Abducens cranial nerve is the sixth cranial nerve. Sixth cranial nerve sends signals to your lateral rectus muscle. This is a small muscle that attaches to the outer side of your eye. When this muscle contracts, your eye moves away from your nose. Each eye has its own lateral rectus muscle served by its own cranial nerve.
The sixth nerve emerges from the lower part of your brain. It travels a long way before reaching the lateral rectus. Damage at any point along its path can cause the nerve to work poorly or not at all. Because the lateral rectus muscle can no longer contract properly, your eye turns inward toward your nose.
Sometimes, sixth nerve palsy happens without any other symptoms. This is called isolated sixth nerve palsy. Other times, sixth nerve palsy may come with other symptoms. This is called non-isolated sixth nerve palsy.
Sometimes, sixth nerve palsy is present from birth. It can also result from other problems that happen later on. In children, injury is a leading cause. In adults, stroke is one of the most common causes. It is relatively rare.
Many problems can disrupt the function of the sixth cranial nerve, causing sixth nerve palsy. Possible causes include:
In congenital sixth nerve palsy, a problem with the sixth cranial nerve is present from birth. This may happen as a result of injury during birth. Sometimes, the cause of sixth nerve palsy is unknown. Sixth nerve palsy that happens without additional symptoms is usually due to one of the following:
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. But not everyone with sixth nerve palsy has this symptom.
The eyes may also be out of alignment, a symptom called strabismus. The eye on the affected side may drift toward the midline. Early on, you might show this symptom only when looking in the direction of the affected eye (like looking to the right in a right sixth nerve palsy). If the palsy worsens, the affected eye may drift toward the midline, even when looking straight ahead.
If you have non-isolated sixth nerve palsy, additional symptoms may be present as well. Depending on the other structures affected, you might have symptoms such as:
Diagnosis begins with a thorough medical history and physical exam. Your healthcare provider will do a detailed neurological exam. This is testing to identify other affected parts of your brain and nervous system. A Neuro-ophthalmologist might first examine you. They will try to diagnose the root cause of the sixth nerve palsy as well.
Your Neuro-ophthalmologist will probably want to order brain imaging tests because the nerve often becomes compressed as it leaves the brain. Brain imaging is also important to make sure a brain tumour isn’t causing symptoms. Possible imaging tests include computed tomography (CT) and magnetic resonance imaging (MRI). MRI provides more information. But it is often hard to do as quickly as a CT. A CT might be needed if your Neuro-ophthalmologist suspects that you have increased pressure inside your brain.
Sometimes, the eye specialist might order other tests if they suspect a specific cause of the sixth nerve palsy. For example, you might need blood tests and a lumbar puncture if meningitis is suspected.
Treatment of sixth nerve palsy depends on its cause. Possible treatments for the underlying cause include:
Sometimes, there is not a direct treatment available for the underlying cause.
Your Neuro-ophthalmologist may want to wait several months before starting additional treatment. Often, symptoms from sixth nerve palsy improve on their own. Sixth nerve palsy following a viral illness often completely goes away within a few months. Symptoms following trauma may also improve over several months. But in cases of trauma, symptoms are less likely to go away completely. Your symptoms may be more likely to go away completely if you have isolated sixth nerve palsy.
If you still have symptoms 6 months or so later, your Neuro-ophthalmologist might recommend further treatments. Some available treatments are:
Isolated sixth nerve palsy itself does not usually cause complications. But many of the possible causes of sixth nerve palsy may have complications. Like any procedure, surgery for sixth nerve palsy carries a risk for complications.
Call your Ophthalmologist if you have any sudden severe symptoms, like vision loss or problems moving an arm or a leg.
Sixth nerve palsy occurs when the sixth cranial nerve is damaged or doesn’t work right. This causes problems with eye movement. The affected eye may not be able to move away from the midline normally.
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