In total darkness, they see almost nothing, but they are able to see in very little light – equivalent to somewhere between 40% and 50% more than us humans. There’s more than one reason for this. The first is that their eyes have a reflective structure – called the tapetal region – which causes a double stimulation of the receptors responsible for perceiving colors and shapes: the cones and rods (which felines, moreover, have three times more than humans ). “The reflection of this mirrored layer is what produces that greenish glow that we see in cats’ eyes at night”, says veterinarian Paulo Sérgio Moraes de Barros, from USP. (The same principle is used in road signs, named, with all propriety, cat’s eyes!)
In addition, the cat’s pupil dilates three times more than the human’s, allowing the maximum entry of light right at the moments when these animals go out hunting: dawn and dusk. On the other hand, when exposed to the sun, the pupil is reduced to a minimum slit, counterbalancing this hypersensitivity to light. Thus, during the day, the eyesight of cats is not as good as that of their owners. They do not distinguish colors well and do not see well from afar.
Behind the retina, felines have a layer of cells called the tapetal region, capable of reflecting light rays. Thus, the light that has already stimulated the retina passes through it again, reinforcing your vision.