Causes and Symptoms of Color Vision Deficiency (Color Blindness)

Cause

1. Congenital color vision deficiency

Color vision deficiency is an X-linked recessive trait. When there is an abnormality in the color vision gene on the X chromosome, males develop color vision deficiency, while females become carriers. Sons inherit from the mother, and daughters inherit from the father. Therefore, if the father has color vision deficiency, it does not mean that the son will also have color vision deficiency; rather, all sons will be normal and all daughters will be carriers.

If the mother is a carrier and the father is normal, the probability of color vision deficiency is 50% with each pregnancy, and the probability that a daughter will be a carrier is also 50% with each pregnancy. Due to the nature of X-linked inheritance, women can be carriers but usually do not become symptomatic individuals with color vision deficiency. However, in very rare cases, if the father has color vision deficiency and the mother is a carrier, color vision deficiency can appear in their daughter. In addition, if one of the two X chromosomes is inactivated, or in Turner syndrome with a color vision deficiency gene, color vision deficiency may also rarely appear in women.

2. Acquired color vision deficiency

Acquired color vision deficiency is caused by optic nerve abnormalities, retinal diseases, nervous system abnormalities, chemicals, and medications, and accounts for less than 1% of all people with color vision deficiency. As for optic nerve abnormalities, major causes include optic neuritis and Leber hereditary optic neuropathy. As for retinal abnormalities, various retinal degenerative diseases such as age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa can be causes. In addition, it can also occur with tuberculosis medications, organic solvents, pesticide poisoning, and other conditions, and acquired color vision deficiency may also appear in brain diseases such as occipital cerebral infarction, brain tumors, and Parkinson's disease. Unlike congenital color vision deficiency, acquired color vision deficiency is mostly tritan defects, meaning blue-weakness or blue-blindness, and the frequency is higher.

Symptoms

If you have color vision deficiency, you perceive colors differently from people with normal color vision, which can be inconvenient in daily life. However, complete inability to distinguish colors is very rare, so most people with color vision deficiency often do not notice anything unusual themselves until it is discovered through a color vision test, and they can go about daily life without major inconvenience.

Among color vision deficiencies, the most common type is green weakness. The spectral sensitivity distribution of the cone cell photopigments is located between the sensitivity of the normal red and green cones, and the degree of symptoms is determined by how far this sensitivity deviates from normal.

Dichromatic color vision defects such as red blindness or green blindness are more severe because one type of cone cell is absent. For example, protanopia, or red blindness, lacks the photopigment that responds to long wavelengths, so it is insensitive to red light above 650 nm. This can lead to seeing red as black or wearing red-toned clothes to a place where black clothing is required.

In deuteranopia, or green blindness, cone cells sensitive to middle wavelengths, that is, green wavelengths, are absent. As a result, wavelengths longer than green are perceived as yellow, and wavelengths shorter than green are perceived as blue, leading to a tendency to perceive the world in two color categories: yellow and blue.

According to one study, 66% of anomalous trichromats and 99% of dichromats feel inconvenienced in daily life due to color vision deficiency.

So far, we have explained the causes and symptoms of color vision deficiency (color blindness).

In the next part, we will look at the diagnosis and treatment of color vision deficiency (color blindness).

Source: Korea Centers for Disease Control and Prevention National Health Information Portal