Keratectomy (LASIK, LASEK or PRK) removes part of the cornea by excimer laser usually after cutting a flap 9mm across. It operates over the centre of the visual zone and it is possible to lift the flap even years later. LASIK weakens the front of the eye by approximately 40%.There are also commonly problems with dry eye, scarring on the line of sight, loss of night vision and, more rarely, surgically induced ectasia (keratoconus)