If true, Grace would be in good company.  Stevie Nicks reportedly had bad eyesight:

“Adversity has its artistic advantages, of course. Vulnerability is an enticing hallmark on much of Nicks' work. For instance, her imaginative images owe something to poor eyesight, she once admitted. 

"I do kind of look at the world differently because of that," she once told The Arizona Republic. "I don't see it clearly. I see it like in a dream."

Older article, but looks legit:  http://rockalittle.com/scottsdalelife_july2000.htm

And,  a fifteen-foot radius is plenty enough to get around on stage the way Grace does.