PRK permanently changes the shape of the cornea. The surgery is performed using topical anesthetic (drops in the eye). The surgery begins with removal of the outer most layer of the cornea. This is done with either the laser or a small spatula. A thin layer of corneal tissue is removed with the light of the excimer laser. The removal of this tissue causes the center of the cornea to flatten in the case of nearsightedness, or steepen in the case of farsightedness or become more rounded in the case of astigmatism, which changes the focusing power of the cornea.