One of the most distinguishing features of cats is how their eyes can glow in the dark. If you’re sitting with one at home and the light catches their eyes just right, it can seem as if a flash of light is coming from them.
What causes their eyes to glow and does it have a use? The glow comes from a special structure they have called the tapetum lucidum, something us humans don’t have. Let’s explore what this structure does and how it enables cats to explore the world.
What Do Glowing Eyes Mean for Cats?
The next question to ask is why do cats have this reflective layer? It means that are able to see much better in low light than humans do. This can be thought of as the difference for humans between looking outside under bright moonlight or on a cloudy night. However, for cats, it’s always like having that bright moonlight as long as they have some light source.
The reason they need to see better in low light is because cats are crepuscular animals. This means they are most active at dawn and dusk. This allows them to hunt at these times where they need to have superior night vision.
Cats have evolved to be able to hunt efficiently in dim environments. Their eyes help with this, but also their other senses, such as their incredible hearing. Cat’s whiskers are also another tool they use to navigate the darkness. With their ability to detect movement, it allows them to easily catch small prey.
The Role of a Cat’s Pupil
Another key factor in their glowing eyes is their pupils. Cats can dilate their pupils to nearly the full circumference of their eyes. This means they can alter from a small vertical slit to nearly a full black hole.
Amazingly, cats can change their pupil size by a factor of 135 from the minimum to maximum size. In humans, this is only 15 times. By doing this, cats can amplify the amount of light which floods into their eye, capturing any light source.
This can also influence how much their eyes glow. The wider the pupil, the more likely you are to see light reflecting off the tapetum lucidum. In bright conditions, cats will contact their pupils and you’ll be unable to see it.
Why Do Cats’ Eyes Glow in Different Colors?
If you’ve observed a variety of cats, you may have noticed their eyes don’t always glow the same color. This can depend on several factors but mostly depends on the amount of minerals that the reflective layer is made from. Namely, how much zinc it contains.
This can mean colors of green, yellow or blue can be more prominent than others. There are also times when their eyes may glow red, which is usually in certain lighting conditions where its blood vessels in the retina are reflecting light.
Other colors can be due to different breeds having a different genetic makeup of this reflective layer. There are also other species that don’t have a prominent tapetum lucidum or have a medical condition causing it to be smaller or mutated.
The Role of the Tapetum Lucidum
We mentioned the tapetum lucidum there but what exactly is it? It’s a layer of reflective tissue that sits behind the retina. It’s one of many fascinating features of a cat’s eyes and works to enhance the light they receive, meaning they can still see in near-total darkness.
For humans, light comes into our eye and we can only use the light that hits our retina. For a cat, the tapetum lucidum acts as a mirror. Any light missed by the retina will bounce back into the retina, means they capture more light than we do.
It’s this light being reflected back that gives cats eyes that eerie glow. The light that is reflected back but missed by the retina will leave the cat’s eye. You don’t always see this glow as it depends on the angle of the light and how bright the surroundings are.
Differences Between Cats and Other Animals
Cats are far from the only animals with a tapetum lucidum. In fact, dogs have this too. However, with dogs, it’s neither big nor as reflective. In some conditions, you can see this glow but it’s usually not as prominent as with cats.
Perhaps the two animals that can closely match the glowing eyes of a cat are deer and foxes, who are also active at night time. Cows and horses have this ability too but aren’t seen as much at night and don’t have the impressive night vision of cats.
A few ferocious hunters have this ability, with alligators and crocodiles being excellent low-light hunters. You have also seen a reflective shine in the eyes of sharks who can still hunt in those deep, dark waters.
However, this glow is the most famous among cats. That’s partly due to them being a household pet but also as their tapetum lucidum is more well-developed than many other species that have it.
Can Cats See in Total Darkness?
Despite this layer, cat’s eyes are quite similar to ours in their key functionality and cannot see in total darkness. We see a very similar range of wavelengths to cats and have the same need for a light source.
Without any light source whatsoever, cats are as blind as a human would be. If there is a minimal light source, then the world would be brighter for a cat than it would be for a human. We may have the advantage when it comes to seeing colors but capturing light is a much different story.
What If a Cat’s Eyes Don’t Glow?
If a cat’s eyes aren’t glowing at all, this isn’t a good sign. Some medical conditions can affect how much light is processed by the eye. It can also be a generic variation or an injury to the eye which may need medical attention.
Age can also decrease the effectiveness of the tapetum lucidum over time. It may also be that your cat’s eyes don’t glow as brightly due to other reasons. Depending on the make-up of this layer, it may just be reflecting less vibrant colors.
