Ibn al-Haytham on binocular vision: a precursor of physiological optics

The modern physiological optics introduces the notions related to the conditions of fusion of binocular images by the concept of correspondence, due to Christiaan Huygens (1704), and by an experiment attributed to Christoph Scheiner (1619). The conceptualization of this experiment dates, in fact, back to Ptolemy (90-168) and Ibn al-Haytham (d. after 1040). The present paper surveys Ibn al-Haytham's knowledge about the mechanisms of binocular vision. The article subsequently explains why Ibn al-Haytham, a mathematician, but here an experimenter, did not give the circular figure of the theoretical horopter, construction due to Gerhard Vieth (1818) and Johannes Müller (1826). But, on the other hand, it is clear that Ibn al-Haytham's experimental study puts in place the notion of corresponding points, the cases of homonymous and cross diplopia, and even prepares the discovery of Panum area.