The human eye contains two different types of cells that interpret light and allow us to see. Rods allow us to see in low light. Because we only have one type of rod, they don’t convey color, which is why we generally don’t see color at night. We have three types of cones, however, which allow us to see colors ranging from red to violet in sufficient light.
Color blindness, more appropriately known as color vision deficiency, occurs when one or more of the cones has a defect, caused by a faulty gene on the X chromosome. Since men only have one X chromosome, they are much more likely than women to experience color blindness. For men, the chances of being colorblind are 1 out of 12, while for women the chance is 1 out of 200.
Types of Color Vision Deficiency
As mentioned above, humans have three types of cones: cones that perceive red light, cones that perceive green light, and cones that perceive blue light. One or more of these cones may have a defect, leading to poor perception of one or more colors. The different types of color blindness are described below.
With this first type of color blindness, each cone can still perceive color, but one does a slightly subpar job. People with this condition may be able to see the colors, just at a slightly reduced rate that makes it harder to distinguish different shades, or they may not be able to perceive the color at all.
Unlike anomalous trichromacy, with dichromacy, one of the cones does not work at all. The individual can only see colors perceived by the two functional cones.
With monochromacy, either only one cone is functional, or all three cones are faulty. In either case, the ability to perceive color is extremely limited, and many individuals only see in shades of black, gray, and white. To those with monochromacy, life is like a black-and-white movie.
What Colorblind People See
When those who see color correctly hear that another individual is colorblind, they often try to ascertain exactly what the world looks like to the other person. The answer can be complicated and changes according to what type of color vision deficiency the other person has one of the following:
- Protanomaly—faulty red cone. The colors red, green, brown, and orange all tend to have a similar hue. Instead of seeing a vivid distinction between red and green objects, both objects have a yellowish tint, with only a slight difference between the two colors. Blues and violets also appear similar, with little distinction.
- Deuteranomaly—faulty green cone. Like protanomaly, individuals have trouble distinguishing between red, green, brown and orange. Individuals with either type are referred to as red-green colorblind.
- Tritanomaly—faulty blue cone. This condition is the least common form of color vision deficiency. Individuals with tritanomaly see the world in shades of pink (standing in for orange, yellow, and red) and turquoise (standing in for blue, green, and violet).
- Protanopia—absent or dysfunctional red cone. The individual can’t detect any red light, so they see the world in shades of green. They can see yellow well but can mix up blues and purples, and dark red, dark orange, and dark green tend to look black or brown.
- Deuteranopia—absent or dysfunctional green cone. Like with protanopia, there is almost no difference between red and green colors. However, deuteranopes tend to see the world with a slightly more yellow hue than protanopes, who see more green.
- Tritanopia—absent or dysfunctional blue cone. This condition is the rarest form of dichromacy. Individuals will see gray instead of light blue, black instead of dark purple, blue instead of medium green, and red instead of orange. Pink is also more pronounced and yellow nearly impossible to see.
Those with color vision deficiency can live normal lives and don’t suffer too greatly because of their condition. Fashion can be a challenge, as a person with a red-green deficiency may not be able to tell whether a shirt is blue or purple or if a pair of socks is green or brown. To such a person, what they perceive as brown is the same as what they perceive as green.
Traffic lights may seem problematic since red and green are hard to differentiate, but colorblind people usually can drive safely based on the position of the light. A real issue is knowing when fruit is ripe or when meat is done cooking. To someone who can’t see subtle nuances between red, pink, and brown, a rare steak looks the same as a well-done steak.
To get an idea of what the world looks like to a colorblind person, try out this vision simulator.
Currently, no cure exists for genetic color blindness. However, a company called EnChroma has developed glasses that allow colorblind individuals to see wavelengths of light they aren’t able to detect naturally. Generally, people can now see red and pink where before they only saw green or brown. The glasses are mostly helpful for those with red-green color blindness, so they don’t work for everyone.
Scientists are also attempting to develop a treatment that involves an injection directly into an individual’s eye. The injection sends a virus into the eye to repair the defect in the cones. So far, the treatment has only been tested on animals, but the initial results show promise.
If you suspect that you or someone you know might be colorblind, visit your eye doctor to get tested. He or she will likely have some advice to keep your vision deficiency from interfering with any aspect of your life.