Pet insurance companies call it a pre-existing condition. I call it horner's syndrome.

Pet Assure is a low-cost pet insurance alternative that covers every medical service - even pre-existing conditions! Learn why more than 100,000 pet households have chosen Pet Assure.
Dog Insurance

Canine Horner's Syndrome

Horner's syndrome is a common disorder of a sudden loss of stimulation of the nerves--of the eyes and area surrounding the eyes.

This syndrome is just a cosmetic issue--it does not cause pain, and does not affect vision.


Horner's syndrome is caused when the nervous system gets damaged and stops functioning in the eye, ear, or neck area.

About half of cases are idiopathic (cause is unknown). Other reasons for damage may include:

  • Eye disease
  • Ear infection
  • Trauma (in the head, neck, or chest)
  • Tumor in the brain or chest
  • Bite wounds
  • Blood clot


The affected side of the face will show the followingsigns suddenly:

  • Eyelids drooping
  • Shrunken pupil
  • Eye is sunken in
  • Third eyelid is protruding
  • Blood vessels constricted, making the area pink and warm to the touch

Sometimes, the dog will also have excessive salivation and difficulty eating on the affected side.


Your veterinarian will do tests to determine the cause of the syndrome, including:

  • A neurologic (brain) exam
  • X-rays: to rule out cancer
  • Blood tests
  • MRI
  • Special eye drops: causes the pupils to widen, showing if the nerve damage is inside or outside the brain


Treatment is not necessary for horner's syndrome because it usually resolves on its own in a few weeks. However, any underlying diseases must be treated.

There are eye drops available for cosmetic purposes.


The best ways to prevent this condition are to avoid chances of trauma, bite wounds, eye disease, and ear infection.


There is a very good prognosis if there is no serious underlying cause.

Additionally, if the damaged nerves are outside of the brain and spinal cord, the prognosis is even better.

Among pet health plans, Pet Assure is the best value pet plan for your dog. It is the best pet insurance alternative and available for any type of pet. Pet Assure covers every medical condition, including horner's syndrome, ear infections, skin allergies, skin infections, gastritis (vomiting), enteritis/diarrhea, arthritis, bladder infections, tumors and hypothyroidism. We're the cheap pet insurance alternative that covers every medical service, including routine visits, dental work, x-rays, laboratory work, vaccines, cremation, spay & neuter, hospitalization and emergency services. Compare pet insurance to us; whether you are looking for dog insurance or cat insurance, insurance for your pet is costly. Choose Pet Assure, the pet discount plan that more than pays for itself.
Does your employer offer the Pet Assure Veterinary Discount Plan? Click here