Because they see in the dark?

The cats cannot see in the total dark, but they have one better visual perception in the penumbra that the human being or other animals. This ability is due to special the ocular anatomy of the cat.

In relation to the size of its head, the cat has the great eyes extremely. The surface of the eye (the cornea) is very curved (convex) what the greater penetration of possible light allows.
The cat can open its rainbow (the colored portion of its eye) very widely to allow a greater entrance of light.
When the luminosity is intense can be observed that the pupil is a fine line, because is contracted by the excess of light, the pupil will be dilated as the luminosity diminishes, dilating to the maximum in the penumbra to then allow the entrance of the little existing light, but with that small amount of light and the anatomical characteristics of his ocular apparatus it will allow him to form the image in his retina and to see in the penumbra.

The retina of an animal (the part of back of the eye where the image forms) is in favor compound mainly of two types of sensible cells to the light called canes and cones. The canes are responsible to harness the small luminance stimuli. The cat has a great number of canes. In relation to the humans, these have by each 5 photosensitive cells, 4 are canes, in the same surface that in the man the relation in the cat is of 25 canes to 26 photosensitive cells in its retina.

The cats also have a developed reflective area in the part of back of their eyes called tapetum lucidum, this one is what causes that their eyes ?shine at night? when they are focused by the lights of an automobile.

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