Laser - PRK What is PRK? PRK is an operation almost similar to LASEK: There is no flap formation. It’s difference from LASEK is that no alcohol is used to remove the epithelium (the uppermost layer of the cornea) and that the epithelium cells are not put back after the laser operation. Contact lenses are placed on the eyes of the patient and the epithelium regenerates in 2-3 days. The patients feel a discernible ache during the operation. PRK operation can be an option for patients with thin corneas.