An Overview of Horner Syndrome

A potential sign of underlying disease

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Horner syndrome is a rare condition characterized by three primary symptoms: drooping upper eyelid, constricted pupil, and loss of sweating on the face. Horner syndrome and its symptoms result from damage to part of the sympathetic nervous system, which can arise from a number of causes.

horner syndrome symptoms
Illustration by JR Bee, Verywell

Horner syndrome was named for a Swiss ophthalmologist who first formally described the condition in 1869. The syndrome is also sometimes referred to as “Bernard-Horner syndrome,” or “oculo-sympathetic palsy.”


Classically, Horner syndrome describes a group of three symptoms that result from the same underlying cause. These symptoms are:

  • Partially drooping upper eyelid (ptosis)
  • Small pupil size (miosis)
  • Loss of sweating on the face (facial anhidrosis)

Normally these eye symptoms themselves do not cause loss of vision or other health problems.

These symptoms occur just on one side of the face—the same side. In other words, only the eyelid and pupil on the same side of the face will be affected. Depending on the exact cause of the Horner syndrome, loss of sweating on the face might occur on half the face or only on the forehead of half the face. In other cases, this symptom might be absent.

Some people with Horner syndrome will experience additional symptoms related to the condition. These symptoms are more variable and might or might not be present, partly depending on the exact nature of the disruption of the nerves. These include facial flushing and eye pain.

Additionally, the underlying cause of Horner syndrome may lead to specific symptoms. For example, someone with Horner syndrome due to lung cancer might have a cough that doesn’t go away. Someone with Horner syndrome from carotid artery dissection might have head, neck, or facial pain. Similarly, someone with Horner syndrome from a stroke might have dizziness or other neurological symptoms.

Horner syndrome occurring in the first couple of years of life usually causes an additional symptom—iris heterochromia. This just means that the iris on the affected side appears lighter than the iris on the non-affected side.


The sympathetic nervous system is a component of the body that helps regulate certain unconscious activities in the body. Specifically, the sympathetic nervous system responds to stressors, which is why it is sometimes called your body’s "fight or flight” response.

The sympathetic nervous system sends messages to many different parts of your body, so you can be optimally supported to respond to dangerous situations. The brain sends these messages to various parts of the body through a complicated system of nerves and neurons.

In Horner syndrome, a specific part of the sympathetic nervous system is damaged: the oculosympathetic pathway. This pathway sends messages from the brain and ultimately to the eye (and parts of the face). The path is a long and complex one. The first neurons start in the brain and travel down through the spinal cord to the level of the chest. Here, the neurons make a connection with another group of neurons that travel back up a different path very close to the spinal cord. They signal another group of neurons that branch out at the level of the neck. These neurons travel alongside an important artery in the neck (the carotid artery) before entering the skull and finally exiting near the eye socket.

Normally, the signals in this pathway send messages to help your body respond to stress. Specifically, they send a message to one of the muscles of the eyelid to help it open more widely. It also sends messages to the pupil, to help it open more and thus let in more light. It also sends a message to sweat glands, to help them sweat.

When this passage is damaged, other nerve signals opposing these messages tend to dominate, leading to a droopy eyelid, small pupil, and lack of sweat.

Because of the long and complex route taken by the oculo-sympathetic pathway, diseases that affect multiple parts of the body may lead to Horner syndrome. This includes diseases affecting the brainstem (lower part of the brain), spinal cord, chest, and neck.

If these nerves are damaged in some way, the pathway can become blocked and the symptoms of Horner syndrome can result. The intensity of symptoms often depends on how severely the nerve pathway is damaged.

This type of Horner syndrome is called acquired Horner, because it results from some other disease and isn't present from birth. For example, problems in the first group of neurons might result from medical issues like:

Damage to the second set of nerves in the pathway might result from other underlying problems, such as:

  • Lung cancer
  • Cervical rib
  • Aneurysm (bulging) of the subclavian artery
  • Dental abscess of the lower jaw
  • Nerve damage from medical procedures (e.g., thyroidectomy, tonsillectomy, carotid angiography)

Damage to the third group of nerves in the pathway might result from types of medical problems, such as:

  • Aneurysm (bulging) or dissection (ripping) of the internal carotid artery
  • Temporal arteritis
  • Herpes zoster infection

In some cases, the cause of Horner syndrome is never identified. This is called “idiopathic” Horner syndrome. 

Congenital Versus Acquired Horner Syndrome

In terms of classification, Horner syndrome that is congenital (present from the newborn period) is usually distinguished from Horner syndrome that occurs later in life (acquired Horner syndrome). Most cases of congenital Horner also arise from damage to the oculo-sympathetic nerves. For example, this might happen from:

  • Nerve damage from birth trauma
  • Neuroblastomas or other brain cancers
  • Congenital abnormalities in the formation of the carotid artery
  • Post-viral damage
  • Cervical disc herniation

Rare Congenital Form

Most cases of acquired and congenital Horner syndrome are not inherited and do not run in families. However, there is an extremely rare congenital form of Horner syndrome caused by a dominant genetic mutation. This rare form of Horner syndrome can be passed down in families. In this situation, there is a 50 percent chance that a child born to someone with this form of the syndrome will also have symptoms.


Proper diagnosis of Horner syndrome can be challenging. Many different medical syndromes might cause a shrunken pupil and/or a drooping eyelid and might be confused with Horner syndrome. It’s important to rule out these other potential conditions (such as optic neuritis or third nerve palsy).

Proper diagnosis of the underlying cause of Horner syndrome is important. Some of the time, the underlying cause is fairly harmless. Other times, Horner syndrome may be a sign of a life-threatening disorder, such as lung cancer, neuroblastoma, or carotid artery dissection.

Horner syndrome that occurs along with pain or with neurological symptoms is particularly concerning for healthcare providers.

A detailed medical history and physical exam are extremely important for diagnosis. Your healthcare provider will ask about symptoms that might give clues about the underlying cause. It’s also important for them to ask questions to assess whether the Horner syndrome might have been caused by a medication you took, or as the result of an injury from a medical procedure.

A detailed eye exam is also critical. For example, your healthcare provider will check how both your pupils respond to light and whether you can move your eyes normally. Healthcare providers will also need to pay extra attention to the neurological, pulmonary, and cardiovascular systems.

One of the first steps in diagnosis is locating the general area of the oculo-sympathetic chain that is damaged. Symptoms and exam can provide some clues about this. There are also tests using eyedrops containing specific drugs that can be very helpful. By giving eyedrops of drugs like apraclonidine and then watching how your eye responds, your healthcare provider may be able to get a better idea of the general area of the problem.

General blood and laboratory tests can also be important. These will vary, based on the context. You might need a test such as:

  • General blood work to test blood chemistries, blood cells, and inflammation
  • Blood tests to rule out infectious causes
  • Urine tests to help rule out neuroblastoma (common brain cancer in young children)
  • Chest X-ray or chest CT (if lung cancer is a concern)
  • Head CT or MRI (to assess stroke or certain other brain problems)

You might need additional tests, depending on your specific situation.


Treatment for Horner syndrome depends on the underlying cause. No treatment can begin until a correct diagnosis is made. Some potential treatment might include:

  • Surgery, radiation, or chemotherapy for cancers
  • Anti-platelet agents and minimally invasive treatments like angioplasty (for carotid artery dissection)
  • Clot-dissolving agents, for specific types of stroke
  • Antibiotics or antiviral drugs, for infectious causes
  • Anti-inflammatory drugs (e.g., for multiple sclerosis)

This may require the intervention of various types of medical specialists, like pulmonologists, neuro-ophthalmologists, and oncologists. In many cases, the symptoms of Horner syndrome will go away once the underlying condition is addressed. In other cases, no treatment is available.

A Word From Verywell

The symptoms of Horner syndrome itself are usually not very severe, and often do not interfere very much with one’s life. However, it’s important to get evaluated if you or someone you care about has Horner syndrome symptoms. It’s especially important to be seen by a medical professional if symptoms begin after a traumatic accident or if symptoms like dizziness, muscle weakness, severe headache, or neck pain are also present. This will give you peace of mind, as your healthcare provider can make sure you don’t have a serious underlying problem. It may take a while to reach an overarching diagnosis, but your healthcare team will work with you to get you the answers you need.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Ruth Jessen Hickman, MD
Ruth Jessen Hickman, MD, is a freelance medical and health writer and published book author.