The optic nerve and the central retinal blood vessels enter the back of the eye at the disc (also called the blind spot). The back 2/3 of the eye is called the retina and gives us our wide field of view vision. It contains millions of rod and cone cells which convert light energy into electrical signals sent to the brain via the optic nerve. The macula (6x7 mm) is the tiny spot on the retina where finer detail focus occurs. The fovea (1.5 mm) is just behind the macula where the highest concentration of cone photoreceptors are concentrated. Light rays are focused by the lens onto the fovea for straight ahead vision and fine detail. The sclera is the tough outer wall of the eye and the choroid is the thin spongy layer between it and the retina filled with blood vessels.