Health encyclopaedia

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Colour vision deficiency

Colour vision deficiency, sometimes inaccurately called colour blindness, occurs when the cells in the retina of the eye which respond to light (cones) are abnormal or not working as well as they should.

The three types of cones are commonly known as red, blue and green, although they actually differ in their ability to recognise high, medium and low wavelength light.When they do not pick up or relay the proper colour signals to the brain, colour deficient vision results. Approximately 8% of men and 1% of women have some form of colour vision deficiency.

There are three main types of colour deficient vision:

• Red-green deficiency (deuteranopia) is the most frequently diagnosed deficiency. Those with this condition cannot distinguish certain shades of red and green.
• Blue deficiency (protanopia) is relatively rare. Blue and yellow are not distinguished by those with this condition, and may be seen as white or grey.
• Total colour blindness (achromatopsia) is extremely rare. In this condition, no colours can be detected and the world is viewed in shades of black, white and grey. People with this condition have poor sight and are extremely sensitive to light.

• Symptoms
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