Sight, illustration. Light enters the eye through the pupil and is focused by the lens (white circle) onto the retina, the photosensitive membrane at the back of the eye. Contraction or relaxation of the muscles and ligaments controlling the lens, focuses it on near or far objects. The retina converts the light into electrical signals that are sent via the optic nerve to the visual cortex at the back of the brain where the information is processed.