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 a unilateral or bilateral palsy
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 also be present at birth (congenital strabismus).
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 obvious 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 to improve eye alignment may eventually be needed.
