The trochlear nerve, also known as cranial nerve 4 (CN IV), controls the superior oblique muscle in your eye. This muscle allows you to move your eyeball down and shift your gaze from side to side.

The trochlear nerve, like the oculomotor nerve, originates in the midbrain. It powers the contralateral superior oblique muscle that allows the eye to point downward and inward.

When the fourth cranial nerve is injured or diseased, it can cause paralysis of the superior oblique muscle. This is known as superior oblique palsy, trochlear nerve palsy, or fourth nerve palsy.

Trochlear nerve palsy. Dr. Jeff Hersh/Daily News Correspondent. Q: My friend had a head injury while playing soccer. She did not lose consciousness or anything, but she developed what the doctor ...

Two cranial nerves — cranial nerve 3, known as the oculomotor nerve, and cranial nerve 4, known as the trochlear nerve — control the muscles that move the eyes vertically.