How can cats see in the dark? The answer is in the obvious, really. A cat’s eyes have to be more sensitive to light than the eyes of other animals including humans.
A good analogy is the modern digital camera. Modern cameras have become progressively more competent under low light conditions. These conditions are typically found inside the home. Nowadays the light receiving sensors inside compact cameras upon which the image is focused are incredibly sensitive so much so that flash is no longer required.
You will see how manufacturers often focus on the low-light abilities of their cameras. However, none of them can match the domestic cat!
The anatomy of human and cat’s eyes are similar. The light sensitive film at the back of the eye, called the retina contains two different types of light sensitive cells (photoreceptors). They convert the focused image to a signal for transmission by the optic nerve to the brain.
The two types of cells are called rods and cones. Rods are more sensitive but less able to detect color while cones detect color well.
This is why at night both humans and cats see less color. The cat has a lot of these super-light sensitive rods and less of the other type of cell, the cones. This is the first reason why cats can see so well at night.
The second reason is that behind the photoreceptors is a mirror-like “film” which boosts the received light by reflecting it back into the retina. People can see the presence of this mirror when taking a flash photo of a cat at night if the cat is facing the camera with eyes wide open. The flashlight goes into the eye and is reflected straight back out to create that famous green glowing eye that is often so bright.
In humans “red eye” is something similar but the red color is not caused by a mirror but by blood vessels feeding the nerves and photoreceptors.
So what does a cat see in the dark with these wonderfully sensitive eyes? The image the top of the page is what I believe they see compared to us. See some more examples in large format.
A trade off for super night vision is a lowered ability to see color, particularly red. However, a cat’s eyes are geared to detecting movement because movement equates to prey to be eaten.