The muscles of a cat’s eyes are set to suit the environment in which the cat grows up in. This means that outdoor cats such as strays and feral cats have eyesight that is slightly longsighted. Long-sightedness means that objects far away are sharp whereas near objects are less sharp. Conversely, all indoor cats tend to be short-sighted meaning that they can focus better on near objects.
Despite this ability of indoor cats, domestic cats in general are unable to focus on anything less than about 12 inches away. This seems to be because of the size of the cat’s eyes, which are almost the same size as ours. They are, therefore, much larger in proportion to their overall size.
When cats eat they check at close range through smell. When hunting cats use their whiskers to compensate for a loss of close focus. You’ll see a cat push his/her whiskers forward when playing at close range near the face. Whiskers are super-sensitive and able to “feel” objects precisely.
Such large eyes are not easy to focus. Humans have muscles which change the shape of the eye’s lens whereas cats seem to move the whole lens back and forth much like a camera lens. This is a more cumbersome method of focusing.
Despite the large size of cats’ eyes they can track fast moving prey by swivelling them in a series of jerks which helps to avoid blurring of the image. This jerky movement is called saccades. Each jerk is about a quarter of a second apart. This allows the brain to process each image. It is rather like the modern digital camera which creates a panoramic image.
Cats are less interested in the colour of objects that they see than their shape, brightness, pattern and size. This is to do with adapting to hunting efficiency.
Cats have binocular vision like us. The signals from each eye is converted to a three dimensional image. Eyes that point forward are able to do this. This allows the cat to gauge the distance of prey making the attack more precise and successful. Despite having miswired neurons causing a squint Siamese cats still have binocular vision.
You can see cats maximising their binocular vision when making a difficult jump which requires a high level of precision. A cat will bob his head and in moving it in this way the eyes and brain build up a more precise image of the target object. Cats who have lost an eye will also do this in an exaggerated way because it allows the brain to gather information about the spatial relationship between the objects being viewed.
The domestic cat has a “movement detection” system. The cat’s brain compares the images constructed by eyes and brain, analysing the differences between one picture and the next. The visual cortex of the cat compares the images 60 times per second (faster than for us). Apparently this means that cats see a old television screen and fluorescent lights as flickering.
Specialist brain cells analyse movements in various directions which allows the domestic cat to isolate changes that occur rapidly. This too is all about hunting efficiency. The differences between our eyes and cat’s eyes are to do with hunting ability and survival.
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Photo by Patrick Feller except for the words.
Source: Cat Sense: The Feline Enigma Revealed.