what your cat's eyes can tell you about her health

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what a cat's pupils can tell about their health
Posted by Dr. Kim Smyth on Sep 30 2014

Updated February 21, 2019

They say that the eyes are the window to the soul, but can they also be a harbinger of disease? Absolutely they can! Today we’ll all see cats’ eyes in a new, wonderful way!

Cat eye colors

Let’s start with color. Cat eyes vary in color from light to dark brown and several shades of blue and green. Some eye color is linked to breed—blues eyes, for example, are common in Siamese cats. Some eye color is highly prized by breeders and those who participate in cat shows—copper color is one of those.

But, copper colored eyes can also mean something more sinister—a portosystemic shunt. It’s important to note that not all cats with cooper colored eyes have a liver shunt (in fact, many breeds of cats have copper colored eyes as a normal trait), but many cats with shunts DO have copper colored eyes.

Typically, a cat will have eyes of the same color. Both green or both brown, or what have you. Occasionally, cats will have heterochromia, or eyes of different colors. This can mean that one eye is blue and one eye is green, or even within one eye, the iris is colored differently. Heterochromia is generally nothing to worry about, especially if a cat is born that way. But if one eye begins to change color over time, there could be trouble brewing, like chronic inflammation or worse.

Cat pupil differences

Next, let’s focus on the pupil. The pupil is responsible for the amount of light that enters the eye. I’m sure you’ve noticed that most of the time, your cat’s pupil is vertical, while yours (and your dog’s) is round. Because cats are meant to be nocturnal hunters, this vertical pupil helps fine tune light, allowing them to catch prey at even the darkest of night. Interestingly, not all cats have vertical pupils. Lions and tigers, for instance, have round pupils like your dog.

So, most of the time, your cat’s pupils are slits, meaning that he or she is content and relaxed. Get your cat riled up, though, and those pupils turn round and large. Eyes like saucers mean you should be on guard, because she’s about to pounce right on that blanket monster! Pupil size is dictated by both light AND emotion.

If you notice an irregularity in your cat’s pupils, you should have her examined by a veterinarian. Whether the two eyes have unequal pupil size (called anisocoria), or one pupil is irregular in shape (D-shaped), there could be an underlying condition that needs addressed, like infectious disease, trauma or cancer.

Why are my cat's eyes always dilated? 

One final word on pupil size—if your cat’s pupils are consistently dilated (large), even in bright light, something is amiss. Check with your veterinarian if this is the case.

While we will never know what cats are thinking when they sit across the room and glare at us, at least now when we glare back, we can pick up a thing or two just by looking them in the eye.