Colour blindness is a slight misnomer and should more accurately be defined as Colour Vision Deficiency (CVD) which is a condition where some people find it difficult to distinguish between different colours under normal lighting conditions. They can normally perceive, or understand, almost every colour in the spectrum but 'shades' of colours can be problematic.
It is usually a genetic or hereditary condition present at birth, although sometimes acquired through ageing, injury to the eye and side effects of some medication. Eye problems like glaucoma (build up of pressure in the eye), cataracts (clouding of the eye lens) or diabetic retinopathy (high blood sugar damaging the back of the eye (retina)) can also contribute to the condition.
Colour blindness affects 1 in 12 men and 1 in 200 women in the world. In Britain 4.5% of people are colour blind. The condition is normally classified as a mild disability but it can affect the future career choices of an individual.
Driving a motor vehicle for instance; some countries in Europe (Romania) and Asia (India) won't allow those with any type of colour blindness to hold a driving licence, particularly for commercial driving. Most people who are red/green colour blind cannot tell the difference between red (stop) and green (go) traffic lights (Fig.1). A person may only be able to tell red and green traffic lights from the position of the lights that are lit - red (stop) is always on the top.
Normal vision is generally essential to becoming a pilot, but depending on the severity of the condition, a mildly colour blind person may still be able to fly following certain tests.
Electricians may have a problem because the electronic wiring, transformers, resistors and capacitors are colour-coded, using black, brown, red, orange, green, yellow, blue, white, silver, violet, grey, white and gold.(Fig.2)
Fire fighters need to be able to identify the variety of colour coded fire safety equipment.
Police officer, essential to have normal vision particularly when someone has to describe an individual and what they were wearing, a bit difficult if they cannot define red or brown.
Hairdressers may have difficulties colouring a customer’s hair. Baggage handlers, since some airlines use colour coded tags for bags to indicate its contents.
The majority of colour blind people are, so-called, anomalous colour blind. That is to say they see colours in a more restricted way compared to colour normal i.e. many colours which look quite distinct to colour normal look quite similar for an anomalous observer. A minority of people with CVD are pure colour blind in that they lack of particular colour sensitive cells (cones) in the back of the eye. Pure colour blind people have a much more severely impaired view of the colour world. There are a third class of colour blind people who lack two (or possibly all) cone sensors. Their vision is mediated by a single cone class or for rod (low-light sensitive sensors) only. However, there are only a small number of people who are truly colour blind and see in monochromatic vision.
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