  In addition to a new theory of sensory qualities, Descartes offered theories of the way in which the spatial properties—size,  shape, distance, and position—are perceived in vision. In  Descartes' day  and before, “optics” was  defined as the theory of vision, including physical, physiological, and psychological aspects. It had been an area of inquiry since antiquity. Euclid and Ptolemy had each written on optical problems. During the Middle Ages, the Arabic natural philosopher Ibn al-Haytham produced an important new theoretical work in which he offered an extensive account of the perception of  spatial properties.