Retina of eye. Light micrograph showing the layers of the retina of the eye in cross section. Light would enter the retina from the bottom of the micrograph. To reach the light-sensitive rod and cone cell layer (top, purple) light must pass through layers of nerve cells and their processes. These include a layer of optic nerve fibres (bottom, blue) and a ganglion cell layer (directly above, black). Two plexiform layers (purple) are where synapses between the nerve cells take place. Two nuclear layers (black dots) contain the nerve cell nuclei. When the light reaches the rod and cone cells, they send impulses to the brain via the optic nerve. Magnification unknown.