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Aina Meducci 2012


The following blog posts is not genuinely from my research but through readings and citation from trusted website. I do not own any of the copyright and therefore you may use it at your own risk


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Horner's syndrome

I dropped into these words at last semester during my ophthalmology class. But it is then repeated in our neurological class. Seems to have interrelation on it right?


Horner's syndrome in a cat

Horner's Syndrome is a common neurological disorder of the eye and facial muscles, caused by dysfunction of the sympathetic nervous system. The condition usually occurs suddenly and without warning. The most common clinical signs of Horner's Syndrome are
  • Drooping of the eyelid on the affected side (ptosis)
  • The pupil of the affected eye will be constricted (miosis), or smaller than usual
  • The affected eye often appears sunken (enophthalmos)
  • The third eyelid of the affected eye may appear red and raised or protruded (conjunctival hyperemia)


Horner's syndrome is not a disease but a CONDITION!

What causes Horner's syndrome?

If the sympathetic nervous system that supplies the eyes is damaged or is malfunctioning, the parasympathetic system 'takes over', and the symptoms of Horner's Syndrome appear. The damage or malfunction can occur in the neck area, the ear area or the eye area. Damage may occur because of blunt force trauma such as that caused by an automobile accident or because of a bite wound from another animal.

Other problems that can cause damage or inflammation of the nerves in this area include diseases within the eye or in the retrobulbar (behind the eye) area, problems in the middle ear (otitis media), or tumors in the chest, neck or brain.In dogs, Horner's Syndrome is 'idiopathic', which means it has an unknown cause, in about half the cases. In cats, however, a cause is virtually always found, and idiopathic Horner's Syndrome is very rare. With many cats that develop Horner's Syndrome there is a recent history of trauma, particularly being hit by a car.

Nasopharyngeal polys removal in cats can also cause the development of Horner Syndrome due to nerve damage. It is usually temporary and does not effect cat's behavior.

Depending on the cat's recent history and other physical findings on examination, veterinarian may recommend a series of diagnostic tests to determine if there is an underlying cause. Initial tests will usually include a neurologic evaluation, an otoscopic examination (examination of the ears) and x-rays of the chest and neck area.

How can sympathetic damage occurs?

Chart showing Horner's Syndrome

The nerve carrying the tiny nerve fibers that provide sympathetic control to the eye have a long path. The damage may have occurred anywhere along this path.The nerves originate in the brain stem and travel down the spinal cord in the neck area exiting just inside the chest (at the level of the second thoracic vertebra). The nerves then form the cervical sympathetic trunk, a bundle of nerves that travels back up the neck, this time outside the spinal cord, to the middle ear (this area is shown in red).These nerves then connect to new nerves just below the ear. The new nerves continue their journey to the eye. The damage can occur in the neck area, the ear area or the eye area. Damage can occur in the form of trauma, tumor involvement, infarction (abnormal blood clot), middle ear infection, or diseases of the eye itself.


Localizing which area of the sympathetic nervous system is affected goes a long way in determining the nature of the damage as different areas of the system are prone to different types of injury. Certain eye drops can be used to stimulate different areas of the nervous system and determine if the lesion is in the first nerve segment or in the second nerve segment. Most injuries turn out to be in the second nerve segment.

With second nerve segment involvement: If ear infection is not obvious and disease of the eye beyond the Horner's syndrome itself is not obvious, then it is probably prudent to allow the syndrome to resolve on its own. This usually occurs within 6 to 8 weeks. Further diagnostics may be undertaken if new developments occur or if the syndrome persists beyond this time.

With first nerve segment involvement: Involvement of the first nerve segment indicates a problem in the chest or spinal cord and is more significant. Chest radiographs should be taken to rule out cancer spread to the chest (the only sign of this may be the Horner's syndrome). The front leg should be carefully checked for evidence of function loss as a tumor or protruding intervertebral disc could be exerting pressure on the spinal cord. Trauma to the neck as with a strong jerk from a collar or straining against a leash can also produce Horner's syndrome from this section of the nerve.

Generally more diagnostic work is needed for cases involving the first nerve segment as there is potential for more serious underlying causes. If the syndrome stemmed from pulling on the leash, it should resolve uneventfully, depending on how badly damaged the nerve is.


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. Symptomatic treatment usually involves phenylephrine drops placed in each eye every 12-24 hours to dilate the pupil. Other eye medications might be useful to avoid development of corneal ulcers from the exposed keratitis.


Prognosis and recovery rate

The prognosis depends on the underlying cause. Patients with chest trauma tend to have a quicker recovery rate (days to weeks) than patients with other lesions. If the underlying problem is Feline Dysautonomia, the prognosis is poor.

Sources: The pet health library; Wendy C brooks, Horner's syndrome in cat VCA Animal hospitals, Nasopharyngeal polyps in cats; ACVS Veterinary surgeon Karen Tobias

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