How do photoreceptors work?

Photoreceptors contain chemicals that change when they are hit by light. This causes an electrical signal, which is then sent to the brain along the optic nerve. Different types of photoreceptor allow us to see an enormous range of light: from starlight to full sunshine, and all the colours of the rainbow.

Back to top


Photoreceptors in the eye.

What is colour 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.

Back to top


An Ishihara colour-blindness test.


Principal Funder:

Wellcome trust

Major Sponsors:

GlaxoSmithKline life technologies