My son underwent a medical examination for a job recently. He passed but he was told that he was colour blind. Can you tell me what this means?
Colour blindness, also known as dyschromatopsia, is a condition which affects how some people perceive colours. It is usually present from birth but can often go unnoticed unless formally assessed.
Although sometimes due to a problem with how the brain interprets colour, most sufferers with colour blindness lack certain photo-receptors at the back of the eye. The majority of cases of dyschromatopsia are due to a relative deficiency or abnormality of one of the photoreceptor types, with red/green colour blindness the most common form.
I have three other children, all girls. As I've heard colour blindness tends to run in families, should I have them tested?
Colour blindness is a hereditary condition linked to the x linked recessive gene. This means that it nearly always occurs in men who have the gene. While women can carry the gene and pass it on to their children, they rarely suffer from colour blindness themselves.
Given that your other children are female it is unlikely that they will suffer from colour blindness, but should they have the gene they could pass it on to their own children in time.
What does the test involve?
A variety of tests can be used to detect a reduced ability to perceive certain colours. A series of coloured charts known as "Ishihara plates" are commonly used. These are made up of patterns of small, coloured circles assembled closely together to form a large circle on a white background.
The circles are arranged so that people with normal colour vision will be able to discern a particular number made up of some of the circles in one colour, among the other circles, which will be in a different colour.
People with colour blindness will either see another number completely or none at all, depending on the type of colour-blindness they have. For most people being colour blind is a minor inconvenience rather than a major problem in their lives. The only exception to this rule would be for those whose occupation involves distinguishing colours. For example, airline pilots must have perfect colour vision as the ability to discern colour is an integral part of their job.