Fourth Nerve Palsy (Trochlear Nerve Palsy)

What is fourth nerve palsy?

Fourth nerve palsy (trochlear nerve palsy) happens when issues with your fourth cranial nerve cause vertical (up and down) eye movement and vision issues. It usually affects one eye (unilateral) but can affect both (bilateral).

When working properly, your fourth cranial nerve (trochlear nerve) and the eye muscle it controls make it possible for you to look down. They also enable you to move your eyes toward your nose or away from it.

How common is fourth nerve palsy?

Fourth nerve palsy (trochlear nerve palsy) is rare. It affects about 5 per 100,000 people each year in the United States. That’s about 17,100 cases a year.

What are the symptoms of fourth nerve palsy?

Symptoms of fourth nerve palsy include:

• Double vision vertically (vertical diplopia).
• Vision being tilted or rotated (torsional diplopia).
• Vision problems when looking down, like when reading a book or going down the stairs.
• Tilting your head to compensate for eye movement or vision challenges.
• Crossing of your eyes (strabismus).

Strabismus in fourth nerve palsy can look like:

• Hypertropia, in which one eye turns upward.
• Esotropia, in which one or both eyes turn inward (crossed eyes).

It’s important to see a healthcare provider if you or your child have these symptoms.

What causes fourth nerve palsy?

Fourth nerve palsy can happen with any condition or event that damages your fourth nerve.

In some cases, healthcare providers may not be able to find a cause. They call this idiopathic fourth nerve palsy.

Congenital fourth nerve palsy and superior oblique palsy

The most common cause of fourth nerve palsy is congenital, meaning you have it from birth. But researchers don’t know exactly why it develops. Healthcare providers may also call this congenital superior oblique palsy. This is the muscle that your fourth cranial nerve controls.

Most people with congenital fourth nerve palsy are born without a trochlear nerve, and their superior oblique muscle is weak (atrophied). For others, the trochlear nerve appears healthy, but the tendon of the superior oblique doesn’t function properly.

Even though this form is present from birth, your baby may have no or just subtle symptoms. Their symptoms may become more noticeable with age. Many people with congenital fourth nerve palsy don’t receive a diagnosis until childhood or early adulthood.

Fourth nerve palsy due to head trauma

Your trochlear nerve has a long path through your head, so it’s vulnerable to damage from head trauma. Common causes of acquired (developed after birth) fourth nerve palsy include vehicle accidents and boxing. This is likely due to the “whiplash” movement (rapid deceleration) of your head in these scenarios. But even mild head injuries can lead to trochlear nerve damage.

Other causes of fourth nerve palsy

Other health conditions can cause damage to your trochlear nerve, leading to fourth nerve palsy. These causes are less common and include:

• Blood vessel disease (typically due to diabetes).
• Pressure from a nearby tumor, like a meningioma.
• Increased intracranial pressure.
• Lyme disease (caused by a tick bite).
• Guillain-Barré syndrome.
• Shingles (herpes zoster).
• Accidental damage from brain surgery.

How is fourth nerve palsy diagnosed?

Healthcare providers can typically diagnose fourth nerve palsy based on your symptoms and by assessing your vision and eye movements with simple tests.

You’ll likely need to see an ophthalmologist (eye doctor) or a neurologist to get a diagnosis. Your provider will ask about the vision issues you have and if they get better or worse when you look in certain directions. They’ll have you look at objects, and you’ll tell your provider how the objects appear to you.

If you develop symptoms after head trauma, your provider will likely recommend imaging of your brain, like a brain MRI.

What is the treatment for fourth nerve palsy?

The treatment that’s right for you depends on what’s causing fourth nerve palsy. When an injury or damage is the cause, many cases resolve on their own once your nerve heals — typically within six months.

While your fourth nerve is healing, you may need to wear prism eyeglasses to correct double vision. If these aren’t effective, wearing an eye patch over your affected eye may help.

If your symptoms don’t improve after six months, your healthcare provider may recommend surgery. This typically involves adjusting other eye muscles that are overcompensating for a weak superior oblique muscle. It can help correct eye movement issues.

Your provider will go over the treatment options and details with you, which will be unique to your case.

Can I prevent fourth nerve palsy?

Some causes of fourth nerve palsy are unpreventable, like congenital (present from birth) cases. But you can take steps to prevent head injuries that could damage your fourth cranial nerve. These include:

• Using a seatbelt when you’re in a vehicle and practicing car seat safety for your child.
• Wearing a helmet when riding a bicycle or motorcycle or playing contact sports.
• Making your house safe if you have a baby or toddler (childproofing) to help prevent dangerous falls or head injuries.
• Making safe living areas for loved ones with balance issues or an increased fall risk.

What is the prognosis for someone with fourth nerve palsy?

Many cases of acquired fourth nerve palsy improve on their own with time — usually within six months. For cases that require surgery, the success rate is usually good.

Your healthcare provider will be able to give you a better idea of what to expect based on your own situation.

When should I see my healthcare provider?

You should see your healthcare provider as recommended for follow-up visits so they can track any changes and modify your treatment if necessary. Fourth nerve palsy isn’t an emergency, but it’s a condition that you should get properly diagnosed and treated for.