Today we will talk about how dog see. Many people believe that dogs do not see as well as humans, but is it really so? Let’s first dive into the physiology of a dog’s eyes.
Just like humans a dog’s eyes consists of the cornea and lense in the front of the eye. The cornea and lense break down the light and bring it to the retina, found in the very 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 photoreceptors of the eye. The cones are used during day time to visualize colors while the rods are used during nighttime.
Humans have 3 different types of cones, enabling them to see red, green and blue (Trichromatic), while dogs only have 2 types, enabling them to see only green and blue (Dichromatic). The rest of the colors 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 also 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, so in this case the myth holds true. However, researchers have now found that this holds true only for dogs with a long snout but that breeds with short snouts (brachycephalic), such as the pug, has a more round visual streak, very 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 and they are able to see details further away than breeds with long snouts.
But the rods in the ganglion cells are not only used for visual detail resolution, they are also used for night vision and 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, making the eye more light-sensitive as it increases the light received by the photoreceptors. Although the image received might be slightly blurred, dogs will still see better in the dark then any human.
But interestingly dogs also exceed humans when it comes to perceiving speed. This is due to them having a greater temporal resolution, meaning that they are able to notice shorter durations 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, which 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°.
But what does all this mean?
Dogs use their vision mainly during hunting and during interactions with conspecifics and humans and so through evolution has adapted to do just that. They cannot see colors as well as us, and 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 color cues. Whether it is dark or light doesn’t really matter for 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 behavior. 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 dogs do not see as well as us is not valid as it certainly depends on what you are comparing.
Until next week, and I apologize for the delay of this week’s post!