What Are the Causes of Red Green Color Blindness?

Color blindness is not the inability to see colors, as the name implies, but rather a vision disorder that affects how you see colors. According to the Colblindor website, red-green colorblindness, or deuteranopia, is the most common type of colorblindness, afflicting 6 percent of the male population. People with deuteranopia have difficulty distinguishing between reds and greens. There are two main causes: genetics and cone dysfunction or absence.

Genetics

• Red-green color blindness can be a congenital disorder. It is a sex-linked trait, present on a recessive X chromosome, typically passed from a carrier mother to her son. Women have a less than 1 percent chance of being colorblind because they carry two X chromosomes; for color blindness to become manifest, both of her X chromosomes would have to be affected.

Rates of Genetic Passage

• If both parents are unaffected, it is impossible for their offspring to be colorblind. If they are both affected, their sons will be colorblind; this is also the only scenario where a daughter can be affected. If the father is affected and the mother is not a carrier, the sons will not become colorblind, but the daughters will become carriers. If the father is unaffected and the mother is a carrier, the sons have a 50 percent chance of being colorblind.

Cones

• Sometimes red-green color blindness is caused by an abnormality of the retinal cones. Cones are receptor cells that read colors through wavelengths of light, allowing us to see the entire spectrum of colors. Blue cones read short wavelengths; medium are read by green and long by red. Abnormalities or lack of certain cones cause different forms of color blindness.

Cone Abnormalities

• Dichromats are people who are blind to green; they have no green cones and can only distinguish two to three hues in the color spectrum. Then there are people who are green weak, making it hard for them to distinguish between different shades of green. Seventy-five percent of cases of deuteranopia are caused by defects or absence of the medium wavelength green-sensitive cones in the retina of the eye.

Considerations

• As we age, wear and tear on the eyes and the brain can result in deterioration of color vision, and certain diseases can cause retinal damage, resulting in color blindness. Examples include Parkinson's disease, cataracts and Kallman's syndrome. The drug Tiagabine, used to treat seizures, reduces color vision. Leber hereditary optic neuropathy is an inherited condition affecting mostly males that can cause distortion in red-green color vision.