Sixth nerve palsy is a disorder that affects eye movement. It’s caused by damage to the sixth cranial nerve. The primary function of the sixth cranial nerve is to send signals to your lateral rectus muscle.
This small muscle is located on the outer side in your eye. It is responsible for turning your eye away from your nose. When the lateral rectus muscle weakens, your eye crosses inward toward your nose.
Because each eye has its own lateral rectus muscle and sixth cranial nerve, sixth nerve palsy can affect one or both eyes. Your symptoms and the severity of the condition depend on whether both eyes are affected.
Double vision is the most common symptom of sixth nerve palsy. You may notice this vision impairment when both eyes are open or when you're looking at something in the distance. Sometimes, double vision occurs when looking in the direction of the damaged eye. It’s also possible to have sixth nerve palsy without double vision.
Another symptom of this condition is poor eye alignment or strabismus, also called crossed eyes. This is when your eyes don’t look in the same direction at the same time.
Double vision and strabismus are typical with sixth nerve palsy. But you may have other symptoms. The sixth cranial nerve travels from the brainstem to the lateral rectus muscle. This means neurologic disorders may cause sixth nerve palsy.
When sixth nerve palsy occurs without other symptoms, it’s known as isolated sixth nerve palsy. The addition of other symptoms may suggest involvement of more than just the sixth nerve.
There are several causes of sixth nerve palsy. The condition can be congenital and affect a person from birth. This is sometimes due to injury of the sixth cranial nerve during labor or delivery. But sometimes the cause of congenital sixth nerve palsy is unknown.
Various circumstances and illnesses can also cause the disorder. This includes a head injury or skull fracture that damages the sixth cranial nerve. The disorder may also develop as the result of inflammation in the sixth cranial nerve.
Other conditions that can cause sixth cranial nerve damage or inflammation include:
- Lyme disease
- brain tumor
- diabetic neuropathy
- multiple sclerosis
- brain aneurysm
The most common cause of sixth nerve palsy in children is trauma, like from an accident involving a head injury. In adults, the most common cause is a stroke.
Anyone can develop sixth nerve palsy, and there’s no particular group of people at higher risk for this disorder. But you can take steps to protect yourself. Since trauma is a common cause, you should use caution and protect your head from injuries when playing sports or riding a bicycle.
Likewise, since stroke is a common cause of sixth nerve palsy in adults, you can take precautions to reduce your risk of stroke. These measures include:
- controlling high blood pressure
- increasing physical activity
- losing weight
- maintaining a healthy diet
If you have double vision or if your eyes aren’t aligning properly, see your doctor. To diagnose sixth nerve palsy, your doctor will ask questions about your medical history and do a complete physical examination.
Because sixth nerve palsy has various possible causes, your doctor may order a series of tests. Treating the underlying problem may gradually correct the disorder. These tests include:
- brain scan to check for a brain tumor, skull fracture, brain injury, or increased pressure in the brain
- blood test or a lumbar puncture to diagnose or rule out meningitis
- neurological tests to check for abnormalities in your nervous system
In some cases, treatment is unnecessary and sixth nerve palsy improves in time, such as when the disorder is caused by a viral infection that has to run its course. Other times, the disorder only improves once the underlying cause has been treated.
Treatment depends on your diagnosis. Your doctor may prescribe antibiotics if your sixth nerve palsy is caused by a bacterial infection.
Prescription-strength corticosteroids can treat sixth nerve palsy caused by inflammation.
If you have a brain tumor, symptoms of sixth nerve palsy may not improve until you have surgery, chemotherapy, or other treatments to remove the tumor or kill cancer cells.
You may never recover from sixth nerve palsy caused by trauma. Your doctor may monitor your condition over a six-month period. If double vision or strabismus hasn’t improved or worsens, options include wearing an eye patch over the affected eye long-term to alleviate double vision. Your doctor may also recommend prism glasses to provide single binocular vision and align your eyes.
Some medical procedures are also effective. These include Botulinum toxin injections (Botox) where your doctor paralyzes the muscles on one side of your eye to correct poor alignment. Eye surgery is another option. If successful, surgery can stop an affected eye from pulling inward toward the nose.
Sixth nerve palsy doesn’t cause complications. But you may have complications from underlying conditions. This is why it’s important to understand the cause of your disorder.
The long-term outlook for this condition depends on the cause. With treatment, symptoms of sixth nerve palsy usually go away within the first six months of onset. Even though symptoms may not completely go away after a trauma, you may notice some vision improvement as your body heals.