USAF's pilot vision requirements shift based on need and also aircraft type (which relates to number of applicants).
For fighter aircraft they generally require 20/20 vision but permit correction for some candidates (particularly USAF Academy grads), usually up to 20/50-20/70 range. Many more people want to be fighter pilots than fly other kinds of aircraft so they can be picky here.
For heavies (cargo, bomber) and helicopters that are less popular they may permit that range of correction for all candidates, not just Academy grads.
For getting vision corrected, it was PRK only for a long time, no LASIK. I'm not sure the present rules. So long as your initial vision was within some range (I think better than 20/200 for a while there, again not sure of the current rules) and was corrected to 20/20-20/70 or so then you could qualify to become a pilot. Above 20/200 there are other issues with vision that start creeping in which causes them to ignore those candidates.
However, it depends on current need. If they feel they have enough candidates and current pilots then they'll be stricter on the vision requirement (and other waiverable requirements like being just above/below the height range), when they hit their next pilot deficit because they were moronic and created another bathtub curve they'll relax the requirements again. Happens every decade.