Every other laser method works under something: a flap folded back, or a disc lifted out through a small opening. PRK works on the surface of the cornea instead. There is no flap and no incision at any point.
The thin outer layer of the cornea is removed, an excimer laser (the ZEISS MEL 90) reshapes the surface underneath to the plan built from your own scan, and a protective contact lens goes on while that outer layer grows back over the following days.
That regrowth is what PRK asks of you, and it is also why nothing in your cornea has to be cut to get the laser where it needs to be.
The end result is the same as the other methods. It just takes longer to get there.