Understanding Sixth Nerve Palsy
Sixth nerve palsy is a problem with eye movement. It happens because of a problem with the sixth cranial nerve, also called the sixth nerve. In some cases sixth nerve palsy is present at birth. It can also result from other problems that occur later on. In adults, stroke is one of the most common causes of sixth nerve palsy.
How the sixth cranial nerve affects the eye
The sixth cranial nerve sends signals to the lateral rectus muscle. This is a small muscle that attaches to the outer side of the eye. When this muscle contracts, the eye turns outward, away from the nose. Each eye has its own lateral rectus muscle and its own cranial nerve, the sixth nerve.
What causes sixth nerve palsy?
The sixth nerve leads from the lower part of the brain. It’s a long nerve. Damage at any point on the nerve can cause it to work poorly or not at all. If this happens, the lateral rectus muscle won’t get signals. It then won’t contract properly. Your eye will turn inward toward your nose.
A variety of problems can disrupt the function of the sixth cranial nerve, causing sixth nerve palsy. Possible causes include:
Injury, especially a skull fracture
Infection such as Lyme disease or a virus
Inflammation of the nerve, such as from an inflammatory disease like multiple sclerosis
Increased pressure in the brain, from meningitis or other causes
High blood pressure
Diseases that are present at birth (congenital diseases)
In some cases, the cause of sixth nerve palsy is not known.
Symptoms of sixth nerve palsy
Sixth nerve palsy may affect one or both eyes, depending on its cause.
The most common symptom of sixth nerve palsy is double vision when both eyes are open. This is more common when looking far away or when looking in the direction of the affected eye. Not everyone with sixth nerve palsy has this symptom.
Your eyes may also be out of alignment. This is called strabismus. The eye on the affected side may turn toward the midline. Early on you may have this only when looking in the direction of the affected eye. If the palsy gets worse, the eye may turn toward the midline even when you look straight ahead.
If eye movement problems are the only symptoms, this is called isolated sixth nerve palsy. If there are also neurological or other symptoms, this is called nonisolated sixth nerve palsy.
Other symptoms may include:
Diagnosing sixth nerve palsy
The healthcare provider will ask about your health history and symptoms. You will have a physical exam. This will include a detailed neurological exam. This type of exam uses tests to see which parts of your brain and nervous system may be affected. You may be examined by a neurologist or a neuro-ophthalmologist. These are doctors who specialize in the nervous system. The doctor will also try to diagnose the cause of the sixth nerve palsy.
You may have brain imaging tests such as:
CT scan. This test uses a series of X-rays and a computer to make detailed images. A CT scan might be needed if you might have increased pressure in the brain.
MRI. This test uses strong magnets and a computer to make images of the brain.
You may need other tests to find the cause of sixth nerve palsy. These may include blood tests or a lumbar puncture to look for an infection, such as meningitis.