What is color blindness?

What is color blindness?

Color blindness is also known as color vision deficiency (CVD). It occurs when you are unable to see colors in a normal way which means with difficulty of distinguishing certain colors. This usually happens between greens and reds, and occasionally blues [1]. X chromosome has two genes that produce red and green light sensitive proteins. Mutations in these genes can cause color blindness. This is a common, sex-linked inherited disorder.

In the retina, there are two types of cells that detect light. They are called rods and cones. Rods detect only light and dark and are very sensitive to low light levels. Cone cells detect color and are concentrated near the center of your vision. There are three types of cones that see color: red, green and blue which transmit color information to the optic nerve. The brain uses input from these cone cells to determine our color perception.

Color blindness can happen when one or more of the color cone cells are absent, not working, or detect a different color than normal. Severe color blindness occurs when all three cone cells are absent. Mild color blindness happens when all three cone cells are present but one cone cell does not work right. It detects a different color than normal.

Causes of color blindness

Most people with color blind are born with it. This is called a congenital condition. These defects are due to partial or complete lack of cones in the retina.

Most color vision problems that occur later in life are a result of:

Color vision defects from disease are less understood than congenital color vision problems. Disease-specific color blind often affects both eyes differently. Color vision defect caused by disease usually gets worse over time. Acquired color vision loss can be the result  of damage to the retina or optic nerve.

Importance of color vision

Color is used as a systematic identifier in some learning systems in school. In addition, students start growing their interest in career selection at school level. It is regrettable that a large section of school students unaware of their color vision status. However, employment in certain professions like working as pilot, loco driver, traffic police, defense servant and a few others require a normal color vision.

How to diagnose?

Around the the world, approximately 1 in 12 men and 1 in 200 women are affected by color blindness [2]. this fairly common condition often goes undiagnosed. A test called Ishihara test, makes numbers out of dots that are a different color than the dots surrounding them. It is a fast and simple test which can easily determine the level of your color vision. You will get an instant result by doing the test even online using your computer. Just look at the below picture and write down the letters you see.

What is color blindness?
The photo credit goes to - https://www.allaboutvision.com/eye-exam/color-blind-tests.htm

How did it go for you? Was it difficult and took so much time to identify the number in the circles? Anyone who experiences a difficulty in color identifying should see an ophthalmologist.

Types of Color Blindness

There are different degrees of color blindness. Some people with mild color deficiencies can see colors normally in good light but have difficulty in dim light. Others cannot distinguish certain colors in any light. The most severe form of color blindness, in which everything is seen in shades of gray, is uncommon. Color blindness usually affects both eyes equally and remains stable throughout life.

There are two main types of red green color blindness. One is the protan type which is a disorder of the first type of retinal cones. Another name for this is l cones. Second one is the deutan type which is a disorder of the second type of retinal cone. M cone is an another name for this second type

What is color blindness?
The photo credit goes to - https://enchroma.com/pages/types-of-color-blindness

Protan Color Blindness

This is an anomaly of the l-cones which the l stands for long wavelength light. It appears on red color. In Protan-type CVD, the spectral sensitivity of the L-cone is shifted toward shorter wavelengths, so that it does not receive enough red light, and receives too much green light comparatively. There are two types of Protan-type CVD, protanopia and protanomaly which is partial and complete shift of L cone respectively.  About 25% if cases of red green color blindness are of the proton type.

A person with protan type color blindness tends to see greens, yellows, oranges, reds, and browns as being more similar shades of color than normal, especially in low light. A very common problem is that purple colors look more like blue. Another common issue is that pink colors appear to be gray, especially if the pink is a more reddish pink or salmon color. Another symptom specific to this deficiency is that red colors look darker than normal. For example, if red text is printed on a black background, it can be very hard to read because the red appears to be very dark.

The photo credit goes to - https://enchroma.com/pages/types-of-color-blindness

Deutan Color Blindness

Deutan Color Blindness is an anomaly of the M – cone. The M – stands for medium wavelength light. It appears as green light.In Deutan-type CVD, the spectral sensitivity of the M-cone is shifted toward longer wavelengths so that it effectively receives too much red light and not enough green light.

A person with deutan CVD may experience confusions between colors such as green and yellow, or blue and purple. Another common symptom is that green traffic signals appear to be a very pale green or sometimes white. Common color confusion also occurs between pink and gray or white, especially if the pink is similar to a light purple.

What is color blindness?
The photo credit goes to - http://www.colourblindawareness.org/colour-blindness/

Tritan Color Blindness / Tritanomaly

This type includes tritanomaly and tritanopia. It is also sometimes called blue-yellow color blindness. Tritan color blindness most commonly acquired later in life due to aging of the eye or a medical condition such as glaucoma. Generally characterized by a reduced sensitivity in the blue-sensitive “S” cone cells. “S” stands for Short Wavelength Light.

People having this do not see blue colors properly and may have difficulty seeing the difference between blue and green. Cataracts, glaucoma, and age-related macular degeneration can cause symptoms of tritan color blindness

How to treat?

There is no known cure for color blindness. Contact lenses and glasses are available with filters to help color deficiencies, if needed. Fortunately, the vision of most colorblind people is normal in all other respects and certain adaptation methods are all that is required.


[1]         B. Wong, “Color blindness,” Nat. Methods, vol. 8, no. 6, p. 441, 2011.

[2]         D. R. Keene, “A Review of Color Blindness for Microscopists: Guidelines and Tools for Accommodating and Coping with Color Vision Deficiency,” Microsc. Microanal., vol. 21, no. 2, pp. 279–289, 2014.

Article By,

Patalee Weerasinghe – Research Chemist

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