For machining lenses by a CNC lens cutting machine, relevant data in regard to eyes, spectacle frame, and lenses are entered in the computer that compares the optical data of lenses and frame openings. When the lens is too small, it is moved by calculation relative to the shape of the frame edge until it is completely within the lens. The computer checks whether the carried-out movement is within given tolerances and, if not, the lenses are rejected; if the tolerances are met, the computer checks whether the carried-out movement of one lens requires movement of the other in order to meet the tolerances. If this is so, the computer calculates the minimum movement and checks whether this movement is within the tolerances and, if not, the lens pair is rejected. If the tolerances are met, the computer drives the machine for machining the shape of the spectacle lenses.