Color blindness (patient information)

For the WikiDoc page for this topic, click here


 * Assistant Editor(s)-In-Chief: Erin E. Lord

Overview
Color blindness, a color vision deficiency, is the inability to perceive differences between some of the colors that others can distinguish.

There are different classifications of color blindness. It can be classified by cause or by clinical appearance.

By cause:
 * Acquired
 * Inherited:
 * Monochromacy - Also known as "total color blindness"
 * Rod monochromacy (achromatopsia) - The condition of having only rods in the retina. A rod monochromat will be unable to see well in normal daylight levels of illumination.
 * Cone monochromacy - A rare total color blindness that is accompanied by relatively normal vision, electoretinogram, and electrooculogram.
 * Dichromacy - A moderately severe color vision defect in which one of the three basic color mechanisms is absent or not functioning. It occurs when one of the cone pigments is missing and color is reduced to two dimensions.
 * Protanopia - A severe type of color vision deficiency caused by the complete absence of red retinal photoreceptors.
 * Deuteranopia - A color vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red-green hue discrimination.
 * Tritanopia - A very rare color vision disturbance in which there are only two cone pigments present and a total absence of blue retinal receptors.
 * Anomalous trichromacy - A common type of inherited color vision deficiency, occurring when one of the three cone pigments is altered in its spectral sensitivity. This results in an impairment, rather than loss, of trichromacy (normal three-dimensional color vision).
 * Protanomaly - A mild color vision defect that results in poor red-green hue discrimination
 * Deuteranomaly - By far the most common type of color vision deficiency, mildly affecting red-green hue discrimination
 * Deuteranomaly - A rare, hereditary color vision deficiency affecting blue-yellow hue discrimination; unlike most other forms, is not sex-linked

By clinical appearance:
 * Total color blindness
 * Partial color blindness
 * Red-green
 * Dichromacy (protanopia and deuteranopia)
 * Anomalous trichromacy (protanomaly and deuteranomaly)
 * Blue-yellow
 * Dichromacy (tritanopia)
 * Anomalous trichromacy (tritanomaly)

What are the symptoms of Color blindness?
Symptoms vary from person to person, but may include:


 * Trouble seeing colors and the brightness of colors in the usual way
 * Trouble telling the difference between red and green
 * Trouble telling the difference between blue and yellow
 * Inability to tell the difference between shades of the same or similar colors

Often, the symptoms may be so mild that some persons do not know they are color blind. A parent may notice signs of color blindness when a child is learning his or her colors.

Rapid, side-to-side eye movements and other symptoms may occur in severe cases.

What causes Color blindness?
Color blindness occurs when there is a problem with the color-sensing materials (pigments) in certain nerve cells of the eye. These cells are called cones. They are found in the retina, the light-sensitive layer of tissue at the back of the inner eye. If you are missing just one pigment, you might have trouble telling the difference between red and green. This is the most common type of color blindness. Other times, people have trouble seeing blue-yellow colors. People with blue-yellow color blindness almost always have problems identify reds and greens, too.

Color blindness is often inherited genetically. It is most commonly inherited from mutations in a X-linked recessive fashion, but the mapping of the human genome has shown there are many causative mutations – mutations capable of causing color blindness originate from at least 19 different chromosomes and many different genes (as shown online at the Online Mendelian Inheritance in Man (OMIM) database at Johns Hopkins University).

Inherited color blindness can be congenital (from birth), or it can commence in childhood or adulthood. Some of the inherited diseases known to cause color blindness are:


 * Cone dystrophy
 * Cone-rod dystrophy
 * Achromatopsia (aka rod monochromatism, aka stationary cone dystrophy, aka cone dysfunction syndrome)
 * Blue cone monochromatism
 * Leber's congenital amaurosis
 * Retinitis pigmentosa (initially affects rods but can later progress to cones and therefore color blindness)

Other causes of color blindness include:
 * Brain or retinal damage caused by shaken baby syndrome or other accidents and trauma which produce swelling of the brain in the occipital lobe
 * Damage to the retina caused by exposure to ultraviolet light
 * The drug hydroxychloroquine (Plaquenil), which is used to treat rheumatoid arthritis, among other conditions

Who is at highest risk?
Men are at a higher risk for color blindness than women. As color blindness is commonly inherited in a X-linked recessive fashion, about 8 percent of males, but only 0.5 percent of females, are color blind in some way or another, whether it be one color, a color combination, or another mutation. The reason males are at a greater risk of inheriting an X linked mutation is because males only have one X chromosome (XY, with the Y chromosome being significantly shorter than the X chromosome), and females have two (XX); if a woman inherits a normal X chromosome in addition to the one which carries the mutation, she will not display the mutation. Men do not have a second X chromosome to override the chromosome which carries the mutation. If 5% of variants of a given gene are defective, the probability of a single copy being defective is 5%, but the probability that two copies are both defective is 0.05 &times; 0.05 = 0.0025, or just 0.25%.

In addition to those who are genetically predisposed to color blindness, people who suffer from brain or retinal damage, or who take the drug hydroxychloroquine (Plaquenil), are at an increased risk of color blindness.

Diagnosis
While some people notice that they have difficulty telling the differences between certain colors, others may have such a mild case that they do not even notice any symptoms.

To be certain, your eye care specialist can check your color vision in several ways. Testing for color blindness is commonly done during an eye exam. The Ishihara color test, which consists of a series of pictures of colored spots, is the test most often used to diagnose red-green color deficiencies. A figure (usually one or more Arabic digits) is embedded in the picture as a number of spots in a slightly different color, and can be seen with normal color vision, but not with a particular color defect.

When to seek urgent medical care?
Color blindness is not considered a medical emergency.

However, make an appointment with your optometrist or ophthalmologist if you think you (or your child) have color blindness.

Treatment options
There is generally no treatment to cure color deficiencies. However, certain types of tinted filters and contact lenses may help an individual to better distinguish different colors. Optometrists can supply a singular red-tint contact lens to wear on the non-dominant eye. This may enable the wearer to pass some color blindness tests, but they have little practical use.

Additionally, computer software and cybernetic devices have been developed to assist those with visual color difficulties such as an eyeborg, a "cybernetic eye" that allows individuals with color blindness to hear sounds representing colors.

The GNOME desktop environment provides colorblind accessibility using the gnome-mag and the libcolorblind software. Using a gnome applet, the user may use color filters to choose from a set of possible color transformations. The filters will displace the colors on the screen so that the user can distinguish between them. The software enables, for instance, a color blind person to see the numbers in the Ishihara color test.

In September 2009, the journal Nature reported that researchers at the University of Washington and University of Florida were able to give trichromatic vision to squirrel monkeys using gene therapy.

Where to find medical care for Color blindness?
Directions to Hospitals Treating color blindness

Prevention of Color blindness
Color blindness cannot typically be prevented, as most cases are due to one's genetics.

Avoiding brain or retinal damage as best as possible may prevent certain acquired cases of color blindness, as well as other serious problems.

Additionally, while taking hydroxychloroquine (Plaquenil), be sure to carefully follow the doctor's instructions and immediately report any adverse affects.

What to expect (Outlook/Prognosis)?
Color blindness is a life-long condition. Most persons are able to adjust without difficulty or disability.

Although those who are colorblind can succeed at many jobs, they may not be able to get a job that requires color vision. For example, a pilot needs to be able to see color

Possible complications
People who are colorblind may not be able to get a job that requires the ability to see colors accurately. For example, electricians (color-coded wires), painters, fashion designers (fabrics), and cooks (using the color of meat to tell whether it's done) need to be able to see colors accurately.

Additional Links
http://www.nlm.nih.gov/medlineplus/ency/article/001002.htm