There are an estimated 350 million people in the world with red-green colour blindness (deutan-type and protan-type vision deficiency), or 4% of the total population. Red-green colour blindness is acquired genetically through your parents and is expressed by genes on the X-chromosome. Because of the X-linked recessive biology behind red-green colour blindness, the condition affects mainly men: about one in 12 men (8%), but also includes about one in 200 women (.5%).

Less precise statistics are known about blue-yellow colour deficiency, which is most often caused by progressive or age-related eye conditions. Some estimates place the total number at least as high as those for red-green colour blindness, and may be increasing due to the trend toward an aging population demographic worldwide.

The more rare forms of colour blindness include achromatopsia and progressive eye diseases, such as retinitis pigmentosa. Estimates of these conditions are about 1 in 2000 people, or lower, but are known to be greater in certain subpopulations.

The most common types of colour blindness are the red-green types which are also called protan ("pro-tan") colour blindness and deutan (“do-tan”) colour blindness (see Types of Colour Blindness for more information about these). Red-green colour blindness is an inherited condition caused by recessive genes on the X-chromosome. These genes cause a molecular substitution to be expressed in the retinal photopigment molecule, which in turn, causes its spectral absorption to be shifted in such a way that the available information is reduced (we also call this an “overlap”).

Colour vision also declines with age. Studies have shown the Total Error Score on the FM-100 colour vision test increases from about 100 at age 20 to over 200 by age 70.

Colour blindness and colour vision deficiency can also be caused by natural aging processes in the eye, and by low vision disorders such as glaucoma, cataracts, and macular degeneration, as well as metabolic and vascular diseases.

Colour vision loss can also be a side effect of drugs, or a result from exposure to neuro-toxic chemicals such as styrene, perchloroethylene, toluene, carbon disulfide, n-hexane, and mercury.

Our eyes have two kinds of specialized light receptors (rods and cones) located in the retina in the back layer of the eye to help us see. Rods allow us to see in low light conditions, like at night. Cones allow us to see in bright light, like during the day—and convert light into colour vision.

There are three kinds of cones that translate light into colour, each with a range of sensitivity to blues, greens, and reds. If we look at the cones of a person with typical colour vision, their cones will be arranged in a way that is only slightly overlapping, as seen in the graph below. The three separate regions of colour response enable human colour vision to see up to 1 million distinct shades of colour. In people with colour blindness (specifically, red-green colour blindness), there is a greater overlap, sometimes to the point of complete overlap, between the red and green cones.

When the curve of the cone sensitive to greens shifts its sensitivity to the right, it causes an excessive overlap of the green and red making the green cone act more like a red cone (this describes deutan-type colour blindness; for protan-type the red cone shifts to the left). Because this cone is no longer sensitive to the greens and other wavelengths that help to make up more colours, this reduces the colours seen and causes a dullness in the way the world's colours appear. Instead of responding separately to reds and greens, the red and green cones’ responses are highly similar. This result is colour confusion between specific colours, including blue versus purple, and green versus brown, yellow, orange, and red. That’s why some people with colour blindness may have trouble discerning the red and green in traffic lights. The more the cone’s sensitivity shifts, the more colour confusion ensues.

The most common type of colour blindness, red-green colour blindness which includes protan-type and deutan-type colour vision deficiencies, is a genetic condition. 1 in 12 men have this common form of colour blindness, while only 1 in 200 women have it. That’s because the genes responsible for this type of colour blindness are located on the X chromosome, and men have only one X chromosome. If the recessive trait is present, they are colour blind. A woman must have this recessive trait on both of her X chromosomes to be colour blind. If only one, then it doesn’t affect her, but she can pass this onto a male child.  

Women can be carriers of the colour blind gene and pass the mutation down the family line. If only the father is colour blind, there is a 100% chance that his daughters will carry the gene, but they will not be colour blind themselves. His sons will neither carry the gene nor be colour blind. If the mother carries the gene but is not colour blind, there is a 50% chance that her sons will be colour blind and a 50% chance that her daughters will carry the gene.

When a colour blind father and a mother who carries the colour blind gene have children, there is a 50% chance that their sons will be colour blind. Their daughters, however, will have a 50% chance of being colour blind and 100% chance of being carriers of the gene. Alternatively, a colour blind mother and a non-colour blind father will have all colour blind sons and will have daughters who all carry the colour blind gene. Finally, if both parents are colour blind, their sons and daughters have a 100% chance of being colour blind and their daughters have a 100% chance of carrying the gene.

Some types of colour blindness increase with age or develop as a symptom of certain diseases or exposure to toxins like mercury and are not linked to heredity.

The primary symptom of colour blindness is colour confusion, which means that the person may mis-identify a colour as being something other than what people with “normal colour vision” see. Another symptom is that details or objects may be overlooked or not readily seen if they have a colour that is confused with other colours in the surrounding visual scene. Colour blindness is not known to be correlated with other eye conditions such as myopia, nor with learning disabilities.

If you can’t see any colour at all and see only in shades of gray, you may have the rare condition called achromatopsia. Read more about Types of Colour Blindness.

As a person with colour blindness, colour confusion can show itself in many everyday tasks, resulting in frustrating outcomes such as a mismatched outfit, questionable paint choices, incorrect colouur naming and difficulty interpreting colour coded information such as charts, graphs and maps, which may cause problems at school or work.

Another task that can be frustrating is driving a car when colour blind since for the colour blind person, green light tends to look very pale green or nearly white, and red light may seem closer to orange. Colour blind drivers often say they look more for the traffic light’s position or to what other cars are doing on the road, rather than at the colours of lights.

Although there is no cure or treatment for inherited colour blindness, there are a number of things that colour blind people can do to cope. For school children with colour blindness, accommodations can be made in the classroom so that the colour blind student is on a more equal footing with their peers. Awareness of the condition by teachers and students is important to facilitate an optimal learning environment. Although adults with colour blindness may be excluded from certain jobs depending on the country where they live (airline pilot, graphic designer and electrician for example) in many jobs a person with colour blindness can find creative strategies to perform colour-dependent tasks, such as using an app to identify colours, getting help from co-workers, or using EnChroma glasses to aid colour discrimination.

Perhaps the most dramatic example of helpful tools for the colour blind are colour blind glasses from EnChroma. EnChroma has developed optical lens technology that selectively filters out wavelengths of light at the precise point where the confusion or excessive overlap of colour sensitivity occurs. This increases contrast between the red and green colour signals, alleviating symptoms of colour blindness for a richer experience of the world.

EnChroma colour blind glasses are uniquely engineered to give those with colour blindness the ability to see a broader spectrum of bright colour. Utilizing a patented light filter technique, EnChroma’s lens technology is applied with mathematical precision to address common forms of red-green colourblindness. Although EnChroma glasses are not a cure, they are helpful for approximately 80% of people with colour blindness. Learn more about How EnChroma Glasses Work.

If colour blindness is caused by a medical condition, treating the underlying disease may help so EnChroma recommends that people get a comprehensive eye exam from a qualified eye care professional.

EnChroma's colour blind lens technology selectively filters light to increase contrast between the red and green colour signals to account for the overlap and alleviate symptoms of red-green colour blindness for a richer, more colourful experience of the world.

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