Deuteranopia is a type of color blindness more commonly known as red-green color blindness. People with this condition have difficulty distinguishing between shades of green and shades of red. In addition, they also might have an altered spectrum for several other colors, including certain shades of purple, blue and gray. Other types of red-green color blindness include protanopia and deuteranomaly. All of these conditions are dichromatic vision disorders, meaning that one of the three color pigments cannot be viewed, and the person with the condition can see only two.
Organisms with color vision have the ability to distinguish different colors and sometimes different shades of colors. In the case of humans, colors can be viewed if they are within the 380 nanometer to 740 nanometer range of the color spectrum. This is referred to as the visible spectrum. Color is perceived because of the presence of photoreceptors in the eyes. These photoreceptors are sensitive to light of different spectral ranges.
Humans and other closely-related primates have three different types of photoreceptors: red, blue and green. When all three of these receptor types function in typical fashion, the eye can distinguish all visible colors. Color blindness results when one or more receptor types is absent or malfunctioning.
People with deuteranopia see shades of red in dark yellow, somewhat muddy tones. Greens are viewed similarly or might appear as a lighter yellow. While people with typical vision see reds and greens as very different colors and have no difficulty distinguishing between the two, people who are red-green color blind usually see no difference. In this condition, and in deuteranomaly, the receptors that detect red light are absent from the eye.
Deuteranomaly is a variation of deuteranopia in which color vision can vary from person to person. Someone with this condition might have near-typical color vision or might have something very close to true red-green color blindness. In the case of protanopia, reds and greens cannot be distinguished, and those colors are much less bright than when perceived by someone with typical vision. This condition is caused by a lack of receptors for red pigments.
Deuteranopia is a sex-linked recessive genetic disorder. In this case, the gene that causes the condition is located on the X chromosome. As a result of the gene’s location, this condition is much more common in males than in females. This is because the male genome contains one X and one Y chromosome, whereas the female genome contains two X chromosomes. For a male to have deuteranopia, he need only inherit a single defective X chromosome from his mother. For a female to have the disorder, she must inherit the defective gene from both her mother and her father.
Red-green color blindness is typically diagnosed on the basis of a deuteranopia test in which the patient is asked to view and comment on a series of diagnostic images. These images are created using colors and patterns chosen to highlight differences in color visions. A person with typical vision will view the images differently from someone with color blindness.
The most common diagnostic test used for red-green color blindness is the Ishihara color test. In this test, each image is a circle of seemingly random colored dots. Someone with typical color vision can read a specific number within each image, whereas someone with red-green color blindness will see either a different number or no number at all.