BLIND SPOT

An oval-shaped spot in the retina where the optic nerve enters from the rear. It is blind to both color and light, as proved by Mariotte in 1668. The reason for this blindne is that the nerve fibers have not spread out at this point, so that when light falls upon it no impre ion is conveyed to the brain. Since vision depends entirely upon the effect. of light waves upon the optic p nerves, it follows that any object which refiects rays so that they fall only upon the blind spot, is not seen.