PhotoRefractive Keratectomy (PRK) and Laser-Assisted Sub-Epithelial Keratectomy (LASEK) both involve removal of the outer epithelial layer of the eye prior to surgery. LASIK (Laser-Assisted in Situ Keratomileusis) on the other hand involves the creation of a thin flap which is removed from the surface of the eye prior to laser shaping of the corneal suface.

The PRK surgery involves physical removal of the epithelium using a rubbing or scrubbing procedure. The epithelium will regenerate over a few days. LASEK surgery instead removes the epithelium but allows it to be replaced.

The procedure I opted for was wavefront PRK. The wavefront concept is simply a series of measurements which check the path of light as it goes through your eye combined with a contour map of the surface. Armed with this refractive mapping, they program the excimer laser to reshape the eye accordingly.

Doing PRK, as opposed to LASIK, allows the laser to work on a larger area of the eye, lowering the potential for issues with respect to night vision and glare issues. If you have large irises and do the LASIK slice, it is possible that the outer region of your lens will not be reshaped, leaving it with different focal properties than the adjusted portion.

Pro's
No long term risk due to flap creation.

Ability to try "monovision" and/or undergo touch-up retreatment in most cases.

Structural integrity of the eyeball is not compromised.

Con's
The original contour and surface of the eye are changed. More pain and longer healing times are required. You can read about my own personal prk recovery experience if you are interested.

My Blog
I also have a relatively inactive blog about my own laser surgery experiences...

For more reading, Wikipedia has a great PRK reference.