Seeing colors across the light spectrum begins with your eyes' ability to distinguish the primary colors red, blue and green.

Light enters your eye through the cornea and passes through the lens and transparent, jelly-like tissue in your eye (vitreous body) to color-sensitive cells (cones) at the back of your eye in the retina. Chemicals in the cones distinguish colors and send that information through your optic nerve to your brain.

If your eyes are normal, you can distinguish different colors, but if your cones lack one or more light-sensitive chemicals, you may see only two of the primary colors.

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.

    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 diabetes, glaucoma, macular degeneration, Alzheimer's disease, Parkinson's disease, chronic alcoholism, leukemia and sickle cell anemia. 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.
Feb. 13, 2014