Color blindness — or more accurately, poor or deficient color vision — is an inability to see the difference between certain colors. Though many people commonly use the term "color blind" for this condition, true color blindness — in which everything is seen in shades of black and white — is rare.

Color blindness is usually inherited. Men are more likely to be born with color blindness. Most people with color blindness can't distinguish between certain shades of red and green. Less commonly, people with color blindness can't distinguish between shades of blue and yellow.

Certain eye diseases and some medications also can cause color blindness.

You may have a color vision deficiency 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 color blindness 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.

When to see a doctor

If you suspect you have problems distinguishing certain colors or your color vision changes, see an eye doctor for testing. It's important that children get comprehensive eye exams, including color vision testing, before starting school.

There's no cure for inherited color deficiencies, but if illness or eye disease is the cause, treatment may improve color vision.

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.

If you have trouble seeing certain colors, your eye doctor can test to see if you have a color deficiency. You'll likely be given a thorough eye exam and shown specially designed pictures made of colored dots that have numbers or shapes in a different color hidden in them.

If you have a color vision deficiency, you'll find it difficult or impossible to see some of the patterns in the dots.

There are no treatments for most types of color vision difficulties, unless the color vision problem is related to the use of certain medicines or eye conditions. Discontinuing the medication causing your vision problem or treating the underlying eye disease may result in better color vision.

Wearing a colored filter over eyeglasses or a colored contact lens may enhance your perception of contrast between the confused colors. But such lenses won't improve your ability to see all colors.

Potential future treatments

Some rare retinal disorders associated with color deficiency could possibly be modified with gene replacement techniques. These treatments are under study and might become available in the future.

Try the following tips to help you work around your color blindness.

• Memorize the order of colored objects. If it's important to know individual colors, such as with traffic lights, memorize the order of the colors.
• Label colored items that you want to match with other items. Have someone with good color vision help you sort and label your clothing. Arrange your clothes in your closet or drawers so that colors that can be worn together are near each other.
• Use technology. There are apps for phones and digital devices that can help you identify colors.

You can start by seeing your family doctor or a general practitioner, or make an appointment with a doctor who specializes in eye disorders (ophthalmologist or optometrist).

Preparing a list of questions can help you make the most of your time with your doctor. For color blindness, some basic questions to ask include:

• How might having color deficiencies affect my life?
• Will color deficiencies affect my current or future occupation?
• Are there treatments for color blindness?
• Do you have any brochures or other printed materials I can have? What websites do you recommend?
• Are there special glasses or contact lenses I can wear to improve my color vision?

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

• When did you first notice having trouble seeing certain colors?
• Does it affect one eye or both?
• Does anyone in your family (including parents and grandparents) have color blindness?
• Do you have any medical conditions?
• Are you exposed to chemicals in your workplace?
• Are you taking any medicines or supplements?