What is Colour Blindness?
Colour vision defects are almost always inherited, although some forms 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 have a defect on their one X chromosome they will exhibit a colour vision defect while females must carry the same type of colour vision defect 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.
In the general population, about 8% of males and 0.5% of females have colour vision deficiencies. Almost all colour deficient people do see a large range of colours but they will have difficulty identifying particular colours. The most common defects lead to 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.
Examples of Ishihara Colour Vision Examination Plates :