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Color vision deficiency
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Color vision deficiency, which many people call color blindness, almost never means seeing in black and white. What happens is that the person sees an altered range of colors, and in most cases they are born with it.
Color is put together in the retina, the layer at the back of the eye. It holds cells called cones, and there are three kinds of cones, each with a different pigment that responds best to red, to green or to blue. The brain compares the three signals, and color comes out of that combination. When one kind of cone is missing, the comparison is made with two signals instead of three. One pigment is missing and color is built from fewer pieces.
Protanopia and deuteranopia are told apart by which cone was lost. In protanopia the red cones are lost, and in deuteranopia the green ones. Both come from alleles, which are versions of a gene, located on the X chromosome, and that is why they show up almost exclusively in males. The most common deficiency of all is in fact the red-green one.
In brief
In color vision deficiency, color is almost never lost: the person sees an altered range, and most forms are congenital.
Color comes from three cone pigments, red, green and blue; protanopia is the loss of the red cones and deuteranopia of the green ones.
One pigment is missing and color is built from fewer pieces.
Both are alleles linked to the X chromosome and occur almost exclusively in males; the most common deficiency is red-green.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingColor Vision, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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