Inroduction When a patient orders a pair of glasses they first choose a set of frames that suits them. The patient must have a prescription must be written by an optometrist which states the needed lens power and pupil distance (PD). Lenses in the needed power are either ordered or taken from stock. These lenses come from the factory as uncut round blanks approximately four inches across. Edging is the process of cutting these optical lens blanks to fit frames, producing a pair of glasses.