What Are the Causes of a Feline's Dilated Pupils?

You know that a slow blink from your cat means, "I love you. I'm content. I'm feeling pretty good right now." But that's body language, and parts of his eyes can be affected by physical factors, too, like the widening or narrowing of his pupils.

Closeup of cute calico cats face with dilated pupils
What Are the Causes of a Feline's Dilated Pupils?
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His pupils are those dark spots at the center of his eyes, technically in the middle of his irises. The brightness of his surroundings is the most common cause for a change, and it's nothing to worry about. His pupils will shrink when there's a lot of light, and they should dilate or widen when light is at a premium. It's a perfectly normal biological response, though other things can cause changes to your feline's pupils as well.

Why are my cat’s pupils always dilated?

The key word here is "always." Occasional dilation can be prompted by a number of emotional or environmental factors, or even by age. You'll want to rule these out before becoming alarmed.

If you turn the lights up, her pupils should constrict. Keep in mind that cats can see in a light one-fifth of the level that humans need for clear perception. She doesn't need a lot of light to see well.

Look for another innocuous cause if they don't narrow. It could be that she's just feeling mellow. Wide pupils are often relaxed pupils, but unfortunately, the exact opposite can be true as well.

Dilation as a result of mood

It can be a bit like putting together a puzzle, so take stock of her surroundings and what's going on at the time. You know your cat better than anyone, so size up her body language to try to get to the cause.

Is she aroused for some reason, throwing off signs of excitement or anger? If so, her pupils might dilate. Think of it this way: If something startles or scares you, don't your own eyes pop open wide?

Try tossing a new toy or object on the floor. Technically, this could be a cat monster, something not to be trusted until it's been completely and warily investigated and, if necessary, rendered dead. Her pupils might dilate at the new, interesting, possibly dangerous intrusion, then narrow again after she's sized up the situation.

Your cat's general disposition

If your cat is hyper by nature, her pupils are probably dilated more often than not. Younger cats are more prone to dilated pupils caused by excitement than older, more relaxed cats.

The key here is timing. What you're looking for more than anything are changes to her pupils. If a cat's eyes are dilated all the time, the situation might require a visit to the vet.

What physiological factors cause a cat’s eyes to dilate? Hypertension

Hypertension, commonly referred to as high blood pressure, is a very common physiological culprit of dilated pupils. High blood pressure can be either a primary or secondary condition.

Secondary means that it's caused by another ailment or illness. Hypertension can be the result of hyperthyroidism or kidney disease. Your veterinarian might shine a light into your cat's eyes to see how his pupils react as a preliminary step toward arriving at a diagnosis. He's also looking for traces of blood in the cat's eyes, which is another sign of hypertension.

Your cat will probably exhibit other symptoms as well if he's suffering from high blood pressure. He might not be grooming himself as fastidiously, or maybe he's gained or lost a few pounds. A decreased interest in food or water can be another sign.

Why do my cat’s pupils stay big? Anisocoria

Compare your cat's left eye to her right. Are both pupils the same? A disorder known as anisocoria can cause a difference.

This is technically not a condition but rather a symptom. It can be caused by retinal disease, feline leukemia, cancer, or an injury or eye ulcer. The injury doesn't have to be recent. Scar tissue can cause anisocoria, too.

You might also notice odd color changes to the other parts of his eyes. Depending on the cause, he might rub at his eyes a lot or seem lethargic. Again, a visit to the vet is in order, sooner rather than later.

Cat's dilated pupils causes: Dysautonomia

Cats with round pupils might also suffer from dysautonomia, sometimes called Key-Gaskell Syndrome. This involves your cat's automatic nervous system, or ANS, which is responsible for prompting all those physiological things your cat doesn't willfully control: hunger or lack of it, heart rate, blood pressure, respiration, and pupil dilation.

You might notice other symptoms of dysautonomia, too, if this is the cause of her dilated pupils. The most obvious are difficulties with urinating or defecating, or diarrhea. Her reflexes might seem off, and her nose might feel unnaturally dry to the touch. Vomiting is a symptom, as are weight loss, coughing, and lethargy.

For cats with round pupils, you'll want to visit the veterinarian as soon as possible.

What will the vet do?

Blood and urine samples can tell your veterinarian a lot, no matter the physiological cause of your cat's wide pupils.

If it's secondary hypertension, your vet will treat the underlying condition, no doubt extending your feline's life, and all because you noticed something strange was going on with her eyes. Primary hypertension can be treated and controlled with daily medication.

Anisocoria demands immediate medical care because the underlying condition can be very serious. Again, your vet will have to investigate, do some tests, narrow down the cause, and treat the cause, not the symptom. Not acting quickly enough can mean your cat loses his vision or worse. It's generally not reversible if your cat has lost his vision, but many blind cats continue to get around just fine.

Your vet can ease your mind

Even if your feline isn't exhibiting any other symptoms, but he just walks around with dilated eyes all the time, you'll want to have the situation checked out. In virtually all cases, constant dilation indicates an underlying medical condition. Occasional dilation is normally just the result of a cat's interesting life.

Of course, it's possible that your feline's often-dilated pupils are prompted by his personality, but you won't know this until your veterinarian tells you for sure.