How is the vision of a cat?
Cats have their eyes in the same frontal plane as all predators, which gives them binocular vision, as it happens to us humans.
Each eye, by itself, creates a 2D image, which in the brain, when combined with the image of the other eye, forms the three-dimensional image, thus being able to have depth perception. What is called stereoscopic vision . This type of vision is essential for hunting.
However, cats do not have good short-distance vision. They can see any object from 25 cm away and perfectly between 2 and 6 m. While closer, they are not able to see well.
For this reason, you may see that your cat puts his paw in the drinking fountain to touch the water before drinking, or when he goes to play with a stuffed animal up close, it seems that he does not finish seeing it very well.
The exception would be Siamese cats, which have fewer nerve fibers going to the brain, which makes their stereoscopic vision worse. That is why we see strabismic Siamese cats. This strabismus allows them to converge the two images and try to improve their vision.
What are the colors that cats see?
When light enters the eye, it travels a short path from the iris to the retina and stimulates receptors that will be responsible, through nerve fibers, for sending the necessary signals so that the images are formed in the brain. .
In cats, as in people, there are two types of receptors
- The Canes. They owe their name to their shape. In the cat, the density of this type of receptors in the retina is three times higher than in humans , and they are grouped together to improve their efficiency when sending the signal through the optic nerve. In cats the density can reach up to 460 x 10 3 /mm 3 , while in humans 160 x 10 3 /mm These receptors are responsible for the cat being able to see in low light , despite forming images in black and white, although grainier and less defined than in people.
- The cones , also named for their shape, are responsible for determining the colors and sharpness of images in high-light conditions.
Just as cats have a high density of rods in their retina, they have a low density of cones. For this reason, the colors that they are capable of perceiving will be more attenuated.
On the other hand, these cones are capable of perceiving two colors ( dichromatic vision ), blue and green, and their combinations. Contrary to people who have a trichromatic vision, being able to detect the three primary colors (blue, green and red) and their combinations.
This type of vision can be even traumatic for people, not being able to differentiate bright and different colors. But for the cat it is the most appropriate , being a hunter who lives between green and brown colors.
The prey is brown, moving over a green field, usually at night, in low light, which is when cats have better image quality. Being able to detect small movements, without the distraction of bright colors.
Why do cats see better at night?
The relationship of rods and cones in the retina of cats, among other things, is responsible for this type of improvement in vision. But they are not the only ones responsible.
If you shine a light on a cat at night, you will see that its eyes dazzle. This is not that they are diabolical beings that shoot rays through their eyes, as has been said in other times.
This glare is due to the Tapetum lucidum .
This Tapetum lucidum is a second layer that the retina presents, behind which are the rods and cones, which reflects light, allowing a second chance for this light to be absorbed by the receptors in low light situations. It is estimated that this mechanism allows up to 40% more light to be absorbed.
Finally, we must not forget the pupils . If we look at how the pupils dilate and contract, we can see that they can go from hyperdilated pupils ( up to 3 times the dilation of the human pupil ) to pupils that are almost non-existent and are just a thin vertical line.
This dilation and contraction capacity allows the amount of light that penetrates the eyes to be greater.
These adaptations allow the cat to see much better than people in the dark, needing up to a sixth less light than we do.
References:
Bradshaw, J. (2013). Cat sense: The feline enigma revealed. Penguin UK, pp 108 – 128.
Berkley, M. A., Warmath, D. S., & Tunkl, J. E. (1978). Movement discrimination capacities in the cat. Journal of comparative and physiological psychology, 92(3), 463.
Bradshaw, J. Cat communication – sight, sound and touch. Proceedings of the International Cat Care 2014, Sept 27th, Windsor, England, pp 7 – 9.
