I've started using a therapy ball for my desk chair, and ... it's interesting. Not uncomfortable, but maybe not transformative, either. Kind of fun to bounce while I'm writing; can that possibly be good for my eyes? One thing it's shown me, though, is that I have an amazing talent for slouching, and am able to do that even when balanced atop a rubber sphere. Can't put my feet up and lounge back, though. Not if I don't want to go sliding across the living-room floor while the dog laughs at me.