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Cat sense organs: vision

When they say that somebody sees like cat, it's an affectation, because cat vision differs much from ours. Cat can see quite well at illumination 10 times lower than that, at which we are able to see. At the same time in the presence of good illumination cats discern details worse then we do. This is the peculiar feature of cat vision, as if cat vision is specialized on perception of environment in presence of faint light. That's why cats prefer shadowy rooms to have a rest and make their toilet. And of cause, some of them that like to chase mice have to do this in faint light, because their preys live crepuscular or nocturnal way of life. But cats, besides hunting have to make love at night too, as we can guess when hear bloodcurdling cries of male cats at spring.

Not long ago cats were considered to have no color vision and see surroundings as black-and-white, something like that what we see on a TV screen. However today it's ascertained that cats are nevertheless able to discern, though worse than humans, some colors. But what they discern much better than we do is tints of gray color - up to 25 of them.

The same peculiarity of cat vision may be explained by the coloring of their preys - mice and voles, whose fur color varies from light-gray to dark-gray and brownish-gray. Primates, including man, have never needed such distinguishing of gray tints, and therefore evolution hasn't provided them with this ability.

Watching a cat or a kitten, chasing a ball or a thread, one will easily establish that they much keenly react on horizontal movements of toy. Thus, a ball that you roll on the floor always stimulates a chasing activity in cat, whereas a ball that you move up-and-down in front of cat stimulates more inertly. This is a reflection of cat hunting instincts, because mice and voles move in horizontal plane solely, and also a reflection of cat vision. It is known that cat traces horizontal movements of objects in detail, in comparison to displacing of the same objects in vertical plane.

Since the main hunting method of cat is an ambush and a momentary and exact jump with opened sharp-clawed paws but not a pursuit, cat vision provides accomplishment of this task. Cats see a near-by space quite well, and objects at distance look slightly fuzzy for it. Both eyes are situated not very far from each other and are directed forward, forming an overlapping field of vision. A stereoscopic effect of binocular vision that appears due to this, make a kind of imposition of one image onto another, creating a three-dimensional representation of environment. A stereoscopic vision allows a cat to estimate location of its' pray more correctly and in accord its' future actions. At that it is important to notice that eyes of rodents, which are chased by cat, are situated at both sides of head and percept two independent pictures. At that they don't have a stereoscopic vision; on the other hand, their watch-space is twice increased in comparison to a cat. Due to this eyes location rodents are able to see their main enemy - cat - more easily.

In that way, we can see that many peculiar features of cat vision somehow or other are concerned to solving the main living task - getting food. Of cause, it was important before a cat has become domestic, and still it's essential for cats that live in the country. As for cats that live in comfortable flats, they don't have to chase mice almost at all. Nevertheless, their vision still keep all adaptation mechanisms, in the same way as cat behavior have kept some hunting instincts. That is why while playing with your cat on a fluffy carpet, don't forget that it is a predatory animal that possesses a good vision and a keen weapon - claws. But, of cause, all "ecologic" features of vision may display themselves only owing to a perfect perceptive apparatus consisting of eyes, optic nerves and centers inside a cerebral cortex. A cat eye is very complicated. Cat has big eyes compared to its' head, slightly convex. If a man has such big eyes (regarding his body size), they would by about 20 cm in diameter. An eyeball lies quite deep in an eye-socket, and so movements of cat eyes are restricted. To watch an object that is on the periphery of vision in detail a cat has to turn its' head. An eyeball is fixed and controlled by seven muscles.

Albuminous membrane forms a glassy cornea on the forward, outer part of eyeball, and opaque sclera on remaining part it. A pupil is situated in the center of iris which coloring is diverse and gives peculiar expressiveness to cat eyes. A pupil is stretched down and regulates light by changing its' shape under the influence of illumination or alternations of emotional condition, making cat eyes astonishingly attractive. Looking in them we feel the magic power and unwittingly think about cat intellect.

At the back of pupil lens lies, attached by ligament to a muscular cilia body. In front of pupil there is a front eye-cell, filled with watery moisture, between iris and lens there's a back eye-cell. The cavity of eyeball is filled with opaque body.

In the vascular membrane consisting of multiple blood vessels that nourish an eye, in the point where the optic nerve goes out there is a layer of cells with crystalline inclusions - mirror. In the deep of eyeball there's retina carrying visual cells - sticks and cones. Eyes of cat, for it is a crepuscular animal, are provided mainly with sticks, and only in the middle part of retina in the area of keen vision cones are concentrated.

Eyelids are lined with a mucous membrane that protect an eyeball. Unlike us, there is a third eyelid inside a cat eye that moves the lachrymal liquid on the eye and is an extra protection. By means of eyelids cats regulate incoming light that pass inside the eye. Cat eyes have more perceptive cells than eyes of small primates, the same thing is true for a number of neurons in visual centers of brain.

All this helps a cat catch moving preys in conditions of restricted visibility. But during life in a flat these devices are redundant and are not in full use, as if they are attached to a cat for no particular reason, just in case. But suppose they will become necessary.

Valeriy ILYICHEV, Doctor of Biology, professor
Translated by Tatiana Karpova (Moscow)
(MSU, Biology faculture, Dep. zoology and ecology).