Horner's Syndrome

What is Horner’s syndrome?
Horner’s syndrome is a common neurological disorder of the eye and facial muscles. The condition usually occurs suddenly. The most common clinical signs of Horner’s syndrome are:

  • Drooping of the eyelids on the affected side (ptosis) 
  • The pupil of the affected eye will be constricted (miosis)
  • The affected eye often appears sunken  (enophthalmos)
  • The third eyelid of the affected eye may appear red and raised (prolapse of the third eyelid, conjunctival hyperemia)

What causes Horner’s syndrome?
Horner’s syndrome is due to a dysfunction of the sympathetic nerves of the eyes and surrounding facial muscles. This is part of the autonomic nervous system, which helps to control normal functions such as blinking, muscle tone, etc.

There are many reasons for Horner’s Syndrome. The most common cause is classified as idiopathic which means it is without known cause. The onset of Horner’s syndrome can be sudden and without warning. Within a few hours you observe that your dog has drooping eyelids and may be having difficulty eating on the affected side, with excessive salivation.

The damage to the sympathetic pathway can be in the neck or chest and may be due to tumors or intervertebral disc disease. Sometimes there is known damage to the neck area (bite wounds, blunt trauma, etc.). Middle or inner ear disease (otitis media and interna) can also cause Horner’s Syndrome.

Does it affect any particular breed or age of dog?
Any dog can develop Horner’s Syndrome although Golden retrievers and Cocker Spaniels have a somewhat higher incidence.

What is the treatment?
Most cases of Horner’s Syndrome will resolve spontaneously. It is important to treat any underlying disease. There are several diagnostic tests that will be performed to determine if there is an underlying cause in your pet.

What is the recovery rate?
If the lesion is not due to any pathological cause, a slow recovery can be expected.

What is the outlook?
Very good, if there is no underlying pathological cause present. The condition tends to be self-resolving but may take weeks or months depending on the severity.

Published on December 18, 2007.