“Colorblind” is a term often thrown around in our culture. But strictly speaking, the condition to which the phrase refers is not so much of a blindness as it is a deficiency. Most patients with color deficiency are not entirely without color vision; they simply don’t see the same range of colors that others do. Understanding the different types of color deficiency and how each can impact day to day life can help you be more aware and sympathetic to what life is like for those around us who see the world differently.
The average retina contains millions of tiny cells called cones. Cones are responsible for color vision. There are different types of cones, and each type is responsible for detecting a different color of light. Roughly 64 percent of cones are most sensitive to red light, about 33% are most sensitive to green light, and about 2% are most sensitive to blue light.
The more working cones a person has, the more clearly and vibrantly they see color.
A person with color-deficient vision also has cones, however, they have fewer functional cones than someone with full-color vision. As a result, patients with color deficiency are less sensitive to a specific range of colors. For instance, someone with fewer working green cones will see yellow and green with more of a reddish hue and may have trouble discerning purple from blue. To someone with no working green cones at all, greens will look beige, and reds look more like a brown-yellow.
There are three main types of color deficiency based on which cones are functioning and which ones are not. The severity of some color deficiencies vary depending on how many of those cones are functioning.
This is the most common type of color deficiency, usually caused by genetics. This color deficiency results from a lack of functioning red or green cones. We used a lack of green cones as an example above.
If there are very few functioning red cones, colors can appear duller, and red, yellow, and orange take on a greenish hue. If there are no working red cells whatsoever, red looks black, and some shades of orange and green appear yellow.
Blue-yellow color deficiency occurs when a patient lacks the right amount of working blue cones. If there are a few functioning blue cones, they will have difficulty seeing a difference between yellow and shades of red and pink. Blue will also look more green. If someone has no working blue cones at all, they will see yellow as purple or gray, and blue will look more green.
People with monochromacy have difficulty distinguishing any colors. If two out of three cone types don’t work, the brain still gets some color signals but has no other color signals to which it can compare them. Without these comparisons, the brain can’t distinguish color, and the patient has trouble telling them apart.