Horner's Syndrome & Dilated Pupils in Cats

If kitty's pupils have grown or shrunk, she should have a vet check.

If kitty's pupils have grown or shrunk, she should have a vet check.

If Kitty's eyes have a funny look about them, pay attention to her pupils to learn more about her condition. If a pupil is enlarged (dilated), it may be a simple inflammation or something more serious. If it's constricted, it may be Horner's syndrome.

What is Horner's Syndrome?

Horner's syndrome is a common neurological disorder in a cat's eye and facial muscles. It usually occurs without warning and is typically caused by a dysfunction of Kitty's sympathetic nervous system. The sympathetic nervous system is part of the nervous system that you have no control over. For example, if you become frightened, your heart rate will increase and blood will move to your muscles to help you flee. If Kitty suffers some kind of trauma that impacts the sympathetic nerve in her eye, it can cause Horner's syndrome. Middle ear infections, injury to her neck (from fighting or being hit by a car) or tumors can all trigger Horner's syndrome.

Symptoms of Horner's Syndrome

Since Horner's syndrome is usually caused by an injury in the sympathetic nerve impacting Kitty's eye, the most obvious sign of it will be a change in her eye. Because the nerve is injured, the muscles around it relax, causing the eye to "sink." Her eyelid will droop and the pupil will look smaller than usual. Sometimes the third eyelid of her eye will look red or raised. The symptoms will occur on the same side of her face as the injury. If Kitty's showing these symptoms, it will be fairly easy for her vet to determine that Horner's syndrome is at work. Determining the cause of the nerve injury can be more challenging. The vet will likely need to perform a complete physical on your kitty, potentially including X-rays, blood work and a neurological exam. Although it's rare, occasionally cats have idiopathic Horner's syndrome, meaning there is no apparent cause.

Treatment and Recovery

Treating Horner's syndrome depends on the cause. For example, if Kitty has a middle ear infection or a bite wound, she'll need antibiotics to help her heal. If the cause is idiopathic, the syndrome will usually clear up on its own in about two months. The vet may prescribe eye medication to help make Kitty more comfortable -- after all, she may be unable to blink normally. Your vet may also prescribe drops to dilate her pupil to normal levels.

Dilated Pupils

Cats with Horner's syndrome have smaller pupils, not larger pupils. Enlarged pupils in cats, known as anisocoria, can have many different causes, including injury to the cornea, glaucoma, retinal disease and spastic pupil syndrome. If Kitty's pupil suddenly becomes enlarged, contact her vet immediately to decrease the chance that her vision will be permanently affected.

 

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