Sixth nerve palsy is a nerve disorder. When your sixth nerve isn't working properly, it causes problems with the movement of your eye.
What Is Sixth Nerve Palsy?
Sixth nerve palsy is also known as lateral rectus palsy. Palsy is a type of full or partial paralysis.
Your lateral rectus muscle is one of seven eye muscles located outside your eye. Each muscle moves the eye in one specific direction. The eye muscles work together to allow your eye to move in every direction.
Your sixth cranial nerve sends signals from your brain to your lateral rectus muscle. Unlike the other cranial nerves, it’s not supported by the dural wall of your sinuses. This means that it's easily damaged by trauma, inflammation, or increased pressure within your skull.
When your sixth nerve doesn’t work properly, you won't be able to turn your affected eye outwards in the direction of the corresponding ear.
What Are the Causes of Sixth Nerve Palsy?
There are several different causes of sixth nerve palsy. It may be present at birth, it may be caused by physical trauma, or it may be a result of a medical condition. In some cases, the cause is unknown.
Traumatic injuries linked to sixth nerve palsy include:
- Skull fractures
- Cervical spine fractures
- Brain injury
Some conditions that cause sixth nerve palsy include:
What Are the Symptoms of Sixth Nerve Palsy?
Symptoms of sixth nerve palsy vary from person to person, depending on the cause. One of the main symptoms is eye alignment. Your eye can’t turn fully outward. When you look straight ahead, your eye may turn inward. You may experience double vision when you look in the direction of your affected eye.
Children with sixth nerve palsy usually don’t have constant double vision. Instead, they are more likely to develop lazy eye (amblyopia).
Other symptoms may include:
- Temporary blurring of vision when you suddenly move your head
- Numbness in your face and mouth
How Is Sixth Nerve Palsy Diagnosed?
Sixth nerve palsy is diagnosed through several tests, including a neurological exam that involves different tests and questions used to check the functions of your nerves.
Your doctor will also conduct an eye exam using an ophthalmoscope. This instrument lets them look into your eye and check for problems with your blood vessels and see whether there’s increased pressure within your skull.
Some other tests include:
- Computed tomography (CT) or magnetic resonance imaging (MRI) of your brain. These tests are used to check for tumors that may increase pressure within your skull.
- Spinal tap (lumbar puncture) to see if there’s bleeding or an infection
- Blood tests to check for inflammation
- Tests to check for diabetes, like an oral glucose tolerance test
Some people may go through all these different tests, but the cause of their condition may still remain unknown.
What Is the Treatment for Sixth Nerve Palsy?
For some people, treatment may not be needed, and the condition may disappear on its own within two months.
In a study of 213 people with this condition, 78.4% recovered without treatment. Of those who didn’t recover, 40% had a serious underlying condition.
Treatment usually depends on the cause of your sixth nerve palsy. The disorder usually goes away once the cause is treated. If your doctor thinks that your sixth nerve may be inflamed, though, they may prescribe corticosteroids.
Prism spectacles can help realign images, but when you look in different directions, the misalignment of your eyes are different. This means that prism spectacles can’t get rid of double vision in every eye position. Meanwhile, as your sixth nerve palsy improves, the power of the prism can be decreased.
Your doctor may also recommend putting a patch on one eye to correct your double vision. If your child is to be treated using an eye patch, your doctor may closely monitor them, as children may otherwise develop lazy eye.
Prism correction calls for about six months of observation to see if your eye alignment improves. If it doesn’t, your doctor may recommend strabismus surgery. This involves a loosening or tightening of your eye muscle to improve the alignment of your eyes.
Doctors may also recommend botulinum toxin (botox) injections. This may temporarily weaken the movement of your eye muscle.
If your condition is caused by viral illness or an unknown cause, it’s likely to completely disappear. You may never fully recover, though, if your sixth nerve palsy is due to trauma. Some people may have permanent vision changes.