Fig. 17 A. Variation in Panum's area of binocular fusion with retinal eccentricity. B. The field of geometric disparities of a flat plane viewed at 20 cm and slightly in front of the fixation point. This shows that relatively large disparities can occur in peripheral regions under conditions that might occur while reading or writing. (A. Ogle KN: On the limits of stereoscopic vision. J Exp Psychol 44:253, 1952; B. Nakayama K: Geometric and physiological aspects of depth perception. Proc SPIE 120:2, 1977)