Horner syndrome is a rare condition that affects the nerves to the eye and face.

Horner syndrome can be caused by any interruption in the sympathetic nerve fibers, which start in the part of the brain called the hypothalamus and run to the face.

Sympathetic nerve fiber injuries can result from:

• Injury to the main artery to the brain (carotid artery)
• Injury to the nerves running down the arm (brachial plexus)
• Migraine or cluster headaches
• Stroke or lesion in the brainstem
• Tumor in the top of the lung

Rarely, Horner syndrome may be present at birth (congenital). The condition may occur with a lack of color (pigmentation) of the iris (colored part of the eye).

Eye drops and certain medications may also lead to this condition.

• Decreased sweating on the affected side of the face
• Drooping eyelid (ptosis)
• Sinking of the eyeball into the face
• Small (constricted) pupil

There may also be symptoms of the disorder that is causing the problem.

The health care provider will do a nervous system (neurological) exam to diagnose the problem and find out which, if any, other parts of the nervous system are affected.

Tests may include:

• Blood tests
• Carotid ultrasound
• Chest x-ray
• CT angiogram or magnetic resonance angiography (MRA)
• CT scan of the chest
• Eye drop tests
• MRI of the head

Treatment depends on the cause of the problem. There is no treatment for Horner syndrome itself.

The outcome depends on whether treatment of the cause is successful.

There are no direct complications of Horner syndrome itself. However, there may be complications from the disease that caused Horner syndrome or from its treatment.

Call your health care provider if you have symptoms of Horner syndrome.