Laser-Assisted Sub-Epithelial Keratectomy (LASEK) is a variant of PRK that combines elements of PRK and LASIK. During the procedure, the epithelium is loosened from the underlying tissue with the use of diluted alcohol. This "flap" of surface epithelial cells is then reflected back, and the laser is applied to the surface of the cornea. The "flap" is then repositioned back into place after the laser application. The advantages of LASEK over PRK are a topic of significant controversy. Although some refractive surgeons believe it provides improved comfort and more rapid healing compared to PRK, most studies have not found this to be the case.