Dog - 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 owners are:

• drooping of the eyelids on the affected side
• the eye is often sunken
• the third eyelid in the inner corner of the affected eye will be more visible, i.e. prolapsed across the eyeball itself and may appear more inflamed than the non-affected side
• the pupil of the affected eye will be constricted

What causes Horner’s syndrome?

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

The sympathetic nerve supply to the eye has a long, complicated pathway. It originates in the brain, passes 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?

Any breed can be affected particularly in cases of Horner’s syndrome following known injury, e.g. a bite or blow. Idiopathic Horner’s syndrome affects 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 the Horner’s syndrome should gradually resolve. If the dog is suffering from the idiopathic cause then no specific treatment is indicated and it will usually resolve over time. Despite the odd appearance to the eye, the condition is not painful. Eye drops can be used to temporarily remove the symptoms in some cases. For example if both eyes are affected and the protrusion of the third eyelid is resulting in reduced vision.

What is the recovery rate?

If an underlying cause is identified and treated, Horner’s syndrome normally improves in 2–4 weeks. 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 the symptoms usually resolve fully. If an underlying disease - a bite or middle ear disease for example is present, then the prognosis is also good following treatment. However, in some cases Horner’s syndrome can be due to brain disease and then the outlook can be poor.