You shouldn't have gotten a PRK in 2016, i did my last PRK 20 yrs ago, you should have gotten a LASEK with less pain and quicker healing. you didn't say what your age and original Rx is, however it sounds like you will need an enhancement, which should be free, but is a pain, the chance of...
50 year olds are certainly candidates for Lasik or PRK, if other things are appropriate. High corrections can be treated up to a certain level. Either the eyes will be adjusted for distance and you will wear reading glasses for close or you can have blended monovision.
Typically, you can not tell just by looking with a microscope that a person has had PRK. In most cases, you can't tell just by looking with a microscope that a person has had Lasik either. Testing with topography will reveal the microscopic curvature changes caused by PRK or Lasik.