Fig. 14 A. Effect of fixation disparity on the position of the horopter circle. Upper panel: Exodeviation. Lower panel: Esodeviation. B. Effect of aniseikonia (differential magnification of image in the two eyes) on the form of the horopter circle, which becomes an ellipse, delineated here by the limits of the fusion range on either side of the horopter. (Ogle KN: Researches in Binocular Vision. Philadelphia: WB Saunders, 1950)