When blindness is caused by eye or retinal problems, the visual cortex may be repurposed by the nervous system.

“In individuals that are blind from birth, the so-called occipital cortex, the visual cortex in the back, becomes overtaken by hearing. The neurons there will start to respond to sounds as well as braille touch. And actually there's a one particularly tragic incident where a woman who was blind since birth and because of neuroimaging studies, we knew her visual cortex was no longer visual, it was responsible for braille reading and for hearing, she had a stroke that actually took out most of the function of her visual cortex. So then she was blind, she couldn't braille read or hear. She did recover some aspect of function. Now, most people they don't end up in that highly unfortunate situation. And what we know is that for instance, blind people who use their visual cortex for braille reading and for hearing, have much better auditory acuity and touch acuity.”

“What happens to somebody when they become blind because of problems in the eye, the retina perhaps? You have a big chunk of the cortex, this really valuable [indistinct] for neural processing that has come to expect input from the visual system and there isn't any anymore.”