What is Horner’s syndrome? | Pet Peeves

Horner’s syndrome is an unusual and uncommon disease that affects some dogs. The condition is named after Johann Friedrich Horner, a Swiss Ophthalmologist who first described the syndrome in people in 1969.

When a dog has Horner’s syndrome, it will have a funny appearance to its eye. Only one eye will be affected, and the pet owner will first notice that the lids are droopy. Upon closer examination, the pet owner may notice that the pupil of that eye is smaller than the other eye. Often the third eyelid, which is the pink, fleshy area at the corner of the eye, is raised, drifting upward into the pet’s field of vision. Less noticeable to the owner is the fact that the eye is sunken back into the eye socket, making the eye look smaller.

All of this occurs because something has affected the sympathetic innervation of the eye. The sympathetic nerves that innervate the eye begin in the brain and go down the spinal cord to the chest, where they exit the vertebrae and travel back up the neck, passing the ear to arrive at the eye. When the sympathetic innervation of the eye is affected, the cause can be anywhere on the neck, upper chest, ear or close to the eye itself.

Somewhere along that path, something has interrupted the nervous function. The nerve may be damaged by inflammation, infection or, more seriously, a mass such as a tumor. Intervertebral disc disease, often seen in older dogs, also can cause damage to the sympathetic nervous system. Because the nerves run close to the ear, a severe ear infection can trigger the Horner's presentation.

Often the cause of Horner’s syndrome is never discovered. In these cases, it is called “idiopathic,” or cause unknown. It is usually seen in older dogs, and I’ve noticed a higher incidence in cocker spaniels and retrievers. It may be because these breeds are more likely to have ear problems.

An otoscopic exam in the room will determine if the ear is involved. If an underlying cause is suspected, it is recommended that radiographs of the chest and neck area are done. Blood work is indicated to help rule out any underlying illnesses.

Most cases of Horner’s syndrome resolve on their own in six to eight weeks. If an underlying problem such as an ear infection is noted, it should be treated. Sometimes the symptoms do not completely go away, leaving the pet with a permanently droopy eye, but it does not affect the pet’s vision, and it is not painful.

This article originally appeared on Northwest Florida Daily News: What is Horner’s syndrome? | Pet Peeves