Trochlear Nerve

The trochlear nerve is one of 12 sets of cranial nerves. It enables movement in the eye’s superior oblique muscle. This makes it possible to look down. The nerve also enables you to move your eyes toward your nose or away from it.


What is the trochlear nerve?

The trochlear nerve is one of 12 sets of cranial nerves. It is part of the autonomic nervous system, which supplies (innervates) many of your organs, including the eyes.

This nerve is the fourth set of cranial nerves (CN IV or cranial nerve 4). It is a motor nerve that sends signals from the brain to the muscles. CN IV works with the oculomotor nerve and other eye muscles to control eye movement.


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What is the function of the trochlear nerve?

The trochlear nerve gets its name from the Latin word pulley, “trochleae.” A pulley is a device that lifts an object.

In each eye, the superior oblique muscle functions as the trochlea. The trochlear nerve innervates this muscle to lift the eyes so you can look down. The nerve also enables you to move your eyes toward your nose or away from it.


What is the anatomy of the trochlear nerve?

Cranial nerve 4 starts in the brainstem, the lower part of the brain near the top of your spine. It passes through four areas before reaching the superior oblique muscle. This muscle is near the top of the eyeball.

These areas include:

  1. Trochlear nucleus: This is the part of the trochlear nerve nearest the brain. It is near the top of the brainstem.
  2. Ambient cistern: This area is near the brain’s outer protective tissue (dura).
  3. Cavernous sinus: A hollow space that allows blood from the brain to leave the body. It is in the middle of your skull.
  4. Orbit: The bony sockets of the skull that house the eyeballs.


Conditions and Disorders

What medical conditions affect trochlear nerve functioning?

When the trochlear nerve doesn’t function as it should, it’s often due to fourth nerve palsy. The condition is called trochlear nerve palsy. A palsy occurs when illness or injury paralyzes nerves that control muscle movement.

What causes fourth nerve palsy?

In some people, it’s congenital, meaning they are born with this condition. It may also be due to trauma from rapid head movements, like during motor vehicle accidents. The trochlear nerve is one of the more fragile cranial nerves because it’s thin and long. Cranial nerve palsy sometimes occurs after minor injuries.

Less common causes include:


How is fourth nerve palsy treated?

The treatment that’s right for you depends on what’s causing your symptoms. For vision issues due to minor injuries, symptoms often go away on their own.

For more severe injuries or palsies due to medical conditions, your care may include:

  • Eye patch to help the eye rest.
  • Special glasses to correct double vision.
  • Surgery to repair cranial nerve 4.


How can I protect my trochlear nerve?

It might not be possible to prevent some causes of fourth nerve palsy. If it is present at birth, that’s out of your control.

There are steps you can take to prevent head injuries that damage the trochlear nerve. These include:

  • Babyproofing your home if you have an infant by putting up a baby gate near stairs.
  • Making safe living areas for older adults by using grab bars to lower fall risks.
  • Using a seatbelt when you’re in a car, even for short trips.
  • Wearing a helmet when riding a bicycle or playing contact sports, like hockey.

Additional Common Questions

When should I call a healthcare provider about concerns with CN IV?

Contact your healthcare provider if you experience symptoms of fourth nerve palsy. They often include vision changes that worsen when you look down. These include blurry or double vision.

Tilting your head up and to the side may help you compensate for the vision changes. But this posture strains neck muscles and can become painful.

Other concerning symptoms that need medical attention include:

  • Misalignment of the eyes (strabismus).
  • Esotropia, a form of strabismus in which one or both eyes turn inward (crossed eyes).
  • Hypertropia, a form of strabismus in which both eyes turn upward.
  • Midfacial hypoplasia, which occurs with congenital fourth nerve palsy and distorts facial features, including the eyes.

A note from Cleveland Clinic

The trochlear nerve is fragile. Protecting your head from injury can help keep your trochlear nerve safe. Minor head injuries and more severe ones from trauma can cause fourth nerve palsy. This condition can cause double vision, crossed eyes and more. Depending on the cause, symptoms may go away on their own. Some people need special glasses or surgery.

Medically Reviewed

Last reviewed on 08/10/2021.

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