Superior oblique -damage to the trochlear nerve causes weakness of the superior oblique muscle, resulting in the inability of the orbit to deviate downward when the eye is intorted. to compensate for the classically vertical double vision, the patient tends to tilt his head to the contralateral side, causing the contralateral eye to intort. the trochlear nerve supplies the superior oblique muscle. the trochlear nerve is the only nerve to decussate peripherally, and also to emerge from the dorsal aspect of the brainstem. in this case, the damaged nerve emerged from the right (contralateral) dorsal midbrain. the action of the superior oblique muscle is to rotate the orbit medially and downward. because the trochlear nerve is not only the smallest cranial nerve but also has the longest course of any cranial nerve, it is especially vulnerable to trauma. one of the most common causes of trochlear nerve palsy is trauma.