What is Colour Blindness?


More appropriately referred to as Colour Vision Deficiency (CVD), colour blindness is not related to blindness at all, but rather is a deficiency in the way you see colour. The condition is far more prevalent in men than women, with around 8% of men having some form of CVD and only around 0.4% of women showing any signs of CVD.

Normal colour vision utilises three types of light cones to correctly interpret variations in colours. This type of colour vision is known as Trichromacy. When one of these three types of light cones doesn’t function properly in some fashion, this is known as Anomalous Trichromacy, and this is further broken down into three classifications based on which light cones are misaligned. Protanomaly is reduced sensitivity to red light, Deuteranomaly is reduced sensitivity to green light, and Tritanomaly, the rarest form of colour vision deficiency is reduced sensitivity to blue light.

Red-Green Colour Vision Deficiency

Resulting from either protanomacy or deuteranomaly, red-green CVD makes it difficult for people with the condition to differentiate between red and green hues as well as altering perception of other colours such as pink, purple, orange or yellow. There are some variations between red and green colour blindness. People with irregular red cones will commonly have trouble differentiating some shades of red from black, dark brown with dark green and some shades of green with some shades of orange. People with irregular green cones  are likely to confuse mid red with mid green, bright green with yellow, blue-green with grey or pink, and light blue with lilac or light purple. 

Blue-Yellow Colour Vision Deficiency

The result of tritanomaly, blue-yellow colour vision deficiency is rare, only affecting around 1 in 10,000 people. Unlike other forms of colour vision deficiency, inherited tritanomaly isn’t linked to the X chromosome, so it’s equally present in both females and males. People with blue-yellow CVD will commonly have difficulty differentiating between yellow and pink, grey or light purple, light blue and grey, deep purples and black, and green and blue.

Monochromacy (Achromatopsia)

Very rarely people are unable to perceive colour at all. This condition, known as monochromacy or achromatopsia only affects around one in 33,000 people and renders them incapable of seeing any colour, instead presenting all vision in shades of grey, kind of like a black and white movie that you can’t turn off. The condition is caused in one of two ways - either through a deficiency in two types of light cones, or through a deficiency all three forms of light cone leaving only rods in the retina. Cone monochromats - people with both rods and one kind of cone in the retina - can’t see any colour but typically have good pattern vision in normal light levels. Rod monochromats - people with only rods in the retina - are unable to see normally in daylight and often have to wear dark glasses around any kind of illumination. 

While many people with a form of colour vision deficiency can function perfectly normally and may not even know they have the condition, there may be some difficulties that pose a problem with work or everyday activities. While there are few avenues that are cut off for colour blind people in Australia, there may be some additional restrictions placed upon them. For example, there are no restrictions on obtaining a driver’s licence for most people with colour vision deficiency, but some red-green colourblind people may be restricted from driving at night due to difficulty reading traffic lights. Certain positions in the defence force or police may not be available to those with CVD. You must also pass certain colour vision tests to become a pilot.


If you’d like your colour vision tested, the easiest way to book an appointment with an optometrist near you is to book online with MyHealth1st.


Causes of Colour Vision Deficiency

The most common cause of colour blindness is genetic. Both protanomaly and deuteranomaly are linked to the X chromosome making the inheritance far more common in men than in women. How this works is as follows: all males with red-green colour vision deficiency will pass this gene onto all their daughters, however these daughters will usually not be colour vision defective themselves. But statistically, half these daughters’ sons *will* carry the gene and have defective colour vision.  Blue-yellow colour vision deficiency isn’t linked to the X chromosome so is equally common across both sexes. 

Outside of inheritance there are a number of factors that can lead to different forms of colour blindness. These potential causes include:

  • Cataracts - The clouding of the eye’s natural lens that occurs with cataracts can lead to deficiencies in colour vision, ranging from a general washed out colour palette to more specific difficulties perceiving some hues. This vision deficiency is curable through surgery
  • Solvents - Long term exposure to some solvents has shown to increase anomalies with colour vision, especially in the blue-yellow spectrum.
  • Medication - Some medications can reduce colour perception while it is being taken. The anti-seizure drug, tiagabine, is an example of one such medication and has shown to temporarily impair colour vision in around 40% of people taking it.
  • Head Trauma - Damage to the brain or retina caused by injury can lead to colour vision deficiency.
  • Age-related Macular Degeneration - A tiny central section of the macula known as the fovea contains the highest number of cones in the retina. This concentration of cones is responsible for the majority of detailed colour perception. Damage to the macula due to degeneration can affect the retina’s ability to perceive colours.
  • Disease - A number of diseases, including degenerative eye diseases like AMD, LHON (Leber’s Hereditary Optic Neuropathy), glaucoma, diabetic retinitis and retinitis pigmentosa, and others such as Parkinson’s disease, Alzheimer’s disease, sickle cell anemia, multiple sclerosis and chronic alcoholism can all lead to either eye damage or changes in the brain causing forms of colour blindness.  
  • Age -  Age related damage to retinal cells can also lead to difficulties differentiating between colours. 

“Simple” colour vision deficiency is relatively safe. You’re typically born with it, and it doesn’t change as you grow up and age. So if you do notice any changes to your colour vision, you really should check with your optometrist, as there may be more serious underlying changes that may need treating.

Treatment for an Living With Colour Vision Deficiency

There is no current cure for hereditary colour vision deficiency, but there is a potential genetic treatment still undergoing testing. Gene therapy has been shown to have a positive effect on red-green colour blindness in adult primates , but it will still be some time before human trials. 

For some people, vivid colour vision can be achieved through the use of special lenses that filter wavelengths of light giving users the ability to more easily differentiate between colours giving them the ability to perceive colour in a much clearer way. While not necessarily a “cure” for colour vision deficiency, being able to better understand the differences between hues allows people with the condition to do some things that people with typical colour vision take for granted.

 

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