Cats are well known for being able to see in the dark, but have you ever wondered how they find their way around in darkness?
Cats’ eyes are specially adapted to twilight, the time when their rodent prey are most active. At the back of their eyes is a reflecting layer called a tapetum lucidum. It reflects any unabsorbed light back into the eye, allowing the cells in the retina a second chance of responding, thus making best use of any light available. The reflective flashback, when a cat’s eyes glow in a car’s headlights, comes from the tapetum. In low light, a cat sees three to eight times better than a human. In bright or moderate light, they see less well than we do.
Mammal eyes are made up of low light detector cells called rods, and colour detector cells called cones. Cats have many more rods than cones, so that while they can see in low light (though not in total darkness), they lose out in detecting colour. Whether they are totally colour-blind is still not known for sure, but if they do see colour at all, it is only very weakly. There is also a possibility that they, unlike humans, may be able to see ultra-violet light.
Another adaption in feline anatomy, to assist with twilight hunting, is that cats have relatively large eyes in relation to the size of their small faces, to take in as much light as possible.
They can also widen their pupils about three times more than a human, so as to allow as much light as possible on to the retina (the back of the eyeball that communicates the image to the brain).
In bright light, these pupils also diminish into a narrow slit less than one millimetre wide.