Cats May See Things That Are Invisible to Us

Cats, dogs and certain other animals can see a form of ultraviolet (UV) light that is usually invisible to humans, scientists say.

Scientists have said that cats and dogs can see in ultraviolet, so they can see things that humans can’t. Photo: phoebe_rousseaux/ Flickr

British researchers found that a whole plethora of mammals, including hedgehogs and ferrets can see in UV, giving them a better view at night among other benefits.

“Nobody ever thought these animals could see in ultraviolet, but in fact, they do,” said study leader Ron Douglas, a biologist at City University London, in England.

Humans are able to see many colors of light, but ultraviolet (UV) light is not detectable. Animals such as birds, bees, reptiles, amphibians and fish are already believed to possess UV vision; some mammals such as mice have been suspected of having it as well.

According to LiveScience, bees and other insects use it to see colors or patterns on plants that can direct them to nectar. Rodents use it to follow urine trails. And reindeer may use ultraviolet light to see polar bears, which, in visible light, blend in with the snow.

“There are many examples of things that reflect UV, which UV sensitive animals could see that humans can’t,” co-author Ron Douglas told Discovery News. “Examples are patterns on flowers that indicate where nectar is, urine trails that lead to prey, and reindeer could see polar bears as snow reflects UV, but white fur does not.”

The lens of the human eye blocks UV light, humans who have had this lens removed have reported being able to see the UV light. Some animals have a UV-transparent lens.

For the study the researchers obtained eyes from a smorgasbord of mammals who had died or were killed, donated by zoos, veterinarians, slaughterhouses and science labs. The scientists measured how much light got through the lens of each animal’s eye to its retina.

Scientists found that many of the animals, including cats, dogs, hedgehogs, ferrets and okapi, have lenses that let some ultraviolet light though, suggesting that they can see well in the dark.

Douglas, a professor of biology at City University London, explained that visual pigments are the substances that absorb light and turn it into the electrical activity that nerve cells transmit. They turn out not to be always necessary for UV sensitivity. Instead, the “ocular media” (transparent parts of the eye like the cornea and crystalline lens) in certain animals transmits UV wavelengths.

The ability allows more light to reach the retina, “which would be good for a nocturnal cat,” Douglas said.

Douglas believes the question to ask is “why do human eyes block out UV light.” The researcher believes blocking out UV light helps sharpen vision, like a skier wearing yellow goggles. The animals that blocked out UV light were found to possess the sharpest vision.

Humans have many cones in their retinas which allows them to “produce high-quality images with just a small amount of light,” LiveScience reported. Nocturnal animals have eyes designed to allow as much light in as possible.

“We do all assume that it (UV) may be harmful,” co-author Glen Jeffery, a professor of neuroscience at University College London, told Discovery News.

“I work a lot in the Arctic where UV levels can be very high, particularly in spring and early summer when there is still a lot of snow and ice.

“These surfaces reflect 90 per cent of the UV, so the animals are exposed from above and below. If you do not have snow goggles on, your eyes hurt within 15 minutes,” Jeffery said.

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