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Third Cranial Nerve (Oculomotor Nerve) Palsy

By Michael Rubin, MDCM, Weill Cornell Medical College;New York Presbyterian Hospital-Cornell Medical Center

A palsy of the 3rd cranial nerve can impair eye movements, the response of pupils to light, or both.

  • These palsies can occur when pressure is put on the nerve or the nerve does not get enough blood.

  • People have double vision when they look in a certain direction, the eyelid droops, and the pupil may be widened (dilated).

  • Doctors do a neurologic examination and magnetic resonance imaging (MRI) or computed tomography (CT) of the brain.

  • Treatment depends on the cause.

The most common causes of this palsy are

  • Pressure on (compression of) the nerve

  • Inadequate blood flow to the nerve

Compression tends to result from serious disorders, such as

Herniation occurs when the brain is forced downward through a small natural opening in the sheets of tissue that separate the brain into compartments. Herniation may result from bleeding (sometimes caused by a head injury—see Overview of Head Injuries), a tumor, or another mass in the brain.

Inadequate blood flow is more common and usually less serious. It typically results from

  • Diabetes

  • High blood pressure (hypertension)

  • Other disorders that affect blood vessels

Symptoms

The affected eye turns outward when the unaffected eye looks straight ahead, causing double vision. The affected eye can move only to the middle when looking inward and cannot move up and down. Because the 3rd cranial nerve also raises the eyelids and controls the pupils, the eyelid droops, and the pupil may be widened (dilated) and may not narrow (constrict) in response to light. The pupil is often affected when the cause is compression of a nerve.

The disorder causing the palsy may worsen, resulting in a serious, life-threatening condition. For example, a severe headache may occur suddenly, or a person may become increasingly drowsy or less responsive. In such cases, the cause may be a ruptured aneurysm, which then bleeds. People may go into a coma. In such people, dilation of both pupils and lack of response to light (fixation) by both pupils indicates deep coma and possibly brain death (see Brain Death).

Diagnosis

  • Neurologic examination

  • Magnetic resonance imaging or computed tomography

  • Sometimes other tests

The diagnosis is based on results of a neurologic examination (see Physical Examination) and magnetic resonance imaging (MRI) or computed tomography (CT) of the brain.

If the pupil is affected or if symptoms suggest a serious underlying disorder, brain MRI or CT is done immediately.

If a ruptured aneurysm is suspected and MRI or CT does not detect blood, a spinal tap (lumbar puncture—see Figure: How a Spinal Tap Is Done), magnetic resonance angiography (see Magnetic resonance angiography), CT angiography (see CT angiography), or cerebral angiography is done (see Angiography).

Treatment

  • Treatment of the cause

Treatment depends on the cause. Emergency treatment is required if a life-threatening disorder is the cause.

* This is the Consumer Version. *