Question

Let's talk ptosis. Lesion the CN 3 nucleus- what kind of ptosis will you get? Lesion the CN3 at the nerve, what kind of ptosis will you get?

Answer 1

Lesion at the CN 3 nucleus will cause ipsilateral ptosis potentially with double vision, while lesioning the CN 3 nerve will result in ptosis accompanied by mydriasis, loss of accommodation, and 'down and out' gaze due to paralysis of extraocular muscles innervated by CN 3.

Step-by-step explanation:

When discussing ptosis (drooping of the eyelid) related to cranial nerve III (CN 3), different lesions can lead to different presentations. A lesion at the CN 3 nucleus will result in a ptosis that is typically ipsilateral to the side of the lesion and could include symptoms of diplopia. This occurs because the CN 3 nucleus innervates levator palpebrae superioris muscles of both eyes, although the precise clinical picture can be more complicated due to the presence of bilateral innervation for some parts of the CN 3 complex.

If the lesion occurs at the nerve itself, the ptosis will be accompanied by other oculomotor deficits, such as mydriasis (dilated pupil), loss of accommodation, and extraocular muscle paralysis leading to a 'down and out' gaze due to unopposed action of the lateral rectus and superior oblique muscles. This is because CN 3 innervates most of the extraocular muscles, the levator palpebrae (causing the ptosis), and parasympathetic fibers to the pupil (controlling constriction).