Horner's Syndrome in Dogs

There are other conditions that produce similar symptoms to Horner’s syndrome. Your veterinarian will need to use observations and testing to differentiate between Horner’s syndrome and other conditions such as uveitis. A neurology specialist may be needed to properly diagnose it.

While Horner’s syndrome can affect any dog, there are certain breeds such as the Golden Retriever and Cocker Spaniel that have a higher incidence of occurrence.

Horner’s syndrome is when the nerves that control certain parts of the eye have been disrupted. The automatic functions between the eye and the brain have become disjointed and therefore, the eye is not functioning properly.

The symptoms of Horner’s syndrome in dogs are similar to those of other conditions. If you notice any of these symptoms, contact your veterinarian for an exam. Your veterinarian may refer you to a neurologist for further diagnosing. 

• Drooping of the eyelid on the affected eye
• Constricted pupil of the affected eye
• Sunken appearance of the affected eye
• The third eyelid may appear elevated on the affected eye
• Vision may be impaired

Horner’s syndrome in dogs occurs when a nerve going from the eye to the brain has been damaged. There are three things that can happen to cause the damage to the nerve.

Central Lesion

The nerve has been damaged somewhere before the nerve exits the spinal cord. Blood clots, spinal cord tumors, brain tumors or trauma can cause the damage in this location. Other neurological signs may present such as stumbling or head tilting.

Preganglionic Lesion

There has been nerve damage between the spinal cord and the synapse. Trauma to the neck or tumors in the neck or chest can cause the damage in this location.

Postganglionic Lesion

The nerve has been damaged between the synapse and the actual eye. This can occur when the ear is cleaned vigorously or the dog has middle ear disease. Most postganglionic lesions have an unknown cause.

Most veterinarians will diagnose Horner’s syndrome based on clinical symptoms. Once it has been diagnosed, however, it is important to find out where the interruption between the brain and the eye is occurring. This can be done by your veterinarian or you may be referred to a specialist. 

A phenylephrine solution eye drop will be put in both eyes of your dog. If the affected eye responds to the solution by resolving all clinical symptoms and appears normal, the damage is postganglionic. If the eye does not respond to the eye drops, additional diagnostic testing will be required. Chest x-rays, blood work, radiographs, pharmacological testing on the eye and an MRI are some of the testing that may be required to determine the location of the damage and set a treatment plan.

Horner’s syndrome, in most cases, will resolve itself. However, treatment of the underlying disease is essential. In cases of unidentifiable causes of Horner’s syndrome, natural recovery will usually recur within 16 weeks to 6 months.

In the case where there is a serious underlying condition, your veterinarian and your veterinarian specialist will set a treatment plan in place to alleviate symptoms and treat the underlying condition.

Depending on the location of the damage and the underlying condition, if any, recovery time will vary. If the damage has no known cause, it is best to allow the disease resolve itself. This can take anywhere from 16 weeks to 6 months depending upon the severity of the symptoms.

Your veterinarian will give you a better understanding of recovery time once an underlying condition has been found and a treatment plan has been put in place.