In addition to a general medical examination, your doctor will likely conduct tests to determine the nature of your symptoms and identify a possible cause.

Tests to confirm Horner syndrome

Your doctor may be able to diagnose Horner syndrome based on your history and an assessment of your symptoms.

An eye specialist (ophthalmologist) may also confirm a diagnosis by putting a medicated eye drop in both eyes — either a drop that will dilate the pupil of a healthy eye or a drop that will constrict the pupil in a healthy eye. By comparing the reactions in the healthy eye with that of the suspect eye, the doctor can determine whether nerve damage is the cause of problems in the suspect eye.

Tests to identify the site of nerve damage

The nature of your symptoms may help your doctor narrow the search for the cause of Horner syndrome. Your doctor may also conduct additional tests or order imaging tests to locate the lesion or irregularity disrupting the nerve pathway.

Your doctor may administer a type of eye drop that will significantly dilate the healthy eye and little dilation of the affected eye if Horner syndrome is caused by a third-order neuron irregularity — a disruption somewhere in the neck or above.

Your doctor may order one or more of the following imaging tests to locate the site of a probable irregularity causing Horner syndrome:

  • Magnetic resonance imaging (MRI), a technology that uses radio waves and a magnetic field to produce detailed images
  • Magnetic resonance angiography (MRA), which is used to evaluate blood vessels
  • Chest X-ray
  • Computerized tomography (CT), a specialized X-ray technology


There's no specific treatment for Horner syndrome. Often, Horner syndrome disappears when an underlying medical condition is effectively treated.

Preparing for your appointment

In most nonemergency situations, you typically start by seeing a family doctor or an (ophthalmologist). You may be referred to a doctor who specializes in nervous system disorders (neurologist) or a specialist in both neurological disorders and disorders affecting the eye and visual pathways (neuro-ophthalmologist).

What you can do

Before your appointment, make a list that includes the following:

  • Your symptoms, including any changes that cause you concern
  • Key personal information, including past and recent illnesses and injuries as well as any stresses in your life
  • All medications, vitamins or other supplements you take, including the doses
  • Questions to ask your provider

Take a family member or friend along, if possible, to help you remember the information you're given.

Basic questions to ask your provider include:

  • What's likely causing my symptoms?
  • Other than the most likely cause, what are other possible causes for my symptoms?
  • What tests do I need?
  • Is my condition likely temporary or chronic?
  • What's the best course of action?
  • Will I need any follow-up tests or evaluation?

If possible, bring some relatively recent photographs — ones that were taken before the onset of symptoms — to your appointment. These images may help your doctor assess the current condition of your affected eye.

What to expect from your doctor

Your doctor is likely to take a history of your symptoms and conduct a general medical examination. He or she is likely to ask you a number of questions, including:

  • When did you begin experiencing symptoms?
  • Have the symptoms changed or worsened over time?
  • Do you have a history of cancer?
  • Have you experienced any recent injury or trauma?
  • Have you experienced any head, neck, shoulder or arm pain?
  • Do you have a history of migraines or cluster headaches?

May 13, 2022

  1. Ropper AH, et al. Disorders of ocular movement and pupillary function. In: Adams & Victor's Principles of Neurology. 11th ed. McGraw Hill; 2019. https://accessmedicine.mhmedical.com. Accessed Feb. 19, 2022.
  2. Kedar S, et al. Horner's syndrome. https://www.uptodate.com/contents/search. Accessed March 2, 2018.
  3. Horner's syndrome. National Organization for Rare Diseases. https://rarediseases.org/rare-diseases/horners-syndrome/. Accessed Feb. 19, 2022.
  4. Horner's syndrome. National Center for Advancing Translational Sciences. https://rarediseases.info.nih.gov/diseases/6670/horners-syndrome. Accessed Feb. 19, 2022.
  5. Ferri FF. Horner syndrome. In: Ferri's Clinical Advisor 2022. Elsevier; 2022. https://www.clinicalkey.com. Accessed Feb. 19, 2022.
  6. Martin TJ. Horner syndrome: A clinical review. ACS Chemical Neuroscience. 2018; doi:10.1021/acschemneuro.7b00405.
  7. Graff-Radford J (expert opinion). Mayo Clinic. Feb. 21, 2022.


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