Mononeuropathy means that only one nerve is damaged. This disorder affects the third cranial nerve in the skull. This is one of the cranial nerves that control eye movement and the pupil of the eye.

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.

Cranial mononeuropathy III can also occur in people who don't have diabetes.

Symptoms may include:

• Double vision
• Drooping of one eyelid (ptosis)
• Pain around the eye and forehead
• Change in size of the pupil (anisocoria)

Neuropathy often develops within 7 days of onset of pain.

An exam 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
• Pupil reaction that is often normal

Your health care provider will do a complete exam 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)
• MRI or CT 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).

There is no specific treatment to correct the nerve injury.

Treatments to help symptoms may include:

• Close control of blood sugar level
• Eye patch or glasses with prisms to reduce double vision
• Pain medicines
• Antiplatelet therapy
• Surgery to correct eyelid drooping or eyes that are not aligned

Some people may recover without treatment.

The prognosis is good. Many people get better over 3 to 6 months. However, some people have permanent eye muscle weakness.

Complications may include:

• Permanent eyelid drooping
• Permanent vision changes

Contact your provider if you have double vision and it does not go away in a few minutes, especially if you also have eyelid drooping.

Controlling your blood sugar level may reduce the risk of developing this disorder.

Diabetic third nerve palsy; Pupil-sparing third cranial nerve palsy; Ocular diabetic neuropathy

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Rucker JC, Seay MD. Cranial neuropathies. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 103.

Tamhankar MA. Eye movement disorders: third, fourth, and sixth nerve palsies and other causes of diplopia and ocular misalignment. In: Liu GT, Volpe NJ, Galetta SL, eds. Liu, Volpe, and Galetta's Neuro-Ophthalmology. 3rd ed. Philadelphia, PA: Elsevier; 2019:chap 15.

Thurtell MJ, Rucker JC. Neuro-ophthalmology. In: Winn HR, ed. Youmans and Winn Neurological Surgery. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 15.

Updated by: Joseph V. Campellone, MD, Department of Neurology, Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.