Eye. Historical illustration of a cross-section showing the anatomy of a closed human eye. Front is at left. Light entering an eyeball is refracted by the transparent cornea and is then immediately focused by the lens (disc-shaped) that lies behind the cornea. The focused light produces electrical impulses in the light-sensitive retina inside the eyeball. The impulses are transmitted to the brain via the optic nerve (running right from the back of the eyeball). From a German encyclopedia, Bilder Atlas, by Johann Georg Heck, 1860.