Light micrograph of a section through the optic nerve (centre to bottom left) as it leaves the ocular bulb (eyeball) via the optical canal. The optic nerve collects impulses from the light sensitive cells of the retina and relays them to the brain. The retina, which contains the light sensitive cells is across centre (dark blue) and the sclera, the white of the eye, is pink. The choroid (black) lines the inside of the eye and prevents light from reflecting and distorting the image. There are no light sensitive cells where the optic nerve joins the retina, resulting in a blind spot. Magnification: x40 when printed at 15cm wide.