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What is colour blindness?

London - Our perception of colour varies from person to person - so what you think is purple, someone else will think is pink. This is down to the genes governing the retina, the light- sensing cells at the back of the eyes.

In the retina there are three types of “receptors”, which are stimulated by red, green or blue light. Your brain determines what colour it is seeing by working out the ratio between the signals it gets from each of these types of receptors, or cones.

Some people have gene variations that mean their cones are less sensitive or they have a fewer of them, meaning they see colours less vividly or have trouble telling them apart.

In the most extreme cases, they are diagnosed with colour blindness, which affects one in seven men, but only 0.4 percent of women. Women are the “carriers” of the defect, which is passed down via a female X chromosome.

By far the most common type of colour blindness is when you can’t tell the difference between green and red.

But depending on the gene variants at work, other conditions make it difficult to tell the difference between shades of red, or between blues and yellows. - Daily Mail

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