Horner's disease, more commonly known as Horner's syndrome, is an unusual reaction that your dog's eyes have to nerve dysfunction. It's a rather complex condition with mostly aesthetic implications. Your dog's eyes may look bizarre, but the "deformity" is usually harmless and resolves itself after a few weeks.
You may be shocked to see a strange film, your dog's the "third eyelid," covering half of his eyes. His primary eyelid may also droop down and the eyeball itself looks like it has sunk into his head. These odd symptoms aren't hazardous or uncomfortable, but they can be unsettling for the dog's owner. Horner's can also cause a slight reddening of your dog's ears and nose and may increase skin temperature in these areas. The pupil of the affected eye will also be chronically constricted, so it looks smaller than normal.
Nerve damage in your dog's head, face or neck can lead to the development of Horner's syndrome. Neck injuries from physical abuse or bite wounds are common sources of the nerve damage that produces Horner's. Ear infections, spinal injury and tumors in the neck or chest are also associated with the syndrome, according to VCA Animal Hospitals. Many cases are considered idiopathic, which means there is no identifiable evidence to help the vet figure out what's causing the condition. Idiopathic symptoms emerge suddenly with no recognizable cause.
An astounding 90 percent of canine Horner's syndrome patients are mature golden retrievers, while cocker spaniels come in a distant second in reported cases among purebreds, according to Zigler Veterinary Professional Corp. Physically active pups, particularly those that fight with other dogs, are more likely to get Horner's due to the increased risk of physical injury. Tight collars, especially "choke" types, are another potential source of nerve damage around the neck. Be careful when tugging your dog's leash when you're out for a walk, and avoid dragging him by the neck.
Since Horner's syndrome itself does not impact your pup's vision or cause any pain, there is no reason to treat it aside from improving your dog's appearance, according to Mar Vista Animal Medical Center. It tends to resolve itself after a few weeks unless there's an ongoing underlying cause. Diagnosing Horner's is significant, though, because it means your dog is suffering from nerve damage. If there are no physical injuries present, there's a chance an infection or cancerous growth is interfering with signals sent from his brain to his eyes. The nerves connected to the eyes pass through the neck and chest before reaching the brain, so the damage could occur anywhere along this path.
- Comstock/Comstock/Getty Images