If you are applying under the pilot option for STA-21 then you need to be found physically qualified at the time of selection, but if you are applying under the core option then you can be found physically qualified for a commissioning in the URL and then get PRK later. I was selected this year under the pilot option and I had to pay to get my PRK done several years back. The navy's wait list for the surgery was 3-6 years, so I decided that it would be worth the investment. I would advise you to get the surgery ASAP. Whether the Navy does it or you have to pay out of pocket, you must have it done before getting selected for STA-21, otherwise your selection will be withdrawn.