A system and method for determining the measurements needed to fabricateprescription eyeglasses. The system andmethod take into account how the frames (12) fit naturally on the head and howthe person' s posture orients the head alters the line ofsight through the lens (14) of the eyeglasses. A sensor unit (16) is providedthat is attached to the eyeglass frames (12). The individualthen wears the eyeglass frames (12) and moves through at least one situationalsimulation. The sensor unit (16) generates data thatcorresponds to changes in orientation. The data is used to determine howperson's line of sight is altered by the anatomy of the faceand the posture of the head.
