Third nerve palsy

Definition

Third nerve palsy describes a condition involving the third cranial nerve (also called the oculomotor nerve), which is responsible for innervating some of the muscles responsible for eye movement.

Description

Third nerve palsy results in an inability to move the eye normally in all directions. Injury to the third nerve can occur anywhere along its path, from where it originates within the brain to where it innervates the muscles that move the eyeball. Third nerve palsy prevents the proper functioning of the medial, superior, and inferior recti, and inferior oblique muscles. As a result, the eye cannot move up, down, or in. When at rest, the eye tends to look down and to the side, due to an inequality of muscle functioning. The muscle responsible for keeping the upper eyelid open (levator palpebrae superioris) is also affected, resulting in a drooping upper eyelid (ptosis).

Causes and symptoms

A wide variety of conditions can result in third nerve palsy, including pressure and damage from tumors; blocked arteries or aneurysms leading to oxygen deprivation of nerves; meningitis; vascular complications of diabetes or high blood pressure; complications of migraine headaches; traumatic injury; birth injury; congenital defects; and conditions that strip nerve fibers of their myelin coating, resulting in slowed nervous transmission.

Some patients have severe pain and double vision (diplopia), in addition to problems moving their eyes normally. The affected eye tends to move down and out, due to an inequality in muscle functioning. The eye cannot move up, down, or in. In some cases, the pupil remains fixed in a dilated state. The upper eyelid is droopy (ptosis). The eyeball itself may actually be slightly displaced, pushed more forward than normal (proptosis).

Additionally, after the acute phase of third nerve palsy, as the nerve attempts to regenerate, a phenomenon called oculomotor synkinesis may take place. In this associated condition, nerve sprouts accidentally misdirect nerve transmission, so that efforts to utilize certain muscle groups accidentally prompt the functioning of other muscle groups. Therefore, attempts to accomplish certain muscular tasks actually result in different muscular tasks occurring. For example, as an individual with oculomotor synkinesis attempts to look down, the eyelid may raise up; when attempting to look up, the eye instead moves towards the midline; when attempting to look towards the midline, the pupil constricts.

Diagnosis

Eye muscle dysfunction is usually revealed during the course of a basic physical examination, which should always include testing of eye movements and examination of the pupils. MRI , CT , or angiography (a dye test that lights up the arteries throughout the brain, allowing the arteries to be better visualized on CT or MRI) may reveal the underlying cause of third nerve palsy.

Treatment team

Ophthalmologists and neurologists may work together to care for patients with third nerve palsy. In addition, physicians who manage diabetes, high blood pressure, or other underlying causative conditions will be involved in the patient's care.

Treatment

Steroids may treat pain and double vision. Special lenses with prisms may improve diplopia. Surgery on the eye muscles or eyelid may be necessary in some cases, although most clinicians recommend waiting six months from onset so that the patient's condition stabilizes.

Prognosis

In individuals who have no pupil involvement, and whose third nerve palsy is due to complications of diabetes or high blood pressure, symptoms may actually resolve within three to six months of onset. Other patients have a variable outcome, depending on the underlying condition responsible for the third nerve palsy.

Resources

BOOKS

Donahue, Sean P. "Nuclear and Fascicular Disorders of Eye Movement." In Opthalmology, edited by Myron Yanoff, et al. St. Louis: Mosby, 2003.

Goodwin, James. "Cranial Nerves III, IV, and VI: The Oculomotor System." In Textbook of Clinical Neurology, edited by Christopher G. Goetz. Philadelphia: W. B. Saunders Company, 2003.

Noble, John, et al., eds. Noble: Textbook of Primary Care Medicine. St. Louis: W. B. Saunders Company, 2001.

Rosalyn Carson-DeWitt, MD