Your retina is covered with millions of special cells called rods and cones that process light from the lens. Cones detect colors (people who are colour blind are missing cone cells for a particular color), while the rods process light information. Scientists can guess at how animals perceive vision by counting the rods and cones in their eyes. Cats, for instance, have eight times as many rods as humans but far fewer cones, which explain their excellent night vision and their relative color blindness.
Photoreceptors cells take light focused by the cornea and lens and convert it into chemical and nervous signals which are transported to visual centers in the brain by way of the optic nerve.
In the visual cortex of the brain (which, ironically, is located in the back of the brain), these signals are converted into images and visual perceptions.
Picture Credit : Google