The condition is far more prevalent in men than women, with only 0.4 percent of European females being colour deficient. That’s because the condition is linked to the X chromosome.Women have two X’s. If women have one good X, then there’s no problem. Because men only have one X, they are more likely to get the colour deficiency. For most people with colour blindness, it can be frustrating and occasionally dangerous, depending on the severity of the condition.Traffic lights are not so bad because colour blind people get to know the position of the colours. But sometimes caution lights – when there is just one light that could be red or green – can cause a problem. Several tests are available for colour blindness. The most common is the Ishihara test, featuring circles of dots appearing randomised in colour and size. Within the pattern are dots which form a number or a shape that is visible to those with normal colour vision. If someone is not colour deficient, the colours of the dots are clearly different. The test doesn’t rank severity, however. Until recently it was thought that if you were colour blind, you were stuck with it for life. However a professor who worked with Dr Ishihara, the Japanese man who created the original test for colour blindness, has developed his work further. After many years of study he has come up with a new lens that can help significantly. The lens works by separating the peak absorbencies of the cones, taking out the light in the middle. There’s a tint in the lens which absorbs some light but a mirror coat reflects targeted rays of light.It refines the different light allowed through. Thanks to optometrist Molly Whittington. Clockwise from top left you should see 12, 6, 2 and 74. Test yourself The most common test for colour blindness is the Ishihara test.Within these patterns are dots which form a number visible to those with normal colour vision. Can you see them? Resene Pearl Lusta | 41