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Fourth Cranial Nerve (Trochlear Nerve) Palsy

By Michael Rubin, MDCM

A palsy of the 4th cranial nerve affects vertical eye movements.

  • Often doctors cannot identify the cause, but when they can, the cause is usually a head injury, sometimes a minor one.

  • People see double images, but tilting the head to side opposite the affected eye can eliminate them.

  • Doctors suspect palsy of the 4th cranial nerve based on the symptoms, but computed tomography or magnetic resonance imaging may be done.

  • The cause, if identified, is treated.

Often, the cause cannot be identified. The most common identified cause is

  • A head injury, often due to a motorcycle accident but sometimes even relatively minor head trauma

Occasionally, diabetes causes this palsy. Rarely, the cause is a tumor, a bulge (aneurysm) in an artery in the skull, or multiple sclerosis.

One or both eyes may be affected. The affected eye cannot turn inward and down. As a result, people see double images, one above and slightly to the side of the other. Thus, going down stairs, which requires looking inward and down, is difficult. However, tilting the head to the side opposite the affected eye muscle can compensate and eliminate the double images. This position can eliminate the double images because people use eye muscles that are unaffected by the palsy to focus both eyes on an object.

Diagnosis

  • Limited eye movement

  • Computed tomography or magnetic resonance imaging

Usually, the diagnosis is suspected if a person has characteristic limited eye movement. Computed tomography (CT) or magnetic resonance imaging (MRI) of the brain may be done.

Treatment

  • Treatment of the cause, if identified

  • Eye exercises

  • Prism glasses

The disorder causing the palsy, if identified, is treated.

Eye exercises may help, as may wearing prism glasses.

The palsy usually resolves over time.

* This is the Consumer Version. *