 Most early modern philosophers were impressed by the facts of geometrical optics, which teach that light imprints an inverted, left-right reversed image of the external world on the concave surface of the back of the eye. If we accept that the eye is the means of visual perception, then this teaching appears to imply that the eyes filter out information about the distance at which objects are set outwards from us and transmit just information about position along the horizon and the azimuth to the mind. After all, while points at different angles of inclination upwards or downwards from the horizon, or at different compass directions will project light to different parts of the retina, points that differ only with reference to their distance outwards from the eye will project light onto the same part of the eye. But if differences in distance outwards make no difference to the impression on the eye, and the mind is only affected as a consequence of how the eye is affected, then information about outward distances is not conveyed to the mind. It would seem, therefore, that visual perception must originally lack information about distance outwards. It must consist of an awareness of images that are only two-dimensional projections of solid objects in a three dimensional space. 