Disparity in visual images occurs between the two retinas facing different fields because of the the physics of light (pin-hole camera effect). There is visual field inversion and inappropriate reversal of the two eye images reaching the cerebral cortex, i.e. the head of the horse is chasing the tail and down is up and up is down.

Disparity in visual images occurs between the two retinas facing different fields because of the the physics of light (pin-hole camera effect). There is visual field inversion and inappropriate reversal of the two eye images reaching the cerebral cortex, i.e. the head of the horse is chasing the tail and down is up and up is down.
EVOLUTION has corrected lens-reversal by crossing pathways to the cerebral cortex through an optic chiasm (decussation). Thus the efficient mapping of binocular image fields is re-instated to symmetrical continuity of the two image fields but they remain inverted.

EVOLUTION has corrected lens-reversal by crossing pathways to the cerebral cortex through an optic chiasm (decussation). Thus the efficient mapping of binocular image fields is re-instated to symmetrical continuity of the two image fields but they remain inverted.