Laser Assisted In-Situ Keratomileusis is a variant of excimer laser photorefractive keratectomy.

Although LASIK is a newer procedure, it is becoming much more common as surgical techniques and instruments improve. 

The primary difference between LASIK and PRK is that prior to the use of the laser to change the shape of the cornea, a machine called a microkeratome is used to create a thin flap of cornea, which is folded back, and the laser treatment is then performed under this flap.

This provides similarly effective correction of visual problems, as the change in the shape of the cornea still takes place, but deeper within the corneal tissue.

Because the surface layer of the cornea is not removed, a protective contact lens is generally not necessary after LASIK.

There is generally less postoperative discomfort, because the eye's natural surface is returned to its original position after the laser treatment is done. 

Visual recovery is usually faster as well, because the surface layer of the eye does not need to re-heal after being removed as it does in PRK. Some patients and surgeons prefer LASIK to PRK because of these advantages of less discomfort and more rapid visual recovery.  Eye drops are still used, but often for a shorter period of time.

LASIK does offer significant advantages for those patients with high degrees of nearsightedness, because the risk of scarring with PRK increases when large amounts of tissue must be removed from the cornea.  While LASIK does not eliminate this scarring entirely, it tends to be much less common when the laser treatment is performed deeper within the cornea as it is in LASIK.