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Ask a Vet: Pupils can alert owners to problems
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You’ve seen it on television or in movies. The injured individual, possibly deceased, and someone with a light shines it in their eyes to check the pupils. But what does it really mean?

Your pupil and your pet’s is the hole created by your iris. The iris expands or contracts to regulate the size of the hole, controlling how much light gets into the eye.

In a regular pupil, shining light into the eye causes the iris to constrict and the pupil shrinks. But did you know this has little to do with real vision? The reflex involved in this doesn’t involve the brain. A loop of nerve cells detects the light intensity and shrinks or dilates the pupil. So knowing if the pupil reacts tells you about the eye, but not the brain or the vision.

In pets, a more sensitive test for true vision is called the “menace response.” I could go into detail, but no explanation will do it justice in a column.

The test detects if the eye can take in light, form an image, transmit the image to the brain, assess the image and send signals to several other nerves and portions of the body to react. The test looks like you’re trying to poke the dog or cat in the eye, but stopping just short.

Literally, it is one of the most complex common tests done on the nervous system. But it looks like a bully leaning on a dog for lunch money.

Still, the premise is sound. If your dog or cat has been showing signs of decreasing vision (running into things, difficulty drinking or eating), take a deep look into his or her eyes. The pupils can tell you something, especially if one is significantly larger than the other, but they don’t tell you everything.

Diseases that can affect pupil activity range from diabetes and resulting blindness to glaucoma and rabies. Making yourself familiar with your pets eyes and behavior may let you catch changes early. And for the eye, that can make a mammoth difference.

Matthew Sisk is a practicing veterinarian from Habersham County. Have questions about your pet? He can be reached at