Color blindness

The term “color blindness” is used to describe various conditions that affect a person’s ability to see colors.

Color blindness or impaired color vision is caused by missing or defective sensory cells (receptors) in the retina in the eye. People who are able to see all colors have three types of color receptors called cone cells in the retina. Red cones only respond to red light, green cones only respond to green light, and blue cones only respond to blue light.

If a person is color blind, one, two or even all three types of cone cells are not working normally or are completely missing.

Doctors distinguish between different types of color blindness depending on which and how many cones are missing:

• Achromatopsia or total color blindness: all three cone types are missing.
• Monochromacy: only one type of cone type – generally the blue – is working normally.
• Dichromacy: two of the three cone types are functioning normally.

People with true or total color blindness only perceive shades of gray and contrasts. In other types of color blindness, there are one or two colors that people are unable to perceive.

With dichromacy (i.e. two functioning cone types), there is one color that people are unable to perceive. People with blindness to red, also known as protanopia, have no cones with the ability to respond to red light. Blindness to green is known as deuteranopia, while blindness to blue is called tritanopia.

In most cases, color blindness is genetically determined, i.e. present at birth. More rarely, color blindness may develop at a later point in life, for example, as a result of an eye disease such as diabetic retinopathy, a stroke or a brain injury.

If color blindness is inherited, it is present at birth and affects both eyes to the same extent.

The perception of color is altered based on which type of cone is affected. For example, people who have blindness to red or green find it more difficult to distinguish between red and green than between yellow and green. However, they have no difficulty distinguishing between black, white, gray and blue.

People with true or total color blindness are missing all three types of cone in the retina and, as a result, are unable to perceive any colors at all. They are only able to distinguish contrasts.

Other symptoms are:

• severe visual impairment
• particularly light-sensitive eyes
• uncontrolled eye movements (nystagmus)

These symptoms also occur in monochromacy – a type of color blindness in which only one type of cone (often blue) is working correctly.

Color blindness is usually inherited. Color blindness occurs predominantly in men because the genes for red and green color receptors are on the X chromosome and men have only one of these, while women have two.

If one or both color receptor genes is altered or absent, this can be compensated for in women by the second X chromosome so that color vision is unaffected. For a woman to be born with color blindness, the gene must be absent or defective on both X chromosomes – and this scenario is much rarer.

It is rarer for color blindness to be acquired. However, it can be caused by a number of conditions. These include diseases of the retina and eyes, such as diabetic retinopathy, cataract and glaucoma, or stroke.

A brain injury can also impair the perception of colors, as the brain processes the sensory input from the eyes.

Some medications, such as certain antibiotics for bacterial infections or drugs used to treat epilepsy may cause temporary color vision deficiencies.

About 8 percent of all men and 0.4 percent of all women have color blindness. These figures include those with mild deficiencies such as red-green color blindness.

True or total color blindness is rare – in German, around 2,700 people are completely color blind (a condition known as achromatopsia).

Following a detailed discussion with the patient about their color vision and any pre-existing diseases, the eye specialist will conduct a number of vision tests. The tests are based on color plates depicting shapes or numbers that differ from the background only in terms of color but not brightness or saturation. This means that a person with normal color vision can detect the hidden shapes or numbers without difficulty.

An electroretinography test, also known as an electroretinogram (ERG), determines how well the retina is functioning. Optical coherence tomography (OCT) is used to examine the internal structures of the eye.

To date, no effective method of curing color blindness has been found.

Specially colored glasses and soft contact lenses in specific shades can relieve light sensitivity, correct impaired clarity of vision and improve the perception of colors. For example, red-toned contact lenses may help a person with a color vision deficiency to distinguish between red and green tones.

Electronic color identification devices can simplify everyday life – for example, by helping people choose the color of their clothes.