Horner’s syndrome in dogs

Horner’s syndrome, sometimes called Horner’s disease, is an unusual and very unique health condition that can affect your dog’s eyes, and which occurs as the result of nerve problems or damage to the nerves in certain areas of the body.

Horner’s syndrome can affect dogs of any breed or type, although for reasons that are unclear, the vast majority of diagnoses of Horner’s syndrome occur in the Golden retriever dog breed, and so owners of dogs of this breed in particular should familiarise themselves with the symptoms, risk factors, and how the condition presents.

In this article, we will look at Horner’s syndrome in dogs in more detail, including how it develops, what it looks like, and what can be done about it. Read on to learn more.

What is Horner’s syndrome?

Horner’s syndrome is a condition that occurs in the eyes, but that comes about due to nerve problems in the head, neck or even spinal cord in some cases. The nerves affected are known as sympathetic nerves, which serve certain muscles of the face, and when these sympathetic nerves are damaged or dysfunctional, the appearance of the eyes and eyelids changes from the norm, because the muscles and nerves surrounding and supporting the eyes are unable to work properly.

Injuries, impacts and accidents that damage the sympathetic nerves in the brain, face and upper part of the spinal cord where it joins the head can cause Horner’s syndrome, as can certain nerve conditions that cause degeneration, weakness, or growths or lesions on the nerves themselves.

The physical indications of Horner’s syndrome present in and around the eyes, which can of course lead dog owners to believe that the eyes themselves have been injured or are developing a problem, and the condition can potentially be confused with a wide range of different eye diseases and conditions during the early stages of assessment and diagnosis.

How is the condition caused?

There are a wide range of different factors that can contribute to the development of Horner’s syndrome in dogs, or cause damage to the sympathetic nerves that lead to the syndrome developing. However, in anything up to 50% of cases, the root cause or how the nerves came to be damaged or compromised may remain a mystery, and cannot always be attributed to a specific problem or starting point.

In cases of Horner’s syndrome with a known cause, the most common reasons for the onset of the condition include:

• Injuries and accidents such as the dog running into a wall or hard surface, or being hit by a car.
• Being bitten on the head, face, neck or scruff by another dog.
• Ear infections, or even improperly performed ear cleaning, which can damage the structure of the inner ear and its nerve pathways.
• Tumours, diseases and other conditions that affect the eyes or the area of the skull behind the eyes.
• Intervertebral disc disease, or other health conditions that lead to spinal degeneration or damage to the nerves of the spine.
• High-impact exercise that leads to jarring of the spine, spinal misalignments or other forms of damage that compromise the nerve pathways.

What type of dogs are at risk of the condition?

Any dog of any breed, sex or age can develop Horner’s syndrome, although the Golden retriever breed tends to be the most prone to the condition, for reasons that are unclear.

What are the symptoms of Horner’s syndrome in dogs?

Horner’s syndrome presents with several very obvious physical signs in and around the eyes, which will may affect either one eye and side of the face or both, depending on the nerves involved and what areas of the face and eyes they serve. The symptoms are also usually fairly fast in onset, with a dog often appearing fine but developing symptoms overnight or within a few hours, although this is not always the case.

The main symptoms of Horner’s syndrome to look out for are:

• Heat or warmth in one side of the face but not the other, due to blood vessel dilation in the affected area.
• Redness of the mucous membranes of the eyes.
• Sunken, deeply set eyes which will usually be very noticeable.
• The third eyelid being visible across the affected eye or eyes, and not retracting into its normal position.
• Small or pinprick pupils in either one or both eyes.
• Drooping eyelids that make the dog look very tired or unwell, affecting either one or both eyes.

Not all dogs with Horner’s syndrome will display all of these symptoms, and how acute or mild they are can also vary significantly from case to case too. Horner’s syndrome is not painful for your dog-the effects on your dog themselves are generally limited to the change in the appearance of their face and eyes, as well as of course potentially compromised vision.

Can the condition be treated?

While it can naturally be very shocking to suddenly see your dog displaying such obvious and acute symptoms as those that Horner’s syndrome usually produces, particularly if your dog looked perfectly fine shortly beforehand, the condition is not as critical as it may first appear.

It is of course important to take your dog to the vet as soon as possible to confirm or rule out Horner’s syndrome and establish if anything should be done-such as treating the injury or condition that caused the nerve damage that triggered the condition-but Horner’s syndrome actually usually resolves itself within six weeks to two months, assuming that the cause of the damage or nerve problems are treated or resolve themselves.