From Ed Yong at Not Exactly Rocket Science:
The video above seems completely unremarkable at first - man walks down a corridor, navigating his way around easily visible and conspicuous obstacles. But it's far from an easy task; in fact, it should be nigh-impossible. The man, known only as TN, is totally blind.
His inability to see stems from a failure in his brain rather than his eyes. Those work normally, but his visual cortex - the part of the brain that processes visual information - is inactive. As a result, TN is completely unaware of the ability to see and in his everyday life, he behaves like a blind person, using a stick to find his way around. Nevertheless, he can clearly make his way through a gauntlet of obstacles without making a single mistake.