Trochlear nerve palsy

Trochlear nerve palsy paralyzes the superior oblique muscle. The affected eye deviates upward and slightly inward, i.e., medially, toward the side of the normal eye. The deviation is most evident, and the diplopia most extreme, when the patient looks downward and inward. Another way of bringing out the upward-and-inward deviation of the affected eye and the resulting diplopia is by having the patient tilt the head to the affected side while fixating on an object with the normal eye (Bielschowsky test). The more common causes of trochlear nerve palsy are trauma (30–60 % of cases), vascular lesions, and tumors.