james,
The way the Flight Surgeon explained it to me when I got my Flight Physical, was due mainly to the way the cornea is cut in PRK vs. Lasik...you can find forums on the PRK listing that go in detail, but basically when you got lasik, your epithelium is basically "water sealed" by the flap they cut. In the event of say, a sudden cabin pressure change, that could be enough to break open that seal, and thus more tests need to be done for LASIK in such scenarios. PRK on the other hand, is a more in depth (and I've heard more painful) cut of the epithelium/cornea, and takes longer to heal, but as a result, is not a "water seal", but rather, heals like any other non eye muscle surgery, and seems to be more permanent. Any other posters feel free to add/critique on my terminology here, but you get the main idea as to why LASIK is not approved yet....