelength-sensitive chemicals, you will be unable to perceive one or more of the primary colors — red, blue or yellow.

Poor color vision has several causes:

• Inherited disorder. Inherited poor color vision is much more common in males than in females. The most common color deficiency is red-green, with blue-yellow deficiency being much less common. It is rare to have no color vision at all.

You can inherit a mild, moderate or severe degree of the disorder. Inherited poor color vision usually affects both eyes, and the severity doesn't change over your lifetime.

• Diseases. Some conditions that can cause color deficits are sickle cell anemia, diabetes, macular degeneration, Alzheimer's disease, glaucoma, Parkinson's disease, chronic alcoholism and leukemia. One eye may be more affected than the other, and the color deficit may get better if the underlying disease can be treated.
• Certain medications. Some medications can alter color vision, such as some drugs that treat heart problems, high blood pressure, erectile dysfunction, infections, nervous disorders and psychological problems.
• Aging. Your ability to see colors deteriorates slowly as you age.
• Chemicals. Exposure to some chemicals in the workplace, such as carbon disulfide and fertilizers, may cause loss of color vision.