Trochlear Nerve Palsy

What is the Trochlear Nerve?

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

It is the fourth cranial nerve — a motor nerve that carries signals from the brain to the muscles. The fourth cranial nerve works with the oculomotor nerve and the other eye muscles to control eye movement.

It powers the eye’s superior oblique muscle, which makes it possible to look down. The nerve also allows you to move your eyes towards your nose or away from it.

What is the function of the Trochlear Nerve?

The trochlear nerve takes its name from the Latin word for pulley, “trochlea”. A pulley is a device used to lift an object.

In each eye, the superior oblique muscle acts as the trochlea. The trochlear nerve stimulates this muscle so that you can look down, and it also enables you to move your eyes towards your nose or away from it.

What medical conditions affect Trochlear Nerve functioning?

When the trochlear nerve does not work as it should, the cause is often fourth nerve palsy, a condition known as trochlear nerve palsy. A palsy occurs when illness or injury paralyses the nerves that control muscle movement.

What causes Trochlear Nerve Palsy?

In some people the palsy is congenital, meaning they are born with the condition. It may also result from trauma caused by rapid head movement, as in a road traffic accident. The trochlear nerve is one of the more fragile cranial nerves because it is long and thin, and palsy sometimes follows even minor injuries.

Less common causes include:

• Cavernous sinus syndrome, in which an abnormal growth affects the trochlear nerve.
• Guillain-Barré syndrome.
• Lyme disease.
• Meningioma.
• Microvascular disease (small-vessel disease, e.g. from diabetes or hypertension).
• Shingles (Herpes Zoster) infection.
• Superior oblique myokymia — episodes of involuntary tightening of the superior oblique muscle that distort vision.

How is Trochlear Nerve Palsy treated?

The right treatment depends on what is causing your symptoms. Where vision problems follow a minor injury, symptoms often resolve on their own.

For more severe injuries, or palsies caused by an underlying medical condition, your care may include:

• An eye patch to rest the eye.
• Special glasses to correct double vision.
• Surgery to repair the fourth cranial nerve.

When should I call an eye specialist about concerns with Trochlear Nerve?

Contact your eye specialist if you experience symptoms of trochlear nerve palsy. These often include changes in vision that worsen when you look down, such as blurred or double vision.

Tilting your head up and to the side may help you compensate for the changes in vision, but this posture strains the 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 inwards (crossed eyes).
• Hypertropia, a form of strabismus in which both eyes turn upwards.
• Midfacial hypoplasia, which occurs with congenital fourth nerve palsy and distorts facial features, including the eyes.

A note from Athens EyeCare Clinic

The trochlear nerve is fragile, and protecting your head from injury helps keep it safe. Both minor head injuries and more severe trauma can cause fourth nerve palsy, which may lead to double vision, crossed eyes and other problems. Depending on the cause, symptoms may resolve on their own; some people need special glasses or surgery.