Horner syndrome: What causes it?

What causes Horner syndrome? Is it serious?

- Gennifer / Michigan

Mayo Clinic ophthalmologist Dennis Robertson, M.D., and colleagues answer select questions from readers.

Answer

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Horner syndrome

Horner syndrome is a rare disorder caused by damage to the sympathetic nerves of the face and eye. The sympathetic nerves control circulation and perspiration.

Horner syndrome isn't a disease but a sign of an underlying — often serious — disorder. Causes of Horner syndrome include:

Brainstem stroke
Tumor in the upper part of the lung and low cervical spinal cord
Cluster headaches
Injury to the carotid artery in the neck

Signs and symptoms of Horner syndrome occur on the side of the face on which the sympathetic nerve has been damaged and include:

Drooping of the upper eyelid (ptosis) and slight elevation of the lower lid
Decreased pupil size in the affected eye
Decreased or absent sweating on the affected side of the face (anhidrosis)

The physical signs of Horner syndrome are so subtle that they often go undetected. An ophthalmologist may confirm a diagnosis by special eye tests. There's no specific treatment for Horner syndrome. Treatment is directed at the underlying cause when possible.