Vision Perception: Defects in Color Perception
Pigment in the cones allows us to see color, and lack of pigments leads to color blindness. There are other causes of color blindness, but problems due to pigments are the most common.
Some people cannot accurately perceive color. In addition, with age, the lens yellows, and color perception changes. Therefore, any sign or device to be used by the public should not rely entirely on color for important instructions or distinctions. Also, critical information should be placed near the center of the visual field so as to take advantage of the photoreceptors’ ability to process details.
View the PDF transcript for Types of Color Blindness
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Types of Color Blindness
Color blindness is genetic and is carried on the X chromosome. As women have two X chromosomes, a normal gene on one X chromosome compensates for a defective gene on the other X chromosome. But because men have a single X chromosome (XY), color blindness is more prevalent in men than in women. Most cases of color blindness involve the absence of red or green cones.
Normal: People with normal vision have red, green, and blue cones.
Protanopia: People with protanopia do not have red cones.
Deuteranopia: People with deuteranopia do not have green cones.
Tritanopia: People with tritanopia cannot distinguish blues and yellows.
Achromatopsia: It is a rare vision disorder in which people do not perceive color at all. Their cones are not functional, which also means they can neither see much detail nor see well in daylight. Oliver Sacks wrote a book titled Island of the Colorblind that investigated people on a small Micronesian island where achromatopsia affects about 5 percent of the population.