I realize this is MD, but after the first post, the subsequent questions about the blind guy seem rather silly. You guys do realize that in the real world, many blind people wear sunglasses / dark glasses, right? And that they can navigate by means such as a seeing eye dog, and that they can sometimes detect the presence of other people by, I dunno, hearing them? Or even speaking with them?
As far as why do many blind people wear sunglasses - I believe the biggest reason is to reduce awkwardness when interacting with others. Sighted people normally try to make eye contact, and can be discomfited by eyes that don't respond the normal way. Using sunglasses is a common way for blind people to make this a non-issue - the other (equally valid) response being to simply expect the sighted person to get over it. [ December 12, 2005: Message edited by: Jim Yingst ]