PRK is a similar procedure to the more popular LASIK. In LASIK a flap is cut in the cornea and set aside, the correction is performed underneath, and the flap is then placed back over the insulted area, providing a natural bandage. The scar from the flap never entirely heals, which is not a problem for most people most of the time. It is a concern if you get punched in the face. I box, which is to say I get punched in the face. In PRK the epithelium is abraded away, the correction performed, and then you just sort of hang out for a few weeks or a few months waiting for the epithelium to regenerate and shed and regenerate a few times – after which point there is no residual effects and you can go back to getting punched in the face, with no more concern than getting punched in the face normally warrants. LASIK was only approved by NASA in 2007, and is still frowned upon at SF HALO and SCUBA schools. The message is clear: if you want to keep the space marine option available, opt for PRK.