<p>Visual stimuli enters the eye, and through the retinal photoceptors is converted into an electric impulse, carried through the optic nerve (cranial nerve II) to the brain, where it connects to the pretectal nucleus of the high midbrain. It bypasses the lateral geniculate nucleus and the primary visual cortex. From the pretectal nucleus neurons send axons to neurons of the Edinger-Westphal nucleus whose visceromotor axons run along both the left and right oculomotor nerves. Visceromotor nerve axons (which constitute a portion of the III cranial nerve, along with the somatomotor portion derived from the Edinger-Westphal nucleus) synapse on ciliary ganglion neurons, whose parasympathetic axons innervate the constrictor muscle of the iris, producing <strong><strong class="selflink">miosis</strong></strong>. [1]</p>