Time for a bit of an eye opener of a lesson! It has become a human peeve of mine to hear all about how us dogs have such terrible vision. Most of you tall, fur-less, folk like to think of us as having the same eyesight as you do. I can live with that I suppose... ignorance is bliss. However, another group of you seem to enjoy calling us color-blind while making fun of our inability to see fine detail.
Wake up call! A dog's vision is different from a human's in every way. Yup, that's right, different, not worse! Our vision has a special purpose and it has evolved perfectly to fit that goal. So sit back and open your eyes to the truth about ours!
Dogs perceive color using a very different spectrum to that of a human. (The spectrum is the way that our eyes see color) We do not see rich and vibrant colors like a human because we don't need to. We have difficulty seeing the difference between warm colors like red, orange, and yellow. Also because we don't need to... in nature, how many things do you see that are bright red or orange? The odd butterfly? Not really a danger to us.
In order to make it easier for you to understand I have got some pictures for you that I had my human make for me. What you see below is an image of both the human and dog color spectrum.
You will notice that we cannot tell the difference between yellow, red, and orange but can see a muted transition between the other colors of the spectrum. To us, bright green appears completely white and purple appears to be gray. In order to help you small nosed types really get the picture, here is one where the human version of the color is on the left and the dog version of the color is on the right.
Next we come to visual acuteness. Visual acuteness is how detailed things are when we look at them. You humans need very acute vision, you look at computer screens and read those wee little words all the time. We dogs, do not, we can easily understand what is going on without having to see every tiny detail which often can be distracting.
In comparison to an ideal human a dog's vision is very nearsighted. When compared to the vision of a two legged with 20/20 vision the average dog would have 20/50 or 20/100. To make this easy for you I have another nice chart comparing what a few black lines would look like to one of us fuzzy folk.
As you can see, those lines look to be a line of gray or more simply the lines are very blurry. I guess you people have the advantage in this regard.
In order to really pound the reality of what I have said to you so far I have created 3 images of a plaything you fur-impaired really seem to hate. You always continually throw it far away. (It is so much fun to bring it back to you!) In the pictures below are 3 different colored balls on some summer grass.
As you can plainly see we would have the greatest difficulty in seeing the red ball but would easily be able to pick out the blue one. So, yes, this is a bit of a learning opportunity... Stop buying red balls to play fetch with! We can't see them on grass so cut it out! It is damn annoying! Especially when you make fun of us by joking about how we should be able to see bright red against the yellowish-green of grass! That would be like us laughing at you because you can't smell someone that is several blocks away!
Field of Vision
Next comes our field of vision which is how much we can see without having to turn our head. Guess what? In this particular comparison we win! Yup, in the more important survival trait of being able to see what is sneaking up from behind you humans sorely lose. Humans have a field of vision of 180° in front of them where as we superior dog types have between 240° and 250°. Again, I have provided another picture. The red area represents the human's vision and the blue AND red combined represents the dog's field of vision.
So what happens when the light goes out? Have you ever noticed that unlike humans, the eyes of dogs and cats can sometimes seem to glow in the dark? This is caused by something called the tapetum lucidum which is a layer of cells that reflects light within our eyes allowing us to better see in dim light. While we don't come close to rivaling our feline cousins in night vision we easily surpass humans in our ability to see stuff at night.
However, like humans, our vision does get worse in the dark. In the middle of the night we do become completely colorblind which is quite a bit better than you toilet flushers who just go totally blind!
What? Ya... funky word... don't worry it isn't as complicated as it sounds. Spatial Acuity is just how easily an eye can detect movement. In order for a human to detect movement there must be a change of between 10 and 20 diopters where as a dog only requires change in a single diopter of space. A diopter is a unit used when measuring lenses. (please take my word for it, I don't feel like explaining exactly what a diopter is)
To put it in very plain English for you less scientific folk: Dogs can detect movement that is 10-20 times more subtle than you can!
As you probably very much agree, dogs and humans have very different eyes both designed to serve very different goals. We of the furry brethren have eyes that are much better suited to surviving and thriving in the wild while you humans are better at seeing pretty pictures.
OK... so maybe we win, our vision is actually useful... What do you think? Any Questions?
- Dog Behaviour, Evolution, and Cognition, Adam Miklosi, 2009
- Wolves; Behavior, Ecology, and Conservation, David Mech and Luigi Boitani, 2006
- Dr. P's Dog Training: Vision in Dogs & People.