At night, cats are quite active. This nocturnal activity is especially possible thanks to their excellent vision in the dark. It helps them to hunt especially at sunset and at sunrise.
The structure of the cat’s eyes
Everything in the structure of a cat’s eye can exacerbate this ability to see in the dark, from their shape to the size of their pupils through their brilliant irises.
If you’ve ever wondered why cat’s pupil is upright during the day, but becomes round and wide when the light goes down, here’s an answer. The pupil adapts to the ambient luminosity, like those of humans. The wider it is, the more it brings light into the eye. Thus, in good weather and bright sun, the pupil will be very fine. On the contrary, when the light falls, it widens to bring as much light as possible. In the cat, when the pupil is vertical and thin, it allows a certain amount of light to enter and especially to have a clear vision. When it starts to get dark, the pupil becomes round, and takes a lot more room on the eye. The vision is less clear, but the amount of incoming light is then sufficient to see well.
The size of the dilated pupil of a cat can be 135 to 300 times greater than when it is thin and vertical. The human pupil, for example, only increases by 15 times its size. Thus, the cat can bring much more light and therefore better see in the dark.
Do cats see in total darkness?
Although cats have very good night vision, they still need a minimum of light to see “in the dark”.
When light enters the eye, its rays hit the retina, the sensitive organ of vision. The retina is a thin multi-layered membrane at the bottom of the eye that houses the photoreceptor cells. Each retina has two types of photoreceptors, cones and rods. Cones are very active in daytime vision and colors, while sticks allow twilight and night vision in black and white.
Cats and dogs have many more sticks than cones in their retinas. That’s what differentiates them from humans. We have more cones than rods, which explains why we see colors better.
This large concentration of rods allows the cat to have a very good vision in the dark by absorbing much more light. The cat needs only 1/6 of the light a human needs to see. The sticks thus greatly help the cat to hunt at night. Although their vision is more blurred, they are very sensitive to subtle movements and variations in light (for example: the movement of a shadow).
Why do cats have eyes that glow in the dark?
Behind the cat’s retina is a reflective layer called the tapetum lucidum. This layer increases the amount of light captured by the retina through reflection. The low-light vision is thus further improved, although the perceived image is a little disturbed due to interference between the incoming light and reflected light. Thus, this reflective layer returns the perceived light, which is why the eyes of cats glow when you take a picture with flash for example. The reflection can be in a wide range of colors including blue, green, yellow and pink. The cat is not the only one to have this peculiarity. It can be seen in most animals, especially those that are used to hunting or being active at night.