How does our vision work?

The eye is often compared to a basic camera, and indeed the
very first camera was designed with the concept of the eye
in mind. We can reduce the complex process that occurs to
process light into vision within the eye to a relatively basic sequence of
events. First, light passes through the cornea, which refracts the light
so that it enters the eye in the right direction, and aqueous humour,
into the main body of the eye through the pupil. The iris contracts to
control pupil size and this limits the amount of light that is let through
into the eye so that light-sensitive parts of the eye are not damaged.
The pupil can vary in size between 2mm and 8mm, increasing to
allow up to 30 times more light in than the minimum. The light is
then passed through the lens, which further refracts the light, which
then travels through the vitreous humour to the back of the eye and is
reflected onto the retina, the centre point of which is the macula.
The retina is where the rods and cones are situated, rods being
responsible for vision when low levels of light are present and cones
being responsible for colour vision and specific detail. All the light
information that has been received by the eye is then converted
into electrical impulses by a chemical in the retina called rhodopsin,
also known as purple visual, and the impulses are then transmitted
through the optic nerve to the brain where they are perceived as
‘vision’. The eye moves to allow a range of vision of approximately 180
degrees and to do this it has four primary muscles which control the
movement of the eyeball. These allow the eye to move up and down
and across, while restricting movement so that the eye does not rotate
back into the socket.