The retina is sensitive to light and we see things by the light that is reflected off an object, entering our eyes and projecting an image on the retina. The retina is made up of rods and cones, these are light sensitive cells. Rods are very sensitive to light and are situated on the outside corners of the retina; rods work in black and white. Cones however are found in the middle of the eye and whilst they are not very sensitive to light, they are responsible for picking up colour.
Information from the retina travels along the optic nerve to the brain, the informatin goes to both sides of the brain so both paths eventually cross over. This spot is called the optic chaisma. The optic nerves cross the optic chiasma to opposite sides of the brain and they enter a part of the brain called the visual cortex.