Colour blindness, or colour vision deficiency, is the
inability or decreased ability to see colour, or perceive colour differences
under normal lighting conditions.
There is no actual blindness but there is a lack of colour
vision. Colour blindness affects a significant percentage of the population,
and is much more common in men. It is believed that 8% of the world’s male
population suffers from a degree of colour blindness. In Britain this means
that there are approximately 2.7 million colour blind people (about 4.5% of the
entire population).
Types of colour blindness -
Red-Green Colour Blindness
The most common types of hereditary colour blindness are due
to the loss or limited function of red cone, known as protan, or green cone,
deutran, photo-pigments. This kind of colour blindness is commonly referred to
as red-green colour blindness.
Protanomaly:
In people with protanomaly, the red cone photopigment is abnormal. Red, orange,
and yellow appear greener and colours are not as bright
Protanopia:
In people with protanopia, there are no working red cone cells. Red appears as
black. Certain shades of orange, yellow, and green all appear as yellow.
Deuteranomaly:
In people with deuteranomaly, the green cone photopigment is abnormal. Yellow
and green appear redder and it is difficult to tell violet from blue.
Deuteranopia:
In people with deuteranopia, there are no working green cone cells. They tend
to see reds as brownish-yellow and greens as beige.
Blue-Yellow Colour Blindness
Blue-yellow colour blindness is rarer than red-green colour
blindness. Blue-cone, known as tritan photopigments are either missing or have
limited function.
Tritanomaly:
People with tritanomaly have functionally limited blue cone cells. Blue appears
greener and it can be difficult to tell yellow and red from pink. Tritanomaly
is extremely rare.
Tritanopia:
People with tritanopia, also known as blue-yellow colour blindness, lack blue
cone cells. Blue appears green and yellow appears violet or light grey.
Complete colour blindness
Complete colour blindness is called monochromacy. People
with monochromacy cannot see colour at all and the clearness of their vision may
also be affected.
Colour blindness can be difficult to identify, particularly
in children with inherited colour vision deficiency as they may be unaware that
they have any problems with their colour vision. A child with a severe
condition such as deuteranopia may seemingly be able to accurately identify
colours which they can’t see because they have been taught the colour of
objects from an early age and will know for example that grass is green and the
sky is blue even if they have no concept of their true colours.
In the UK colour blindness is not considered to be a disability,
but in other countries colour blindness can be regarded as a great deficiency.
In Japan, for example, colour blind people can be not permitted to drive
because they are not always able to read coloured lights correctly. You cannot
do the following jobs if you are colour blind –
- Pilot
- Electrician
- Fire-fighter
- Baggage Handler
- Police Officer
Being colour blind shouldn’t have that big an impact of your
day to life, and is usually seen as a very minor inconvenience. Undoubtedly the
most important oversight is the difficulty of colour blind school children who
are left to struggle at school due to lack of awareness of the effects of their
disability.
