Merck Manual

Please confirm that you are a health care professional

honeypot link

Fourth Cranial (Trochlear) Nerve Palsy


Michael Rubin

, MDCM, New York Presbyterian Hospital-Cornell Medical Center

Reviewed/Revised Feb 2022 | Modified Sep 2022
View Patient Education

Fourth cranial nerve palsy impairs the superior oblique muscle, causing paresis of vertical gaze, mainly in adduction.

Fourth cranial (trochlear) nerve palsy is often idiopathic. Few causes have been identified. Causes include the following:

  • Closed head injury (common), which may cause unilateral or bilateral palsies

  • Infarction due to small-vessel disease (eg, in diabetes)

Rarely, this palsy results from aneurysms, tumors (eg, tentorial meningioma, pinealoma), or multiple sclerosis.

Fourth cranial nerve palsy may affect one or both eyes. Because the superior oblique muscle is paretic, the eyes do not adduct normally. Patients see double images, one above and slightly to the side of the other; thus, going down stairs, which requires looking down and inward, is difficult. However, tilting the head to the side opposite the palsied muscle can compensate and eliminate the double images.

Examination may detect subtle impaired ocular motility, causing symptoms but not signs. CT or MRI may be done to identify the cause.

Treatment of Fourth Cranial Nerve Palsy

  • Oculomotor exercises

  • Prism glasses

  • Possibly surgery

Oculomotor exercises or prism glasses may help restore concordant vision. If the palsy does not resolve, surgery, mainly for congenital strabismus, may eventually be needed.

View Patient Education
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
quiz link

Test your knowledge

Take a Quiz!