The axis visualis was also central to Bruneleschi's experiment which insisted on the picture being seen from a single point . Ptolemy's optical treatise provided the most useful explanation of central rays for artists, for it ellaborated on the nature of rays being closest to the axis. According to this explanation the center ray, making a right angle with the surface of what was seen, carried back the clearest impression to the observer. Leonardo argued that purely geometrical laws would not portray reality. Pictorial representation in the case of binocular vision requires two different perspective projection each having its centre at the respective eye.
Sterescopic devices create the illusion of three dimension by doing just that.
It encompassed all of the areas of studies we now seperate into geometrical, physical, and psychological optics. Ancient opticians concieved sight in terms of touch. With their apex in the eye and bases on the surface of objects these lines supported the geometric design of Eucledian space. Galen's model showed a lense behind the pupil. The image entering the eye through this lense was transfered by visual spirit or pneuma through the hollow optic nerv to the brain.18 Leonardo discussed the faculty of sight and the anatomy of the eye in his notes similarily and pointed out that the pupil in the center of the eyeball is shaped spherically.