Can't speak for the Navy but I can for the Marines in a second hand sort of way.
Short story is my kid contracted PLC NFO went thru OCS (OCC 195), then went back to college and finished up his last semester. He has not commissioned yet.
He had PRK to fix his eyes which are now 20/15. He just went down to P'Cola for his fight physical and did fine.
His package is now complete and he has applied for a switch from SNFO to SNA. OSO says that it shouldn't be a problem to make the switch. That said his package was just submitted last week so no word yet.
The key in doing this I'm told is to get it done before you commission.
After that, the switch is much harder.