Which cranial nerve innervates the superior oblique muscle involved in eye movements?

• A. Trochlear
• B. Oculomotor
• C. Abducens
• D. Facial

Answer: (A)

The superior oblique muscle is innervated by the trochlear nerve, the fourth cranial nerve. This nerve specifically sends motor fibers to that muscle, enabling the eye to intort and to depress when it is adducted. Other cranial nerves control other eye muscles: the oculomotor nerve handles most extraocular muscles and eyelid elevation, the abducens nerve moves the eye outward (abduction) via the lateral rectus, and the facial nerve does not innervate eye muscles. So, the nerve that supplies the superior oblique is the trochlear nerve. If the trochlear nerve is impaired, vertical diplopia worsens when looking downward, often causing compensatory head tilt.