Colour blindness

                                                             The ishihara test is one of the best tests for clour blindness
The most common form of 'colour blindness' is red-green colour deficiency, which affects 7-10% of people. This is not actually blindness, but a difficulty in distinguishing shades between red and green. It is caused by a change to or loss of the light responsive chemical in certain photoreceptors. Total absence of colour vision, where everything is seen in shades of black and grey, is very rare, and is usually caused by brain damage.colour blindness