What is colour-blindness?

Colour-blindness is a condition where you lack the ability to distinguish between a specific set of different colours, and the state is usually stable throughout your entire life. Red and green are the most frequent colours that affect people who are born color-blind. People who are not born with the condition tend to develop colour-blindness to yellow and blue. A complete loss of colour vision is very rare. For people with colour-blindness to red and green, they will see these colours as one or more grey nuances. In this instance, however, it is rare for people to be completely colour-blind to these colours. Usually, it is only some of the colour nuances which these people cannot distinguish between, and thus colour-blind people should be able to distinguish between the colours in traffic lights. Globally, it affects approx. 1 in 12 men and 1 in 200 women, and there is an interesting explanation for this difference.


What allows you to see colours?

The ability to see colours depends on a specific set of nerve cells in the retina of the eye. The retina consists of two types of nerve cells called ‘rods’ and ‘cones’. The cones enable us to see all the different types of colours. The cones are divided into green, blue and red cones, and together they send signals to the brain, allowing us to see all the colours of the rainbow. The cones are stimulated by light to form chemical reactions through colour sensitive substances, and this is what allows us to distinguish between the colours. This means that if cones, stimulated by green light, are then stimulated simultaneously with rods, which are stimulated by red light, our brain will detect it as yellow. If all cones are stimulated simultaneously, we detect the colour as white.


What are the causes of colour-blindness?

People experience colour-blindness for different reasons. Some people are colour-blind because some of their cones do not function correctly, while others have the condition because the cones are not connected with the brain in a normal way, whereby the brain detects the colours incorrectly. Some may also lack one or more colour sensitive substances, and thus the ability to detect the colours correctly. Usually, this is because of hereditary colour-blindness where a lack of colour sensitive substances can be due to genetic errors. These genes are placed on the X-chromosome, and they are recessive. This means that if you have a healthy gene for colour sensitive substances and a non-functional gene for the substances, you will not be colour-blind. However, if you only have non-functional genes, preventing you from forming the colour sensitive substances, you will be colour-blind.

Men only have a single X-chromosome, and they are therefore more at risk of developing the condition as their ability to distinguish between colours depends on a single gene. Women have two X-chromosomes and therefore two genes for every colour sensitive substances, which means that they can develop a functional and a non-functional gene without becoming colour blind. This explains why men are at higher risk of developing the condition. A man inherits his X-chromosome from his mother, so a colour-blind boy has usually inherited the condition from his non-colour-blind mother. The condition can also be acquired later in life as it can be a result of eye diseases such as cataract, glaucoma or age-conditioned sclerosis in the eye. It can also be due to conditions such as multiple sclerosis, diabetes, leukaemia and Alzheimer’s.  


What are the treatments for colour-blindness?

Currently, it is not possible to treat or prevent hereditary colour-blindness, and it is thus a condition which people must learn to live with. The condition neither improves nor worsens with age. If colour-blindness is caused by a secondary disease, treating the underlying disease can occasionally improve the state in the eye, but it depends on the severity of the disease.

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