Animals / Dogs / Health & Nutrition

Horner’s Syndrome in Dogs

Horner’s syndrome is a nerve disorder that is characterized by a drooping eye, an eyelid that is protruding from the eye, or a severely constricted eye pupil. Any brain or spinal injury may cause this syndrome, and it has also been linked to conditions affecting the middle ear, but in many cases the origin remains unknown. The cause of Horner’s syndrome remains elusive in most cases, and it may affect any breed of dog, though it appears to be more common in male golden retrievers.

Symptoms and Types

  • Smaller size eye pupil (miosis)
  • Abnormal elevation of inner eyelid - located between cornea and inner corner of eyelids (third eyelid)
  • Drooping of upper eyelid
  • Eyes appear sunken into eye socket
  • Inflammation of ear


  • Unknown (idiopathic) in most cases
  • Brain injury, brain stem lesions
  • Brain tumor
  • Spinal cord lesions
  • Infections


You will need to give a detailed history of your dog's health, onset and nature of symptoms, and possible incidents that might have brought this condition on, such as brain trauma, injury to the head or back, ear infections, and any other previous health problems. The veterinarian will perform a thorough physical exam on your dog, with a standard blood blood count, blood profile, and urinalysis. The routine laboratory tests are not required for diagnosis of this syndrome, but may be useful for determining other diseases or infections that may be present.

Radiography remains the important technique for evaluating brain and spinal cord lesions, and skull X-rays are helpful for evaluation of ear problems. More advanced techniques like computed tomography (CT-scan), magnetic resonance imaging (MRI), and ultrasonography are also frequently used to diagnose this syndrome. In some cases, a cerebrospinal fluid (CSF) sample is taken to analyze for brain and spinal cord disease.

Horner’s syndrome itself doesn’t require any specific treatment, though your dog will need to be treated for the underlying causes leading to the symptoms of Horner’s syndrome. The medication and treatment protocol will depend on the underlying cause. If bite wound or ear infection is present, treatment is required for complete recovery, and eye medication can be prescribed to relieve the clinical signs.

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