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your life: My son found out he's colour blind; Ask the Doc.

Byline: Dr James Briscoe

Q MY son has recently turned 17 and has found out that he is colour-blind. What is colour blindness, how is it caused, is there any treatment for it and are there any careers he will need to avoid because of it?

PAUL, Warwick

A ABOUT one in 20 men (and one in 200 women) is affected by colourblindness, Paul.

The condition occurs due to a defect in the perception of light by the retina.

White light is made up of three beams - red, green and blue all combined in equal proportions. If these three beams of light are combined in unequal proportions, other colour hues are produced.

A colour-blind person cannot tell the difference between two of the primary colours and most have a distortion in the hues produced by the primary colours.

The most common form is red/green colour blindness, which involves the confusion of red and green.

A person with red/green colour-blindness perceives different shades of red as dull and indistinct. Greens, oranges, pale reds and browns all appear as the same hue, distinguished only by their intensity.

A more serious condition occurs if there is no colour discrimination at all. For these people, life is seen in black and white.

The reason why people are affected with colour blindness is due to how the retina interprets lightwaves.

At the back of the retina are light receptors, known as cones, of which there are about 130 million.

About seven million of these are used to detect colour vision.

There are three types of cones that operate in people with normal colour vision: those that respond best to long wavelengths of light (red), those that respond to middle wavelengths (green) and those that respond to short wavelengths (blue).

Damage to the optic nerve that affects the cones' message to the brain can cause colour blindness. It has been shown that certain drugs, such as alcohol, tobacco, LSD and oral contraceptives can also affect colour vision.

The ageing process can also affect colour perception, especially with regard to blue light. Most colour-blind people, however, are born with the defect.

The Ishihara test is used to detect colourblindness.

A card made up of a background of dots of one colour with a wavy pattern or a number spelled out in dots of a different colour is shown. A colour-blind individual will not be able to differentiate between the colours so cannot pick out the pattern from the dots.

There is no treatment but colourblindness need not stop someone driving, because traffic lights can be distinguished by the position of the light.

It can, however, be an obstacle to particular careers where good colour vision is important, including pilots, electricians, train drivers and some jobs in the printing, fashion and design industries.

If YOU have a question about health and wellbeing, write to: Ask the Doc, Sunday Mercury, Weaman Street, Birmingham B4 6AY, or e-mail SundayMercury@mrn.co.uk
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Title Annotation:Features
Publication:Sunday Mercury (Birmingham, England)
Date:Dec 2, 2007
Words:494
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