The entire structure of cats’ beautiful and unique eyes helps enhance their ability to see in the dark — from the shape and size of their pupils to their glowing irises.
If you’ve ever wondered why a cat’s pupil can look like a vertical line during the day, but expand to saucer-sized proportions at night, it’s all to do with the amount of light the cat needs in order to see. “In the light, the cat's vertical pupil allows different amounts of light through different areas of the lens as it constricts to help them focus,” Proietto explains. “In the dark, however, their vertical pupil actually dilates to be round like ours. While this makes vision more blurry, it allows for more light to enter the eye.”
A domestic cat’s dilated pupil can be 135 to 300 times the size of its constricted state, according to a study out of the University of California, Berkeley, whereas a human’s circular pupil can only undergo a 15-fold change in area — in short, cats’ pupils can get much bigger than humans’, letting in more light.