Discovery Fit & Health
Not all forms of colorblindness are created equal. There are as many different degrees of the condition as there are shades of gray in an Ansel Adams photograph. The most common forms don't necessarily prevent individuals from seeing colors so much as make it difficult for them to distinguish between certain colors. Colorblindness, which is usually hereditary, is caused by a problem with the color-sensing pigments found in the nerve cells at the back of a person's eye, in the light-sensitive layer of tissue known as the retina. When on of these pigments is missing, a person is most likely to experience red-green colorblindness, the most common type. As the name suggests, people with red-green colorblindness, or protanopia, have difficulty telling apart the colors green and red, or green and blue. Less common forms affect a person's ability to distinguish between red and purple, green and purple or yellow and green.
Complete color blindness, or achromatopsia (meaning "without color"), affects far fewer people -- roughly 1 in every 33,000 to 50,000 births [source: Low Vision Centers of Indiana]. Even among achromats, though, there are differences. Rod monochromatism is the more common form, while blue-cone monochromatism is less common, occurring in approximately 1 in 50-100,000 males and 1 in 10 billion females [source: Low Vision Centers of Indiana].
Though some rod monochromats may retain traces of limited color vision, most people with either form of achromatopsia experience a total loss of color vision and view objects in varying shades of gray. Along with profound colorblindness, achromats also experience a severe intolerance to light, reduced visual acuity and nystagmus, or a regular shaking of the eyes.
An interesting aspect of colorblindness is that it is much more prevalent in men due to its transmission on the X chromosome. Because it is X-linked recessive, colorblindness occurs in approximately 1 out of 10 men but in very few women [source: National Institutes of Health].Retina of eye showing rod cells (photoreceptors) x600. Tinted B&W scanning electron micrograph. (Ron Boardman/Riser/Getty Images)
"Colorblind" is a misleading term. Most people who are colorblind see some color, and there are different color vision problems and severities of colorblindness. "Color vision deficiency" more closely describes what people who are colorblind experience. People who have anomalous trichromacy have mild colorblindness, and those with deuteranomaly (the mildest form of colorblindness) or protanomaly have red-green colorblindness. Tritanomaly is the rarest type of colorblindness; people with this condition have difficulty distinguishing between yellow and blue. People with monochromacy can see only black and white.
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