Deuteranopia, a type of red-green color blindness, affects the ability to distinguish between shades of green and red. It is caused by a lack of red pigment receptors and is more common in males due to its location on the X chromosome. Diagnosis is typically done through the Ishihara color test.
Deuteranopia is a type of color blindness more commonly known as red-green color blindness. People with the condition have difficulty distinguishing between shades of green and shades of red. Additionally, they may also have an altered spectrum for many other colors, including some 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 visualized and the person with the condition can only see 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 fall within the 380 nanometer to 740 nanometer range of the color spectrum. This is referred to as the visible spectrum. Color is perceived due to the presence of photoreceptors in the eye. 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 are functioning typically, the eye can distinguish all visible colors. Color blindness occurs when one or more types of receptors are absent or malfunctioning.
People with deuteranopia see shades of red in dark, somewhat muddy yellow tones. Greens are seen similarly or might appear as a lighter yellow. While people with typical vision see red and green as very different colors and have no difficulty distinguishing between the two, people who are red-green colorblind usually see no difference. In this condition, and in deuteranomaly, the receptors that detect red light are absent from the eye.
Deuteranomaly is a variant of deuteranopia in which color vision can vary from person to person. Someone with this condition might have near-typical color vision, or they 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 red pigment receptors.
Deuteranopia is a sex-linked recessive genetic disease. In this case, the gene that causes the condition is found on the X chromosome. Due to the location of the gene, this condition is much more common in males than females. This is because the male genome contains one X and one Y chromosome, while the female genome contains two X chromosomes. For a male to have deuteranopia, he must inherit only a single defective X chromosome from his mother. For a female to have the disease, she must inherit the defective gene from both her mother and father.
Red-green color blindness is typically diagnosed based on 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 see images differently from a person who is color blind.
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, while someone with red-green color blindness will see a different number or no number at all.
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