Diabetic third nerve palsy; Pupil-sparing third cranial nerve palsy

Cranial mononeuropathy III — diabetic type — is usually a complication of diabetes that causes double vision and eyelid drooping.

Causes, incidence, and risk factors

Cranial mononeuropathy III – diabetic type is a mononeuropathy, which means that only one nerve is damaged. It affects the third cranial (oculomotor) nerve, which is one of the cranial nerves that controls eye movement.

This type of damage may occur along with diabetic peripheral neuropathy. Cranial mononeuropathy III is the most common cranial nerve disorder in people with diabetes. It is due to damage to the small blood vessels that feed the nerve.

Other causes may include:

• Infarction of the nerve (tissue damage from loss of blood flow)
• Pressure on the nerve
• Mononeuritis multiplex
• Double vision
• Drooping of one eyelid (ptosis)
• Pain in the head or behind the eye

Symptoms

Signs and tests

An examination of the eyes will determine whether only the third nerve is affected or if other nerves have also been damaged. Signs may include:

• Eyes that are not aligned (dysconjugate gaze)
• Pupil reaction that is almost always normal

Your health care provider will do a complete examination to determine the possible effect on other parts of the nervous system. Depending on the suspected cause, you may need:

• Blood tests
• Tests to look at blood vessels in the brain (cerebral angiogram, CT angiogram,MR angiogram)
• MRIorCT scan of the brain
• Spinal tap (lumbar puncture)

You may need to be referred to a doctor who specializes in vision problems related to the nerves in the eye (neuro-ophthalmologist).

Treatment

There is no specific treatment to correct the nerve injury.

Treatments may include:

• Close control ofblood sugar levels
• Eye patch or glasses with prisms to reduce double vision
• Pain medications
• Surgery to correct eyelid drooping or eyes that are not aligned

Some people may recover without treatment.

Expectations (prognosis)

Many patients get better over 3 – 6 months, although some have permanent eye muscle weakness.

Complications

• Permanent eyelid drooping
• Permanent vision changes

Calling your health care provider

Call your health care provider if you have double vision and it doesn’t go away in a few minutes, especially if you also have eyelid drooping.

Prevention

Control of blood sugar levels in people with diabetes may reduce the risk of developing this disorder.