Color Blindness. It affects every part of our lives. Color is emotional, experiential, and tactical. It gives art life. It entices us to eat certain foods and buy certain jewelry, and sometimes it literally defines these things. We also use color to interpret information such as signs and lights. It is deeply ingrained in our basic perception of the world. When the ability to see color is deficient, as in the case of color blindness, there is a dulling of what is seen; or one might say there is a dulling effect in how we see.
Definition of Color Blindness
Color blindness is a reduced ability to distinguish between colors when compared to the standard for normal human color vision. When a person is color blind, also called color vision deficiency (CVD), they usually have difficulty distinguishing between certain colors such as yellow and orange, green and brown, pink and gray, or blue and purple. These confusions are typical of what is called “red-green color blindness,” which includes protan-type CVD (protanomaly and protanopia) and deutan-type CVD (deuteranomaly and deuteranopia).
Red-green color blindness is usually inherited via X-linked recessive genes. Other types of color blindness exist also, such as tritan-type CVD, also called blue-yellow color blindness, which is associated with the inability to see shades of blue, and confusions between blue and green colors. Blue-yellow color blindness is usually caused by age-related eye conditions such as glaucoma, or exposure to certain chemicals or medical treatments. In very rare cases, a person can be completely color blind, meaning they see only the intensity of light, but not its color.
This is called monochromacy or achromatopsia. Achromatopsia can be inherited but can also result from progressive eye diseases such as retinitis pigmentosa. In summary, there are many types and degrees of what can be considered “color blindness,” ranging from partial to complete lack of color discrimination.
What Do Color Blind People See?
Many assume because of its name that “color blind” means a person can only see in black and white. In actuality, the vast majority of people with color blindness do see color, but they see a much smaller range of shades of color compared to a person with normal color vision.
In addition, a person with color blindness may miss out on details or not notice objects that would normally be plainly visible, because the color of the details or object is confusingly similar to surrounding visual context. A classic example is not noticing a ripe red apple in a tree when it is surrounded by green leaves.
Humans have three primary types of light receptor cells in the retina that respond broadly to red, green, and blue light. Signals from these receptor cells form the basis of color vision, by transmitting neural signals to the brain about the relative amount of each primary color to the visual cortex. It is estimated that the human visual cortex can perceive about 100 levels of sensitivity for each primary channel: 100 x 100 x 100 = 1 million, which is where we get to 1 million perceived shades of distinct color.
However, if a person is color blind, for example having red-green color blindness, then the red and green primary channels have an overlap in their signals causing the channels to contain almost the same information. In the most extreme case, called dichromacy, the red and green channels are completely indistinguishable, such that the total number of colors that can be seen is just 100 x 100 = 10 thousand or just 1% of the normal range.
Most people with color blindness have only a partial loss of sensitivity, meaning the information is there, but is harder to notice. Depending on the severity, the number of unique shades of color that can be seen is more often estimated to be around 10% of normal.
Learn more about what color blind people see in our Website.
How Many People are Color Blind?
There are an estimated 350 million people in the world with red-green color blindness (deutan-type and protan-type vision deficiency), or 4% of the total population. Red-green color blindness is acquired genetically through your parents and is expressed by genes on the X-chromosome. Because of the X-linked recessive biology behind red-green color blindness, the condition affects mainly men: about one in 12 men (8%), but also includes about one in 200 women (.5%). Read more about the genetics of color blindness.
Less precise statistics are known about blue-yellow color deficiency, which is most often caused by progressive or age-related eye conditions. Some estimates place the total number at least as high as those for red-green color blindness, and may be increasing due to the trend toward an aging population demographic worldwide.
The more rare forms of color blindness include achromatopsia and progressive eye diseases, such as retinitis pigmentosa. Estimates of these conditions are about 1 in 2000 people, or lower, but are known to be greater in certain subpopulations.
What Are the Genetics of Color Blindness
The most common type of color blindness, red-green color blindness which includes protan-type and deutan-type color vision deficiencies, is a genetic condition. 1 in 12 men have this common form of color blindness, while only 1 in 200 women have it. That’s because the genes responsible for this type of color blindness are located on the X chromosome, and men have only one X chromosome. If the recessive trait is present, they are color blind. A woman must have this recessive trait on both of her X chromosomes to be color blind. If only one, then it doesn’t affect her, but she can pass this onto a male child.
Women can be carriers of the color blind gene and pass the mutation down the family line. If only the father is color blind, there is a 100% chance that his daughters will carry the gene, but they will not be color blind themselves. His sons will neither carry the gene nor be color blind. If the mother carries the gene but is not color blind, there is a 50% chance that her sons will be color blind and a 50% chance that her daughters will carry the gene.
When a color blind father and a mother who carries the color blind gene have children, there is a 50% chance that their sons will be color blind. Their daughters, however, will have a 50% chance of being color blind and 100% chance of being carriers of the gene. Alternatively, a color blind mother and a non-color blind father will have all color blind sons and will have daughters who all carry the color blind gene. Finally, if both parents are color blind, their sons and daughters have a 100% chance of being color blind and their daughters have a 100% chance of carrying the gene.
Some types of color blindness increase with age or develop as a symptom of certain diseases or exposure to toxins like mercury and are not linked to heredity.