An Eye for an Eye

The retina lives at the back of the eyeball, and with its thin layers of modified neurons, it is almost like a small additional patch of brain. The rearmost layer consists of photo receptor cells that convert patterns of light and dark (collected by the eye’s lens) into a set of electrical impulses. Those impulses provide the raw data of the visual universe. As with brain cells, the neurons of the retina are basically irreplaceable. Vision diseases such as macular degeneration and retinitis pigmentosa, which kill off photoreceptor cells, usually end in blindness.