keratectomy, photorefractive

keratectomy, photorefractive Laser eye surgery designed to change the shape of the cornea, reducing or eliminating the need for glasses and contact lenses. The laser removes the outer layer of the cornea and then flattens it. This is intended to correct nearsightedness (myopia) and uneven curvature of the cornea that distorts vision (astigmatism). Photorefractive keratectomy is an outpatient procedure that is done in an office with numbing eye drops. Abbreviated PRK. The same type of laser is used for PRK and LASIK. The major difference between the two surgeries is the way that the stroma, the middle layer of the cornea, is exposed before it is vaporized with the laser. In PRK, the top layer of the cornea, called the epithelium, is scraped away to expose the stromal layer underneath. In LASIK, a flap is cut in the stromal layer and the flap is folded back. See also LASIK.