Congenital Fourth Nerve Palsy - Pathophysiology

Pathophysiology

The fourth cranial nerve innervates the superior oblique muscle for each eye. The superior oblique muscle is one of the six extraocular muscles that allow movement of eye. Specifically, the superior oblique muscle primarily intorts the eye (such that the top of the eye rolls toward the nose), with secondary actions of depression (downgaze) and abduction (looking away from the nose). When this muscle’s function is diminished due to a fourth cranial nerve (CN IV) palsy, the affected eye will extort, deviate upward (hypertropia), and, to a smaller extent, drift inward.