In accordance with the invention there is disclosed a method for determining the amount of prism needed to be placed in spectacle lenses to correct ones fixation disparity and or proprioceptive misalignment, wherein target objects viewed by each eye will be perceived to be at optical infinity and the objects to be viewed by each eye are seen separately but also simultaneously, the method comprising: adding Base Out prism in a smooth and continuous manner until the target objects jump together, switch sides or are suppressed; decreasing Base Out prism and thereafter continuing to add Base In prism until the target objects return to their original position; and recording amount of prism needed to achieve the target objects returning to their original position.