Bright Sight

Oliver Backhouse, Consultant Eye Surgeon www.cataract.org.uk

Microvascual cranial nerve palsy

Microvascular cranial nerve palsy (MCNP) 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. This condition almost always resolves on its own without leaving any double vision. Six muscles coordinate to move your eye in any particular direction. These muscles receive their signals from three cranial nerves that begin in the brainstem.

1] What is Microvascular Cranial Nerve Palsy.

Any nerve can not function properly when its blood flow is blocked. If the 6th (Abducens) cranial nerve is affected, your eye will not be able to move to the outerside and you will be aware of double vision seeing side-by-side images. The double vision will be worse when looking in the direction of the affected muscle. If the 4th (Trochlear) cranial nerve is affected you will be aware of vertical double vision. You may be able to eliminate or decrease the double vision by tilting your head towards the opposite shoulder.

The 3rd (Oculomotor) cranial nerve supplies 4 of the 6 muscles. It also controls the height of the eyelid and pupil size. When this nerve is affected, your eye may be limited in its up and down movement and gaze towards the nose. The eyelid may droop. You usually experience side-by-side and vertical double vision.

2] What causes MCNP?

It is not always clear what causes the blockage to the tiny blood vessels to the cranial nerves. In some cases diabetes or high blood pressure may be risk factors. In young patients, migraine may affect these tiny vessels. Occasionally there may be also be a blocked vessel in the covering of the brain which can be associated with pain around the eye. The nerves are not permanently injured, and over a period of 6-12 weeks, normal function should recover. If the double vision does not go away it is very important to tell your ophthalmologist.

3] What are the signs and symptoms of MCNP?

The signs of MCNP are usually problems with movement of your eyes which lead to blurred or double vision. If severely affected, your eye may not be ale to move at all in one or more directions. Sometimes there may only be a slowing of movement.

Symptoms and findings may include:

  • Weakness in one or more eye muscles.
  • Blurred vision that improves by closing the other eye.
  • Double vision.
  • Pain in or around the eye (related to lack of blood flow to the covering of the brain) which commonly occurs at the onset of double vision.
  • Drooping eyelid (called ptosis)
  • Enlarged pupil.

A careful description of these symptoms is important to your ophthalmologist. He or she will perform a complete medical eye examination to help determine what pattern your double vision fits and whether or not it is an isolated cranial nerve weakness. If you have multiple MCNPs, involvement of the pupil or have a younger age of onset, a neurological exam and imaging study may be necessary (such as an MRI scan or angiogram). Anyone diagnosed with MCNP should have their blood pressure and blood sugar checked to make sure they do not have diabetes or hypertension.

4] How is MCNP treated?

There is no known method of accelerating the natural recovery time for MCNP. Double vision may be treated by patching the other eye. If the double vision persists, it may be possible to use prism glasses or to consider eye muscle surgery if recovery has not been complete. Medication such as Ibuprofen may help if there is associated pain. It is important to make sure that the blood pressure and blood sugar are adequately controlled.

It is very important to tell your doctor if your double vision fails to resolve or you have new symptoms as additional tests may be required. Risk factors that increase the chance of MCNP (such as diabetes, high blood pressure and smoking) also increase the risk of having a stroke. It is important that your doctor checks these risk factors to see if any can be better controlled.

Does this mean I am about to have a stroke?

Microvascular interruption probably has a different cause than most other forms of stroke. Thus patients with MCNP are not necessarily at risk for other types of stroke. On the other hand, some of the risk factors that increase the chance of MCNP (such as diabetes, high blood pressure and smoking) also increase the risk of having a stroke. It is important that your doctor checks these risk factors to see if any can be better controlled.

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 does not go away?

It is important to let your doctor know this as further investigation may be undertaken. If there is remaining double vision, that is stable, it is possible to realign the eyes either with prisms built into the glasses or with eye muscle surgery.

When will the pain go away?

The pain associated with MCNP 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 meantime. If the pain persists you should inform your doctor.

Disclaimer: Adapted from Nanos.