In PRK, LASIK and ASA, a cool beam of laser light is used to gently reshape the cornea to correct nearsightedness, farsightedness, astigmatism and presbyopia.  There is no sensation during treatment, and the whole procedure is over in a matter of minutes.

With Photorefractive Keratectomy (PRK), cells on the cornea's surface are removed prior to application of the laser light.

Laser-assisted in Situ Keratomileusis (LASIK) is performed below a protective layer of corneal tissue, leaving the surface cells intact.  There is less area to heal in LASIK, and minimal or no discomfort.  As such, it has been generally considered the procedure of choice.

Advanced Surface Ablation (ASA) is a recent development that provides for a fast, more efficient removal of surface cells.  In ASA, fewer cells are withdrawn before using the laser, and the procedure time is shorter.