OCULOMOTOR NUCLEAR COMPLEX (C.N. III)

The oculomotor nucleus proper is comprised of cells that innervate all extraocular eye muscles except the lateral rectus (LR6) and superior oblique (SO4). Remember that it also innervates the levator palpebrae. The EDINGER-WESTPHAL nucleus, which lies dorsal to the oculomotor nucleus proper, contains preganglionic parasympathetic (visceromotor) neurons whose axons end in the ciliary ganglion. Short postganglionic parasympathetic axons then pass from the ciliary ganglion to the sphincter pupillae of the iris and the ciliary muscles of the eye (for changing shape of lens in accommodation). Input to the EdingerWestphal nucleus arises from a cell group called the pretectum, a cell complex that receives retinal input and is part of the pathway involved in reducing the size of the pupil upon light stimulation of the retina. Don’t worry about the pretectum now!

A lesion involving C.N. III involves the axons headed for the eye muscles and the levator, as well as the visceromotor preganglionic parasympathetics destined for the ciliary ganglion. Following a unilateral lesion of C.N. III there will be outward and slightly downward deviation of the ipsilateral eye (due to unopposed action of the lateral rectus and superior oblique) and the inability to rotate the eye upward, downward or inward. You have to raise the eyelid to see the position of the eyeball, because the levator is not working! Because the eyelid is closed, the DIPLOPIA that would result from the lack of alignment of the visual axes of the two eyes is masked. There also is drooping of the eyelid or PTOSIS (levator palpebrae is not working), and DILATION of the pupil (unopposed action of sympathetics due to loss of parasympathetics). Other deficits that you DO NOT have to deal with are loss of the pupillary light reflex and convergence, and loss of accommodation of the lens. I want you to remember the PTOSIS and DILATED PUPIL in the eye ipsilateral to the lesion of C.N. III. DON’T WORRY ABOUT CONVERGENCE AND ACCOMMODATION AT THIS TIME!