Euclid proposed to trace pyramids as artifacts to facilitate the study of visual perception. The artifact assumes that the object seen delimits the base of a pyramid at the apex of which is the perceived eye. The artifact faces a serious difficulty when we notice that visual perception is carried out with two cooperating eyes. The article discusses two attempts to modify the Euclidean artifact to make it work without giving up the central assumptions. These attempts correspond to the classical (...) studies of Ptolemy’s binocular vision and Ewald Hering’s contributions in the 19th century. (shrink)