 Müller’s explanation appeals to an a priori perception of the retina by itself, and to the activity of projecting two points onto a theoretical projection surface a priori. Müller tries to use Kantian philosophy to support his theory, arguing that by the “manifold accessible to pure intuition” Kant meant, or could have meant, the a priori possible manifold of physical points that could be perceived by the retina. Robert DiSalle presents evidence that this view is not Kantian (DiSalle 1993, 502ff).