Horner syndrome is rare condition caused by injury to the sympathetic nerves of the face. It involves a collection of symptoms, including:

• Sinking of the eyeball into the face
• Small (constricted) pupil
• Drooping eyelid (ptosis)
• Lack of face sweating

There are many potential causes of Horner syndrome. It can be caused by any interruption of the sympathetic nerve fibers, which start in the hypothalamus (a central brain region) and run via the upper spinal cord near the carotid artery to the face.

Sympathetic nerve fiber injuries can result from a stroke in the brainstem, injury to the carotid artery, a tumor in the upper lobe of the lung, and cluster headaches.

Rarely, Horner syndrome may be congenital (present at birth) and associated with a lack of pigmentation of the iris (colored part of the eye). Eye drops and certain medications may also lead to this condition.

Symptoms may include drooping of the eyelid, constriction of the pupil, and decreased sweating on the affected side of the face. These symptoms may vary. Other symptoms associated with the underlying cause may also occur.

A careful neurological exam is necessary to establish the diagnosis and to find the cause by determining which, if any, other parts of the nervous system are affected. Tests may include:

• MRI of the head
• Carotid ultrasound
• Chest x-ray
• CT scan of the chest
• Blood tests
• Angiogram
• Eye drop tests

Treatment depends on the underlying cause. There is no specific treatment for Horner syndrome itself.

Prognosis is dependent on whether treatment of the underlying cause is successful.

There are no direct complications of Horner syndrome itself, but complications may be associated with the underlying disease or its treatment.

Call your health care provider if you have any symptoms that may be linked with Horner syndrome.