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Cats can see in almost complete darkness. The secret is the structure of their eyes.
Cats are master hunters, even in the dark. But how do they do that? And is it actually true that cats are colourblind? We will explain how cats see the world and how their eyes are constructed. We will also give you tips should you have a cat with poor vision at home.
Known as rods, the sensory cells located in the retina are responsible for perceiving brightness. Light that enters through the pupil stimulates these rods. The more rods that are stimulated, the stronger the perception of brightness in the brain.
But why do cats see so much better in the dark than us humans? On the one hand, the eyes of cats have far more rods than the eyes of their owners, therefore they specialise in light-dark vision.
On the other hand, cats’ eyes have another structure that supports nighttime vision. This is known is tapetum lucidum (Latin for bright tapestry). This is usually a crescent-shaped structure found in the eye’s choroid. Not just cats have this, but dogs and cows too.
The tapetum lucidum consists of many small, crystal-like shapes that reflect incident light like a mirror. This in turn intensifies the stimulation of the rods. Hence, cats are able to see something even when there is hardly any light.
Take a look at your cat during its next nighttime stroll: if the moonlight or light from a streetlamp properly enters its eyes, you can perceive this structure as a yellowish or blue-green glowing layer.
However, even cats’ eyes are overwhelmed in complete darkness and in this case cats have to orient themselves differently, but they have another pronounced sense for this purpose.
It’s unbelievable how quickly cats can react to moving objects. Whilst people mostly struggle to catch flies, cats can catch them with just one attempt.
The rods in the retina of cats’ eyes are also the reason for this. The amount of rods determines what is known as the flicker fusion frequency. This is the frequency from which repeated changes from light to dark are perceived as a blurred image.
Whilst human eyes can perceive around 10 to 60 stimuli per second, this frequency is much higher with cats’ eyes. This is how humans see a neon tube as a uniform shining lamp, whilst cats perceive the light as flickers.
Cats can see very well in the dark, although their ability to perceive colours is less pronounced. The number of sensory cells specialising in colours (pins) is much lower than the number of rods reacting to brightness.
Cats’ dichromatic eyes (in Latin di = two and chroma = colour) can distinguish between yellow and blue without problems. The perception of red or green is more difficult, although this isn’t an issue for cats in day-to-day life.
In comparison, the six million pins in our retina are able to perceive primary colours like red, blue and green. By stimulating different types of pins, we can also perceive mixed colours like lilac, orange or turquoise.
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In order to better understand the physiology of cats’ eyes, it’s very helpful to take a closer look at the anatomy. Since it is a very complex organ, the eye is divided into three different layers:
The white sclera and cornea together form the outer eye layer. Both structures give the eye its required shape. In addition, the curved cornea contributes to the eye’s refractive power. This is hugely important for the cat’s ability to see.
The middle eye layer is known as the uvea (in Latin uva = grape). It is made up of the iris, ciliary body, vitreous body (Corpus vitreum) and choroid (Chorioidea).
The iris is by far the best-known chromophoric structure. Its many muscular fibres also contribute to the widening of the pupil (accommodation). When the muscles tense, the pupil opens. When they relax, the pupil contracts again. This allows the incidence of light into the eye to be controlled.
The ciliary body is responsible for the suspension of the lens and adjusting the refractive power. It is also where aqueous fluid is produced. It determines intraocular pressure and provides the eye with vital nutrients. The choroid is heavily pigmented with strong blood circulation and likewise plays an important role in providing the different ocular structures with nutrients.
The inner ocular layer is formed of the retina and optic nerve. The retina behind the vitreous body consists of a multitude of different sensory cells, including the rods and pins that specialise in perceiving colour and brightness. If they are stimulated by sudden light incidence, the stimulation is transmitted via the optic nerve to the visual cortex, where it is processed as a perception.
There are numerous ocular diseases that can lead to blindness in cats. These include, for instance, glaucoma, which permanently damages the optic nerve due to an increase in intraocular pressure. Injuries or tumourous changes can lead to a cat’s vision deteriorating.
The first signs of a cat going blind are it stumbling on things or walking into walls. However, owners can also detect disorientation by their cat staying in one spot for a long time or moving with particular caution.
Although cats can still rely on their good sense of smell and hearing, you should definitely take your cat to the vet as soon as you identify such symptoms. It’s also recommended to support your cat with the following measures:
At the Justus-Liebig-University of Giessen I was extensively trained as a veterinarian and was able to gain experience in various fields such as small animal, large animal and exotic animal medicine as well as pharmacology, pathology and food hygiene. Since then, I have been working not only as a veterinary author, but also on my scientifically driven dissertation. My goal is to better protect animals from pathogenic bacterial organisms in the future. Besides my veterinary knowledge, I also share my own experiences as a happy dog owner and can thus understand and enlighten fears and problems as well as other important questions about animal health.
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