Horner Syndrome

Horner syndrome (HS) is a condition caused by a decreased sympathetic supply to the eye and resulting in miosis, often also ptosis, enophthalmos, and protrusion of the nictitating membrane in dogs. Due to its very long pathway, many disease processes may affect the sympathetic supply to the eye. Among the most common causes of HS are the idiopathic form, middle ear diseases, trauma to the neck, pathology affecting the brachial plexus and cranial mediastinal masses. HS is usually classified based on the level of the lesion along the sympathetic pathway (first, second and third order HS).