Insurance will not pay, paid for it myself. Don't think there is a min vision loss to be a candidate, more based on if they can correct your vision, thickness of your cornea, etc. Mine went from about 20/100 to 20/15 (was actually 20/10 for a few weeks afterwards)! My vision is now probably 20/20 or slightly better, and that's 8yrs after having it done.
I would do it again and pay double if I had it to do over again, knowing what I know now! Have to admit it was pretty weird when they first cut the flap and flipped it over - looked like a kaleidoscope! Couldn't see anything except a spectrum of colors... Kinda weird! But 2-3hrs and a nap later and I could see perfectly!
