Light enters the eye through a transparent window in the sclera called the cornea. The light is then focused by an elastic lens just behind the iris.

An image of what the eye is seeing is projected onto the retina at the back of the eye. The light forming this image stimulates special nerve cells in the retina.

Nerve fibres from these cells leave the eye through a group of perforations in the sclera, at the blind spot, to form the optic nerve. This carries the stimuli from the eye to the brain.