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Horner's Syndrome in Dogs

Horner’s syndrome is an nerve problem that affects an dog’s eye.

Horner's syndrome is a neurological problem that affects a dog's eye and the muscles of the face.

Signs of Horner's Syndrome in Dogs

Dogs suffering from Horner's syndrome usually develop signs quite suddenly, and many people fear that their dog has had a stroke when they see them. If your dog develops Horner's syndrome, the signs you see will affect one side of the dog's face and may include:

  • Sagging cheek muscles
  • Drooping eyelid
  • Constricted pupil
  • Retracted eyeball
  • Prolapsed third eyelid
  • Drooling
  • Difficulty chewing on affected side

Causes of Canine Horner's Syndrome

The nerves that control the muscles of the face and eye travel from the brain through the spinal cord to the chest, where they exit the spine and travel back up to the ear. At that point, they attach to other nerves and continue on to the eye.

Because of this long, complicated nerve route, there are many places and ways in which interruption can occur. Some of the most common causes of Horner's Syndrome in dogs include:

Diagnosis of Horner's Syndrome in Dogs

Diagnosis of Horner's syndrome requires a thorough history and physical examination by a veterinarian. Once the syndrome is recognized and diagnosed, the doctor will be trying to determine its underlying cause. A close exam of the eyes and ears and a neurological exam will be performed at your dog's presenting visit for this condition.

Basic blood and urine tests may be done to look for obvious medical problems.

More specialized tests such as x-rays, CT scan, or MRI may be recommended based on the results of initial testing.

Treatment of Canine Horner's Syndrome

Treatment of the Horner's syndrome itself isn't necessary, but any underlying conditions that can be identified will need appropriate treatment. For example, if an ear infection is diagnosed and suspected to be the cause of the nerve dysfunction, the infection will need to be properly treated.

If no cause is found for the Horner's syndrome and it is determined to be idiopathic, as more than half of cases are, the signs may improve on their own over the following two months or so. During that time, your dog may need some symptomatic care such as softer food if he's having trouble chewing or artificial tear drops to keep his eye comfortable.

You can learn about other eye problems that dogs can develop here: "Common Eye Conditions in Dogs."

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