Colour Blindness

Colour Blindness Explained

Contrary to its name, colour blindness does not refer to actual blindness, it is a condition in which the ability to properly see colours, or differentiate between them, is either diminished or completely lacking.

In most cases, its origins are purely genetic and affects the development of one or more sets of retinal cones that perceive colour in light. However, in rare cases, it can be caused by injury or specific drugs

Colour blindness affects males much more than females, and is found in 8% of males and 1% of females. While it is typically considered to be a mild disability, there are some circumstances where some types of colour blindness can be advantageous. 

Due to the way colours are processed differently, certain types of camouflage, which are intended to blend in with their surroundings, may appear to stand out more to people with certain types of colour blindness than those with normal colour perception. For example, some colour-blind people can differentiate between two similar colours that most people would perceive as the same colour.

Types of Colour Blindness

In some rare situations, colour blindness can be caused by an injury to the eye, optic nerve, or brain, affecting the ability to process colours properly. Some diseases, drugs, or chemicals can also trigger the condition but are incredibly uncommon. 

A vast majority of colour blindness is genetic, so it is inherited. Depending on the genes inherited and the way their brain and eyes develop will alter the details and parameters of the colour blindness. 

It may be surprising to know that there are quite a few different variations of colour blindness, we list most of the common ones below:-

• Monochromacy – Often referred to as “total colour blindness", monochromacy is the inability to distinguish colours at all. Anyone with this type of colour blindness views the world in black and white, like old television and movies. It is caused when two, or all three, of the cone pigments within the eye are missing or defective, causing colour and lightness in vision to be reduced to a single dimension. Under monochromacy, there are two subtypes.
  
  • Rod Monochromacy – Also called achromatopsia, this form is an exceptionally rare disorder. Those who have this form of colour blindness are totally unable to distinguish any colours as a result of either absent or non-functioning retinal cones. Issues commonly associated with this form are light sensitivity, involuntary eye oscillations, and poor vision.
  • Cone Monochromacy - A rare total colour blindness that usually doesn't affect visual acuity at all, unlike rod monochromacy. However, cone monochromancy can be the result of having multiple forms of dichromatic colour blindness (see below) simultaneously. For instance, someone with both protanopia and tritanopia can be considered to have cone monochromacy.
• Dichromacy - A relatively severe form of colour blindness in which one of the three basic colour mechanisms is either absent or non-functional. It is hereditary in nature, and affects the X chromosome, hence, is it found predominantly in males. There are three subcategories of dichromacy - protanopia, deuteranopia, and tritanopia, each occurring when one of the cone pigments is missing and colour is reduced to two dimensions.
  
  • Protanopia - In reference to the three primary colours, and stemming from the Greek “prot”, meaning “first”, this form of dichromacy is caused by the complete absence of red retinal photoreceptors. People with this form of colour blindness have difficulty distinguishing between blues and greens, as well as between reds and greens. Completely pure red cannot be seen at all and appears black. Purples and blues cannot be distinguished from one another, and orange-reds appear like very pale or dim yellows. It is hereditary and present in only 1% of males.
  • Deuteranopia - “Dueter”, Greek for “second”, refers to the next primary colour, green. This form of colour blindness is caused by the absence of green photoreceptors within the eye. It affects differentiating between colours much in the same way as protanopia but without the dimming effect. Like protanopia, it is found in about 6% of the male population, not in females.
  • Tritanopia - “Trit”, Greek for “third”, refers to blue, and the complete lack of colour receptors responsible for detecting it. This form of colour blindness is very rare, and involves the presence of only two cone pigments, red and green. For people with this form, blues appear greenish, yellows and oranges appear pinkish, and purple colours appear deep red. It is hereditary, but unlike protanopia and deuteranopia, tritanopia is not sex-linked, meaning it appears in both males and females.
• Anomalous Trichromacy – A more common type of colour blindness, it is hereditary in nature, and involves one of the three cone pigments being less sensitive, rather than completely absent or damaged. The symptoms are very similar to their dichromacy, but less severe.
• Protanomaly - A mild form of colour blindness in which the sensitivity of red retinal receptors is diminished, but not absent. The result is poor discrimination between reds and greens. It is hereditary and sex-linked, and present in 1% of males.
• Deuteranomaly, - By far the most common type of colour blindness, this form of colour vision deficiency mildly affects the discrimination of reds and greens. It is found in approximately 5% of European males, but not females.
• Tritanomaly - A very rare form of colour blindness that mildly affects discrimination of blues and greens, as well as yellows and reds. Like all the other forms, it is hereditary, but can be found in both males and females alike.

What Causes Colour Blindness?

The vast majority of colour blindness is due to genetics, with the condition being passed down from parent to child. In fact, there are at least 19 different chromosomes and 56 individual gene mutations that are capable of causing colour blindness. Because of the nature of these anomalies, which are typically linked to the X chromosome, they affect men far more than women. If a mutated X chromosome is inherited by a woman, the second, normal X chromosome can override it, resulting in normal vision. Men, however, only have one X chromosome and will be affected should they inherit a mutated gene.

Hereditary forms of colour blindness can be present at birth or may develop sometime during childhood, adolescence, or even adulthood. Different genetic mutations have different ways of affecting vision, not just in terms of colour identification, but in the progression of the condition. Some forms will stay consistent throughout life, while others may worsen over time.

In far fewer instances, colour blindness can be caused by injury, or another form of trauma. Brain or retinal damage can certainly affect vision, as well as any type of injury that causes swelling in the occipital lobe of the brain. Prolonged exposure to UV light can also lead to colour blindness. Not all of these injuries will result in colour blindness immediately, as the damage may not present itself until later on in life. Colour blindness can also be caused by a serious deficiency in vitamin A.

How Is Colour Blindness Diagnosed?

There are various test that can be used to detect colour blindness, the most common are:-

• Ishihara Colour Test
  This is the most popular test to detect red-green colour blindness, which consists of a series of images comprised of coloured spots. A figure, such as a letter or a number, is "hidden" in the image, composed of one colour of spots while being completely surrounded by an alternate colour. With normal visual abilities, the image will appear to stand out and can be identified easily. However, with a condition of colour blindness, the image may not be perceived at all. Different colours and contrasts are used to isolate different forms of colour blindness.
  One of the disadvantages of this test is that it relies on the subject’s ability to identify numbers or letters, which means it isn't useful for use with small children who have not yet learned those symbols.
• Farnsworth Lantern test
  Several branches of the United States military use the Farnsworth Lantern test, which allows anyone with mild colour blindness to pass. Approximately 30% of all colour-blind people who attempt the Farnsworth Lantern test pass.
• Farnsworth-Munsell 100 hue test
  This involves arranging a set of coloured objects in order, which is based on a transitional colour gradient. Two distinct colours are placed at either end, and you have to arrange the other items in an ordered fashion between them. Those with difficulty distinguishing between some colours will unlikely be able to complete the test accurately.

Possible Treatment For Colour Blindness?

Unfortunately, there is currently no cure for colour blindness. There are lenses available, both contact lenses and eyeglasses, that will help differentiate between colours that might otherwise appear very similar or even identical, but they can not help the wearer perceive the true and accurate colour. In some cases, the coloured lenses might make it easier to distinguish between some colours, but harder for others.

Modern technology is providing some solutions, however. Often referred to as “colour blind mode” computers, tablets, and cell phones can adjust the colours they display to those more easily recognized by the user. While the image on the screen may not be an accurate representation of the original work, it can be tailored to individual types of colour blindness, making the device more usable and less confusing.

Researchers have successfully used gene therapy to cure red-green color blindness in adult squirrel monkeys, which naturally only have dichromatic vision. By using gene therapy, they have been able to alter the monkey's eyes, enabling trichromatic vision, like humans. There is still much more research and testing needed, but this shows promise for possible future treatments of colour blindness in humans. 

If you want to find out more about colour blindness check out the Colour Blindness Awareness website, they are a non-profit organisation intended to be the main source of information for those seeking to find out more about colour blindness worldwide.