Fig. 10. A typical spectacle-fitting situation. Most glasses are worn with the bottom of the frame tilted toward the face (pantoscopic tilt). The optical center of the lens should be below the straight-ahead line of sight so that the optic axis of the lens passes through the center of rotation of the eye. (Modified from Davis JK: Prescribing for visibility. Probl Optom 2:131, 1990.)