Why Do Cat Eyes glow? Simple Explanation

It’s always strange to humans how cats’ eyes will glow green or yellow in the dark. Other animals don’t do that, although some will flash a red, yellow, or green glow when you shine a light on them. 

Why do cat eyes glow? Simple explanation is they have a reflective layer in their eyes that makes them glow. This thin layer, known as the tapetum lucidum, reflects light on eye receptors. That is what causes the glow. 

Read further to find out more about a cat’s glowing eyes. 

The Eyes Aren’t Really Glowing

While we refer to the green glistening eyes as glowing, they aren’t truly glowing. A cat’s eyes are reflecting light rather than glowing. 

What the Tapetum Lucidum Does?

Animal doctors and researchers aren’t altogether certain about everything this layer in a cat’s eyes do but they believe it makes a cat’s surroundings appear brighter in the dark. They also know glowing eyes, also called eyeshine, is common among crepuscular and nocturnal animals. 

Felines are crepuscular, which means their biological clock has them up from sunset to sunrise. This is the time cats like to hunt and even domesticated cats prefer to creep around this time. 

Doctors state a cat’s eyes have rods that absorb light while it travels to the back of the eye. A light that isn’t absorbed hits the tapetum lucidum and that reflects it, giving the rods another chance to take in the light.

Some of the light that is bouncing around the tapetum lucidum misses the retina. It travels out of the cat’s lights and reflects green, which is what we call eyeshine or glowing eyes. 

Read: Do Cats Get Oily Fur When Stressed and Why?

A Cat’s Sight

A debate over how much eyeshine helps a cat’s sight exists among animal doctors and researchers. Most believe the number of rods in a cat’s eye plays a role in a cat’s ability to see at night but no one can test the difference in how much a cat sees during the day compared to at night. 

Scientists also can’t test to what level the tapetum lucidum helps a cat see better. 

Differences in Cats

Scientists have determined that different cats, breeds, species, those with different eye colors and even different coat colors have variations in the tapetum development. This can affect how useful it is for the cat. 

Siamese cats don’t have a well-developed tapetum lucidum so it’s thought they have worse night vision than other felines. However, scientists state this is a belief because of the stories from pet owners since the cats can’t be tested to know exactly.

Not all cats have green eyeshine, although that is the most common way we see their eyes at night. Some cats shine yellow eyes at you in the dark. 

The eyeshine color depends mostly on the breed, according to animal experts. The color specifically depends on how much riboflavin or zinc is in the tapetum. While that can vary from cat to cat, it mostly varies from breed to breed.

Read: What Smells Will Keep Cats Away?

Why Can’t Humans’ Eyes Glow?

Humans don’t have a tapetum lucidum. It is mostly in animals that thrive at night. There are other differences between how a cat’s eyes work and how humans see. 

Both have rods and cones, which are photoreceptor cells that absorb light. Humans have more cones, which means we can better distinguish color than a cat. That doesn’t make them fully color-blind but colors aren’t as defined for them. 

Cats see most things in tones of yellows, grays, and blues. They can see enough distinction to know a cat they are familiar with from those they don’t, as with other animals and people. 

Felines also depend highly on smell to identify their “tribe” which includes all humans and pets in their household as well as their territory and other things they claim.

The Truth About a Cat’s Nightime Vision

Generally, the consensus among scientists is that a cat can’t see much better than a human can at night. Their eyes aren’t functionally better. The difference is they have three adaptions that enable them to take in and use more light. 

A cat’s eye can take in a lot more light than a human’s eye. That’s because a cat’s pupils are vertical while a human pupil is circular. A cat’s pupil can open and close much more quickly than that of a human. 

A feline’s pupil is much like a camera aperture and allows in light as needed. This means the cat takes in much more light than a human on a nighttime prowl.

Once light enter’s the cat’s eye, the rods and tapetum enable it to work better in dim light than a human’s eye. The rods switch off during the day when they aren’t needed.

Cats have more rods than humans, so they can function better in the dark. The downside is that doesn’t mean a cat can make out the details of an object better. A cat must be closer to the object to see it as sharply as a human can in the darkness. 

The reason for this dilemma is that light scatters in many directions when it hits the tapetum lucidum. This decreases the ability to see details and lowers the sharpness. A feline needs to be seven times closer to something to see it fully in the dark. 

Read: 3 Reasons Why Your Cat Is Scared of the TV All of a Sudden? 

Non-Glowing Cat Eyes

Some people have felines where eyes don’t glow in the dark. Some cats don’t have eyeshine because the tapetum lucidum was never fully developed. Cat owners express concern that only one eye glow.

Either the light isn’t hitting it at the right angle or that eye doesn’t have a fully-formed tapetum. 

Cats’ Eyes Aren’t Always Perfect

Cats can be like people in the sense that some may not see them as good as others. Cats can be near-sighted and far-sighted. You will likely notice that when they play because they will miss toys, treats and other things thrown around them. 

You can test your cat’s vision at home but should have your cat’s eyes checked during their annual vet visit anyway to stay on top of any possible problems.

Read: Why Is My Cat Walking Slow?

When to Get Worried?

Overall, you shouldn’t worry about your cat’s eyeshine unless there is a dramatic change. A sudden change can be especially troublesome because it could be a sign of an underlying illness. 

Illnesses that can affect eyeshine include infections, cataracts, corneal changes, and cancer. It could also be glaucoma or conjunctivitis. The age of your cat may narrow down the problem as older cats are more susceptible to things like cataracts and glaucoma.

Those who see cloudy eyes of their favorite furball staring back at them should have their cat checked for cataracts. That is a symptom as healthy cats have clear eyes 

It’s best to take your cat to the vet if it has a change in eyeshine. A veterinarian is the only one who can give a good diagnosis.

Read: What Does Unhealthy Cat Fur Look Like?

Final Thoughts

Cats are given the qualities they need to survive in the wild and those qualities, like glowing eyes, remain even among domesticated cats. They make it interesting when you get up in the middle of the night for a glass of milk and a cookie and see glowing green eyes following you. Enjoy the eyeshine!