Can cats really see in the dark?
If you've ever lived with a cat, you know that they can be incredibly active at night, often sprinting up and down corridors — and over their owners' beds — without ever crashing into walls or doors.
Given their ability to avoid collisions during these nocturnal exercise sessions, you may think that cats have natural night vision. But do they?
According to Caryn Plummer, a clinical veterinary ophthalmology specialist at the University of Florida College of Veterinary Medicine, that's not quite the right question to ask.
"It's not a matter of seeing in the dark or not seeing in the dark," she told Live Science in an email. "The perception of vision — you might say the 'quality' — is more of a spectrum than a yes or no."
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Plummer explained that the amount of ambient light present influences what an individual — be it a human or a cat — can see. However, compared with humans, cats are far better at making out objects when very little light is available, and this is largely due to how their eyes have evolved.
"Cats can see in the dark because the structure of their eyes, and specifically their retinas, permits them 'better' vision than humans when light levels are low," Plummer said. "Cats have a higher percentage and concentration of rod photoreceptors than humans, which means they have better sensitivity to light, and can see more in low levels of illumination than we can."
According to the Cats Protection charity, this abundance of rods means that cats can see "six to eight times better" than humans when it is dark.
So why have cats evolved to have such exceptional night vision?
"Adaptations for vision are the direct result of a species' need to interact with its environment," Plummer said. "Cats are obligate carnivores, meaning they must eat meat in order to stay healthy. They are unable to produce certain required proteins and must ingest them from an external source. Many of their potential prey items are active at night or in dim light."
Despite being more active than the average human during the night, cats are not strictly nocturnal animals. Rather, they are considered "crepuscular," or active during twilight, owing to their fondness for hunting at dusk and dawn.
However, although feline eyes are designed for night-time jaunts, cats' ability to successfully navigate their environment during periods of near darkness is about more than the composition of their eyes. According to Plummer, cats also rely on their other senses.
"Cats have very acute hearing and olfaction [the sense of smell], which aids their ability to navigate," Plummer said. "Interacting with the environment requires the collaboration of all of the senses."
So, cats are far more adept at wandering at night than humans are, but when it comes to vision quality, they certainly don't trump humans during the daytime.
"In evolution, there is usually a price to be paid for every advantage," Ron Ofri, a professor of veterinary ophthalmology at the Hebrew University of Jerusalem's Koret School of Veterinary Medicine in Israel, told Live Science in an email.
For cats, the trade-off for having superb night vision is having to make do with relatively poor vision during the day.
"As a result of the adaptations that allow such sensitive night vision, their daytime visual acuity is only about 1/7 of ours," Ofri said. "This shocks people who believe that cats always have superb vision: they do, but only at night; they have horrible daytime vision."
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According to Plummer, there are other differences between the eyes of humans and cats. For example, cats don't register color the same way humans do.
"Cats have a lower absolute number and concentration of cone photoreceptors compared to humans, so they do not perceive color the way we do, nor do they have the degree of detail resolution that we have," Plummer said.
Cones in the eye are responsible for determining "day vision" color. Humans have three types of cones, which enable us to perceive the colors blue, green and red, while cats have only two types of cones, meaning what we see as green and red appear gray to cats. It was long thought that cats are colorblind, but many scientists no longer believe that to be the case — though discussion rages on. It is now widely thought that cats can see blues and grays, and potentially also some shades of yellow and green, but the truth is that nobody can say for sure.
"Cats are dichromats, which means they have two types of cone photoreceptors, compared to our three types," Plummer said. "So they do not see as many colors or colors as brightly as we do. We would perceive their daytime visual resolution as fuzzy and out of focus."
Originally published on Live Science.
