Microvascular cranial nerve palsy (MCNP) occurs when the blood that flows to the cranial nerves gets blocked leading to sudden double vision. The blockage means that the eye loses its ability to move in a particular way. Double vision involves seeing two images of the same object. The double image may be manifested in a one-above-the-other or side-by-side manner.
Usually, the brain sends signals to the eye muscles through three out of six cranial nerves. When a blockage affects the 6th cranial nerve (abducens nerve), specific muscles will not move the eye.
If the 4th cranial nerve (trochlear nerve) is affected, vertical double vision will result.
The 3rd cranial nerve (oculomotor nerve) controls the eyelid and the size of the pupil. MCNP affecting this nerve will cause limited functions in the eye’s up-and-down movement. The eye may turn away from the nose. It also causes drooping of the eyelid.
Disturbances in the 3rd cranial nerve result in a combined vertical and side-by-side double vision.
Also Known As
- Diabetic palsy
Causes and Risk Factors
Doctors do not know the cause of the blocked vessels involving the nerves. It is thought that a blocked vessel in the brain may be the cause of the disease. This vessel is often associated with pain in and around the eye. A closed head injury may also cause the 4th cranial nerve palsy. The following are the risk factors for MCNP:
- Older adults are likely to develop it
- Individuals with diabetes
- People with hypertension or high blood pressure
- Individuals who smoke
- Young people with migraines
Signs & Symptoms
The following are the symptoms of MCNP:
- Blurry vision which improves when one eye is closed
- Vertical double vision
- Eye movement may take longer than usual
- Inability to move the eye in one or more directions
- Ptosis (droopy eyelid)
- Pain in and around the eye just before an individual notices double vision
- The pupil may enlarge though this is rare
- Weakness in one or more muscles
The eye care professional will conduct a complete medical examination by:
- Taking a comprehensive medical history. He/she will want to know the exact nature of the double vision. This helps to determine which nerves are involved
- Performing a visual acuity test which determines how far one can see
- Checking the pupils using a flashing light. The pupils should dilate in dim light and constrict in bright light
- Checking peripheral vision to see how well an individual can see from the sides
- Establishing if the eyes are aligned and if the eye muscles are working correctly using ocular motility
- Measuring the intraocular pressure using tonometry. High pressure is cause for concern
- Checking the eye using a slit lamp examination
- Dilating the eye to check on the health of the retina
- Other tests may include magnetic resonance imaging (MRI), a CT scan and fluorescein angiography if images will give better results. Because the disease is neurological, the professional might refer one to a neurologist. This is because the disease predisposes someone to a stroke.
Treatment of MCNP is directed towards reducing the symptoms of double vision.
In most patients, MCNP resolves on its own. There are no medications that can quicken the recovery of normal vision from double vision.
In case of pain, a patient can take anti-inflammatory medications like ibuprofen.
The doctor will also recommend that high blood sugar and high blood pressure be controlled. There are medications to control hypertension and diabetes.
Eye muscle surgery can help to restore the functions of the muscles. Surgery will be undertaken if the muscles don’t fully recover on their own.
Patients have several options to help them manage double vision at home. One way involves wearing a patch on either of the eyes. Another way is to wear prism glasses which will be prescribed by the doctor.
Also, an individual can try tilting the head in the direction of one shoulder. This action may reduce or even eliminate double vision.
Oculomotor exercises may help to restore normal vision.
Most patients with MCNP get better in about 6-12 weeks. MCNP resolves on its own and vision returns to normal. The pain associated with MCNP usually disappears in a few days. If the pain persists after medication, the patient should consult an eye doctor.
However, if the double vision persists or if new double vision develops, an individual should seek medical attention.