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Horner's Syndrome in Cats: Causes, Symptoms, & Treatment

Horner's Syndrome is a neurological disorder affecting eyes and face muscles, causing ptosis, miosis, enophthalmos, and conjunctival hyperemia. Today, our South Florida vets detail Horner's Syndrome, how it can afeect your cat, and some treatment options.

What is Horner's Syndrome?

Horner's syndrome is a neurological disorder that affects the muscles around the eyes and face. It's caused by a dysfunction the the sympathetic nervous system. It usually only affects one side of the face, but in rare cases, it can affect both sides.

What is the sympathetic nervous system?

The sympathetic nervous system, which is part of the autonomic nervous system, controls the body's automatic or involuntary functions. These include the normal functioning of the face and eye muscles and can encompass blinking, muscle tone, and pupil dilation or constriction.

What causes Horner's Syndrome in cats?

Both the sympathetic and parasympathetic systems can affect the pupil, making it impossible for the eye muscles to contract and relax. Some of the triggers can include:

  • Trauma: Injuries to the spine, neck, or head can lead to Horner’s syndrome. this trauma can occur from various sources, such as car accidents, bite wounds from another animal, or certain surgeries like thoracic surgeries.
  • Tumors: A tumor can affect the nerve fibers in the brain, brain stem, or spinal cord.
  • Blood clots: An abnormal blood clot (infarction) in the spinal cord may cause a lesion that affects typical function and causes Horner’s syndrome.
  • Middle ear infection: Inflammation in the middle ear, where some of the nerves of the face travel, can lead to Horner’s Syndrome.
  • Eye diseases: Certain eye conditions, such as keratitis, glaucoma, and conjunctivitis, can cause symptoms associated with Horner’s syndrome.

Despite all this, it's important to note that roughly 40% of Horner's Syndrome cases are idiopathic, meaning the cause remains unknown. The above are just some issues we already know can cause Horner's Syndrome.

What are the symptoms of Horner's Syndrome?

The most common symptoms of Horner's Syndrome include:

  • Ptosis: the upper eyelid dropping on the affected side
  • Miosis: the pupil will be constricted, or smaller than usual
  • Enophthalmos: the eye appears sunken
  • Conjunctival Hyperemia: the third eyelid may appear red and raised or protruded.

Is there treatment for Horner's Syndrome?

Horner's syndrome usually goes away on its own with time. Veterinarians may suggest eye drops with phenylephrine to make the pupil bigger and eye lubricants to prevent corneal ulcers from exposure keratitis. 

If another disease, however, is the cause of your cat’s Horner’s Syndrome, it’s important to have a veterinarian treat that disease. As a symptomatic treatment, eye lubricants and phenylephrine drops may help.

What is the prognosis for a cat with Horner's Syndrome?

This really depends on the underlying cause. If caused by another disease, Horner's Syndrome will generally resolves after the disease does. Cats who develop Horner's Syndrome as thoracic surgery often improve too.

If the Horner's is a result of a bulla osteotomy, about 75% will recover from Horner's Syndrome.  

Some cats only experience a partial recovery. They might still have a drooping eyelid, sunken eye, or shrunken pupil. But these are cosmetic and shouldn't affect your cat's quality of life.

If you believe your cat might be suffering from Horner's Syndrome, contact Animal Eye Guys today. Our vets specialize in eye-related conditions and can come up with a treatment plan for your cat.

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