The 3rd cranial nerve innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior oblique, and inferior rectus. The pupillary fibers follow the inferior oblique muscle. Pupil involvement in CN III palsy is an efferent defect (unrelated to a relative afferent pupillary defect).
In patients with non-traumatic cranial nerve III palsy and ipsilateral pupillary dilation (efferent defect), posterior communicating artery aneurysm must be excluded.
Children <8 years of age should be closely monitored for amblyopia. Congenital 3rd nerve palsies may be caused by birth trauma. Compared with adults, it is rare for aneurysms to cause CN III palsy in children. Ophthalmoplegic migraine is a diagnosis of exclusion, with onset in childhood. Ophthalmoplegic migraine is uncommon and the ophthalmoplegia develops days after the onset of head pain.
It is not common to have 3rd nerve palsy in pregnancy. Exclude pituitary apoplexy, gestational diabetes, or hypertension.
The pupillary fibers of the oculomotor nerve are located superficially along the medial aspect of the nerve, close to the posterior communicating artery. The pupillary fibers travel in the outer layers of the nerve and are closer to the vasa nervorum nutrient blood supply. As such, the pupillary fibers are less likely to be affected by microvascular ischemia; however, they can be compressed by a posterior communicating artery aneurysm.
• Microvascular (e.g., diabetes, hypertension)
• Tumor/infiltration (e.g., lymphoma, carcinoma)
• Inflammation (e.g., sarcoidosis)
• Infection (e.g., meningitis)
The patient may have binocular diplopia with diagonal separation. If the ptosis is severe enough to occlude the visual axis, the patient will not complain of diplopia.
• With a complete 3rd nerve palsy, there is a ptosis, and the eye is positioned downward and outward.
– A truly pupil-sparing 3rd nerve palsy shows normal pupillary function but complete loss of eyelid and eye movement subserved by the oculomotor nerve.
– Aberrant regeneration may occur if the disrupted 3rd cranial nerve fibers reroute themselves along anomalous pathways. Most commonly, the ptotic lid will elevate on adduction or infraduction if there is lid-gaze synkinesis. The pupil may constrict with adduction with pupil-gaze synkinesis.
– Aberrant regeneration is primary if there is no preceding acute 3rd nerve palsy, and it is seen with cavernous sinus lesions such as meningioma or aneurysm. Aberrant regeneration is secondary if it follows recovery from a 3rd nerve palsy (e.g., post-trauma or compression).
DIAGNOSTIC TESTS & INTERPRETATION
Blood sugar, glycosylated hemoglobin if is diabetes suspected. Serum lipids can be drawn. Westergren erythrocyte sedimentation rate and C-reactive protein if giant cell arteritis is suspected
CT angiogram or MR angiogram, if the pupil is involved
Follow-up & special considerations
In patients that were not initially imaged, but have persistent non-improving deficit at 4 months, consider MRI.
Lumbar puncture may be considered if neuroimaging and blood tests are not diagnostic.
• Myasthenia can mimic pupil-sparing 3rd nerve palsy. An “isolated medial rectus palsy” is unlikely to represent a partial 3rd nerve palsy, but is more likely to be an internuclear ophthalmoplegia or, perhaps, myasthenia. Giant cell arteritis can cause extraocular muscle ischemia or 3rd nerve palsy appearance. Closely check for intorsion to ensure that CN IV is intact, and check CN V1 and V2 sensation to exclude a cavernous sinus lesion.
• If there is isolated efferent pupillary dysfunction with intact lid function and eye movement in an alert patient, Adie’s pupil should be suspected.
If giant cell arteritis is suspected, give intravenous steroids or minimum 60 mg p.o. prednisone.
Optimize the patient’s blood pressure, blood sugar, and cholesterol. If the adult patient has bothersome diplopia, the palsied eye can be patched. Prism glasses can be attempted but usually are of limited benefit because there is marked incomitance. Children <8 years of age should be monitored closely to determine the need for amblyopia treatment.
Issues for Referral
Pupil involving 3rd nerve palsy requires referral to neurosurgery or neurology. Diabetes, hypertension, collagen vascular disease, or temporal arteritis suspects should be referred to primary care doctor or medicine service.
Pupil involving CN III palsies requiring neuroimaging (e.g., CT angiogram or MR angiogram) should be assessed by neurosurgery or neurology
In patients with new-onset CN III palsy and pupil-sparing, follow the pupil daily for 5–7 days to ensure the pupil does not become involved.
Patients with ischemic 3rd nerve palsies may have significant recovery of function. If patients with CN III palsy have not recovered after 12 months, strabismus surgery or ptosis repair can be considered. The surgical rehabilitation of partial 3rd nerve palsy is better than that for complete 3rd nerve palsy. With complete 3rd nerve palsy, fixation of the globe to the medial canthal tendon and frontalis sling for ptosis may provide cosmetic improvement; however, the patient may have chronic diplopia. In patients with severe ptosis and poor Bells’ phenomenon, corneal exposure may be a relative contraindication to frontalis sling ptosis repair.
Aneurysmal 3rd nerve palsy is a potentially life-threatening condition. Unrecognized giant cell arteritis may lead to bilateral blindness.
1. Lanning B. Kline. Neuro-ophthalmology review manual, 6th ed. Slack Incorporated: Thorofare, NJ, 2008.
2. Lanning B. Kline. Neuro-ophthalmology. Section 5. Basic and Clinical Science Course. American Academy of Ophthalmology: San Francisco, CA, 2009.
3. Burde RM, Savino PJ, Trobe JD. Clinical decisions in neuro-ophthalmology, 3rd ed. Mosby: St. Louis, MO, 2002.