Laser-assisted sub-epithelial keratomileusis, or LASEK, is often considered a sub-category of PRK. LASEK, like PRK, is a procedure that permanently changes the shape of the cornea using an excimer laser to remove a small amount of tissue from the stroma under the epithelium. In LASEK, however, the epithelium is preserved at the beginning of the procedure and replaced afterward to act as a natural bandage. Recovery of vision after LASEK often takes longer than PRK because the replaced epithelial layer takes longer to heal than the growth of a new epithelial layer.