1 2 1 3 6 7 7 8 9 8 8 9 10 11 Heterophoria (or dissociated phoria). This represents the fusion-free position of the eyes, and therefore the magnitude of the deviation which has to be overcome by the vergence system. Fixation disparity. 12 1 5 Associated heterophoria 13 14 15 Fusional vergence reserves. 16 8 9 2 17 17 15 5 17 18 1 18 2 19 20