You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Horner's Syndrome is a neurological problem which affects one eye, and which can be caused by a variety of different disorders

Although Horner's Syndrome affects the eye the actual cause of the problem is in the neck, in the spinal cord or in the chest. In Horner's Syndrome only one eye is affected and the following signs are noticed :

• The affected eye sinks back into it's socket (called enophthalmos) and looks smaller
• The pupil of the affected eye constricts forming a pinpoint pupil (called miosis). The pupil size in the opposite eye is normal.
• In cats, dogs and other species with 3 eyelids, the third eyelid (or nictitating membrane) moves across to partly cover the surface of the eye
• The upper eyelid droops down over the eye (called ptosis or blepharoptosis)
• Congestion of the conjunctiva occurs causing "red eye" which looks like conjunctivitis.

Horner's syndrome is actually caused by loss of sympathetic nerve supply to the structures of the eye, and may be due to a variety of disorders including :

• First order lesions - damage in the brain or spinal cord :
  • Diseases of the spinal cord in the:
    • cervical (neck) region (cranial cervical ganglion), or 
    • cranial thoracic (chest) region - especially T1-T3, or mediastinal region
  • Diseases affecting the optic nerve
• Second order lesions:
  • Tumours
  • Non-cancerous masses (such as enlarged lymph nodes) causing pressure on the nerves
  • Infection
  • Trauma. In dogs a common cause is excessive use of a choke chain. 
• Third order lesions
  • Infection of the middle ear (otitis media) or external ear (otitis externa)

In many cases no underlying cause can be found

Treatment

There is no specific treatment for Horner's syndrome so therapy is aimed at possible underlying causes. Many cases get better without treatment, but the prognosis depends upon the underlying cause.

Updated October 2013