What Is

Colour Blindness

What Is

Colour Blindness

Colour. It affects every part of our lives. Colour is emotional, experiential, and tactical. It gives art life. It entices us to eat certain foods and buy certain jewelry, and sometimes it literally defines these things. We also use colour to interpret information such as signs and lights. It is deeply ingrained in our basic perception of the world. When the ability to see colour is deficient, as in the case of colour blindness, there is a dulling of what is seen; or one might say there is a dulling effect in how we see.

Definition of Colour Blindness

Colour blindness is a reduced ability to distinguish between colours when compared to the standard for normal human colour vision. When a person is colour blind, also called colour vision deficiency (CVD), they usually have difficulty distinguishing between certain colours such as yellow and orange, green and brown, pink and gray, or blue and purple. These confusions are typical of what is called “red-green colour blindness,” which includes protan-type CVD (protanomaly and protanopia) and deutan-type CVD (deuteranomaly and deuteranopia). Red-green colour blindness is usually inherited via X-linked recessive genes. Other types of colour blindness exist also, such as tritan-type CVD, also called blue-yellow colour blindness, which is associated with the inability to see shades of blue, and confusions between blue and green colours. Blue-yellow colour blindness is usually caused by age-related eye conditions such as glaucoma, or exposure to certain chemicals or medical treatments. In very rare cases, a person can be completely colour blind, meaning they see only the intensity of light, but not its colour. This is called monochromacy or achromatopsia. Achromatopsia can be inherited but can also result from progressive eye diseases such as retinitis pigmentosa. In summary, there are many types and degrees of what can be considered “colour blindness,” ranging from partial to complete lack of colour discrimination.

To learn if you are colour blind, take the EnChroma Colour Blind Test. If you have colour blindness, our test can tell you your type of colour vision and if your colour vision deficiency is mild, moderate, or strong — in less than two minutes.

Normal Colour Vision

Colour Vision Deficient

Image colours are simulated. Colour Vision Deficiency varies by individual.

What Do Colour Blind People See?

Many assume because of its name that “colour blind” means a person can only see in black and white. In actuality, the vast majority of people with colour blindness do see colour, but they see a much smaller range of shades of colour compared to a person with normal colour vision. In addition, a person with colour blindness may miss out on details or not notice objects that would normally be plainly visible, because the colour of the details or object is confusingly similar to surrounding visual context. A classic example is not noticing a ripe red apple in a tree when it is surrounded by green leaves.

Humans have three primary types of light receptor cells in the retina that respond broadly to red, green, and blue light. Signals from these receptor cells form the basis of colour vision, by transmitting neural signals to the brain about the relative amount of each primary colour to the visual cortex. It is estimated that the human visual cortex can perceive about 100 levels of sensitivity for each primary channel: 100 x 100 x 100 = 1 million, which is where we get to 1 million perceived shades of distinct colour.

Normal Colour Vision

Normal Colour Vision

Normal Colour Vision

Colour Blind View

Colour Blind View

Colour Blind View

However, if a person is colour blind, for example having red-green colour blindness, then the red and green primary channels have an overlap in their signals causing the channels to contain almost the same information. In the most extreme case, called dichromacy, the red and green channels are completely indistinguishable, such that the total number of colours that can be seen is just 100 x 100 = 10 thousand or just 1% of the normal range. Most people with colour blindness have only a partial loss of sensitivity, meaning the information is there, but is harder to notice. Depending on the severity, the number of unique shades of colour that can be seen is more often estimated to be around 10% of normal.

How Many People are Colour Blind?

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.

Types of Colour Blindness

Colour blindness or colour vision deficiency (CVD) includes a wide range of causes and conditions and is actually quite complex. Usually when people talk about colour blindness, they are referring to the most common forms of red-green colour blindness, which are genetic conditions caused by a recessive gene on the X-chromosome, but there are other types as well.

What Causes Colour Blindness?

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.

How Spectral Overlap Causes Color Blindness

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.







What Are the Genetics of Colour Blindness

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.

What Are the Symptoms of Colour Blindness?

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 colour 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.

What Are Coping Strategies and Solutions for Colour Blindness?

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 colour blindness. 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.

Testing for Colour blindness

If you or a family member are having problems recognizing or distinguishing between colours that other people seem to see, it’s easy enough to determine whether you are colour blind without visiting a doctor. The EnChroma Colour Blind Test is an online colour blind test designed to estimate the type and level of colour blindness. Created by EnChroma, an independent company based in California, the EnChroma colour blind test is the #1 online colour blind tool for colour vision deficiency that has so far been taken by more than one million people worldwide.

The EnChroma test is based on the classic and widely-used Ishihara “hidden digit” test method and is combined with a computer-adaptive algorithm to measure the type and level of colour vision deficiency (CVD). It is available in a numbers mode for adults and children ages 10+ and in a shape mode for kids ages 5+.

The Ishihara test for colour blindness is named after ophthalmologist Shinobu Ishihara who invented the test for the Japanese army in 1917. Ishihara has been a good screening test, but it is 100 years old and does not leverage the benefits of today’s computer-based adaptive testing protocols. The EnChroma test deters memorisation and cheating and can be self-administered on a phone or laptop.

Who Should Take a Colour Blind Test?

Since the EnChroma Colour Blind Test is easy, quick and free, it’s really something that anyone can do to satisfy their curiosity about their colour vision. In some cases, colour vision deficiency can be very mild and may not be noticed until it becomes a problem, such as when applying for a job that requires a high degree of colour discrimination. Anyone with a family history of colour blindness should consider taking the test. For certain professions where colour perception is an important factor, including electricians, pilots, designers, and artists to name a few – a colour blind test can identify potential issues that might crop up in the course of employment.

Fun Facts About Colour Blindness

The world of colour vision is full of intricacies and interesting facts. At EnChroma, we want you to know everything there is to know about being colour blind. So here’s a list of some of the most fun facts we know about colour blindness.

Babies are born colour blind! As they grow, their colour vision improves and is typically fully developed by the age of 6 months. Overall colour discrimination capability reaches its peak by age 20, and then starts to decline again.

Dogs & Colour Blindness: Contrary to popular belief, dogs don’t actually see in black and white. Dogs are dichromats, which means they have two types of cone cells, and see in mostly blue and yellow. Their vision is somewhat similar to that of a person with protanopia.

People who are red-green colour blind are often surprised to find out that peanut butter is NOT green! Green and brown is a common colour confusion that seems to be particularly relevant to the shade of peanut butter. Also, because colour blind people have a hard time distinguishing between green and yellow, they often have a hard time knowing when a banana is ripe. Many are accustomed to the bitter taste of an unripe banana!

To the normally sighted person, a rainbow features all the colours of the rainbow. For many colour blind people, however, a rainbow only appears to have 2 bands of colour: blue and yellow.

To a colour blind person, the green light on a stoplight may appear white or even blue, while the red and yellow lights may look similar to each other.