The patient is immobilized by way of a mask and a bite block, both custom made. Since the eye is not immobilized itself, it is very important that the patient not move the eye during treatment. However, to help the patient, the room lights are turned off and the patient is asked to stare at a small flashing light. The position of the eye is monitored during treatment by closed circuit television. If for any reason the patient moves the eye, the beam is stopped to avoid damage to other parts of the eye. If the eye being treated is blind, then the other eye can be used to fixate on the small flashing light instead.