Horner’s Syndrome in Dogs: Everything You Need to Know About

Which parts in the body of your dog that you think to play the most important role in his daily activities? Even though the answers will depend on personal thoughts, I believe that most of us will come to the same conclusion: eyes.

Quite cliche, but eyes are truly the windows to the soul of humans as well as pets. Therefore, it is important to help your dog keep healthy eyes. In this post, we want to share with you some information about a quite common eye condition which could happen in dogs: Horner syndrome.

What is Horner Syndrome?

The eyes and some surrounding parts basically have a lot of complex nerves to control the movements and function. In general, Horner syndrome is a neurological condition of the facial muscles and eye that commonly happens in dogs, horses, cats, and many other pets. It is known as the results of a dysfunction in the sympathetic nerves which feed your dog’s eyes.

In most dogs, the sympathetic nerves basically belong to the autonomic nervous system, which is also known as the “flight or fight” system. These parts play an essential role in keeping:

  • Pupils open properly
  • Upper eyelids raise fully
  • Third eyelid or nictitans recess
  • Eyes in the front of your dog’s socket

When these sympathetic nerves of your dog’s eyes are not functioning normally, some of those anatomic functions listed above will not happen. As a result, it causes Horner syndrome. Generally, this condition could be caused by some sorts of injury in the nerves or lesion. And these injuries might happen at the upper spinal cord, the brain level, or between the face and the spinal cord.

While Horner syndrome could have an effect on any dogs, there are actually certain breeds like Cocker or Golden Retriever which have a higher level of occurrence.

Watch this short clip to get an overall understanding about this special condition:

Clinical signs

If your dog suffers from Horner syndrome, one or both of his eyes will be affected. In general, there is no sex, age, or breed predilection.

There are typically 4 significant changes when this condition occurs:

  • Enophthalmos – sunken appearance in the eyes: As the result of dysfunctional sympathetic nerves, the muscle of the orbit might slightly retract, which eventually cause the globe to be sunken in its orbit.
  • Ptosis – dropping in the upper eyelid: If the sympathetic nerves coming out of the Muller or superior tarsal muscle is not functioning correctly, your dog cannot fully open his eyelid.
  • Protrusion in the third eyelid: In this case, the third eyelid of your dog cannot retract fully without proper function in the sympathetic nerves
  • Miosis – small size of pupil: Dysfunction of the sympathetic nerves makes the affected pupil to shrink

Apart from these 4 common signs, the blood vessels on the affected area of your dog’s face might be dilated. Eventually, it would get warmer when you touch it. Additionally, there would be pinky appearance in the skin of your dog’s ears and mild nasal congestion. However, these symptoms are quite hard to notice.

Common underlying causes of Horner syndrome in dogs

Approximately 50 percent of the cases of canine Horner syndrome are idiopathic, which means that the underlying cause is not basically identifiable. In other words, idiopathic is just a simple medical word to say: “I do not know”.

Before you can call the Horner syndrome in your dog idiopathic, however, it is necessary to rule out the following common causes of this condition:

  • Diabetes mellitus: Many studies have recently proved that diabetes mellitus is one of the main causes of nerve dysfunction, which eventually leads to Horner syndrome in dogs.
  • Trauma: Most of the injuries in the spinal or cervical cord can lead to bilateral and unilateral Horner syndrome in dogs. Additionally, an accident with trauma to the chest, neck, or head of your dog can also be a cause.
  • Disease in the inner ear: Tumors, inflammation, or infection in the inner ear of your dog’s body might have a negative effect on the sympathetic nerves and eventually cause Horner syndrome.
  • Central lesion: In this cases, the sympathetic nerves of your dog might be interrupted somewhere before they exit the spinal cord due to a trauma, blood clots, or spinal cord and brain tumors. You can also notice some other neurologic symptoms such as incoordination, stumbling, or head tilt.
  • Pre-ganglionic lesion: The interruption of the sympathetic nerves might occur between the synapse and the spinal cord as the result of trauma or tumors in the neck or chest.
  • Post-ganglionic lesion: Because of vigorous ear cleaning or disease in the middle ear, the sympathetic nerves of your dog might be interrupted between the eye itself and the synapse. From 42 to 55 percent of post-ganglionic lesion cases are known as idiopathic.

Apart from these common causes, there might be some other reasons for Horner syndrome in dogs such as chest or brain cancer, bite wounds, or results of a medication or treatment.

Diagnosis of Horner syndrome in dogs

In general, it is quite easy to diagnose Horner syndrome in dogs. For example, you can observe and notice this condition when your pet has a constricted pupil, sunken eye, elevated third eyelid, or partially raised upper eyelid. However, as there are some other disorders that have the same signs as Horner syndrome, a vet might need to perform some tests and use observation to distinguish.

Once diagnosed, the vet should start a logical process to find out the underlying cause of the problem. After doing a comprehensive physical examination, the vet will continue to perform some more specific tests such as:

  • Comprehensive blood count: This is typically a non-invasive test of blood to evaluate platelets, white blood cells, and red blood cells.
  • Urinalysis: As its names implies, urinalysis is a non-invasive test of urine to measure the kidney function as well as check any infection or inflammation in your dog’s urinary tract
  • Serum biochemical profile: Similarly, this is also a non-invasive test of blood to determine the function of kidney and liver, as well as a couple of gastrointestinal enzymes and electrolytes such as potassium or sodium.
  • X-rays or chest radiographs: This non-invasive imaging technique is commonly used to look for any evidence of masses in your dog’s chest cavity.
  • Advanced imaging: In some serious cases, the vet might apply some advanced imaging techniques such as CT – computed tomography or MRI – magnetic resonance imaging

In most cases, sympathetic nerves in the eye of your dog are quite long and consist of 3 neurons, which are basically a nerve cell which helps to transmit the nerve impulses. The first one begins at the hypothalamus in your dog’s brain and finishes at the first end of his thoracic spinal cord, while the second one begins at this area and follows a specific pathway to come out of your dog’s spinal cord onto the sympathetic trunk and then finishes in a location known as the cranial cervical ganglion.

Because the third and the second neuron generally meet in the cranial cervical ganglion, the vet can perform a non-invasive pharmacologic test to find out the exact place of the lesion along the nerve’s course. In medical terms, a lesion that is involved in the second neuron is called pre-ganglionic and the other one that affects the third neuron is known as post-ganglionic.

How to treat canine Horner syndrome

In fact, there is not any specific treatment for the idiopathic Horner syndrome in dogs. Most of the vets will try their best to find out the underlying cause, and then provide the treatment accordingly. Depending on the area of the injury, the vet will prescribe phenylephrine eye drops to alleviate some clinical symptoms.

Generally, post-ganglionic lesions will have a more favorable prognosis than pre-ganglionic ones. Approximately 50 percent of these with an idiopathic disease will resolve or improve itself within 6 to 8 weeks. Luckily, Horner syndrome is actually not painful, for dogs and a patient is not away of the noticed eye changes.

Recovery of Horner syndrome in Dogs

Depending on the underlying condition and area of the damage, the time of recovery would be different. If you and the vet cannot find out any cause for the damage, it is always better to allow the condition to resolve itself. In general, it can take approximately from 4 months to 6 months, depending on the severity of the cases.

The vet will show you a better overall understanding of this recovery time right after he or she found out the underlying cause and make a specific treatment plan for your dog.

Final thoughts

To sum up, Horner syndrome is a quite common condition in dogs. In most cases when you notice any signs of this disorder, it is better to take your dog to the nearest vet to find out the underlying cause and seek for a better treatment. Do not worry a lot because this problem will resolve itself after several weeks or months, depending on the severity and condition of your dog.

Do you have any experience with Horner syndrome in dogs? Leave us a comment on the section below. Thank you for reading and remember to share this useful post to your friend.

2 thoughts on “Horner’s Syndrome in Dogs: Everything You Need to Know About”

  1. We just got a diagnosis of this syndrome with our Rottie, Ashar. At first, we thought she had a stroke. She is 9 years old (this August 2020). The third eyelid made us think her eyes were rolling in back of her head. Other than cosmetic; at this point we don’t notice much change in her. She does have drooling issues and from time to time has a hard time eating….but so far that really hasn’t stopped her. The vet put her on steroids and eye drops. I will try to update as things move along.

  2. My dog was recently diagnosed with Horner’s Syndrome. 12 year female spayed rough collie. Noticed her left pupil was much smaller than right and was squinty. I brought her to animal hospital I work at – first thought it was uveitis as her pressures were extremely low, was administering pred acetate drops. During this time she was also being treated for a UTI which since then has resolved and pressures were better readings.

    Last week she was seen by an opthalmologist and diagnosed with Horner’s.

    Her history is : adopted 6 years ago. Came with an untreated but old /healed injury to right hind leg/hip. Right hind leg is shorter than left- apparently had been HBC or some other trauma – right side of pelvis is smashed and pushed to the left, femoral head is not attached to anything. Amazingly enough she is able to walk and use to run when she was younger. Now experiencing some balance issues. Dragging left hind left when on walks (short ) Has been seeing a chiropractor for adjustments/acupuncture for about 2 years now.

    Recent behavior changes: Anxious especially at night (sun downers?) , always seems hungry but not increase water intake. Blood work done two weeks ago came back normal .

    Plan on getting a radiograph of her chest but will not pursue an MRI.


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