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What Nerve Is Involved In Horner’s Syndrome & What Cranial Nerves Are Affected?

In Horner’s syndrome, on one side of the face, the eyelids hang down; the pupils become smaller (constriction), and sweating decreases. The cause is a disruption of nerve fibers that connect the brain to the eyes.

Horner’s syndrome can occur spontaneously or due to a disease that cuts nerve fibers from the brain to the eye. Eyelids may sag, the pupils may remain constricted, and the affected face may not sweat much. Your doctor may want to see if your pupils are dilated and do imaging tests to find the cause. Horner’s syndrome can occur in people of any age.(1)

What Nerve Is Involved In Horner's Syndrome?

What Nerve Is Involved In Horner’s Syndrome?

Some nerve fibers that connect the eye and brain follow a circuitous path. Such nerve fibers first descend from the brain into the spinal cord. After exiting the spinal cord at the chest, it returns to the head, by the carotid artery in the neck, and through the interior of the skull to the eyes. Horner’s syndrome occurs when nerve fibers break apart somewhere in this pathway.

What Cranial Nerves Are Affected?

It is the sympathetic nerve that is affected along with the 6th cranial nerve. This is due to a break in the sympathetic nerves going to the eyes.

Horner’s syndrome can occur spontaneously or due to other illnesses. For example, it can be caused by a brain, head, neck, or spinal cord diseases, such as:

  • Dissection of the aorta or carotid artery (torn inner wall of an artery)
  • Injury
  • Lung cancer
  • Other tumors
  • Swollen neck lymph nodes (cervical lymphadenopathy)
  • Thoracic aortic aneurysm (a disease in which the wall of the aorta swells)
  • Horner’s syndrome may exist since birth (congenital Horner’s syndrome).(2)(3)

Symptoms Of The Disease

Horner’s syndrome affects the eye on the same side as the severed nerve fiber. Symptoms of Horner’s syndrome include ptosis (drooping of the upper eyelid) and pupil constriction (miosis). Some people find it difficult to see in dark places as the pupils get contracted. However, most patients do not notice a change in vision.

The face on the affected side may sweat less than normal, may not sweat at all, and may appear to be flushing in rare cases.

In congenital Horner’s syndrome, the iris of the affected eye is bluish-grey from birth and does not change color as it grows.(2)

Diagnosis Of Horner’s Syndrome

  • Eye drop test
  • MRI or CT examination
  • The disease is suspected by symptoms
  • Doctors perform a two-stage test to confirm the diagnosis and determine where the abnormality is.

First, they apply an eye drop containing a small amount of cocaine or another drug (apraclonidine) to both eyes. Pupillary responses indicate whether Horner’s syndrome is present or not.

If the likelihood of Horner’s syndrome is high, another test is done 48 hours later. In this test, hydroxyamphetamine eye drops are applied to both eyes. By seeing how the pupil responds to this drug, the doctor can determine the general location of the abnormality.

MRI and CT scan of the brain, spinal cord, chest, or neck are often needed to look for tumors or other serious illnesses that have disrupted the nerve fibers that connect the brain to the eyes.(4)

Treatment For Horner’s Syndrome

If the cause is identified, treatment is directed to remove or ease the cause. However, there is no specific cure for Horner’s syndrome. A typical symptom is that the eyelids hang down only slightly and often do not require any treatment.

The acute episode of painful Horner’s syndrome must be considered a neurological emergency, and the internal carotid artery of the topic should be evaluated as shown below. These patients have an increased risk of cerebral infarction.

The first step in treating Horner’s syndrome patients is to conduct appropriate research to determine the cause. Imaging studies usually appear in new episodes of Horner syndrome unless they occur during trauma or surgery. High-yield imaging locations can be determined based on the accompanying signs and symptoms. These radiological evaluations may include the brain, spinal cord, cervix, cerebral blood vessels, head, neck, and chest. Treatment depends on the cause of Horner syndrome.(4)


  1. Davagnanam I, Fraser C, Miszkiel K, Daniel C, Plant G. Adult Horner’s syndrome: a combined clinical, pharmacological, and imaging algorithm. Eye. 2013;27(3):291-298.
  2. González-Aguado R, Morales-Angulo C, Obeso-Agüera S, Longarela-Herrero Y, García-Zornoza R, Cervera LA. Horner’s syndrome after neck surgery. Acta Otorrinolaringologica (English Edition). 2012;63(4):299-302.
  3. Smit DP. Pharmacological testing in Horner’s syndrome–a new paradigm. South African Medical Journal. 2010;100(11):738-740.
  4. Nasser BA, Mesned A, Moazamy YE, Kabbani MS. Horner’s syndrome after paediatric cardiac surgery: case report and review of the literature. Cardiology in the Young. 2015;25(3):569-572.
Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:February 28, 2020

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