DD is -2.5/-3 and she needs her glasses to watch tv across the room. She now actually wears them. This seems to be the point at which they make a difference to things other than the board at school. I'm -5.5 and I need my specs to do anything. I think -6 on is considered pretty strong.
I thought that the lady testing today seemed rather stroppy with DD when she couldn't read the first set of letters - she kept telling DD just to guess but DD wouldn't - she said she could not see them.