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.