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Is the myth that humans see better than dogs really true? Many people believe that dogs do not see as well as humans, but is it really so or is there more behind your dog’s cute puppy eyes then what you think? Let’s dive into the physiology of a dog’s eyes and how a dog’s vision can affect their behaviour.
Physiology behind a dog’s vision
Just like humans, a dog’s eyes consists of the cornea and lens. The cornea and lens breaks down the light and brings it to the retina, found in the back of the eye. The retina is the home for the cones and rods, as well as the ganglion cells.
The rod and cones are the photo receptors of the eye. The cones are used during day time to visualize colours while the rods are used during night time.
Humans have 3 different types of cones, enabling them to see red, green and blue (Trichromatic). Dogs only have 2 types, enabling them to only see green and blue (Dichromatic). The rest of the colours that we humans see are perceived as different grey nuances for a dog.
In front of the cones and rods in the retina we find the ganglion cells. Ganglion cells are the decision makers for the resolution in the eye and contains a wide distribution of rods. If many rods attach to one ganglion cell you get a very broad resolution. Whereas if only one rod attach to one ganglion cell you get a more specific resolution.
Humans have a round formation of ganglion cells in their eyes, causing them to be able to see more details from a greater distance. Dog’s, on the other hand, have a more elongated visual streak causing them to have 3-4 times worse visual acuity than humans.
The myth for visual acuity therefor holds true, as humans do have better detail vision then dogs.
However, researchers have now found that this holds true only for dogs with a long snout. Breeds with short snouts (brachycephalic), such as the pug, has a more round visual streak. Similar to the ganglion formation found in the human eye.
This means that brachycephalic dogs has a detail resolution on the same level as humans. They are able to see details further away than breeds with long snouts (read more here about how the domestication of dogs has affected their physiology).
But the rods in the ganglion cells are not only used for visual detail resolution. They are also used for night vision.
Here, the myth seems to fail, as dogs excel humans when it comes to night vision. This is due to the little thing called tapetum lucidum (the thing that makes your dog’s eyes glow when you take a picture of them in the dark).
Tapetum lucidum is a small tissue layer found right behind the retina. The tapetum lucidum reflects visible light back through the retina. This makes the eye more light-sensitive, as it increases the light received by the photo receptors. Although the image received might be slightly blurred, dogs will still see better in the dark then any human.
But interestingly a dog’s vision also exceed human vision when it comes to perceiving speed. This is due to them having a greater temporal resolution. Meaning that they are able to notice shorter duration between two light flashes coming from the same light source.
An example might come in handy here. Say that you and your dog are watching TV. You are seeing continuous coherent pictures, but your dog sees all the empty black spots in between each picture. No wonder they give up after a while!
Their greater temporal resolution also makes them more sensitive to rapid movements in their environment. This is why they will typically have noticed the hare running over the field long before you even spot it. This is, of course, also helped by their wider visual field found to be up to 250° compared to humans only reaching c. 180°.
Does the myth hold true?
Dogs use their vision mainly during hunting and during interactions with con-specifics and humans. Their vision has adapted during the time of evolution to adapt to those needs. They cannot see colours as well as humans. That nice orange cone in the green grass is a plain grey nuance for them.
They don’t care much about patterns, and due to their greater temporal resolution TV doesn’t work for them, as the images simply moves too slow.
Dogs can learn to differentiate between different patterns but prefer to rely on colour cues. Whether it is dark or light doesn’t really matter to them, but if something moves in the distance they will catch sight of it faster than you. Of course also due to their advantage of having a wider visual field.
By understanding how your dog works physically you automatically get a better understanding of his/her behaviour. You might be able to improve your training methods, or simply increase your understanding as to how a dog perceives the world.
Finally, as you might have guessed from the above, the myth that a dog’s vision should not be as good as human vision is not valid, as it certainly depends on what you are comparing.