Who might have faulty colour vision?
It is usually an inherited condition that mostly affects men and boys. Around 8 males in 100 have some degree of faulty colour vision, compared to with only 1 female in 200. Very rarely, colour vision can become faulty as a result of a medical condition.

How does it affect eyesight?
Most people with faulty colour vision are not colour blind. They are simply less sensitive to particular colours – often green, sometimes red – than those with normal vision. They still see grass as green! But have difficulty distinguishing different shades of green or red. They may also have difficulty if there is only a very small amount of colour, such as in a distant traffic light.

How do we test for faulty colour vision?
The most common test consists of circles made up of coloured dots.  People with normal colour vision can correctly read a number among the dots. This is the “Ishihara” test, which is very good at picking up even tiny defects. We also use other tests such as the City University Test to distinguish moderate and severe defects, although slight defects can pass without any problem. The police often require applicants to the force to take the City University Test, but this depends on the individual Police Force.

Why does it matter?
Most people with a small degree of faulty colour vision go through life with no trouble at all. It doesn’t affect vision or general health. However, certain kinds of work need excellent colour vision:
•    Colour printing
•    Paint matching (such as to repair cars)
•    Driving trains
•    Electrical work
•    Police work
•    Fire service
•    Certain jobs in the armed forces
•    Commercial flying

If a child has faulty colour vision it is useful to find out early as possible as they will have problems with colours in class and teachers need to know. In most cases the defect is so slight it just needs to be borne in mind when considering a career.