CRANIAL NERVE PALSY

Your doctor thinks that you have a microvascular cranial nerve palsy. This is one of the most common causes of acute double vision in the older population. It occurs more often in patients with diabetes and high blood pressure. Microvascular cranial nerve palsies have often been referred to as "diabetic" palsies. They will get better and essentially always resolve without leaving any double vision.

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ANATOMY

The eyes are moved by 6 extra-ocular muscles. These 6 muscles receive their signals from 3 cranial nerves which originate in the brain stem (at the base of the brain) and enter the eye socket through a fissure in the bone of the skull behind the eye.

PHYSIOLOGY

Interruption of the blood supply to one of the cranial nerves causes it not to work. In the case of microvascular interruption we are not sure what causes the loss of blood flow (which deprives the nerve of oxygen). This may occur due to blockage of small arteries related to high blood pressure or hardening of the arteries. In young patients this may occasionally occur in patients with migraine. The affected vessels usually supply the nerves between the brain stem and the muscles within the eye socket. Occasionally there may be a problem of blood flow to the nerves within the substance of the brain stem. Associated with the blocked vessel there is often a decrease in the blood flow to the covering of the brain (the dura). This decrease in blood flow can produce pain that is felt around the eye. The nerves are not permanently injured and over a period of 6 to 12 weeks the function should recover.

SYMPTOMS

Dysfunction of one cranial nerve will produce weakness in one or more muscles. If the eyes aren't moving together the patient will experience blurred or double vision. This will vary depending on the direction of gaze. Pain in or around the eye is related to lack of blood flow to the dura (covering of the brain) and commonly occurs at the onset of double vision. This pain should disappear over a few days.

SIGNS

The signs of a microvascular cranial nerve palsy are usually problems with eye movement. If severely affected, the eye may not be able to move at all in one or more directions. With incomplete involvement there may only be a slowing of movement. 

DIAGNOSIS

The most important issue in diagnosing a microvascular cranial nerve palsy is whether it fits an expected pattern and whether it is "isolated." While it is possible for multiple cranial nerve palsies to have a microvascular cause all patients with more than a single nerve palsy or with other neurologic findings must have a work up (neurologic examination and imaging study) before the diagnosis is accepted. Even more importantly (whether or not the patient has had a work-up) if the cranial nerve palsy fails to resolve completely over 3 months additional work-up is indicated. All patients with presumed microvascular cranial nerve palsies should have their blood pressure and blood sugar checked to make sure they do not have diabetes or hypertension. There are many other causes of cranial nerve palsies so additional work up such as CT or MRI scans or even an angiogram to rule out an aneurysm may be necessary. A decision to order other tests depends on your symptoms and most importantly how you do.

TREATMENT

There is no known means of accelerating the natural recovery characteristic of a microvascular cranial nerve palsy. Anti-inflammatory drugs such as ibuprofen (Advil or Motrin) may help if there is associated pain. It is important to make sure that blood pressure and blood sugar are adequately controlled. The double vision may be treated acutely with patching either eye. This may be worn over either eye. This will not hurt the eye under the cover, slow the rate of recovery, or strain the eye that is being used. There are no exercises known that will speed recovery. 

FOLLOW-UP

Microvascular cranial nerve palsies should recover. It is very important that patients report any new symptoms or failure of the double vision to resolve. Even with a previously negative work up development of new symptoms suggests that there may be something else going on and additional studies may be necessary.

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FREQUENTLY ASKED QUESTIONS

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Does this mean I'm going to have a stroke with weakness?

Microvascular interruption probably has a different cause than most other forms of stroke. Thus patients with microvascular cranial nerve palsies are not necessarily at risk for other types of stroke. On the other hand, some of the risk factors that increase the chance of a microvascular palsy (such as diabetes, high blood pressure, and smoking) also increase the risk of stroke. It is important that your doctor check to make sure that any risk factors that may be reduced are treated.

What do I do about the double vision?

Since we expect the double vision to clear up on its own any treatment will hopefully be necessary for only a few weeks or months. The easiest way to get rid of the double vision is to wear a patch. Alternatively one lens of your glasses may be fogged using frosted cellophane tape on the inside.

What if the double vision doesn't go away?

If the double vision fails to resolve on its own it is very important that your doctor knows so that he can make sure you don't have some other unexpected diagnosis (cause of your double vision). If there is remaining double vision, that is stable, it is possible to realign the eyes either with prisms built into glasses or with eye muscle surgery.

When will the pain go away?

The pain associated with microvascular cranial nerve palsies usually disappears within a few days. Over the counter non-steroidal anti-inflammatory medications such as ibuprofen may be effective in reducing the symptoms in the mean time. If the pain persists you should inform your doctor.