Horner's Syndrome

What is Horner’s syndrome?

Horner’s syndrome is a common neurological disorder of the eye and facial muscles. The condition is usually sudden in onset. The most common signs noted by the owner are:

• drooping of the eyelids on the affected side.
• the pupil of the affected eye will be constricted.
• the eye is often sunken.
• the third eyelid of the affected eye will be elevated - i.e. prolapsed across the eyeball itself and might appear more red in colour than the non-affected side.

What causes Horner’s syndrome?

Horner’s syndrome is due to a dysfunction of the sympathetic nerve supply to the eye and surrounding muscles. This is part of the autonomic nervous system which helps to control normal functions such as blinking, muscle tone and pupil size for example.

The sympathetic nerve supply to the eye has a long, complicated pathway, originating in the brain, then passing down the spinal cord before looping back up the neck, past the middle ear and into the eye. Disruption to the supply along any part of this long route can lead to Horner’s syndrome. Thus the underlying cause might be far away from the eye – a wound in the neck or chest following a dog fight, a slipped disc in the neck, or middle ear disease for example. A quite common form is termed ‘idiopathic’ which means that it develops spontaneously and the underlying cause is unknown.

Does it affect any particular breed or age of dog?

Apart from the cases of Horner’s syndrome following known injury such as a bite or blow, idiopathic Horner’s syndrome is the most common type and appears to affect the middle aged Golden Retriever more than any other breed of dog.

What is the treatment?

If an underlying cause is identified then this should be treated and should allow the Horner’s syndrome to gradually resolve. However if the dog is suffering from the idiopathic cause then no specific treatment is usually required – the condition is not painful despite the odd appearance to the eye. Occasionally eye drops can be used to temporarily remove the symptoms - for example if both eyes are affected and the protrusion of the third eyelid is resulting in reduced vision.

"However if the dog is suffering from the idiopathic cause then no specific treatment is usually required – the condition is not painful despite the odd appearance to the eye."

What is the recovery rate?

If the lesion is not due to any discernable pathological cause, slow recovery can be expected – in 8-12 weeks. If there has not been any improvement over this time then specialist examination might be advised in an attempt to identify any underlying abnormalities. For example a neurologist might suggest magnetic resonance imaging (MRI) to look at the brain and spinal cord in great detail.

What is the outlook?

Very good in the majority of idiopathic cases - it takes several weeks but the condition gradually improves - with dog appearing more normal in the morning but with the symptoms returning during the day as the dog becomes tired. Eventually clinical signs fully resolve.  If an underlying disease - a bite or middle ear disease for example is present, then the prognosis is also good. However, in some cases in which the Horner’s syndrome is due to brain disease, and the outlook can be poor.