Pet Factsheets

Horner’s syndrome

Horner's syndrome is rare in rabbits. The condition is typically demonstrated by constriction of the pupil (miosis) and drooping of the upper eyelid (ptosis).

Why has my rabbit got Horner’s syndrome?

The condition is caused by an interruption in the nerve supply to the eye. In a part of the rabbit’s brain, called the hindbrain, a three-neuron pathway originates. This passes down the spinal cord, exiting in the thoracic spine, then via the top of the rib cage and the end of the cervical spine and eventually back through the middle ear before entering the eye.

If the nerve is damaged at any point along its pathway the rabbit will show clinical signs of Horner’s syndrome. Middle ear disease is the most common cause.

What signs will my rabbit show?

Commonly rabbits will exhibit the following signs:

  • Miosis (drooping of the upper eyelid).
  • Constriction of the pupil (so the affected pupil will be smaller than the unaffected pupil).
  • Conjunctival hyperaemia (reddening of the white of the eye).

Other signs may include: 

  • Enlarged third eyelid covering part of the eye.
  • Soreness around the eye if the rabbit has been rubbing it.

The rabbit may also show signs of gastrointestinal stasis if the underlying cause of Horner’s syndrome (often middle ear disease) is causing pain.

How will my vet diagnose it?

Ideally your rabbit will need to have an MRI scan to determine where the damage to the affected nerve is and if treatment is possible. If the underlying cause is middle ear disease then treatment will also be required for this, as well as any necessary supportive treatment such as pain relief and supportive feeding.

Can it be treated?

There is no specific treatment for Horner's syndrome. The treatment is aimed at management/treatment of the underlying cause/s of the disease and supportive care. Therefore, advanced imaging is imperative to ascertain if middle ear disease or another disease process (tumour, etc) is the underlying cause, and the most appropriate treatment, ie surgery on the middle ear, drainage options or medical management.

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