Cats, dogs and certain other animals can see a form of ultraviolet (UV) light that is usually invisible to humans, scientists say.
Researchers have determined that cats, dogs, rodents, hedgehogs, bats, ferrets and okapis all detect substantial levels of UV.
"It has been known for nearly a hundred years that many invertebrates, such as bees, see UV," said study co-author Ronald Douglas, a professor of biology at City University London.
Birds, fish, and some reptiles and amphibians have been added to the list in more recent decades, he added.
"However, it was assumed that most mammals do not see UV because they have no visual pigment maximally sensitive in the UV and (instead possess) lenses like those of man, that prevent UV reaching the retina," he said.
Douglas explained that visual pigments are the substances that absorb light and turn it into the electrical activity that nerve cells transmit.
Researchers found they are not 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.
"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.
Cats and other animals built to detect UV might be protected from this visual damage in some way. It's also thought that UV light tends to create more blurry images.
"Now, if there is one thing humans are good at, it's seeing detail. Perhaps that's why they have a lens that removes the UV. If they didn't, the world would appear more blurred," Douglas said.
The study is published in the journal Proceedings of the Royal Society B.