Cranial mononeuropathy III is a problem with the function of the third cranial nerve, which is located behind the eye.

Cranial mononeuropathy III - compression type is a mononeuropathy, which means that only one nerve is affected. It affects the third cranial (oculomotor) nerve, one of the cranial nerves that controls eye movement. Local tumors or swelling can press down on and damage the nerve.

Causes may include:

• Brain aneurysms
• Disorders such as mononeuritis multiplex
• Infections
• Poorly formed blood vessels (vascular malformations)
• Sinus thrombosis
• Tissue damage from loss of blood flow (infarction)
• Trauma (from head injury or caused accidentally during surgery)
• Tumors or other lesions (especially tumors at the base of the brain and pituitary gland)

Rarely, people with migraine headaches may have a temporary problem with the oculomotor nerve. This is probably due to a spasm of the blood vessels. In some cases, no cause can be found.

• Double vision
• Drooping of one eyelid
• Headache or eye pain

Other symptoms may occur if the cause is a tumor or trauma. Decreasing consciousness is a serious sign, because it could indicate brain damage or death.

An eye examination may show:

• Enlarged (dilated) pupil of the affected eye
• Eye movement abnormalities
• Eyes that are not aligned (dysconjugate gaze)

A complete medical and nervous system (neurological) examination can show whether any other parts of the body are affected.

Other tests may include:

• Blood tests
• CT angiogram
• CT scan
• MRI
• Spinal tap (lumbar puncture)

Some cases may get better without treatment. Treating the cause (if it can be found) may relieve the symptoms in many cases.

Treatment may include:

• Corticosteroid medications to reduce swelling and relieve pressure on the nerve
• Surgery to treat eyelid drooping or eyes that are not aligned
• Wearing an eye patch or prisms

Some cranial nerve dysfunctions will respond to treatment. A few cases result in some permanent loss of function. If the problem is caused by brain swelling due to a tumor or stroke, those conditions may be life-threatening.

• Permanent eyelid drooping
• Permanent vision changes

Call the local emergency number (such as 911) or go to the emergency room if you have:

• Double vision
• No feeling in or control over parts of your body
• Signs of changed consciousness
• Unusual headache

Quickly treating disorders that could press down on the nerve may reduce the risk of developing cranial mononeuropathy III.