In addition to noting the completeness and pupil involvement of a CN3 palsy, the examiner should also look for signs of aberrant regeneration. Exceptions are exceedingly rare, but do exist, which is why most providers would recommend urgent neuro-imaging to rule out an aneurysm regardless of pupil involvement 1. This distinction is more salient in cases of complete CN3 palsies, in which a lack of pupillary involvement would suggest a non-compressive etiology because the amount of mass effect needed to cause complete ophthalmoplegia would most likely cause pupillary dysfunction. Thus, a compressive lesion will generally cause a pupil-involving CN3 palsy as it will contact and compress the peripheral pupillary fibers first. The pupillary fibers of CN3 run peripherally within the nerve while the motor fibers run centrally within the nerve. Pupil-sparing and pupil-involving is an important distinction to make as it can have implications of the likely etiology of the CN3 palsy. Inferior or superior division of the palsy can be seen in lesions peripheral to the bifurcation of the nerve (anterior cavernous sinus). Partial CN3 palsies may present with varying degrees of ptosis and ophthalmoplegia. There may still by subtle infraduction if CN4 remains intact, although the more prominent indicator of normal CN4 function would be intorsion of the eye in attempted down gaze. The eye is unable to adduct or supraduct. Diplopia is present when the ptotic lid is elevated, revealing an eye that is both exotropic and hypotropic. These patients will present with complete ptosis.

A complete CN3 palsy refers to complete dysfunction of the LPS, SR, MR, IR, and IO. All extraocular muscle subnuclei are ipsilateral to the muscle they innervate except for the SR nuclei, which innervate the contralateral SR muscle.ĬN3 palsies are typically categorized as partial vs. Of note, the right and left CN3 nuclei share one LPS subnucleus, but otherwise have separate subnuclei. SR subnucleus, MR subnucleus, IR subnucleus, IO subnucleus, Edinger-Wesphal subnucleus, and LPS subnucleus. Each sub-function of CN3 has its own subnucleus – i.e. The CN3 nucleus is located in the rostral midbrain. In addition, CN3 innervates the levator palpebrae superioris (LPS) which is the major muscle of lid elevation, the ciliary muscle which is responsible for accommodation, and the pupillary sphincter muscle which is responsible for pupillary constriction. Specifically, it innervates the superior rectus (SR), medial rectus (MR), inferior rectus (IR), and inferior oblique (IO) muscles. Keywords/Main Subjects: Cranial nerve, Oculomotor nerveĬranial nerve 3 (CN3) is aptly named the oculomotor nerve as it innervates the majority of the extraocular muscles. Home / Neuro-Ophthalmology / Efferent DisordersĪuthors: Amanda Redfern, MD Meagan Seay, DO

Cranial nerves for pupil measurement