People always told Toph she was blind, but she wasn't. Not really. Because blind implies the inability to see, and while Toph didn't use her eyes to see, she could definitely see.
When she was younger, she couldn't quite understand what the vibrations she felt under her feet were, and found them quite annoying. But once she learned to decipher them, she couldn't imagine how she would live without the earth's pulse as her guide.
With it, Toph could tell where people were, if there were stairs nearby, how high a table was, whether a door was open or closed, as well as many other things that 'sighted' people could see. So it was understandable that, when she was taken away from the earth's sight-giving pulse, Toph felt afraid and lost. And though she could still hear and smell and taste, she couldn't see. Sometimes, if pulled away from the ground long enough, she would begin to wonder if she was ever able to see at all.
But despite all this, she was still, for some inexplicable reason, consumed with happiness when Aang let her fly on his glider with him.