A routine part of our eye examinations is an assessment of colour vision, especially for children.
Colour blindness is almost always inherited, although it can be acquired condition as a result of some diseases or injuries.
The abnormality is sex linked, recessive, and carried on the X chromosomes. This means that males need only have their one X chromosome affected to be colour blind while females must carry the condition on both their X chromosomes to be colour blind. If females have it only on one X chromosome they will carry the condition but still have normal colour vision themselves.
As a result, about 8% of males and 0.5% of females have colour vision deficiencies. Almost all colour deficient people do see most colours but they will have difficulty identifying particular ones, confusing certain shades of red and green for example.
As children, few of these people will be aware that they have a colour vision deficiency but the detection of these problems is important, especially when career choices are affected.