Optics and physiology of vision. Illustration showing how the eye (centre) focuses light from a candle (far left) onto the retina, a layer of light-sensitive cells on the back of the inside of the eye. The lens at the front of the eye focuses the image, and also inverts it. Photochemical responses in the retina are converted to nerve signals that travel along the optic nerve to the brain (far right), where the neural information is processed in the visual processing centre in the occipital lobe (yellow). This results in the sensation of vision.