:)
One of them was improving my vision prescription from -2.75 to -1.75.
If you want to get an idea of how 'impossible' this is, tell an optician you are thinking of trying it. If you want a good laugh, tell them you've done it and let them measure your new prescription. They will claim that the old prescription must have been faulty, that you are cheating on the test.
It would be funny if it didn't mean that half the worlds population were being forced to buy glasses, lenses and surgery they didn't need.