In addition to a general medical examination, your doctor will conduct tests to judge 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 his or her assessment of your symptoms.

Your doctor, often an ophthalmologist, may also confirm a diagnosis by putting a 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, your doctor can determine whether nerve damage is the cause of problems in the suspect eye.

Tests to identify the site of nerve damage

The prominence or nature of certain 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 abnormality disrupting the nerve pathway.

Your doctor may administer a type of eyedrop that will cause significant dilation of the healthy eye and little dilation of the affected eye if Horner syndrome is caused by a third-order neuron abnormality — 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 abnormality causing Horner syndrome:

  • Magnetic resonance imaging (MRI), a technology that uses radio waves and a magnetic field to produce detailed images
  • Computerized tomography (CT), a specialized X-ray technology
  • X-ray imaging

For children with Horner syndrome, a doctor may order blood and urine tests that are used to diagnose a tumor of the hormonal and nervous systems (neuroblastoma).


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 will start by seeing a family doctor or an eye specialist (ophthalmologist). You may be referred to a doctor specializing 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:

  • Signs or symptoms — or any changes from normal — that may be causing concern
  • Past and recent illnesses or injuries
  • All medications — including over-the-counter drugs and dietary supplements — and the dosage you take of each medication
  • Any significant changes or stresses in your life

If possible, provide your doctor with relatively recent photographs — but photos taken before the onset of symptoms. These images may help your doctor assess the current condition of your affected eye.

What to expect from your doctor

Your doctor will 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?
March 10, 2018
  1. Ropper AH, et al. Adams & Victor's Principles of Neurology. 9th ed. New York, N.Y.: The McGraw-Hill Companies; 2009. http://www.accessmedicine.com/content.aspx?aID=3631773. Accessed Dec. 31, 2013.
  2. Kedar S, et al. Horner's syndrome. http://www.uptodate.com/home. Accessed Dec. 31, 2013.
  3. Mughal M, et al. Current pharmacologic testing for Horner syndrome. Current Neurology and Neuroscience Reports 2009;9:384.
  4. Davagnanam I, et al. Adult Horner's syndrome: A combined clinical, pharmacological, and imaging algorithm. Eye 2013;27:291.
  5. Al-Moosa A, et al. Neuroimaging yield in isolated Horner syndrome. Current Opinion in Ophthalmology 2011;22:468.