Cats and many other animals, including most dogs, can reflect light from their eyes. As a result, cats' eyes usually glow brilliantly in photos taken in a darkened room, or when illuminated by a flashlight or car headlight in the dark.
Species with glowing eyes have evolved to see better in low light because they are either foraging or have to watch out for predators all night, or they hunt mainly at dawn and dusk.
In fact, domesticated cats can see only 16 percent of the light that humans need to see.
Cats are able to do this because their pupils - which appear as black rings of light in the middle of their eyes that widen and narrow in light conditions - are special.
The pupils function like Windows, with larger pupils allowing more light into the eye. In the dim light, cat pupils can be up to 50 percent larger than human pupils. They also have more of a particular type of photoreceptor cell in the back of their eyes than we do. These cells, called rod cells, trap low-level light.
The eyes of other animals also glow:
Many other animals that need to be seen at night have a conical choroidal layer. This includes predators and prey, from wild foxes to farmed sheep and goats.
The conical choroid layer is also useful for fish, dolphins, and other aquatic animals because it helps them see better in murky, dark water.
In land animals, the cone is located in the upper half of the eye behind the retina because they need to best see things on the ground. But in aquatic animals, the cone takes up most of the eye, because they need to see everything around them in the dark.
Like the cat, the lemur, a small primate, and its relatives. Jungle baby: Also known as the "night monkey," it also has a super reflective cone made of riboflavin.
Although many animals have eyes, some small domestic dogs lack this feature. Most animals with blue eyes and white or light fur have also lost this trait.
So if your dog or cat's eyes don't glow, don't panic. Other species on the list without a conical choroidal layer include birds, reptiles, and most rodents and primates, including humans.
