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THIRD (OCULOMOTOR) CRANIAL NERVE PALSY

ANATOMY

As the third cranial nerve enters the orbit, the nerve splits into a superior and inferior division. The inferior division supplies the inferior rectus, the inferior oblique, and the medial rectus muscles. The superior division supplies the superior rectus and the levator muscles. The parasympathetic fibers which innervate the pupil, originate in the Edinger Westphal nucleus, enter the orbit with the inferior division of the nerve and later separate from the inferior branch to terminate in the ciliary ganglion.

SIGNS

A third cranial nerve palsy may be partial or complete, and some or all of its functions may be partially or completely affected. The signs of a third cranial nerve defect include a downward and outward displacement of the globe with poor adduction due to paralysis of the medial rectus and poor elevation due to paralysis of the inferior oblique and superior rectus muscles.

Blepharoptosis (ptosis) of the eyelid on the affected side may occlude the visual axis of the affected eye. Patients will compensate for third cranial nerve palsy by contracting their frontalis muscle to elevate the eyelid or by assuming a head back posture to attempt to eliminate diplopia. The pupil will be dilated and unresponsive to light stimulation due to decreased innervation of the constricting muscle of the iris. There will also be a relative paralysis of accommodation. The ocular motility, eyelid, pupillary, and refractive problems which occur with third nerve paralysis are termed ophthalmolplegia.

Aberrant regeneration is seen in patients recovering from trauma, tumors and aneurysms. The signs of aberrant regeneration are listed below.

Signs of aberrant regeneration of the third cranial nerve

1. Horizontal gaze-eyelid synkinesis or elevation of the eyelid on adduction.

2. The pseudograefe sign. Retraction and elevation of the eyelid on attempted down gaze.

3. Adduction of the affected eye on up gaze or down gaze.

4. Pseudo Argyll Robertson pupil. The affected pupil will not react to light stimulation but will constrict on adduction.

SYMPTOMS

The symptoms of a third cranial nerve palsy include diplopia, inability to focus and, potentially, loss of vision due to occlusion of the visual axis if the levator muscle of the lid is significantly involved. The palsy may be partial or complete. An aneurysm should be suspected if the parasympathetic fibers (Weber's syndrome) may occur. If the lesion is more dorsal in its location in the midbrain, it may also involve the red nucleus and the patient will have ipsilateral ophthalmoplegia plus a contralateral intention tremor (Benedikt's syndrome).

ETIOLOGY

In children, third cranial nerve palsies may be congenital or occur as a result of trauma, tumors, inflammatory or infectious processes. When there is elevated intracranial pressure, the third cranial nerve is vulnerable to compression by herniation of the temporal lobe. Intermittent or episodic oculomotor palsy may be rarely seen in children with ophthalmoplegic migraine.

In adults and rarely, in children, a third cranial nerve palsy with pupillary involvement can indicate an aneurysm. If the palsy is due to a microvascular insult associated with atherosclerosis or diabetes, the pupil is usually not involved. Trauma and tumors are also frequent causes of third cranial nerve paralysis in adults.

EVALUATION

Unlike fourth cranial nerve palsies which usually do not require an evaluation, all third cranial nerve palsies must be evaluated to determine their etiology. In children, MRI or CT scanning with contrast enhancement will help to clarify the cause of the third cranial nerve palsy. In adults, evaluation may include imaging studies and glucose tolerance testing. If there is strong suspicion of an aneurysm, a cerebral arteriogram may be requested. In select cases, Tensilon testing may be useful to establish or exclude a diagnosis of myasthenia gravis which may mimic third nerve paralysis.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis of third cranial nerve palsy includes the following conditions:

Ocular motility findings and ptosis

Progressive External Ophthalmoplegia

Early Signs of Thyroid Disease

Myasthenia Gravis

Orbital Inflammatory Disease

Type II Duane's Syndrome

Congenital Blepharoptosis

Generalized Myopathic Conditions

Anisocoria (Pupillary dilation)

Cycloplegic Eye Drops

Adie's Syndrome

Contralateral Horner's Syndrome

Traumatic Mydriasis

TREATMENT

Generally speaking, treatment of an acute cranial nerve palsy should be delayed for six months to permit spontaneous recovery of nerve function. During this recovery period, measures can be taken to eliminate diplopia and make the patient more comfortable. In adults and children over 8 years of age in whom amblyopia is not a consideration, simple occlusion of the affected eye with a patch will eliminate diplopia. In children where amblyopia is a consideration, occlusion of the noninvolved eye 4 - 6 hours per day will help prevent amblyopia.

Head posturing to obtain single binocular vision is helpful in cases of incomplete paralysis. If the affected eye is fairly well centered, occlusion of the non-involved eye may be suggested to prevent a contracture of the lateral rectus muscle. In select patients, injection of botulinum toxin into the lateral rectus muscle may be helpful as a temporizing measure. In patients with significant hypermetropia in whom accommodation is affected, prescription of glasses with a bifocal may be helpful to improve visual acuity. Because the affected eye is displaced downward and out and paralysis of the inferior oblique muscle adds a torsional component to the diplopia, treatment with glasses incorporating prisms is usually unsatisfactory.

Surgical treatment may be considered after a waiting period of six months. The goal of eye muscle surgery is to eliminate diplopia by aligning the eyes in the most important gaze positions, straight ahead gaze and in the reading position. This can be accomplished in most cases with recess-resect procedures or muscle transposition procedures. Realistically, some limitation in the motility of the involved eye will remain after surgery, especially in more severely affected cases.

Strabismus surgery is usually performed prior to correction of the eyelid abnormality. Caution should be exercised in the surgical treatment of blepharoptosis since the patient's Bell's phenomenon is usually absent because of involvement of the superior rectus and inferior oblique muscles (both elevators of the globe). In patients with accompanying fifth cranial nerve paralysis, as occurs with an orbital apex syndrome, elevation of the eyelid will usually cause a breakdown of the corneal epithelium. In these cases it may be judicious to let the involved eyelid cover the cornea.

Following corrective strabismus and eyelid surgery, the position of the eye may be "fine tuned" with glasses incorporating a prism and a bifocal. A realistic goal should be to center the eye in primary gaze and provide the patient comfort in the reading position. If the third cranial nerve palsy is profound, a zone of single binocular vision can usually be achieved. However, diplopia will occur when moving the eyes to look right, left, up or down. Once a zone of single binocular vision has been achieved in a useful position or gaze, the patient must move his or her head to fixate on objects out of the primary gaze position.

SUMMARY

Acute third cranial nerve palsies require thorough evaluation since life threatening conditions such as tumors or aneurysms may be the etiology for the paralysis. Once the evaluation has revealed the cause, a waiting period of 6 months from the time of onset or injury is recommended prior to surgical correction as spontaneous recovery of nerve function may occur. During this waiting period, occlusion, glasses, and head posturing may be required to reduce diplopia. Surgery may be required in cases of permanent paralysis to reduce diplopia. However, since four of the six extraocular muscles, the eyelid, and the accommodation and pupillary response may all be involved to varying degrees, there must be realistic expectations regarding final outcome.

Pediatric Ophthalmology and Strabismus, Inc.

9/25/09