A Range of Color Blindness

Author: Ellie Wang

Editor: Kira Tian

Artist: Nicole Tseng

Have you ever wondered about what it feels like to be color blind and what causes color blindness? Read on to discover the different types of color blindness, their causes, and possible solutions to correct color blindness.

Color blindness affects about 8% of men and 0.5% of women. Globally, around 300 million people are color blind. While it may be commonplace to think that all colorblind people view the world the same way, there are actually many types of color blindness; based on the affected person’s genetics, each type of color blindness affects a different selection of colors.

First of all, what causes color blindness? In most cases, a person’s chromosomes contain genes relating to the functions of the eyes. Red-green color blindness is linked to the X chromosome, one of two sex chromosomes that determine one’s biological sex. Males have an XY combination, and females have an XX combination. Since the condition is X-linked, all X chromosomes must have the affected gene in order for someone to have red-green color blindness. This is why red-green color blindness predominantly affects males: they only have one X chromosome instead of two. Other forms of color blindness, such as blue-yellow color blindness and complete color blindness, are not passed down through the sex chromosomes, and so they affect males and females equally. Genetics are not always the reason for color blindness, though. There are several other causes, including eye diseases, nervous system diseases, medications, and eye or brain injuries. No matter the cause, the result is the altering of the spectral sensitivity of certain cones in one’s eyes, changing the way that these structures receive different wavelengths of light.

The most common type of color blindness is red-green color blindness, of which there are two main types: protan and deutan. Protan color blindness involves a change in the L-cones, or long-wavelength light cones, that normally perceive red light. In the case of red-green color blindness, L-cones’ spectral sensitivity is shifted to perceive shorter wavelengths, making red colors more difficult to see. The protan type can be further separated into protanomaly, a partial L-cone shift, and protanopia, a full L-cone shift. Common symptoms include difficulty differentiating greens, yellows, oranges, reds, and browns. In addition, purple appears bluer, pink appears gray, and red looks darker than usual. Approximately 25% of red-green colorblindness cases consist of protan color blindness. With deutan color blindness, on the other hand, the M-cones that receive medium wavelengths are altered. While they usually perceive green light, they are shifted to perceive longer wavelengths. Therefore, green becomes redder. This type also has subtypes of deuteranomaly and deuteranopia. Symptoms include difficulty telling apart green and yellow, blue and purple, or between pink and either gray or white. Additionally, green traffic lights could appear pale green or white.

Next, tritan color blindness, or blue-yellow color blindness, rarely happens because of genetics. Aging of the eye or eye diseases are the common causes, so most with tritanomaly or tritanopia are elders. Tritanomaly affects the S-cones that make up a mere 1% of retinal cones. Thus, any change with these cones is sure to change someone’s sight. S-cones stand for short-wavelength light cones, and they usually perceive blue light. Someone with tritan color blindness will have difficulty seeing blue and differentiating blue and green.

Besides these more common types, there are several more types of color blindness. Color blindness is not a singular condition: it has many different types and symptoms to be diagnosed. There are few treatments for color blindness, with the exception of age-induced tritan color blindness, but EnChroma glasses are an available solution. These glasses do not perfectly correct color vision, since they are designed to block out the colors that the affected cones are overlapping. Still, they significantly increase a colorblind person’s range of color vision, making them one of the best corrections for red-green colorblindness.

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