Point 21
Intro
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!