People with colour vision deficiency are unable to see colours the same way that most people do.
They may have difficulty distinguishing between certain shades of colour, especially between red and green. Colour vision deficiency is often called colour blindness, but true colour blindness is rare: people with colour blindness see no colour at all, with things appearing black and white or in shades of grey.
Colour vision deficiency is more common in men than women affecting approximately 1 in 12 men and 1 in 250 women. In most cases the condition is inherited, although it can also develop as a result of injury, illness or from ageing. Colour impairment can sometimes be caused by the use of some drugs (both medicinal and illicit), alcohol or the fumes from some chemicals.
The three main types of colour vision deficiency are:
Red-green deficiency where people cannot distinguish between certain shades of red and green.
Blue-yellow deficiency where people cannot distinguish between blue and green. Yellow can appear as a pale grey or purple.
Total colour blindness where no colours can be detected. People with this condition have poor sight and are very sensitive to light.
In most cases people are able to adapt to having colour vision deficiency, although some professions such as the Police and Armed Forces require recruits to have normal colour vision.
Your Visique Optometrist is able to assess any colour vision deficiency and its severity.
Above: An example of an Ishihara color test plate. With properly configured computer displays, people with normal vision should see the number "74". Many people who are color blind see it as "21", and those with total color blindness may not see any numbers.