Horner Syndrome

The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017

Horner Syndrome

Horner syndrome is a relatively rare syndrome that affects the eye, eyelid, pupil, and face of those with this syndrome. It is characterized by three major symptoms including abnormal constriction of the pupil (miosis), a weak droopy eyelid (ptosis), and a decrease or lack of sweating on the surface of the skin of the face on the side affected. These symptoms arise when the sympathetic nerve supply to the eye is decreased or interrupted. The causes of Horner’s syndrome are extensive and can include other medical disease processes, trauma/surgical procedures, and a very long list of medications. Treatment is directed to the initial cause of the interruption of the sympathetic nerve supply, and success will depend on the primary or initial cause of symptoms.


Patients with Horner’s syndrome can present with varying symptoms and a varying severity of symptoms. The most common symptoms include (1) a constricted pupil (miosis) on one side of the face, (2) delayed opening of the pupil affected, (3) drooping of the upper eyelid on the side of the face affected (ptosis), (4) a mild elevation of the lower eyelid on the side of the face affected (reverse ptosis), and (5) a decrease in sweating on the side of the face affected (anhidrosis).

Other clinical symptoms an individual with Horner’s syndrome may experience include (1) impaired vision, particularly difficulty focusing or maintaining depth perception because of the unequal pupil size, (2) dizziness, (3) perceived muscle weakness in the face, particularly on the side of the face affected, and (4) significant headaches or neck pain.


Horner’s syndrome is a result of decreased nerve impulses coming into the face through the sympathetic pathway of the head and neck. The nerves of this system are part of a larger system known as the autonomic nervous system. The specific nerves involved in this syndrome come off the spinal cord at the level of the shoulder and chest and then continue upward to supply the neck, head, and face with sympathetic innervation. This pathway is composed of three distinct parts called the first-order neurons, second-order neurons, and third-order neurons, and depending on which aspect of this pathway is affected, the condition could create varying symptoms in a patient.

The first-order neurons connect the hypothalamus of the brain with the cervical region of the spinal cord. Secondary pathologies such as multiple sclerosis, brain tumors, or encephalitis could affect this neuron pathway, creating the symptoms seen in Horner’s syndrome. The second-order neurons connect the spinal cord with the muscles and other anatomy of the neck. They pass across the chest to get to the neck. Secondary pathologies such as thyroid cancers, tumors of the top or apex of the lung (Pancoast tumor—see https://www.youtube.com/watch?v=c7LD9bdw9ag), trauma to the chest, or a thoracic aortic aneurysm could affect this neuron pathway. The third-order neurons pass from the neck into the face including the skin, muscles, and vessels that supply the face with blood in innervation. Secondary pathologies such as middle ear infections, carotid artery aneurysms or clots, or cluster headaches (Horton’s headaches) can cause the symptoms of Horner’s syndrome.


Treatment for Horner’s syndrome depends on determining which neuron in the pathway may be affected, and then treating the underlying pathology. There are three primary tests used to help determine which neurons in this pathway may be affected. In the cocaine drop test, cocaine drops are placed in the eye. Under normal conditions, this would cause a dilation of the pupil. In Horner’s syndrome this will have no effect on the pupil. The Paredrine test is similar to the cocaine drop test and helps determine if the cause of the pupil constriction is damage to the third-order neurons. The third test is the dilation lag test. When a slit lamp is turned off or removed from the eyes, the affected pupil will dilate at a slower rate or lag compared to the unaffected eye. These tests help to narrow down where the problem may be within the sympathetic pathway. However, treatment still depends on what other pathology may be causing a decrease in nervous system function in this system.

Charles A. Ferguson

See also: Autonomic Nervous System; Dizziness; Ptosis

Further Reading

Bardorf, Christopher M., Enrique Garcia-Valenzuela, & Gregory Van Stavern. (2015). Horner syndrome: Overview, anatomy, pathophysiology. Retrieved from http://emedicine.medscape.com/article/1220091-overview

Ropper, Allan H., & Robert H. Brown. (2005). Disorders of ocular movement and pupillary function. In A. H. Ropper & R. H. Brown, Adams and Victor’s principles of neurology (8th ed., pp. 222—245). New York: McGraw-Hill Professional.