Photorefractive Keratectomy (PRK) uses a laser to sculpt the surface of the cornea.  This contrasts with LASIK, which sculpts inside the cornea.  PRK is useful for treating low to moderate levels of myopia or hyperopia with and without astigmatism.  It is the procedure of choice if the patient has certain corneal dystrophies, certain corneal scars, or a condition called "recurrent corneal erosion".  PRK was FDA approved for myopia in 1995 and for hyperopia in 1998.  PRK involves first removing the outer layer of the cornea, called the epithelium.  A cool laser beam is then applied to the cornea, and a soft contact lens is placed over the eye as a bandage to help the outer layer to grow back.  It usually takes 3-5 days for the outer layer to re-grow over the cornea.  During that period, the patient may experience mild to marked discomfort with blurry vision.  Unlike with LASIK, it takes longer to achieve the final result in PRK since a greater amount of tissue healing takes place.