The Trochlear Nerve

The trochlear nerve innervates the superior oblique muscle, whose primary action is incyclotorsion of the eye. This article reviews the delicate and unique anatomy of the trochlear nerve, which has the longest intracranial course among the cranial nerves. We discuss the various presentations of trochlear nerve palsy, the possible localization of pathology through associated neurologic signs, and review the etiology of fourth nerve palsy, including traumatic, vascular, and congenital causes, among others. We also review the principles of management and treatment of trochlear nerve palsy, including prism glasses and strabismus surgery.