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Horner’s syndrome is a disease in cats that shows noticeable changes in the eyes. It is easy to spot because of the symptoms it has. Finding the cause is often difficult, however, as it is not an eye disease in the strict sense, but rather nerve damage. In this article, we explain what this is all about and how diagnosis and therapy work for the affected cat.

What is Horner Syndrome?

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What at first glance looks like inflammation or a disease of the eye is actually nerve damage to the sympathetic nervous system. Like humans, cats have two nervous systems: the parasympathetic nervous system and the sympathetic. The sympathetic nervous system is responsible for involuntary, uncontrollable tasks. This also includes the supply of the eye muscles. In Horner’s syndrome, the sympathetic nervous system is damaged, so that the muscle function in the area of the cat’s eye is restricted or fails completely.

What are the symptoms of Horner syndrome?

In Horner’s syndrome, the sympathetic nerve usually fails on one side, so that only one eye is affected by the symptoms. The cat shows a number of symptoms in the affected eye, the severity of which depends on the cause of the disease. The following combination of symptoms is typical of Horner’s syndrome in cats.

  • The cat’s pupils are narrowed (miosis);
  • The upper eyelid of the affected animal is drooping (ptosis);
  • The eyeball looks sunken (pseudoenophthalmus);
  • The nictitating membrane at the inner corner of the eye is visible (nictitating membrane prolapse).

What are the causes of Horner syndrome?

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The cause of the damage to the sympathetic system is not always clear. The nerve runs from the brain, through the spinal cord, into the chest, and then back into the head. If Horner’s syndrome occurs in cats, the nerve is damaged in one of these regions. The most common causes include injury to the spine from an accident or impact, a tumor, or a broken bone. Slipped discs or bruises can also be the cause. In cats, chronic otitis media is also a possible cause of sympathetic failure.

How is the diagnosis made by the veterinarian?

If your cat experiences the above symptoms, you should introduce the animal to the veterinarian. This will try to find out exactly where the nerve is damaged. With a pharmacological test using eye drops, the vet can locate the affected area. The cat’s ears will also be examined to see if otitis media is the cause. In addition, x-rays and computed tomography (CT) or magnetic resonance tomography (MRT) can be used in the diagnosis. However, it is also possible that the veterinarian cannot find the cause of Horner’s syndrome in the cat.

How is Horner Syndrome treated?

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The therapy of the disease depends on the cause. For example, if the nerve is crushed by an injury or a tumor, it may be able to be surgically removed. If the sympathetic system is still functioning to a limited extent, medication can help to strengthen the function of the damaged nerve. In some cases, there is also spontaneous healing, so that the function of the nerve is restored on its own.