by Sasha Brown-Worsham
When it comes to cat vision, many humans are simply in the dark.
Melvin, my 22-pound tabby cat, loves to stalk the house by night. When all the lights are off, he goes pouncing; on dust bunnies, on slippers, on all the toys my children have left strewn about the house. In minimal lighting with only the glow from the street lamps outside, our feline is King of the Castle.
“Can he see in the dark?” My 8-year-old asks. She has a lot of questions; like we all do. Here are some of the most common questions (and quite a few myths) when it comes to cat vision.
People often believe that because cats stalk around the house long after the humans go to bed, that must mean they have some kind of night vision that humans lack. As it turns out, that is only partially true.
Cats can certainly see better in the dark than humans, says Dr. Gaylord Brown, chief veterinarian at D.E.L.T.A. Rescue, a large no-kill, care-for-life animal sanctuary. “Cat’s only need about 15 percent of the light humans need to see,” he explains. But felines aren’t walking around with vivid night vision the way many people imagine.
Cats have slit shaped pupils that can control the amount of light that gets into the eye in daylight, which keeps it from getting damaged in the daylight and also manages to give more control over how much light reaches the retina. Humans, with our round pupils, don’t have the same abilities. A slit pupil can also dilate more than a round pupil, which allows more light to enter in the dark.
“It is estimated that cats can see six to eight times better in the dark than humans,” says Veterinary Ophthalmologist DJ Haeussler, who runs the Animal Eye Institute in Southern Ohio.
When it comes to cat vision, the myth that cats “can’t see color” manages to persist despite enormous evidence to the contrary. To be sure, they see color differently than the average human. But their sight isn’t all in black and white.
Cats are generally accepted as dichromats, meaning that they have two types of cones that see colors. There is some evidence that cats may even have three types of cones, which would make them trichromat.
“To see color, animals need to have receptors in the retina known as cones,” says Dr. Brown. “What is true is that cats only have cones that detect blue and green. There are no cones for red. Therefore, cats have a more muted sense of color. Similar to a person who is color blind.”
If you have ever snuck up on your cat accidentally and watched his pupils go from slits to saucers, then you've probably asked yourself this question. The fact is, cats pupils are designed to react to emotional situations and tend to dilate when they are angry or ready to pounce.
“Cats pupils dilate just like dogs, humans, horses, and other species,” says Dr. Haeussler. “The iris is controlled by the brain, which tells the iris to constrict in bright light or dilate in dim light. When the pupil dilates, it allows more light to the retina.”
All of this can mean that a cat’s eyes dilate when they are angry in order to better see their enemy. Spooky.
“Cats' eyes glow when light is shined at them due to a reflective structure that is part of their retina known as the tapetum lucidum,” says Dr. Haeussler. “This structure amplifies light to better allow the cat to see in dim light.”
Cats are not the only animals who have this tapetum lucidum. Dogs, cows, horses, ferrets, and other animals have them, too. Humans don’t have the tapetum lucidum because we are designed to see better during the day.
Even more fascinating, different breeds of cats’ eyes glow differently. While most cats’ eyes glow bright green, a Siamese’s eyes glow more yellow. This variation comes from the amount of zinc or riboflavin present in the pigment cells present within the tapetum lucidum.
Humans typically have 20/20 vision, whereas cats have approximately 20/100 - 20/200. “This means that if a human can see an image very well from 100 feet, a cat would have to be 20 feet from that same object for it to appear sharp,” says Dr. Haeussler. Additionally, Cats do not have the muscles to change the shape of their lenses. This prevents them from seeing objects close up.
“Humans have more cones than cats. In addition, humans have a fovea, where there is a very high concentration of cones. This allows us to see more vibrant colors as well as detailed resolution during the daytime. Cats have many more rods than we do. This allows them to see much better than humans at nighttime.”
Cats are also more adept at seeing fast moving objects than humans. In other words, “good vision” might be a misnomer. Cats see very differently than humans.
According to Dr. Brown, dogs have a smaller area of binocular vision than cats. Binocular vision helps to judge distance. But cats have less peripheral vision than most dogs.
“This is due primarily to the placement of the eyes in the head,” Dr. Brown says. “The cat’s pupil is slit shaped and has a much more complex set of muscles controlling the pupil than the dog. The dog’s pupil is round. The tapetum, which reflects lighting in the eye, is relatively larger in the cat. Cats depend more on contrast and degrees of brightness than dogs, due to the differences in the retinal cones. The muscles of a cat’s eye are much better at rapid eye movement than those in the dog, which allows them to better track small objects such as mice and birds.”
For these reasons cats clearly have an advantage over dogs when it comes to vision.
If you have ever had more than one cat, then you know cat eye color varies. That said, “Feral cats typically have hazel colored eyes,” says Dr. Brown. Of course, specific breeds of cats have different eye colors that range from blue, green, and yellow, to orange and brown. Some cats may even have one blue eye and one of another color; a benign condition called heterochromia.
“All kittens are born with blue eyes and at about 6 weeks of age they begin to develop their adult color,” Dr. Brown says.
A 2014 study at City University in London found that cats and dogs really do see ultraviolent light that humans cannot.
“What we call visible light is part of the electromagnetic spectrum, which covers many things ranging from radio waves to x-rays,” says study leader Ron Douglas. “The little segment between wavelengths of 400 - 750nm is what humans call visible light. Wavelengths below 400nm (down to about 10nm) are called ultraviolet. Humans cannot see these wavelengths as our lens absorbs them.”
Though Douglas’s primary work has been with fish, his studies were still fascinating for cat lovers everywhere. Many animals are known to have UV vision. They include insects, birds, fish, some amphibians and reptiles, and a handful of mammals.
Cats and dogs have lenses that allow a certain amount of UV to pass through. This is a huge part of what allows them to see so well in low light levels.
In fact, they do have a third eyelid! The third eyelid is between the regular eyelids and the cornea, giving the eyes added protection. That third has a gland at the bottom that produces extra tears. The third eyelid is not normally visible, but for some cats it is normal for their inner eyelid to show when they are resting. If the eyelid does not retract back into place and stays visible when the cat is not at rest, that is usually indicative of an illness that needs attention.
Answer: Unfortunately, yes.
According to Dr. Brown, the four most common causes of vision loss in cats are:
1. Uveitis. This is an inflammation of the middle portion of the eye, which is most often brought on by an infection of some type. These infections include FIP, Felv, or FIV.
4. Traumatic eye injuries.
This is a common question that makes many veterinarians laugh. “Your cat is probably staring because he loves you,” Dr. Haeussler says.
The fact is, cat vision is a fascinating topic, as anyone who has ever loved a cat can tell you. Cats have numerous visual advantages. Everything in cats has evolved to make them hunters who can stalk by night. Kind of explains their nocturnal roaming, right?
Working with All Animal Eye Clinic and Penn Vet, visual artist Nickolay Lamm undertook a project to try to create a sense of “cat vision.” He took side by side photos, one from the perspective of a human, the other from the perspective of a cat. The photos are amazing and Lamm himself said he was moved by the project.
“It kind of makes me think more about seeing from a cat's point of view,” he says. “We love looking at them because they are cute, but I didn't think that much before about what they see, how they perceive us and the world.”
We, as their human caretakers, have a big responsibility, not only to understand how cat vision differs from our own and what they see versus what we see, but also to protect their eyes.
“Other than acute trauma, most vision loss occurs slowly over time,” says Dr. Brown “The sooner a disorder affecting the vision is diagnosed the better the probability of stopping the progression and reversing the vision loss. The single most important thing a cat owner can do is have their cat’s eyes examined at least once a year.”
Protect these magnificent creatures and they will live long, healthy, highly visual lives. Let’s all do our part to see that through.