eMedicine Specialties > Ophthalmology > Extraocular Muscles

Oculomotor Nerve Palsy

Author: James Goodwin, MD, Director of Neuro-Ophthalmology, Associate Professor, Departments of Neurology and Ophthalmology, University of Illinois College of Medicine
Contributor Information and Disclosures

Updated: Dec 3, 2008

Introduction

Background

The third, fourth, and sixth cranial nerves innervate the extraocular muscles that position the globes in the orbits. Extraocular muscle paralysis resulting from destructive lesions in one or all of these cranial nerves results in failure of one or both eyes to rotate in concert with the other eye.

The primary symptom is diplopia from misalignment of the visual axes, and the pattern of image separation is the key to diagnosing which particular cranial nerve (and extraocular muscle) is involved. With unilateral third cranial nerve palsy, the involved eye usually is deviated down and out (infraducted, abducted), and there is ptosis, which may be severe enough to cover the pupil. In addition, pupillary dilatation can cause symptomatic glare in bright light (if the ptotic lid does not cover the pupil), and paralysis of accommodation causes blurred vision for near objects.

See related CME at Highlights of the Annual North American Neuro-ophthalmology Society Meeting.

Pathophysiology

The anatomical relationship of the various portions of the third cranial nerve accounts for many of the clinical features of third cranial nerve palsy as outlined below.

Nuclear portion: The cell bodies for axons that travel in the oculomotor nerve reside in the column-shaped nuclear groups on either side of the midbrain tegmentum. The axons destined for each extraocular and intraocular muscle derive from a specific subnucleus.¹

Fascicular intraparenchymal midbrain portion: The fascicular portion of the oculomotor nerve courses ventrally from the nucleus in the dorsal midbrain tegmentum, passes through the red nucleus, and emerges from the medial aspect of the cerebral peduncle.

Fascicular subarachnoid portion: The cisternal portion of the nerve is in the subarachnoid space anterior to the midbrain and in close proximity to the posterior communicating artery. Berry aneurysm at the junction between the posterior communicating artery and the internal carotid artery is an important cause of oculomotor nerve palsy.

Fascicular cavernous sinus portion: The next segment of the oculomotor nerve runs through the lateral wall of the cavernous sinus superiorly. It enters the cavernous sinus just above the petroclinoid ligament and inferior to the interclinoid ligament. Masses invading the cavernous sinus from within the sella are most likely to cause third cranial nerve dysfunction prior to involvement of the other cranial nerves in the cavernous sinus. This is probably because of the oculomotor nerve's close proximity to the unyielding interclinoid ligament above and the petroclinoid ligament below.

Fascicular orbital portion: The oculomotor nerve enters the orbit through the superior orbital fissure adjacent to the fourth cranial nerve. The nerve branches into superior and inferior divisions, usually within the posterior orbit, but, occasionally, the branching occurs as far back as the cavernous sinus segment. The superior division innervates the levator palpebrae and the superior rectus muscles; the inferior division innervates all the other muscles, including the iris sphincter, which constricts the pupil.

The axons for most of the muscles are uncrossed from the nucleus to the eye, but there are 2 exceptions. (1) Axons for the levator palpebrae come from both sides of the central caudal subnucleus via crossed and uncrossed pathways. (2) Those for the superior rectus muscle come from the superior rectus subnucleus on the contralateral side.

The pupillomotor and ciliary muscle neurons derive from the Edinger-Westphal subnucleus, which is in the midline in the most rostral and anterior part of the oculomotor nerve nucleus. These autonomic pathways are all ipsilateral or uncrossed.

The oculomotor nerve innervates the following extraocular muscles of either eye: superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae, ciliary muscle, and iris sphincter.

Frequency

United States

Rare

Mortality/Morbidity

• Morbidity and mortality are essentially those of the diseases that cause oculomotor nerve palsy and are beyond the scope of this article.
• The most significant causes of mortality and morbidity along with oculomotor nerve palsy are subarachnoid hemorrhage from berry aneurysm of the posterior communicating artery, and meningitis or meningeal infiltrative disorders, both infectious and neoplastic.

Clinical

History

• The following symptoms are encountered with lesions producing third cranial nerve dysfunction.
  • The most common lesions to affect the third cranial nerve involve the fascicular portions of the nerve at some level. The symptoms reflect reduced function in the muscles innervated by the nerve, usually in combination; isolated involvement of one or another muscle from fascicular third cranial nerve lesions is very rare. The prime symptom is mixed horizontal and vertical binocular diplopia from deviation of the 2 visual axes.
  • Ptosis may be sufficient to cover the pupil in which case the patients complain that they cannot see from the eye on the involved side. In fact, this component may mask the symptom of diplopia if the ptosis is prominent before the visual axes diverge.
  • Pupil enlargement and lack of light reaction produces little in the way of symptoms, although there may be some glare sensation and photoaversion in bright light.
• Neurologic symptoms associated with lesions involving various portions of the third cranial nerve include the following:
  • Nuclear portion: Most of the lesions causing nuclear, third cranial nerve palsy are from dorsal midbrain infarction. These tend to be small lesions with few associated neurologic symptoms or signs.
  • Fascicular midbrain portion
    • Benedikt syndrome of the upper mid brain includes third cranial nerve palsy on the side of the lesion, ipsilateral flapping hand tremor (rubral tremor from red nucleus involvement), and ataxia.
    • Weber syndrome results from a slightly more ventral lesion at the level of the third cranial nerve fascicles in the mid brain, with involvement of the cerebral peduncle giving rise to contralateral hemiplegia or hemiparesis along with ipsilateral third cranial nerve palsy.
  • Fascicular subarachnoid portion
    • The fascicles of the third cranial nerve exit the mid brain through the medial aspect of the cerebral peduncles and are not near any of the other cranial nerves at this point.
    • The findings of third cranial nerve palsy tend to occur in isolation from lesions in this location.
    • Since the most common lesion to affect the third cranial nerve in the subarachnoid space is aneurysm, the signs and symptoms of subarachnoid hemorrhage, including sudden severe headache, stiff neck, and loss of consciousness, may be present.
    • Infundibulum refers to widening of the proximal segment of the posterior communicating and other arteries, and, unlike aneurysm in this location, it is usually asymptomatic.  A case of posterior communicating artery infundibulum has been documented causing recurrent ipsilateral third cranial nerve palsy and headache that masqueraded as ophthalmoplegic migraine.²
    • Basal meningeal infection, neoplastic infiltration, and miscellaneous inflammatory lesions may involve the third and all the other cranial nerves. The primary symptoms of meningitis are often present, including headache, stiff neck, fever, and alteration of consciousness. Eventually, these diseases tend to involve other cranial nerves, which is not the case with a very localized lesion, such as berry aneurysm.
    • Ophthalmoplegic migraine presents in childhood with recurring bouts of unilateral headache and ipsilateral third cranial nerve palsy that can last several weeks at a time. The link to migraine in general has come under question because many or most of these patients demonstrate thickening and enhancement of the cisternal portion of the third cranial nerve on MRI with gadolinium.³
  • Fascicular cavernous sinus portion
    • The third cranial nerve is more susceptible to compression against the interclinoid ligaments above and the petroclinoid ligament below than are the other cranial nerves in the cavernous sinus. For this reason, isolated third cranial nerve palsy may result from lateral extension of pituitary adenoma or other primary intrasellar mass.
    • More diffuse lesions within the cavernous sinus, often inflammatory in nature, typically give rise to simultaneous involvement of the third, fourth, sixth, and first 2 divisions of the fifth cranial nerves in various combinations, which serve to define a cavernous sinus syndrome. Nonspecific or granulomatous inflammation within the cavernous sinus is referred to as Tolosa-Hunt syndrome.
    • Carotid artery dural branch to cavernous sinus fistulas typically present with third cranial nerve palsy plus other cranial nerve involvement in the cavernous sinus and proptosis with arterialized conjunctival veins due to a large volume shunt of arterial blood into the anterior draining veins of the cavernous sinus.  Isolated third cranial nerve involvement without the orbital congestion can occur when the primary drainage is posterior from the cavernous sinus, the so-called white eye fistulas.⁴
    • Involvement of the fourth cranial nerve does not add any symptoms to patients with Tolosa-Hunt syndrome since the eye on the side of the third cranial nerve palsy already has a deficit of depression from involvement of the inferior rectus muscle.
    • Involvement of the sixth cranial nerve in patients with Tolosa-Hunt syndrome leads to an associated deficit of ocular abduction, but this does not change the symptom complex when there is associated third cranial nerve palsy.
    • Often, the involvement of the first 2 divisions of the fifth cranial nerve (trigeminal) presents with severe pain and numbness in the face, including the forehead back to the interaural line and the cheek down to the angle of the mouth. The pain may be constant and burning with unpleasant paresthesia, or it may include a lancinating component that can be confused with trigeminal neuralgia.
  • Fascicular orbital portion
    • Lesions in the orbit tend to produce associated proptosis, lid swelling, conjunctival injection, and chemosis.
    • There also may be involvement of the other cranial nerves that innervate extraocular muscles (fourth and sixth) or involvement of the muscles themselves.
    • Nonspecific or granulomatous inflammation in the orbit is referred to as orbital inflammatory pseudotumor.

Physical

Initially, physical findings attributable to involvement of the fascicles of one or the other third cranial nerve are described. Subsequently, additional physical findings that are associated with lesions of particular portions or segments of the third cranial nerve are described.

• Unilateral third cranial nerve palsy
  • Horizontal deviation is divergent or temporal (exotropia) because of weakness of the medial rectus muscle of the involved side. Vertical deviation results from weakness of the superior rectus, inferior oblique (both elevators), and inferior rectus (depressor) muscles.
  • Residual function of the superior oblique muscle (depressor, intact fourth cranial nerve function) tends to produce downward deviation of the involved eye. A way to remember this combination is to think of a losing boxer, "down and out".
  • Diagnosing partial third cranial nerve palsy is facilitated by an alert patient. The deficit of adduction, supraduction, and infraduction should be apparent even if partially paralyzed.
  • In very mild cases, one might have to resort to eliciting latent deviation or phoria with Maddox rod or alternate cover testing (to dissociate the 2 eyes and interrupt fusion).
  • Ptosis results from weakness of the levator palpebrae, and this often is complete or nearly so, in which case the pupil is covered and the patient cannot see from the involved eye.
  • Milder degrees of ptosis are examined best using measurements of the palpebral fissure width; more information can be gained from measuring the margin reflex distances (MRD).
    • The examiner sits in front of the patient and directs a point source of light (eg, handlight, Finnoff head, penlight) into both the eyes of the patient.
    • The examiner can observe the pinpoint light reflex in the center of the cornea. The position of this reflex is not affected by deviation of the eye, which makes it a useful reference point for measuring the distance to the upper and lower lids, respectively.
    • The MRD1 usually refers to the distance from the light reflex to the upper lid margin, and the MRD2 is the distance to the lower lid margin.
    • Levator palpebrae weakness reduces the MRD1 but will not affect the MRD2. On the other hand, ptosis from ocular sympathetic palsy (Horner or Claude Bernard syndrome) causes weakness of Mueller muscle in both the upper and lower lids, with consequent reduction of both the MRD1 and the MRD2.
    • Pseudoptosis from widening of the contralateral palpebral fissure may result from mild or old contralateral seventh cranial nerve lesion and orbicularis oculi weakness. In both these cases, MRD1 and MRD2 are increased on the side opposite to the apparent ptosis.
    • Careful examination of facial muscle strength and symmetry usually confirms the cause of the apparent ptosis in these cases.
  • Pupillary dilatation and sluggish or absent reaction to light results from involvement of parasympathetic fibers that originate in the Edinger-Westphal subnucleus of the third cranial nerve complex.
    • Fascicular involvement from compressive lesions often affects these autonomic fibers because they are situated very superficially within the nerve trunk.
    • This contingent of fibers are medially placed as the nerve exits the brainstem and gradually migrate to a more inferior and lateral position as they proceed anteriorly along the nerve.
  • If there is partial preservation of parasympathetic pupillary innervation with third cranial nerve disorders, the pupil on the involved side may react to light nearly as briskly as the pupil of the other eye.
    • Distinguishing pupillary involvement caused by third cranial nerve lesions from ocular sympathetic palsy (Horner or Claude Bernard syndrome) or physiological anisocoria requires detailed examination of pupil size in dim and in bright, ambient light.
    • With sphincter weakness due to parasympathetic involvement in third cranial nerve lesions, the involved pupil is larger than the fellow pupil.
    • The size difference between the 2 pupils (anisocoria) is greater in bright light (when the sphincter is called upon to act most strongly) and less in dim light (when the sympathetically innervated dilator fibers are the dominant contributors to pupil size). The reverse is true for ocular sympathetic lesions, the pathological pupil is the smaller one and the difference (anisocoria) is greater in dim light than in bright light. The anisocoria remains the same in dim and bright light in simple central anisocoria, also called physiological anisocoria.
• Nuclear portion
  • Nuclear third cranial nerve palsy demonstrates in addition to the ipsilateral findings, contralateral partial ptosis and elevation palsy.
  • The contralateral partial ptosis stems from the bilateral distribution of innervation to the levator from the caudal central subnucleus.
  • Ptosis is more complete ipsilateral to the lesion because function is lost in both the ipsilateral neural cell bodies and their fibers on the lesioned side, plus the crossed fibers coursing through the lesion from the other side.
  • There is partial ptosis contralateral to the lesion because of the residual integrity of the uncrossed neural cell bodies and fibers from the caudal central subnucleus contralateral to the lesion.
  • Superior rectus nucleus output is totally contralateral with fascicles from the nucleus on one side coursing through the opposite superior rectus subnucleus. A lesion of the superior rectus subnucleus on one side causes bilateral elevation palsy. The deficit ipsilateral to the lesioned nucleus reflects involvement of fascicles coming from cell bodies on the opposite side, and the deficit contralateral to the lesion reflects loss of the cell bodies in the lesioned nucleus.
• Fascicular midbrain portion
  • Ask the patient to hold both arms outstretched in front of them.
  • Patients with Benedikt syndrome have a gross "flapping" tremor that has been attributed to red nucleus involvement, usually from midbrain infarction. The tremor and ataxia is ipsilateral to the lesion and to the third cranial nerve palsy.
  • In Weber syndrome, the patient usually has a dense hemiplegia contralateral to the third cranial nerve palsy resulting from a lesion that also involves the pyramidal tract motor pathways in the cerebral peduncle. This should be obvious on simple inspection of the patient, since it is usually a fairly prominent hemiplegia.
    • Subtle hemiparesis may be observed by asking the patient to hold both arms outstretched forward with palms rotated upward. Slight pronation of the turned-up hand and downward drift of the outstretched arm are sensitive indicators of even very mild hemiparesis.
    • The hemiparetic gait is also characteristic with foot drop causing circumduction as the involved leg is swung out and forward before the next step. The arm on the involved side typically is held semiflexed at the elbow and wrist as the patient walks.
    • Another subtle sign in very mild hemiparesis is loss of the associated arm swing on the involved side as the patient walks.
• Fascicular subarachnoid portion
  • Many patients who have had subarachnoid hemorrhage from rupture of a berry aneurysm have alteration of consciousness and may be difficult to examine. Even if they cannot co-operate with ocular motility assessment, the findings of a dense third cranial nerve palsy should be obvious. The eye on the involved side is deviated "down and out" from residual tone in the fourth cranial nerve (superior oblique muscle) and the sixth cranial nerve (lateral rectus muscle).
  • Usually, there is prominent ptosis also, but this may be difficult to observe if the patient is unconscious with eyes closed. Efforts should be made to arouse the patient at least to the point that there is some effort at eye opening, when the ptosis should be apparent.
  • The dilated, light-fixed pupil should be apparent on inspection without requiring any co-operation from the patient.
  • Pupillary involvement is the rule in third cranial nerve palsy resulting from posterior communicating artery aneurysm, with or without overt subarachnoid hemorrhage. This is probably because the pathophysiology of the third cranial nerve lesion involves leakage of blood from the aneurysm dome into the nerve across its outer margin. The pupil fibers are located very superficially and are nearly always involved in this process. On the other hand, pupil-sparing third cranial nerve palsy is a hallmark of ischemic lesions that tend to involve the central core of the nerve. This is the type of nonsurgical or medical third cranial nerve palsy that often results from microvascular disease and tends to resolve uneventfully within a few weeks.
• Fascicular cavernous sinus portion
  • Fourth cranial nerve palsy is difficult to diagnose in the presence of third cranial nerve palsy because the small increment of depressor deficit (superior oblique muscle) cannot be discerned readily from the depressor palsy that results from weakness of the third nerve innervated depressor (inferior rectus muscle).
    • The superior oblique muscle depresses the globe most efficiently with the eye in adduction, a position that may not be achievable with medial rectus palsy from third cranial nerve involvement.
    • The best marker for fourth cranial nerve function in the presence of dense third cranial nerve palsy is intorsion of the globe on attempted down gaze. If no intorsion is present, one should suspect concomitant fourth cranial nerve palsy as part of a cavernous sinus syndrome. Torsion of the globe can be discerned by simultaneously watching landmarks, such as conjunctival vessels lateral and medial to the iris. With intorsion, the lateral vessels rise and the nasal vessels drop.
  • Trigeminal nerve sensory function can be tested with the aid of a cotton-tipped applicator. Tease a few fibers of the cotton into a pointed bundle by twirling it between the thumb and the forefinger after a small tuft of cotton is pulled free of the tip.
    • This little wisp of cotton can be touched to the cornea near the limbus to test the corneal reflex. It should elicit a blink response that is symmetric between the sides.
    • Failure to blink may indicate reduced sensory function in the first division of the trigeminal nerve on the side of decreased response. The cotton wisp can be dragged lightly across the skin in various locations. With the eyes closed, the patient is asked to indicate when it is felt.
    • Asymmetry of light touch between sides should be sought. The wooden stick, when broken, can serve as a "pinprick" tester. Usually, the break is jagged and there is a pointed end that can be used like a pin to test for pain sensation. Lightly tap the point on the skin at various points. The patient should compare the "sharpness" of the feeling at homologous points on the right and left sides of the face.
• Fascicular orbital portion
  • Orbital signs are usually matters for direct inspection, including conjunctival injection and chemosis; proptosis; and lid swelling.
  • Obtain exophthalmometry measurements with a Hertel instrument or similar equipment since it provides a more sensitive measure of relative proptosis.

Causes

Any focally destructive lesion along the course of the third cranial nerve can cause oculomotor nerve palsy or dysfunction. Some of the most frequent causes include the following:

• Nuclear portion
  • Infarction
  • Hemorrhage
  • Neoplasm
  • Abscess
• Fascicular midbrain portion
  • Infarction
  • Hemorrhage
  • Neoplasm
  • Abscess
• Fascicular subarachnoid portion
  • Aneurysm
  • Infectious meningitis - Bacterial, fungal/parasitic, viral
  • Meningeal infiltrative
  • Carcinomatous/lymphomatous/leukemic infiltration, granulomatous inflammation (sarcoidosis, lymphomatoid granulomatosis, Wegener granulomatosis)
  • Ophthalmoplegic migraine
• Fascicular cavernous sinus portion
  • Tumor - Pituitary adenoma, meningioma, craniopharyngioma, metastatic carcinoma
  • Pituitary apoplexy (infarction within existing pituitary adenoma)⁵
  • Vascular
  • Giant intracavernous aneurysm
  • Carotid artery-cavernous sinus fistula
  • Carotid dural branch-cavernous sinus fistula
  • Cavernous sinus thrombosis
  • Ischemia from microvascular disease in vasa nervosa
  • Inflammatory - Tolosa-Hunt syndrome (idiopathic or granulomatous inflammation)
• Fascicular orbital portion
  • Inflammatory - Orbital inflammatory pseudotumor, orbital myositis
  • Endocrine (thyroid orbitopathy)
  • Tumor (eg, hemangioma, lymphangioma, meningioma)

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