Q: Can cats see in the dark?

Answer: Animals see because light enters the eye and stimulates the never ending of the light sensitive layer, the retina. These sensation are then transmitted along the never fibers of the optic never to the brain and there interpreted as a ‘picture’. If there is absolutely no light present, then the cat will be quite unable to see anything, simply because there will be no light entering the eye to stimulate the retinal never endings. So in total darkness the cat has no advantage over any other animal.

But in dim light, indeed sometimes do dim that to human eyes it may appear as complete darkness, the cat is much better able then ourselves to perceive objects, especially if they move. There are three main reasons for this:

1 In the retina there are two types of never ending which are named, according to there shape, as rods and cones. The cones are most strongly stimulated by bright light and these never endings are responsible for color vision in man and for the perception of fine details. The rods, on the other hand, are stimulated by light of lover intensity but are not capable of producing such sharp images.

Night vision, or more correctly, twilight vision, in all animals in due to the functioning of the rods. The eye of the cat contains a much higher proportion of rods to cones (approximately 20:1) then the human eye (approximately 4:1).

2 The cat, in common with many other domesticated animals but unlikely man, has a reflecting layer (tapetum lucidum) situated just behind the retina. The effect of this is the light lays which have entered the eye and penetrated the retina, thereby stimulating the never endings, are immediately reflected back onto exactly the same never endings. Consequently each ray of light produce double stimulation of a particular never ending giving o type of image intensification.

The presence of the tapetum also account for the typical cat’s eye’s effect when a beam of light. e.g. from car headlights, is shone in to the eyes in the dark. The light is reflected back from the greenish yellow tapetum so that the eyes appear to glow yellow or green in the dark.

3 In all animals the pupil of the eyes dilates in dim light and constrict in bright light in an attempt to keep the amount of light entering the eye constant at the level at which the eye works best. The pupil of the cat is able to dilate to a very considerable extent. When constricted in bright light, the cat’s pupil appears as a mere vertical slit, but when fully dilated in dim light, it is circular and can be almost half an inch in diameter. The of the cat large in relation to its body size anyway and this ability of the pupil to open so wide in dim light obviously permits much more light to enter the eye and to stimulate the roads.

The combined effect of these three factors in such that in poor lighting conditions the cat received much more visual information compared with a human. In fact it is able to detect objects and other animals with less then 2% of the minimum amount of light needed by the human eye.