Color Blindness

By Gretchyn Bailey and Marilyn Haddrill;
reviewed by Gary Heiting, OD

Color blindness is not a form of blindness at all, but a deficiency in the way you see color. With this vision problem, you have difficulty distinguishing certain colors, such as blue and yellow or red and green.

Red-green color deficiency is the most common form of color blindness, affecting about 2 percent to 6 percent of all men because of the way the trait is inherited.*

Much more rarely, a person may inherit a trait that reduces the ability to see blue and yellow hues. This blue-yellow color deficiency usually affects men and women equally.

Color Blindness Symptoms and Signs

Do you have difficulty telling if colors are blue and yellow, or red and green? Do other people sometimes inform you that the color you think you are seeing is wrong? If so, these are primary signs that you have a color vision deficiency.

Contrary to popular belief, it is rare for a color blind person to see only in shades of gray. Therefore, most people who are considered "color blind" don't necessarily have a complete lack of ability to see a full range of colors. But certain colors they do see are significantly different or less pronounced than what a person with normal color vision would see.

If you develop color vision problems when normally you have been able to see a full range of color, then you definitely should visit your doctor. Sudden or gradual loss of color vision can indicate any number of underlying health problems, such as cataracts.

Color blindness testing can help determine the kind of color deficiency you have.

What Causes Color Blindness?

Color blindness occurs when light-sensitive cells in the retina fail to respond appropriately to variations in wavelengths of light that enable people to see an array of colors.

More men than women have color blindness. And usually people with a color deficiency are born with it.

Photoreceptors in the retina include rods that enhance vision in low lighting, and cones that help us see in color vision. Inherited forms of color blindness often are related to deficiencies in certain types of cones or outright absence of these cones.

Besides differences in genetic makeup, other causes of color vision defects or loss include:

• Parkinson's disease (PD). Because Parkinson's disease is a neurological disorder, light-sensitive nerve cells in the retina where vision processing occurs may be damaged and cannot function properly.
• Cataracts. Clouding of the eye's natural lens that occurs with cataracts can "wash out" color vision, making it much less bright. Fortunately, cataract surgery can restore bright color vision when the cloudy natural lens is removed and replaced with an artificial intraocular lens.
• 
  Electricians must be able to spot different colors in wiring, so for them a color deficiency can be a big problem.
  Tiagabine for epilepsy. An antiepileptic drug known as tiagabine has been shown to reduce color vision in about 41 percent of those taking the drug, although effects do not appear to be permanent.**
• Leber's hereditary optic neuropathy (LHON). Particularly prevalent among males, this type of inherited optic neuropathy can affect even carriers who don't have other symptoms but do have a degree of color blindness. Red-green color vision defects primarily are noted with this condition.
• Kallman's syndrome. This inherited condition involves failure of the pituitary gland, which can lead to incomplete or unusual gender-related development such as of sexual organs. Color blindness can be one symptom of this condition.

Color blindness also can occur when aging processes damage retinal cells. An injury or damage to areas of the brain where vision processing takes place also can cause color vision deficiencies.

Red-Green Color Blindness

The most common inherited form of color blindness (red-green) is caused by a common X-linked recessive gene.

Mothers have an X-X pairing of chromosomes carrying genetic material, and fathers have an X-Y pairing of chromosomes. A mother and father each contribute chromosomes that determine the sex of their baby. When X chromosomes pair with another X, you are female. And when the X pairs with the Y, you are male.

If you have a common form of color blindness caused by an X-linked recessive gene, your mother must be a carrier of the gene or be color deficient herself.

Fathers with this inherited form of red-green color blindness pass the X-linked gene to their daughters but not to their sons, because a son cannot receive X-linked genetic material from his father.

A daughter who inherits the color-deficient gene from her father will be only a carrier unless her mother also has the color-deficient gene. If a daughter inherits the X-linked trait from both her father and her mother, then she will be color blind as well as a carrier.

Any time a mother passes along this X-linked trait to her son, he will inherit the color vision deficiency and have trouble distinguishing reds and greens. Again, a daughter can be a carrier but will have this form of color blindness herself only when both her father and mother pass along the X-linked gene. This is why more men than women are color blind.

Color Blindness Treatment & Strategies

Gene therapy has cured color blindness in monkeys, according to study results announced in September 2009 by researchers at the University of Washington and University of Florida.

While early findings look promising, gene therapy would not be considered for humans until treatments are proven to be safe.

Meanwhile, there is no cure for color blindness. But some coping strategies may help you function better in a color-oriented world.

Most people are able to adapt to color vision deficiencies without too much trouble. But some professions, such as graphic design and occupations that require handling various colors of electrical wiring, depend on accurate color perception.

If you become aware of a color deficiency early enough in life, you may be able to compensate by training for one of the many careers that are not as dependent on the ability to see in a full range of colors.

Diagnosing color vision deficiency early also may prevent learning problems during school years, particularly because many learning materials rely heavily on color perception. If your child has a color deficiency, be sure to speak with his or her teachers about it, so they can plan their lessons and presentations accordingly.

Some people use special lenses to enhance color perception, which are filters available in either contact lens or eyeglass lens form. These types of lenses are available from a limited number of eye care practitioners in the United States and other countries. If your regular eye doctor doesn't handle these types of lenses, ask for a referral so that you can seek out someone who might be able to assist you.

You also can learn ways to work around your inability to pick out certain colors. For example, you might organize and label your clothing to avoid color clashes. (Ask friends or family members to help!) And you might remember items by their order rather than their color. An example would be to recognize that the red light is at the top of the traffic light, and green is at the bottom.

Make sure you see your eye care practitioner for extra advice if you have difficulty distinguishing colors or if you've observed this difficulty in your child.

Resources:

*Color vision. Ophthalmology, 3rd ed. 2008.

**Antiepileptic drugs and visual function. Pediatric Neurology. June 2007.

Potential early markers of Parkinson disease in idiopathic REM sleep behavior disorder. Neurology. March 2006.

Male prevalence of acquired color vision defects in asymptomatic carriers of Leber's hereditary optic neuropathy. Investigative Ophthalmology Vision Science. May 2007.

[Page updated October 2009]