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Horner syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Horner syndrome

Horner syndrome is a disorder affecting the eye and surrounding tissues on one side of the face, characterized by a drooping eyelid, constricted pupil, and absent sweating, resulting from damage to cervical sympathetic nerves.

Overview

Horner syndrome is a disorder that affects the eye and surrounding tissues on one side of the face and results from paralysis of certain nerves. Horner syndrome can appear at any time of life; in about 5 percent of affected individuals, the disorder is present from birth (congenital).

Horner syndrome is characterized by drooping of the upper eyelid (ptosis) on the affected side, a constricted pupil in the affected eye (miosis) resulting in unequal pupil size (anisocoria), and absent sweating (anhidrosis) on the affected side of the face. Sinking of the eye into its cavity (enophthalmos) and a bloodshot eye often occur in this disorder. In people with Horner syndrome that occurs before the age of 2, the colored part (iris) of the eyes may differ in color (iris heterochromia), with the iris of the affected eye being lighter in color than that of the unaffected eye. Individuals who develop Horner syndrome after age 2 do not generally have iris heterochromia.

The abnormalities in the eye area related to Horner syndrome do not generally affect vision or health. However, the nerve damage that causes Horner syndrome may result from other health problems, some of which can be life-threatening.

Frequency

About 1 in 6,250 babies are born with Horner syndrome. The incidence of Horner syndrome that appears later is unknown, but it is considered an uncommon disorder.

Causes & Risk Factors

Although congenital Horner syndrome can be passed down in families, no associated genes have been identified. Horner syndrome that appears after the newborn period (acquired Horner syndrome) and most cases of congenital Horner syndrome result from damage to nerves called the cervical sympathetics. These nerves belong to the part of the nervous system that controls involuntary functions (the autonomic nervous system). Within the autonomic nervous system, the nerves are part of a subdivision called the sympathetic nervous system. The cervical sympathetic nerves control several functions in the eye and face such as dilation of the pupil and sweating. Problems with the function of these nerves cause the signs and symptoms of Horner syndrome. Horner syndrome that occurs very early in life can lead to iris heterochromia because the development of the pigmentation (coloring) of the iris is under the control of the cervical sympathetic nerves.

Damage to the cervical sympathetic nerves can be caused by a direct injury to the nerves themselves, which can result from trauma that might occur during a difficult birth, surgery, or accidental injury. The nerves related to Horner syndrome can also be damaged by a benign or cancerous tumor, for example a childhood cancer of the nerve tissues called a neuroblastoma.

Horner syndrome can also be caused by problems with the artery that supplies blood to the head and neck (the

Frequently Asked Questions

sudden unilateral ptosis with miosis and lack of sweating strongly suggests Horner syndrome; because it can be caused by serious underlying problems such as a carotid artery dissection or tumor, you should be evaluated promptly by a physician, preferably in an emergency or urgent‑care setting.
Clinicians often start with a thorough eye exam and then perform pharmacologic tests (e.g., apraclonidine or cocaine drops) that reveal an abnormal pupil response. Imaging studies such as MRI or CT of the brain, neck, and chest are ordered to identify lesions along the sympathetic pathway—ranging from brainstem strokes to neck masses.
Congenital Horner syndrome usually causes only cosmetic differences (ptosis, mild anisocoria, possible iris heterochromia) and does not impair visual acuity. Treatment is optional and may involve eyelid surgery for cosmetic reasons; no medication is needed unless an associated structural problem is found.
The outlook depends on the cause. If the underlying lesion is reversible (e.g., a compressive tumor removed surgically), the sympathetic function may recover partially or fully. In cases of permanent nerve injury (such as after a stroke or severe trauma), the ocular signs often persist, though they rarely cause functional problems.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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