Color Blindness
For some color deficient individuals, the names red, orange, yellow, and green are simply
different names for the same color. The same is true for violet, lavender, purple, and blue.
Among the colors most often confused are pink/gray, orange/red, white/green, green/brown,
blue green/gray, green/yellow, and beige/green. Pastels and muted tones are especially
difficult to distinguish. The color vision defect may be so bad that the affected person
cannot distinguish brown socks from green socks, a red traffic light from an amber one,
or green grass from brown soil by color alone.
5% to 8% of men and 0.5% of women are born colorblind. That's as high as one out of twelve men and one out of two hundred women. The commonest forms of congenital defective color vision, the red-green deficiencies, are due to sex-linked "X" chromosomes and recessive hereditary traits.
What causes colorblindness?
The human eye sees by light stimulating the retina (a neuro-membrane lining the inside back of the eye). The retina is made up of what are called rods and cones. The rods, located in the peripheral retina, give us our night vision, but do not distinguish color. Cones, located in the center of the retina (called the macula), do not function well at night but allow us to perceive fine detail and color during daylight conditions.
There are three types of cones, each containing a different photo pigment. The photo pigment
is responsible for detecting three main wavelengths of light, namely red, green and blue.
Genes contain the coding instructions for these pigments. If the coding instructions are
wrong, then the wrong pigments will be produced and the cones will be sensitive to incorrect
wavelengths of light (color deficient).
The colors that we see are completely dependent on the sensitivity ranges of those pigments. Many people think anyone labeled as "colorblind" only sees black and white - like watching a black and white movie or television. This is a big misconception and not true. It is extremely rare to be totally color blind There are many different types and degrees of colorblindness - more correctly called color deficiencies.
Protanomaly (one out of 100 males): Protanomaly is referred to as "red-weakness", an apt description of this form of color deficiency. Any redness seen in a color by a normal observer is seen more weakly by the protanomalous viewer, both in terms of its "coloring power" (saturation, or depth of color) and its brightness. Red, orange, yellow, yellow-green, and green, appear somewhat shifted in hue towards green, and all appear paler than they do to the normal observer. Under poor viewing conditions, such as when driving in dazzling sunlight or in rainy or foggy weather, it is easy for protanomalous individuals to mistake a blinking red traffic light for a blinking yellow or amber one, or to fail to distinguish a green traffic light from the various "white" lights in store fronts, signs, and street lights.
Deuteranomaly (five out of 100 males): The deuteranomalous person is considered "green weak". Similar to the protanomalous person, he is poor at discriminating small differences in hues in the red, orange, yellow, green region of the spectrum. He makes errors in the naming of hues in this region because they appear somewhat shifted towards red.
From a practical stand point though, many protanomalous and deuteranomalous people breeze through life with very little difficulty doing tasks that require normal color vision. Some may not even be aware that their color perception is not normal. They are usually unaware they have a problem until they fail to pass a color vision test.
 Normal - sees 7 |
 Protanomaly |
 Deuteranomaly |
The color vision plates above demonstrate how the same plate would be seen by those with normal color vision and by those with the two most common color vision defects.
What about "color vision aids"?
Color-deficient applicants are routinely denied employment in certain occupations like airline pilot, train engineer, fire fighter and police officer. While there is no "cure" for color blindness, there are aids which can help these individuals pass a color vision test.
The X-chrome Contact Lens (a red tinted monocular contact lens for colorblindness) has been on the market for decades. These lenses can help some color-deficient individuals pass a color vision test. For a demonstration, try looking through a red glass lens or piece of red cellophane placed in front of one eye. However, whether an examiner (e.g. Federal Aviation Administration, etc.) will accept test results obtained while wearing such a lens is always open to question. Always check in advance with any prospective employers.
Final comments
Children not only have to "learn their colors" but color-enhanced instructional materials have become commonplace throughout the classroom. It is important that parents have their children tested before the children start school. In the event that a color deficiency is detected, teachers should be made aware so they understand the special needs of the student.
Total colorblindness is rare. Protanomalous or deuteranomalous individuals make up the majority of "colorblind" people. They can usually pass as a normal observer in everyday activities. They may make occasional errors in color names, or may encounter difficulties in discriminating small differences in colors, but usually they do not perform very differently from those with normal color vision, except on color vision tests.
Source:
American Optometric Association
