The puff of air test is done at an opticians at regular intervals, and you have to present the results to the medic. I think it tests for high internal eye pressure, and the puff of air deforms the eye slightly and they measure somehow the restoration in shape (I think). I hate my eyes being fiddled with and I really dislike it, but it must be done and it's harmless. Look stop crapping yourself about this. It really is no big deal. If your eyesight is not going to make it, better to find out now rather than waste a lot of money. Let them worry about getting you through. You don't even have to do your best! Just do...... nothing.