Horner syndrome is a disorder associated with nerve damage leading to a peculiar change in the appearance on one side of the face. Clinical features include narrowing of the pupil, mild drooping of the upper lid, and slightly recessed eyeball. A number of diseases and disorders may cause this condition. The nerve involved in Horner syndrome travels a long pathway, arising from the spinal cord at the level of the first or second rib, traveling up the neck to the head, and passing close to the middle ear, before ending at the eye muscle. An ear infection, a neck wound, or a tumor, can damage it and cause Horner syndrome. In the neck area, the nerve can be damaged by an injury caused by a severe choke-chain or some surgical interference. Thrombosis of the carotid artery is often recognised first as a drooping eye as one sign of Horner syndrome due to pressure on the nerve. Horner syndrome is not painful. There is no treatment for the changes in the eye, but if the nerve inflammation or damage is mild, it can heal on its own, and the dog's appearance will return to normal. The majority of dogs seem to resolve the condition in three months or so, but steps should be taken to moisten or lubricate and exposed eye surfaces.
- Betsy Brevitz. Hound Health Handbook: The Definitive Guide to Keeping Your Dog Happy, Healthy & Active
- Dick Lane, Neil Ewart. A-Z of Dog Diseases & Health Problems: Signs, Diagnosis, Causes, Treatment