Optician India

Welcome to question of the Day #20

How common is colour blindness?

I’ll start by saying that very very few people are colour blind. And those who are have very poor visual acuity, photophobia and often nystagmus. People with these visual and ocular characteristics have monochromatism and they do see everything in shades of grey. People who are frequently referred to as colour blind are actually colour deficient. It is estimated that 300 million people are colour vision deficient. Colour vision deficiency affects approximately 1 in 12 males (8%) and 1 in 200 females. I will continue here with the genetic type of colour vision deficiency while recognising that there are acquired types. The inherited gene comes on the X chromosome from the mother. As it is recessive, if there is another X chromosome then colour vision is normal. Females have two X chromosomes and this accounts for the low incidence of colour vision deficiency. The normal X cancels out the X with the recessive gene. If males have the X chromosome with the faulty gene they don’t have another X chromosome to cancel it.

Colour vision deficiency is often referred to as ‘red/green colour blindness’. I’ve already mentioned that ‘blindness’ is a misnomer. So is the ‘red/green’. This suggests that a person can’t see the colour of anything that is red or green or mixes up things which are red with things that are green. What actually happens is that they mix colours which have an element of red or green as part of the main colour.

Someone who has a red colour vision deficiency will confuse blue and purple because they can’t see the red element of the colour purple. Purple without the red element looks blue. Other colours a person with a red deficiency will confuse are: black with many shades of red; dark brown with dark green, dark orange and dark red; some blues with some reds, purples and dark pinks; mid-greens with some oranges.

A person with a green deficiency will confuse: mid-reds with mid-greens; blue-greens with grey and mid-pinks; bright greens with yellows; pale pinks with light grey; mid-reds with mid-brown; light blues with lilac.

It is important to become aware of a person’s colour vision deficiency from an earlier because many educational activities involve colour coding, e.g. maps and chemical reactions and stories and some careers preclude people with colour vision deficiency. Teachers can take this into account in the classroom. And better to find out you can’t be a fighter pilot aged 4 than aged 18.