Colorblindness | Types, causes, testing and management

Colorblindness | Types, causes, testing and management

Colorblindness is better described as a color-deficiency because in the vast majority of people with the condition they can see colors, but lack the ability to perceive them the way most people do. By far most people with colorblindness have a red-green deficiency. When a colorblind person looks at a red apple, they will say it is red because they know it is red, but will perceive the actual color differently.

It is an inherited trait that mainly affects men because it is an X-linked recessive gene. There is no treatment for the condition. However, a red contact lens can be used to help with detecting different hues. It may limit some in the career choices they make.

Colorblindness | Types, causes, testing and management

How Color Vision Works

Humans see colors because light-detecting cells in our eyes respond differently to different wavelengths of light. When light enters one of your eyes, the lens focuses it on the retina, a thin layer of tissue at the back of the eyeball. There it activates light sensitive cells, called rod cells and cone cells. Activated cells send electrical signals to the brain, where they are translated into images.

Rods and Cones

Rod cells are the most sensitive cells in your retina. They allow you to see in extremely dim light, but they can’t tell different colors apart. Cone cells are responsible for color vision. Each cell contains one of three different light absorbing molecules, called photo pigments, which detect blue, green, or red light. Combining these three main colors allows you to see thousands of colors. When one or more photo pigments aren’t functioning properly, though, color blindness results.


Different Types of Color Blindness

Red-Green Color Blindness Red-green color blindness, which causes difficulty when it comes to telling the difference between red and green, is the most common type of color vision problem. It’s hereditary, found most often in people of northern European ancestry. It’s also more common in men, of which it affects one out of twelve, than in women, of which it affects only one in two hundred.

Red-green color blindness is usually caused by defects in the green photopigment. Without the green photopigment, green and yellow objects appear reddish in color. Defects in the red photopigment also cause red-green color blindness. In this case, red, orange, and yellow objects appear green or black. Although people with red-green color blindness have trouble distinguishing colors, they can still see clearly. That’s because red and green cones have some overlap in the wavelengths of light they detect. Their eyes can still detect incoming light even if one type of cone is missing or malfunctioning.

Blue-Yellow Color Blindness

Blue-yellow color blindness occurs when the blue photopigment is defective or missing. It’s fairly rare, only occurring in about one out of every ten thousand people worldwide. Unlike red-green color blindness, it’s equally common in men and women. Some people with blue-yellow color blindness have no blue cone cells at all, which causes them to see blue as green and to see yellow as violet or gray. More commonly, people who are blue-yellow color blind have partially functional blue cone cells. As a result, they have a difficult time telling yellow and red from pink.

Complete Color Blindness

Complete color blindness is the most severe form of color blindness. It occurs when there are defects in two or more of the three types of cones. You might think that a single kind of cone would be enough to enable color vision, but it’s not. The brain must compare color information from at least two different types of cone cells to identify colors. That means people who have only blue cone cells, for example, are able to see blue wavelengths of light, but they can’t distinguish any colors.

People who are missing two or more types of cones tend to be extra-sensitive to light. They may also have difficulty seeing clearly, especially in bright light. That’s because they have to rely on rod cells for most or all of their vision, and rod cells only work in dim lighting conditions.  Only about one out of thirty thousand people worldwide are missing all three types of cones. People who lack any functioning cone cells see the world in shades of black, white, and gray.


Colorblindness is an inherited trait and is caused by an alteration in the gene that codes for the photopigment in cone cells. Cone cells are what allow us to have detailed and color vision. In colorblind individuals the photopigment functions differently and causes a different color perception. The gene that codes for colorblindness is located on the X chromosome and is recessive (X-linked recessive).

Because of this it affects men much more commonly than women. Men have one X chromosome and get the condition when they have the gene. Women have two X chromosomes and require two of the genes to be colorblind, which is quite rare. Between 2% -6% of men are colorblind and 0.5% of women are colorblind. Women are typically carriers. Below is a pedigree chart that demonstrates the inheritance patterns most commonly seen.

Testing for Color Blindness

The Ishihara Test is the most common test for red-green color vision problems. It uses images made up of dots that are different sizes and colors. People with full-color vision can see numbers or shapes inside the pictures. People with red-green color blindness find it difficult or impossible to identify the hidden symbols. Other, similar tests are used to detect yellow-blue color blindness.


There is no treatment for colorblindness. Special contact lenses can be used to help some people with colorblindness distinguish the difference between colors. Some careers require good color perception like being a lab technician who needs to interpret tests results based color or an electrician who needs to tell the difference between different colored wires. Because of this those with colorblindness may need to limit their career options. In children it is important to know of colorblindness so teachers can adjust their lessons to provide a better learning environment.


Helping our friends that are color blind

● Because people are color blind from birth, they usually don’t know they are color blind. They don’t know that other people see things differently.

● They might think that they are dumb when someone calls them out for putting green things in the same pile as red things, or they might be confused when someone does it correctly.

● Being color blind is not having a disease.

● It is not something that makes a person less clever than someone else.

● It is not something to tease someone about.

● Ask your friends how they feel and if there is anything you can do to make their lives easier.



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