Color Vision Deficiency (Color Blindness)
Color vision deficiency (CVD) is the inability to distinguish certain shades of color or in more severe cases, see colors at all. The term "color blindness" is also used to describe this visual condition, but very few people are completely color blind.
Red-green deficiency results in the inability to distinguish certain shades of red and green.
Most people with CVD can see colors, however they have difficulty differentiating between particular shades of reds and greens (most common) or blues and yellows (less common). People who are totally color blind, a condition called achromatopsia, can only see things as black and white or in shades of gray. The severity of CVD can range from mild to severe depending on the cause. CVD will affect both eyes if it is inherited and usually just one if the cause for the deficiency is injury or illness. The most common form of color deficiency is red-green. This does not
mean that people with this deficiency cannot see these colors at all;
they simply have a harder time differentiating between them. The
difficulty they have in correctly identifying them depends on how dark
or light the colors are. Another form of color deficiency is
blue-yellow. This is a rarer and more severe form of color vision loss
than red-green since persons with blue-yellow deficiency frequently have
red-green blindness too. In both cases, it is common for people with CVD to see neutral or gray areas where a particular
color should appear.
How Do We See?
Color vision is possible due to photoreceptors in the retina of the eye known as cones. These cones have light sensitive pigments that enable us to recognize color. Found in the macula, the central portion of the retina, each cone is sensitive to either red, green, or blue light, which the cones recognize based upon light wavelengths. Normally, the pigments inside the cones register differing colors and send that information through the optic nerve to the brain enabling you to distinguish countless shades of color. But if the cones lack one or more light sensitive pigments, you will be unable to see one or more of the three primary colors thereby causing a deficiency in your color perception.
What causes CVD?
Usually, color deficiency is an inherited condition caused by a common X-linked recessive gene, which is passed from a mother to her son. But disease or injury damaging the optic nerve or retina can also result in loss of color recognition. Some specific diseases that can cause color deficits are:
- Multiple Sclerosis
- Sickle Cell Anemia
- Chronic alcoholism
- Alzheimer's disease
- Parkinson's disease
- Macular Degeneration
- Other causes for CVD include:
Aging - the ability to see colors can gradually lessen with age.
Chemical Exposure - contact with certain chemicals such as fertilizers and styrene have been known to cause loss of color vision.
Medications - certain medications such as drugs used to treat heart problems, high blood pressure, infections, nervous disorders and psychological problems can affect color vision.
In the majority of cases, genetics is the predominate cause for color deficiency. About 8% of Caucasian males are born with some degree of color deficiency. Women are typically just carriers of the color deficient gene, though approximately 0.5% of women have CVD. When the deficiency is hereditary, the severity generally remains constant throughout life. Inherited CVD does not lead to additional vision loss or blindness.
How is color vision deficiency diagnosed?
Example of a pseudoisochromatic plate
Example of a pseudoisochromatic plate traced for emphasis. Patients with red-green color deficiency cannot see the numbers
Color deficiency can be diagnosed
through a comprehensive eye examination. Testing will include the use of
a series of specially designed pictures composed of colored dots,
called pseudisochromatic plates, which include hidden numbers or
embedded figures that can only be correctly seen by persons with normal
Pseudoisochromatic testing plates:
The patient is asked to look for numbers among the various colored dots, which help distinguish between red, green, and blue color deficiencies. Individuals with normal color vision will see a number, while those with a deficiency do not see it. On some plates, a person with normal color vision may see one number, while a person with a deficiency sees a different number.
Pseudoisoschromatic plate testing can be used to determine if a color vision deficiency exists and the type of deficiency. However, additional testing may be needed to determine the exact nature and degree of color deficiency. It is possible for a person to have poor color vision and not know it. Frequently people with red-green deficiency are not even aware of the problem since they've learned to see the "right" color. For example, tree leaves are green, so they call the color they see green. Parents may not suspect the condition in their children until a situation causes confusion or misunderstanding. Early detection of color deficiency is vital since many learning materials rely heavily on color perception or color coding. That is one reason that the American Optometric Association recommends a comprehensive optometric examination before a child begins school.
How is CVD treated?
There is no cure for inherited color deficiency. But if the cause is an illness or eye injury, treating these conditions may improve color vision. Using special tinted eyeglasses or wearing a red tinted contact lens on one eye can increase some people's ability to differentiate between colors, though nothing can make you truly see the deficient color. Most color deficient persons compensate for their inability to distinguish certain colors with color cues and details that are not consciously evident to people with normal color vision. There are ways to work around the inability to see certain colors by:
-Organizing and labeling clothing, furniture, or other colored objects (with the help of friends or family) for ease of recognition.
-Remembering the order of things rather than their color can also increase the chances of correctly identifying colors. For example a traffic light has red on top, yellow in the middle, and green on the bottom.
Though color vision deficiency can be a frustration and may limit participation in some occupations, in most cases it is not a serious threat to vision and can be adapted to your lifestyle with time, patience, and practice.