The site of the optical image in the eye.

Based on good empirical evidence it is generally said that the layer of the retina containing the rod and cone cells is the site where the optical image of the external world falls, and whence the neural signal is transmitted to the brain. The historical path to this idea is traced from the ancient Greeks, through Kepler to modern times. The newer hypothesis suggests that the retinal pigment epithelial (RPE) layer behind the rods and cones may be the actual photoreceptive apparatus. It is supported by clinical pictures, such as retinal detachment and Vitamin A deficiency, and the physical law of Grotthuss and Draper, together with further evidence from recent advances in molecular biology dealing with G protein-coupled receptors, that received the Nobel Prize in 2012.