Here's your chance to be a caracal. Can you survive 10 evenings in the Serengeti? Take the Night Cat Quiz to find out.
A cat's iris is controlled by tiny muscles in the shape of a figure-eight rather than a circle. In the dark, the muscles pull the iris back like castle gates to allow more light into the eye. In bright light, the gates close and the pupil becomes a narrow slit. A cat's eye can do this in a fraction of a second. An animal with circular muscles controlling its iris can't open its pupils as wide or as quickly, and in the light, its pupils constrict to pinholes rather than slits.
A cat's infrared receptors allow it to pick out warm objects like birds and antelopes, which give off more heat than their surroundings. Animal movement is detected by motion detector cells, which respond to shifting light on the retina. Light is detected by photoreceptors, and cats can't detect electrical fields.
Light has to pass through the cornea to enter the eye; the more cornea there is, the more light can get in. This is part of the secret behind night vision. Focus is controlled by the lens. Cats have a wide, not concentrated, field of vision because of their bulging corneas. A cornea's shape has little to do with protection.
A cat's eyes have motion detector cells that help it center in on movement, but when focused in this way its surrounding field of vision appears blurry. A moving animal is nearly always a cat's focal point. It was once thought that cats were nearsighted, meaning they can see close objects better than those in the distance, but recent studies have disproved this.
Cats cannot see in total darkness, but they pick up low levels of light six times better than humans can.
Cats have binocular vision, meaning both eyes face forward to produce a single image. This allows cats to see in three dimensions rather than just two; the extra dimension is distance. Because of binocular vision, a cat can assess precisely how far it has to run to reach its prey, and exactly how far it has to extend its paw to hook it. Without it, cats couldn't hunt successfully.
Looking like a cross between an otter and a cat, the jaguarundi is a diurnal animal, meaning that it is most active during the day. It prowls the scrublands and forest margins of Central and South America, never venturing far from water. Its favorite prey seems to be fish. Another diurnal cat, the fishing cat, is aptly named because it also relies heavily on fish. Cats that fish work best during the day; light travels so poorly in the water that night vision is of little use in spotting the animals.
The <i>tapetum lucidum</i> is a silvery layer of reflecting cells that resides just behind the retina, a membrane that absorbs light. When light reaches the retina, some of it is absorbed by photoreceptors called rods and cones, but some of it keeps on going. The <i>tapetum lucidum</i> bounces light back onto the rods and cones, giving them another chance to absorb it. So essentially, the cat recycles light within its eye to gain a brighter picture of its surroundings.
Cat photoreceptors are laid out in a horizontal strip on the retina, rather than a circle, making cats highly sensitive to movement from side to side. This allows cats to detect animals moving across the ground from great distances.
Sharp vision is determined by photoreceptors that detect color. These are called cones. When cones are grouped together, they can decipher fine detail. Humans have a dense patch of cones on their retina, which gives them very sharp vision. Cats, along with bears and dogs, lack a concentrated area of cones. They have lots of rods, which pick up light, but not color or detail.