Horner’s Syndrome

Horner’s Syndrome is a disorder of the nervous system which produces symptoms in the eyes. This disorder usually occurs after an injury to the sympathetic nerve leading to the eye. Such injury can be due to a trauma to the nerve, viral infection, a tumor or mass which puts pressure on the nerve, or an inflammation of the nerve. Since the nerve travels from the brain down the neck through the chest and then to the eye, trauma in the brain, chest or neck can lead to Horner’s Syndrome.

Due to this specific damage the eyes begin receiving abnormal nerve signals. Due to these abnormal signals one usually sees one or more of the following symptoms: excessive smallness or contraction of the pupil of the eye (miosis), two different sized pupils (the affected pupil will usually be smaller than normal), visibility of third eyelid, drooping eyelids (ptosis), or sinking of the eyeball into the orbital cavity (enophthalmos). These symptoms are usually seen in one side only, however both sides can be affected.

Horner’s syndrome in and of itself is not life threatening and usually will clear up on its own.

Symptoms to look for:

  • Contraction of the pupil
  • Two different sized pupils
  • Visibility of third eyelid
  • Drooping eyelids
  • Sinking of eyelid into orbital cavity


Treatment for Horner’s Syndrome usually relies on treating the underlying cause of the nervous system trauma. Depending on the cause of the trauma this may include things like reducing swelling of the nerves, removing the mass affecting the nerves, treating a viral infection that is affecting the nerves etc. If you suspect your cat has Horner’s Syndrome or any other eye problem see your vet for a proper examination and diagnosis.