Erik Weihenmayer wears sunglasses often. He was wearing them to protect his eyes when he reached the summit of Mount Kilimanjaro in 1997. He had them on when he completed the 2003 Primal Quest, the world's toughest multi-sport adventure race. And, he put on a pair during a recent visit to the National Eye Institute (NEI).

But this last set is no ordinary pair of Oakley sunglasses. 

Weihenmayer looks through them, peering down at a white note card on a table. He silently moves his head back and forth, up and down. After a few moments, he says, "Is that a 12?"