Horner's Syndrome is a neurological (nerve) condition in cats that affects their eyes. The condition, which usually affects just one eye, can appear very quickly. Although there is often an underlying cause, sometimes it can be difficult to find.
Symptoms of Horner's Syndrome
In Horner's Syndrome, the cat will develop the following symptoms:
- The upper eyelid will start drooping (proptosis)
- The pupil of the affected eye appear smaller than the normal eye (miosis)
- The third eyelid comes out over the eye and appears redder than normal
- The eyeball itself seems to have sunk back into the head (enophthalmos)
The condition is caused by a malfunctioning of the 'Autonomic Nervous System' (ANS), which controls all the automatic functions in the body. There are two halves to the ANS, the Sympathetic and Parasympathetic systems. The Sympathetic Nervous System (SNS) controls the body's 'fight or flight' instincts, doing things like increasing the heart rate, widening the pupils, and increasing muscle tone. The Parasympathetic Nervous System (PSNS) is the 'rest and digest' system that deals with all the routine things like digestion and salivation. The two work alongside each other and keep the body in balance.
Normally, the nerve supply to the eye is a combination of the SNS and the PSNS, but if the SNS is damaged, the symptoms of Horner's Syndrome appear. They reflect the PSNS taking over and putting the eye in a 'relaxed' state with the lids drooping and the pupil closing up.
The nerves that carry the SNS take quite a circuitous route to reach the eye, traveling up the neck outside of the spinal cord via the ear and the back of the eye, which leaves them vulnerable.
What Causes Horner's Syndrome?
The common causes of damage to the Sympathetic nerve supply to an eye include:
- The cat suffering a blow to the neck, due to a car accident, for example
- Developing an abscess in the neck region, often after a cat fight
- A problem or infection in the middle ear
- Inflammation behind the eye
- Inflammation of the nerve itself
- A tumor developing in the chest, neck area, or brain that is interfering with the nerve
Diagnosing Horner's Syndrome and How to Treat It
A diagnosis of Horner's Syndrome is made based on the cat having the correct combination of symptoms and if there is evidence of damage or infection in the right areas of the head and neck. To confirm that they are correct, your vet may put special eye drops in the eye that mimic the effects of the SNS. If the problem is Horner's Syndrome, the symptoms will quickly resolve but recur once the drops have worn off. The speed at which the eye corrects is also helpful in identifying where the damage may have occurred.
In order to find the underlying reason for Horner's Syndrome, your vet will likely advise blood tests and imaging such as X-rays, ultrasound, or perhaps a CT or MRI. In some cases, although it is unusual, no issue is found and the condition is termed 'idiopathic.'
The treatment for Horner's Syndrome will involve dealing with the underlying cause and then allowing the SNS nerves to repair on their own time. While this happens, your cat may be prescribed eye drops to keep the eye moist and comfortable.
The majority of cases of Horner's Syndrome will eventually normalize, either because the underlying cause has healed or because the nerves have repaired. However, the period in which this happens can be variable, ranging from just a couple of weeks to a couple of months.
If you suspect that your cat may be suffering from Horner's Syndrome, we recommend that you contact your local veterinarian immediately.