Horner’s syndrome is also known as oculosympathetic palsy and Bernard-Horner syndrome. Horner’s syndrome is a mix of symptoms that are caused when there’s a disruption in the path of the nerves that run from the brain to the face. The most common signs or symptoms are seen in the eye. It’s a fairly rare condition. Horner’s syndrome can affect people of any age.

The symptoms of Horner’s syndrome will usually affect only one side of your face. You may experience a variety of symptoms, including the following:

  • The pupil of one eye is much smaller than that of the other eye, and it will stay smaller.
  • The pupil in the eye that’s having symptoms does not dilate in a darkened room or is very slow to dilate. It may be difficult for you to see in the dark.
  • Your upper eyelid may droop. This is called ptosis.
  • Your lower eyelid may look slightly raised.
  • You may have a lack of sweat on one side or one area of the face. This is called anhidrosis.
  • Infants may have a lighter color iris in the affected eye.
  • Children may not have redness or flushing on the affected side of their face.

The general cause of Horner’s syndrome is damage to the nerve pathway between the brain and the face in what is called the sympathetic nervous system. This nervous system controls many things including pupil size, heart rate, blood pressure, sweat, and others. This system allows your body to respond correctly to any changes in the environment around you.

There are three different sections of the pathway, called neurons, that may be damaged in Horner’s syndrome. They are called first-order neurons, second-order neurons, and third-order neurons. Each part has a different set of possible causes for the damage.

The first-order neuron pathway goes from the base of the brain to the top of the spinal cord. Damage to this path may be caused by the following:

  • trauma to the neck
  • stroke
  • tumor
  • diseases like multiple sclerosis that affect the neurons’ protective outer covering
  • spinal column cavity or cyst

The second-order neuron pathway runs from the spinal column, over the upper chest area, to the side of the neck. Damage to this path may be caused by the following:

  • chest cavity surgery
  • damage to heart’s main blood vessel
  • a tumor on the neurons’ protective outer covering
  • lung cancer
  • a traumatic injury

The third-order neuron pathway runs from the neck to the skin of the face and the muscles that control the iris and eyelids. Damage to this path may be caused by the following:

  • injury or damage to either the carotid artery or jugular vein on the side of your neck
  • severe headaches, including migraines and cluster headaches
  • infection or tumor at the base of your skull

The common causes for children with Horner’s syndrome include:

  • neuroblastoma, which is a tumor in the hormonal and nervous systems
  • injury during birth to their shoulders or neck
  • a defect of the aorta in the heart that they are born with

There is also what is called idiopathic Horner’s syndrome. This means that the cause is unknown.

Horner’s syndrome is diagnosed in stages. It will start with a physical exam by your doctor. Your doctor will also look at your symptoms. If Horner’s syndrome is suspected, your doctor will then refer you to an ophthalmologist.

The ophthalmologist will perform an eye drop test to compare the reaction of both of your pupils. If the results of this test determine that your symptoms are caused by nerve damage, then further testing will be done. This additional testing will be used to find the underlying cause of the damage. Some of those additional tests may include:

  • MRI
  • CT scan
  • X-rays
  • blood tests
  • urine tests

There is not a specific treatment for Horner’s syndrome. Instead, the condition that caused Horner’s syndrome will be treated.

In some cases, if the symptoms are mild, no treatment is needed.

There are some serious symptoms of Horner’s syndrome that you should watch for. If they appear, then you should contact your doctor immediately. These serious symptoms include:

  • dizziness
  • problems seeing
  • neck pain or a headache that is sudden and severe
  • weak muscles or inability to control your muscle movements

Other conditions can have symptoms that are similar to Horner’s syndrome. These conditions are Adie syndrome and Wallenberg syndrome.

Adie syndrome

This is a rare neurological disorder that also affects the eye. Usually, the pupil is larger in the affected eye. However, in some cases, it may appear smaller and look like Horner’s syndrome. Further testing will allow your doctor to confirm this as your diagnosis.

Wallenberg syndrome

This is also a rare disorder. It’s caused by a blood clot. Some of the symptoms will mimic Horner’s syndrome. However, further testing will find other symptoms and causes leading your doctor to this diagnosis.

If you are experiencing any of the symptoms of Horner’s syndrome, it’s important that you make an appointment with a medical professional. Getting a proper diagnosis and finding the cause is important. Even if your symptoms are mild, the underlying cause may be something that needs to be treated.