Why Do Cats’ Eyes Glow?

Cats’ eyes might almost seem magical, but we promise, it’s all science. Let’s answer the question: why do cat eyes glow in the dark?

If you ever find yourself staggering to the kitchen in the middle of the night, half-asleep, in search of water, and you see a pair of glowing eyes staring at you — don’t panic. It’s more likely to be your cat than a monster,  keeping an eye on you in the darkness and wondering whether you’ll be giving them a surprise feed.

At slightly scary moments like this, you might wonder to yourself — why do cats’ eyes glow in the dark? How does it benefit them? Do other animals have eyes that also glow in the dark?

People have wondered about cats’ glowing eyes for years. In fact, the Ancient Egyptians believed that cats captured the glow of the setting sun in their eyes, a gift that kept them safe ‘til morning. The reality isn’t half as exciting or romantic. The real reason cats’ eyes glow in the dark is due to the structure of their eyes. Let’s take a look at the science behind cats’ eyes, why they glow and what other animals share this trait:

While you’re here, check out how cats communicate with their eyes

A (Very Brief) Science Lesson

One thing we have in common with cats is that we both have retinas — a layer of tissue at the back of our eyes near the optic nerve, made up of light-sensitive cells. These cells turn the light we see into electrical signals. Once converted, these signals are sent to the brain, which works out what we’re seeing. This happens instantaneously, quicker than an eye blink. 

Where we differ is that cats are, by nature, nocturnal creatures. They have evolved to hunt and be more active during night-time hours. During the day, cats lie around peacefully, snoozing and gathering their energy so that at night, they can get their exercise in — while keeping you awake!

Because cats are most active at night, when there is less natural light, their eyes have evolved into seeing better in the dark. This is why they have another layer of tissue we lack — something called the tapetum lucidum.

What is Tapetum Lucidum?

Tapetum Lucidum is Latin for “bright tapestry”. It is a thin layer of tissue lying just behind the retina. The tapetum is a retroreflector, meaning it can reflect visible light back through the retina. It’s usually present in nocturnal animals, especially carnivores and deep-sea creatures, although similar adaptations occur in some spiders.

Related: Check out these care tips for indoor cats to keep them mentally and physically stimulated

How Do Cats’ Eyes Reflect Light?

The tapetum is a layer of reflective cells behind a cat’s eye — light bounces off this layer, directing it back towards the eyes’ light-sensitive cells. This gives light a second chance of being detected, which improves the odds of a cat seeing something in the darkness.

However, not all the light is picked up a second time around. Some light simply passes back through the retina and travels out through the front of the eye. This creates the appearance of a glow, which is usually green, yellow or blue.

Why Do Cats’ Eyes Glow in the Dark?

So now we’ve got the mini biology lesson out of the way, let’s look at the “why?”  What’s the evolutionary purpose of glowing eyes? 

According to the American Veterinarian, the tapetum allows cats to detect both changes of light and motion — helping them to become more skilled at hunting, prowling and pouncing in the night-time hours.

Do Other Animals Have Eyes That Glow in the Dark?

When you think of glowing eyes, cat eyes are probably the first to spring to mind. But other animals also possess this striking feature, including some fish, sheep, horses, deer and ferrets.

So next time you see a pair of glowing eyes staring at you in the middle of the night, don’t worry. It’s simply the ambient light reflecting in your furry friend’s eyes. Although if you don’t have a cat, you might want to run.

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