Which cranial nerve governs most of the eye's external movements?

• A. Oculomotor nerve (CN III)
• B. Trochlear nerve (CN IV)
• C. Trigeminal nerve (CN V)
• D. Abducens nerve (CN VI)

Answer: (A)

The eye’s external movements are driven mainly by one nerve because it supplies most of the muscles that move the eyeball. The oculomotor nerve innervates four of the six extraocular muscles—the medial rectus, superior rectus, inferior rectus, and inferior oblique—and it also controls the eyelid via the levator palpebrae. With these muscles, the eye can move in most directions, so this nerve governs the majority of eye movement. The remaining movements come from the trochlear nerve, which activates the superior oblique, and the abducens nerve, which activates the lateral rectus; the trigeminal nerve doesn’t drive eye movements.