In the 1800’s a Swiss eye doctor (Dr. Horner) noticed that some of his patients had a specific combination of signs. Similar signs were recognized in animals. The signs that veterinarians now group together and call Horner’s syndrome are:

Prominent third eye lid

All of these changes in the eye are controlled by the nerves of the sympathetic nervous system. The nerves travel from the brain, through the spinal cord, into the chest, up the neck, through the middle ear and finally to the eye. When there is damage anywhere along this path, a patient will show this unique group of signs. The lesion will be found on the same side of the body as the eye showing the signs and is not usually associated with vision deficits.

Some of these signs can be seen with eye diseases and an examination is appropriate to rule out primary eye disease.  Lesions that result in this syndrome are most often found outside the spinal cord. They can be associated with:

Sometimes no cause is found (this is most common in dogs).

There is no treatment needed for Horner’s. Its importance is to direct the veterinarian toward the location of a problem so that a treatment plan is developed for the condition that has caused the nerve damage. The diagnostic tests that may help find the cause include a physical examination, blood tests, and chest radiographs. The prognosis for trauma patients is good, but it may take several months for the signs to disappear.