Cats are well-known night hunters. But how well can cats see in the dark? Do they see in the dark like we see in the day, or is their night vision only slightly better?
How well do cats see in the dark? They can see in low-light conditions better than we can, but can’t see in the entire absence of light, as this is impossible. Cats have adapted to seeing in the dark by having more rod photoreceptors than cones; rods sense brightness, while cones are for color. Cats further adapted by developing a tapetum lucidum, a thin covering of the back of the eye, which further helps cats see at night. Cats can also open their pupils wider than we can, and their lenses make the most of whatever light there is, focusing it sharply. All these adaptations help cats hunt at night.
The guide below first describes how well cats can see in the dark, and why. It addresses a group of fascinating adaptations that cats have evolved, from their pupils and lenses to parts of the eye that we don’t have. It will also cover exactly why cats need to see so well in the dark in the first place.
Can Cats See in The Dark?
Cats can’t see in full darkness. If there’s no light whatsoever—for example if the cat is in a sealed, light-proof box—then it can’t see, just like we can’t see. But cats have better dim light vision than we do. The reason for this is that the cat’s eye is subtly different to ours, and has adapted to the cat’s lifestyle, just as our eyes adapted to ours.
It’s easy to make a comparison to your own night vision. When you first open your eyes in the dark, you can hardly see a thing. But over the course of ten minutes or so, it will gradually get better. Your cat’s night vision is even better than that, because of all the adaptations described below. It’s not comparable to seeing in the daytime; rather, it’s more like if you turned up the brightness on a dark photograph.
How Do Animals See in The Dark? (Rods & Cones)
To understand how well cats can see at night, we first have to understand how sight works.
You’ll already be familiar with the idea of rods and cones. These are special cells in the eyes called photoreceptors, located in the retina towards the back of the eye. The parts of the eye in front of them, like the lens and the pupil, control how much light comes into the eye and where it goes; it’s the photoreceptors that actually pick up on the light and send signals about it to the brain.
Rods and cones have different roles. Cones are for color vision: the more cones are in the eye, and the more kinds of cones are in the eye, the better color vision the animal has. People with normal eyesight have three cones whereas cats only have two, meaning we can see more colors than cats. Rods, by contrast, help the eye detect brightness and movement. The balance of rod and cone photoreceptors determines whether the animal is good at seeing at night or in the day.
Cat Night Vision Adaptations
Cats have adapted in lots of different ways to seeing at night. What’s fascinating is that cats have most of the same tools as we do—the same structures in the eye—they’ve just subtly changed them to make them better at seeing at night, rather than detail and color.
1) Fovea vs. Area Centralis
One key adaptation is that cats don’t have a fovea. A fovea is part of the anatomy of a human eye. It’s located at the back of the eye, and is the area of the greatest concentration of cone cells. The fovea is what gives us our very fine vision. Without one, you wouldn’t be able to read this sentence: it would be a blur.
Compare what you see at the very center of your vision—this sentence—with what you see in the paragraph above, without moving your eyes. The words above are a bit of a blurred jumble, because you aren’t seeing them with your fovea. The light from the paragraph above falls in a part of the eye with fewer photoreceptor cells, so isn’t as clear. This is the difference between 20/20 vision and worse vision, e.g. 20/40 or 20/60, which require glasses. For comparison’s sake, it’s thought that cats have somewhere between 20/100 and 20/200 vision. 20/200 is considered legally blind!
Cats don’t have a fovea. Instead, they have an area centralis, which is slightly different. It’s in the same place as the fovea, but is a different shape (slit shaped instead of round). It contains a huge amount of rod cells rather than cone cells. This means that cats can distinguish very finely between shades of light and dark at the center of their vision, whereas we can finely distinguish colors and shapes instead. So while our vision has specialized to see small things, a cat’s vision has specialized to distinguish between close shades of grey. Rods are also much better at detecting movement, which is essential for a cat when it’s hunting.
2) Rod Photoreceptors’ Use of Energy
Photoreceptors are like any cells in the body. They need energy to run, and when they do extra work, they do even more energy. That’s why lactic acid builds up in muscle cells when you exercise: lactic acid is a byproduct of burning extra energy.
In the same way, the cat’s light-sensing cells work harder in the dark than normal. They perform glycolysis, a process whereby the body’s glucose is broken down to produce ready-to-use sugars for energy. Scientists discovered this by measuring the pH level around the rod cells after they had to work hard in low light conditions. Just like how lactic acid raises the pH in and around muscle cells during exercise, rod cells do the same thing.
3) The Tapetum Lucidum
While our eyes have some things that a cat’s eyes don’t, cats’ eyes have structures that ours’ don’t, too.
Perhaps the most obvious difference between a human and a cat eye is that cats have a tapetum lucidum. This is like a mirrored backing to the eye that reflects light back to the retina. This helps the retina pick up on more light than it would otherwise. According to the Comparative Physiology of Vision Wiki:
The nocturnal capabilities of the photoreceptors is further enhanced by the Tapetum lucidum, a thin layer of cells that the photoreceptors are embedded in. In humans, this layer is called the Pigment epithelium, and contains dark pigments to prevent the reflection of light within the eye. The Tapetum lucidum contains semi-transparent layers that reflect differing frequencies of light, which preferentially amplify some wavelengths of light as the refelections recombine.
Here, then, is another difference in vision between a person and a cat. Our eyes have grown accustomed to daytime light, while a cat’s eyes have grown accustomed to the night. The tapetum lucidum, if you didn’t know, is what gives cats’ eyes their bright quality when a light is shined at them. The light is shining back at you, with the tapetum acting as a mirror.
4) The Lens & The Optic Nerve
The lens is a crucial part of the eye. It focuses the light and directs it at a certain point, i.e. the back of the eye. It’s shaped exactly like a contact lens, and performs the exact same job.
A cat’s eye has a lens just like a human eye does. It focuses light in the same way. But in cats, the lens is slightly closer to the optic nerve, which means that the light is focused on a smaller but brighter point. Think back to any time you’ve held a magnifying glass in the sun: if you hold it far away from the ground, it produces a big, bright disc of light. But move it closer to the ground and the point becomes smaller, sharper and much brighter. The lens of the cat’s eye is doing the latter, producing a smaller but brighter image on the retina.
This means that your cat picks up whatever light is available and uses it more efficiently to create an image. So in addition to having more brightness-sensing photoreceptors, the cat’s eye physically uses what light there is better than your eye does.
5) The Cat’s Big Pupils
Cats, like us, have pupils that can expand in low light conditions.
Contrary to what you might think, the pupil isn’t actually a thing. Rather, it’s a hole in the eye that can be opened and closed to let in more or less light. It’s controlled by a ring of muscle that runs around it which can expand or contract, making it bigger and smaller. The pupil is black because you’re looking into the darker area behind it.
As stated above, cats have pupils that expand and contract like ours. But a cat’s pupils can extend almost the entire way across the visible eyeball. This means that a cat’s eye can let in more light, for its size, than a person’s eye. Letting in more light in this way during low light conditions means that cats can see better.
It’s for this reason that a cat’s pupils dilate when they’re looking at prey.
Why Do Cats Need Night Vision?
All of these adaptations arose because cats have a need for night vision. They didn’t occur by accident. So why do cats need such good night vision, especially now that they’re kept as pets?
1) Hunting Prey at Night
Cats have adapted to hunting prey at night. They are predators and obligate carnivores, meaning that they have to eat other animals to get the nutrients they need from their diet.
Hunting for these animals at night is a big advantage to a cat. It doesn’t have to have perfect night vision, just better vision than whatever it’s hunting… And it does. The small animals that cats hunt like rodents and birds can’t see at night like cats can, which means the cat can see it, but it can’t see the cat. This is a trend you see in almost all cats, whether they’re domesticated housecats, lions or bobcats—they all hunt at night.
Besides that, predators do well to hunt when their prey is active, and many prey animals are more active at night. Rats are active at night, and at dawn and dusk, for example.
Another factor is that there’s less competition. Most animals are active during the day, or during the dawn and twilight hours. Fewer animals are active when it’s dark, because it’s difficult to see! Cats take that tradeoff, having to operate in poor light conditions, but having fewer other predators around to compete with.
2) Cats Are More Vulnerable in the Day
While cats are predators, that doesn’t mean they can’t also be prey. Birds of prey and wolves, for example, can kill small wildcats. If the cat chooses to hunt in the day, it could be spotted by one of these animals.
But if it hunts at night, that’s less likely. That’s partly because many predators hunt during the day rather than at night, so cats can avoid some species entirely. It’s also because your cat has good night vision, so can use that to spot any predators that are around before they reach it.
3) Cats Aren’t Fully Domesticated
Domestication can change the physiology of an animal. Take the cow, for example: while you don’t keep cows in your home, they are considered domesticated. Cows are much bigger than the animals they were bred from, more docile, and produce much more milk. Their udders are physically bigger, and their musculature better developed. Cat breeds look different to their ancestors because they’ve been bred to have certain traits like different colors, longer fur, differently shaped faces and so on.
But while some things have changed, not all things have. Cats still retain behaviors relevant to their days in the wild. They still have a strong hunting instinct, which they display even if they get more than enough food at home. Even if they don’t hunt, they display these behaviors when they chase, bite and kick their toys. They still have the same physical adaptations in the eye that lent them their night vision prowess even though it’s less relevant to a house cat than to a wild cat.
4) Do Cats Need to See Color & Detail?
So, without a fovea, and without as many cone cells as we have, cats can’t see color as well as we can. They also can’t see fine details like we do. But what makes this tradeoff worth it for a cat? And why have people evolved to have good color vision, but poor night vision?
It all comes down to what we eat. Cats need good movement vision so that they can track, stalk and kill prey. The things that cats eat are small, and will try to escape, so the cat needs to follow its movements.
By contrast, people are omnivores with well-rounded vision. While some of our time is occupied by hunting—which makes some degree of movement-tracking vision necessary—we also eat lots of things that don’t move around. Our ancestors ate lots of fruit and vegetables, and you tell how ripe a berry is, or whether food has gone rotten, by its color. An unripe berry is green, and a perfectly ripe one red; bad food might turn brown or even black. We need to tell the difference, or we could eat something that gives us gastrontestinal distress (or worse). Cats don’t have this problem because they hunt for their food, so they know that it’s fresh anyway.