Sixth nerve palsy, also known as abducens nerve palsy, is a disorder that affects eye movement. It’s caused by damage to the sixth cranial nerve or obstruction anywhere along its path from the brainstem to the eye.
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 of your eye. It’s responsible for turning your eye away from your nose. When the lateral rectus muscle weakens, your eye can cross inward toward your nose.
There are several causes of sixth nerve palsy.
The condition can affect a person from birth. This is sometimes due to an injury to the sixth cranial nerve during labor or delivery.
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.
But sometimes the cause of sixth nerve palsy is unknown.
Conditions known to cause sixth cranial nerve damage or inflammation can include:
- head injury
- skull fracture
- injury during birth
- brain aneurysm
- infection, such as Lyme disease, syphilis, tuberculosis, or meningitis
- inflammatory lesions, such as from sarcoidosis or lupus
- brain tumor or the abnormal growth of tissue in the brain
- diabetic neuropathy
- multiple sclerosis
- injury during a procedure, such as spinal anesthesia or postlumbar puncture
- cavernous sinus thrombosis, a condition caused by a blood clot behind your eye sockets
- mastoiditis, an infection in the bone behind the ear
- temporal arteritis, inflammation of the blood vessels around the scalp
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 stroke.
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.
Symptoms can include:
- Double vision. Double vision or diplopia when looking side to side 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.
- Poor eye alignment or strabismus. Also called crossed eyes, poor eye alignment is when your eyes don’t look in the same direction at the same time.
- Head movement to maintain vision. Sometimes, people with sixth nerve palsy may make a constant turning motion with their head in order to reduce their double vision.
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.
Other symptoms may include:
- papilledema or swelling of the optic nerve
- vision loss
- hearing loss
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.
Sixth nerve palsy can affect both children and adults. Those who have had a head injury may have a higher risk of developing this condition. However, there are steps you can take to prevent long-lasting head injuries. These can include:
- Taking protective measures. You can protect your head from injuries when playing sports or wear a helmet when riding a bicycle.
- Recognizing the effects of a traumatic brain injury (TBI). Vision changes, loss of consciousness, disorientation, sensitivity to light and sound, slurred speech, and other symptoms may be signs of a TBI.
- Seeking immediate medical attention. In cases of suspected head injuries in children and adults, medical professionals can access the risk, locate the area of trauma, and begin treatment.
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
- maintaining a moderate weight
- maintaining a balanced diet
- controlling diabetes mellitus
If you have double vision or if your eyes aren’t aligning properly, talk with a doctor. To diagnose sixth nerve palsy, the doctor will ask questions about your medical history and do a complete physical examination.
Because sixth nerve palsy has various possible causes, the doctor may order a series of tests. Treating the underlying problem may gradually correct the disorder.
Doctors may use neuroimaging to check for a brain tumor, skull fracture, brain injury, or increased pressure in the brain. They may also use blood tests to help diagnose an infection or another condition.
These tests can include:
- computed tomography (CT) scan
- magnetic resonance imaging (MRI)
- positron emission tomography (PET) scan
- a complete blood count or other blood tests
- lumbar puncture
- diabetes testing
- other neurological tests to check the health of 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. The doctor may monitor your condition over a 6-month period.
Other times, the disorder only improves once the underlying cause has been treated.
Treatment depends on your diagnosis and can include:
- Antibiotics. The doctor may prescribe antibiotics if your sixth nerve palsy is caused by a bacterial infection.
- Steroids. Prescription-strength corticosteroids can treat sixth nerve palsy caused by inflammation.
- Surgery. If your condition is caused by intercranial pressure, the doctor may perform surgery to reduce that pressure. Cancer may also be removed surgically.
- Lumbar puncture. This may also be used to reduce pressure in the brain.
- Chemotherapy and other cancer treatments. If your sixth nerve palsy is caused by a brain tumor, complementary therapies may reduce or eliminate cancer cells that remain after surgery.
- Prism therapy. If the palsy is caused by trauma, the doctor may recommend prism glasses to provide single binocular vision and align your eyes.
- Injections. A doctor may inject botulinum toxin to paralyze the muscles on one side of your eye to correct poor alignment.
- Strabismus surgery. This surgery may be used to loosen or tighten the eye muscles if other therapies do not correct the double vision.
- Alternative patching. This therapy is used in children and consists of wearing an eye patch for a few hours each day while alternating eyes. This can help prevent lazy eye.
Sixth nerve palsy doesn’t
The long-term outlook for this condition depends on the cause.
When caused by a virus, vision can be fully restored when you recover from the virus.
Other causes, such as those caused by head injury and trauma, may leave residual effects. Even though symptoms may not completely go away after a trauma, you may notice some vision improvement as your body heals. The biggest improvement usually occurs within the first 6 months.
If it does not improve within that time frame, surgery may be offered as a treatment option.
Sixth nerve palsy is a disorder that can affect the movement of the eye.
It’s caused by damage to the sixth cranial nerve. This nerve is responsible for sending signals to the muscle responsible for turning the eye away from the nose.