A system and method for determining the measurements needed to fabricate prescription eyeglasses. The system and method take into account how the frames fit naturally on the head and how the person's posture orients the head alters the line of sight through the lens of the eyeglasses. A sensor unit is provided that is attached to the eyeglass frames. The individual then wears the eyeglass frames and moves through at least one situational simulation. The sensor unit generates data that corresponds to changes in orientation. The data is used to determine how person's line of site is altered by the anatomy of face and the posture of the head.
