Color Blindness: What It Is, Types, and How It Is Detected

Color blindness is a feature of vision in which a person sees colors differently from most people around them and has difficulty distinguishing certain shades. Let us calmly and systematically explain what this condition is, what forms it takes, and how it is tested.

What color blindness is

Color blindness is the term for a reduced ability or complete inability to distinguish all colors or certain ones. The name comes from John Dalton, who in 1794 described one type of color blindness based on his own perceptions. Color perception is provided by cones — light-sensitive nerve cells in the center of the retina, the inner lining of the eye. There are three types of cones, each with its own pigment — conventionally "red," "green," and "blue." People with all three working pigments are called trichromats, and it is the combination of the three signals that gives the full variety of hues. If one pigment is absent or scarce, a person cannot distinguish some shades.

Types of color blindness

There are three main groups: red-green deficiencies, blue-yellow deficiencies, and complete absence of color vision — achromatopsia. The red-green type is more common than the others. In achromatopsia, colors are not distinguished at all, and in addition visual acuity may be reduced and discomfort may occur in excessive light.

If a pigment is completely absent, a person distinguishes only two primary colors; such people are called dichromats. Absence of the red pigment is protanopia, absence of the green pigment is deuteranopia, and absence of the blue pigment is tritanopia. When the pigment is present but its activity is reduced, this is called anomalous trichromacy: protanomaly, deuteranomaly, or tritanomaly. Red-green deficiencies account for up to 8 percent of men and 0.5 percent of women of Northern European origin.

Why color blindness occurs: causes

Most often color blindness is hereditary. The genes responsible for the most common forms lie on the X chromosome, one of the sex chromosomes. Women have two of them, and a defect in one is usually compensated by the second; men have one, so the disorder manifests in them about twenty times more often. It is often passed from a mother — a carrier of the gene — to her son.

The acquired form occurs with damage to the retina or optic nerve and is characterized by gradual deterioration: blue and yellow colors become increasingly difficult to distinguish. Causes include clouding of the lens (cataract), use of certain medications, eye injuries, as well as glaucoma, diabetes mellitus, liver disease, multiple sclerosis, and stroke. The exact mechanism of the hereditary form is unknown; it is believed to involve disruption of signal transmission from the eye to the brain.

How color blindness manifests in a person

The main sign is difficulty distinguishing some colors from others. Shades are confused when choosing clothes, it is harder to pick ripe fruit or read information conveyed only by color. In a child, the feature can be suspected from everyday details:

• draws with unusual colors, for example purple leaves on trees;
• has difficulty when objects need to be sorted by color;
• shows no interest in coloring;
• smells food before eating it.

A person may not know about their feature for many years. Because of it, in some countries they are not hired for jobs where color is important for safety: pilot, train driver, crane operator, service in the armed forces. At the same time, most people adapt, and they have no noticeable limitations in everyday life.

How color vision deficiency is diagnosed

There are two main tests. The first is the Ishihara plates: a person reads images made up of colored dots. The second is color arrangement: objects are placed in order of shades. Such a test is not part of a routine vision examination, but it can be requested. Online tests exist, but if there are doubts, the examination is performed by a specialist. Genetic testing is also possible.

When to see an ophthalmologist

The reason is any signs of color vision deficiency in you or your child. A separate reason is if colors have become harder to distinguish, suddenly or gradually, against the background of a known disease or medication use: this may be a sign of an acquired disorder.

Color blindness itself is not a reason to call an ambulance. Numbers 103 and 112 are needed if color vision deficiency occurs after a head or eye injury, as well as with signs of stroke.

This material is for reference: it helps to understand the essence but does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer