There are 12 cranial nerves on each side of our brain that control our sight, smell, and taste, control our eye movements, facial and shoulder muscles, swallowing, and sense touch and pain in our face and head.
There are three (3) cranial nerves that control our eye movements:
Any damage to one or more of these nerves will cause the corresponding eye muscles not to work as well, which can result in blurred vision, shadow vision, or frank double vision which clears with covering either eye. In the case of weakness of cranial nerve 3, there is usually ptosis (a droopy lid) on the side of the eye that has trouble moving.
A nerve palsy is an impairment in the function of a nerve, which results in a decrease in function of the corresponding muscles controlled by that nerve.
In microvascular cranial nerve palsy, something affects the blood supply to one of the cranial nerves, causing it not to work. This is usually the result of blockage of the small blood vessels surrounding each nerve, often related to having high blood pressure, diabetes, or high cholesterol.
Although some doctors will call this a “stroke to the nerve,” microvascular cranial nerve palsies are not the same as a stroke to the brain. For this reason, if you have a microvascular cranial nerve palsy, you are not necessarily at risk for other types of stroke, although some of the risk factors for stroke are the same (high blood pressure, high cholesterol, diabetes, smoking). Furthermore, the chance of complete recovery is much higher than in brain strokes.
If one of the nerves that moves the eye is affected, you may experience double vision (seeing two of the same object or a shadow/ghost image of the same object) with both eyes open. Because this is due to a misalignment of the eyes, the double vision will resolve with covering either eye. Depending on the cranial nerve, different symptoms may occur:
Because the other muscles may still be working, looking in certain directions may either improve the double vision or make it worse.
Pain can occur at the same time as the double vision, or precede it. This pain is on the same side as the affected nerve, typically over the brow. The pain can be severe but typically improves over a few weeks. Pain is more common in 3rd nerve palsies and less common in 4th and 6th nerve palsies. If you are over 55 years of age, and in addition to your double vision, are experiencing scalp tenderness, cramping pain in your jaw while chewing, loss of appetite or weight, or low grade fevers, please convey this to your doctor, as this may reflect a serious underlying condition known as giant cell arteritis.
Neuro-ophthalmologists specialize in the cranial nerves affecting the eyes and vision. While your general eye doctor may be comfortable managing the symptoms of your double vision, a neuro-ophthalmologist typically has more knowledge and experience in checking for all of the different possible causes of your double vision.
Your doctor may “wait and see” or order more tests. These tests may include magnetic resonance imaging (MRI) or computed tomography (CT) of the brain, magnetic resonance angiography (MRA) or CT angiography (CTA) of the brain, and/or blood tests. These tests are to rule out alternative non-microvascular causes of the cranial palsy, such as inflammation or compression.
In most cases of microvascular cranial nerve palsy, the nerves are not permanently injured and recovery occurs over 6 to 12 weeks. Sometimes there is some double vision left over, but for most people, all of the double vision completely goes away. Unfortunately, there are no known treatments that can speed up the recovery.
Left: Courtesy of Kevin E. Lai, M.D.
Right: Courtesy of American Academy of Ophthalmology.
Your doctor will determine your next appointment based on what problems you have and if you need further testing. Once the nerve palsy has completely recovered, you will only need routine eye exams with your regular eye doctor. However, if you experience new symptoms, if the double vision does not completely resolve, or if your symptoms worsen, you should let your doctor know.
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This information was developed collaboratively by the Patient Information Committee of the North American Neuro-Ophthalmology Society. This has been written by neuro-ophthalmologists and has been edited, updated, and peer-reviewed by multiple neuro-ophthalmologists. The views expressed in this brochure are of the contributors and not their employers or other organizations. Please note we have made every effort to ensure the content of this is correct at time of publication, but remember that information about the condition and drugs may change. Major revisions are performed on a periodic basis.
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