If you have a cat, you’ve probably spotted a pair of shiny, glowing eyes at the end of the hallway at one point or another.
This occurrence can make you feel like you’ve suddenly become a part of a horror film—until you realize it’s just your cat peering at you in the darkness.
But why do cats eyes glow in the dark? What makes a cats’ eyes shine is light bouncing off the tapetum lucidum and missing the retina. This reflection causes a cat’s eyes to glow.
You’re likely already familiar with a critical part of the eye: the retina. Both cats and humans have retinas.
The retina is a layer of tissue found at the back of the eyeball, which is full of light-sensitive cells that transform light into electrical signals. These signals go to the brain, and the brain interprets them so that we know what we’re seeing.
However, unlike humans, cats are nocturnal animals. They need excellent night vision to hunt in the dark, and their eyes are equipped with a special tool to do this—the tapetum lucidum.
The tapetum lucidum is a reflective layer typical in nocturnal animals. It means “shining layer” in Latin.
You can think of the tapetum lucidum as a small mirror of sorts in the back of a cat’s eye. It allows their eyes to reflect more light and therefore see better at night, making the tapetum lucidum a critical structure for felines.
It also absorbs light that escapes the retina, which delivers a 50 percent boost in a cat’s night vision.
Are Humans’ Eyes Similar to Cats?
In general, our night vision is pretty lackluster compared to that of felines. But you may be surprised to learn that our eyes actually have plenty in common with cat eyes.
Most notably, despite their excellent ability to use light at night, cats still have difficulty distinguishing shapes in the dark as we do.
However, the similarities end there. Let’s take a look at some of the primary differences between cat and human eyes.
Unlike cats, humans lack a tapetum lucidum, and it makes sense that this structure never evolved in humans. We’re more active during the day, so we take advantage of daylight. The tapetum lucidum is simply not necessary for us.
So if you run across another human in the dark, you will not see any reflection like you would with a cat. And if someone shines a flashlight in your face, the only thing you’d experience would likely be annoyance.
However, there is a caveat worth mentioning when it comes to reflection.
Anyone who has ever taken a photo of another person has probably encountered a frustrating problem. The flash of the camera is so bright that it can cause a reflection from the retina, which shows up in photos as red-eye.
Though red-eye looks similar, it’s a different mechanism than in cats: instead of the tapetum lucidum, the red color comes from the blood vessels in our eyes.
Human eyes differ in another way: dilation. When we move from a dimly lit room to a brightly lit one, our pupils dilate to keep our eyes safe from damage. We are unaware of this process and unable to control it.
Cat eyes also dilate, but the animal has a much more active role. Cats can actually use their muscles to modify this process to best fit the current light conditions.
One curious fact is that the eye glow color differs from cat to cat. It may appear blue, green, or even yellow.
The primary reason for the difference in color has to do with having different substances in the cat’s tapetum lucidum, namely riboflavin or zinc. Another reason is that the amount of pigment in the retina varies, which can change the color.
Different species may also give off different colored glows. Most cats have bright green glowing eyes, but Siamese cats are an exception. They tend to have bright yellow glowing eyes instead.
The age of your cat influences glowing intensity as well. In general, younger cats’ eyes glow more strongly than older cats.The tapetum lucidum becomes less powerful as a cat ages, resulting in a weaker glow.
You may even notice that your older cat’s eyes appear red in the dark, which is nothing to be concerned about. Red eyes are a sign that light has stopped reaching the tapetum lucidum the way it used to, a common occurrence in senior cats.
They could also be a sign that your cat was exposed to light unexpectedly, causing their eyes to rapidly dilate and appear bloodshot.
Cat’s eyes should not glow during the day. If they did, it would mean that their pupils are dilated, and in daytime conditions, too much light would be getting into their eyes.
If you notice your cat’s eyes glowing during the day, it’s a strong indication that your pet has a vision problem. You should take your furry friend to the vet to figure out what the problem is.
If you notice that your cat’s eyes don’t glow in the dark, that also indicates a problem. Cat eyes should always be reflective in low-light settings, so if you notice that this isn’t the case, it likely points to an issue with your kitty’s vision.
Some common health issues that may affect glow include:
For your cat’s health and well-being, it’s best to pay your vet a visit. Your vet can help you diagnose and treat the eye issue.
Although it’s most likely that you’ve encountered a cat’s glowing eyes at some point, this ability is not exclusive to felines. Other animals also have a tapetum lucidum, such as dogs, owls, horses, deer, and ferrets.