In PRK (Photorefractive Keratoplasty) eye surgery, an excimer laser is used to correct low to moderate degrees of nearsightedness and farsightedness. In this type of refractive surgery, the thin and weak corneal epithelial layer is removed, and the tougher corneal stromal tissue is ablated (thinned). After the procedure, the corneal surface will replace itself. However, the eye may be irritated for a few days until the corneal surface re-grows.