Causes

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

Light, which contains all color wavelengths, enters your eye through the cornea and passes through the lens and transparent, jellylike tissue in your eye (vitreous humor) to wavelength-sensitive cells (cones) at the back of your eye in the macular area of 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 distinguish the colors red, green or blue.

Color blindness has several causes:

• Inherited disorder. Inherited color deficiencies are 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 color deficiencies usually affect 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, multiple sclerosis, 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 certain autoimmune diseases, 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.