Why can’t we see in the dark like cats and owls?

Was there a time when you camped out on a dark mountain, where navigating was impossible without a flashlight? Or maybe power went out in the middle of the night, and it was so difficult to see what’s in front of you? Well, our visual systems as human beings are not designed to handle low light conditions compared to other species, such as cats and owls.

The human eye allows light to pass through a hole or our pupil. Then, the image goes through a focusing lens. The retina works next by detecting the said image, seemingly like how a projector would display an image on a wall. It has two photoreceptors, regarded as rods and cones, which recognizes light, and transmits the image to our brain.

Rods are found around the outer ring of the retina and are very active in dim light. However, they are unable to detect colors. Meanwhile, cones are located in the center of the retina, which allows us to see color and in exquisite detail. But, they only work when light is abundant.

The human eyes have four times more rods than cones. The said ratio is the main reason why people are able to see vividly during the day. And, while we have more cones than rods, its number is higher than the number of cones many animals have. Thus, allowing us to see incredibly well in the day, and decently fine during the night.

Some animals, however, possess more rods than cones and are blessed with incredible visual systems, allowing them to see better in the dark than humans.

Cats are one of the animals that can see incredibly in the dark. They have an enhanced night vision, thanks to their tapetum lucidum. It is a unique reflective structure found in their eyes just behind the retina. If ever light passing through a cat’s eye fails to hit the photoreceptors, it will also fail to transmit sensory images to the brain. What tapetum lucidum does is it serves as a mirror, sending light back to the photoreceptors field and giving it another opportunity to produce a visual image.

Through that fantastic functionality, cats can see better at night compared to humans, as we don’t have the said reflective structure in our eyes. Moreover, that distinct feature is responsible for making the cat’s eyes glow at night during certain instances. Raccoons and deers also have vision-enhancing structures of their own.

Owls also possess great vision at night. While they are smaller than us, what’s surprising is that the size of their eyes is nearly the same as that of humans. Their big eyes allow them to detect the best amount of light possible, maximizing every glimmer present in the area.

A downfall, though, is that their eyes are so huge, they can no longer swivel them in their eye sockets. With that, owls have to turn their head from side to side. It’s a great thing that they can turn them by as much as 270 degrees without causing damage to the blood vessels in their neck and head. Thus, providing them with a wide field of vision.

Aside from owls, tarsiers are also blessed with huge eyes and functions the same way owls’ eyes would. It would detect all specks of light it can utilize to provide them an incredible vision around their area. Like owls, they can’t also swivel their eyes in their sockets. But, to compensate, they can turn their heads up to 180 degrees.

Different animals also see well in the dark in their own distinctive ways. Bugs, for instance, don’t have rods and cones. However, unique adaptation in their visual system enables some of their species to have great vision at night. Snakes, on the other hand, depends mostly on thermal vision, allowing them to recognize the body heat of mammals.

More Readings:

Eye (Wikipedia)
Cat (Wikipedia)
Owl (Wikipedia)

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