Whether they are the mirror to the canine soul or not, dogs' eyes are worth attending to. They are an incredibly reliable part of a dog's body for ascertaining a dog's emotional state. As a professional behaviorist, I am always observing dogs for any clues about their emotional state or possible future behavior.
The eyes are one of the best places to go for this information. For example, dogs with dilated pupils are often fearful, unless of course low light levels offer another explanation for the eyes' appearance. The stereotypical frightened dog with eyes "wide as saucers" is a dog whose fear has resulted in dilated pupils. Another clue in the eyes of a dog who is afraid is when the dog is looking far to the side and the white part of the eye takes on a crescent shape.
When a dog turns his head away from you but his eyes are turned as far to the side as possible in your direction,the whites of his eyes take on that crescent shape. When a dog's eyes take on this appearance, professionals in the field refer to it as "whale eye." This visual sign is thought to occur because the dog is so afraid that he is not looking at you, but he's too afraid to take his gaze away from you entirely. The result is a dog who is looking at something with his eyes while not facing it. A dog who averts his gaze away from other individuals is often afraid as well.
There's a reason that the expression "puppy dog eyes" has positive connotations. Who doesn't like the soft warm look of a dog's eyes when they are relaxed, happy, and comfortable in their physical and social surroundings? Those eyes are generally recognized as friendly, and even loving.
In sharp contrast is the hard, cold, icy look that some dogs get. It is unknown what causes this harsh look, but most professional behaviorists associate this look with aggression, and my own observations seem to support the idea that dogs who exhibit this "hard eye" are more likely to bite than dogs who never get this look in their eye. If you have never seen this look, it can be hard to describe, other than to say that the dog's eyes get cold and icy looking, as though they are no longer a part of a living being. If you do see this look, you do not need to be told that the dog is not friendly, but rather, may be aggressive, because your body responds, even if your brain doesn?t process exactly what is happening. Even the first time a person sees a dog's eyes go hard, they usually get a nervous feeling in their stomach, or feel the hair on the back of their neck stand up. Dog expert or dog novice, a person seeing this visual signal is unlikely to feel comfortable approaching this dog or remaining in his presence.
An important thing to know about dog's eyes and their gazes is that dogs do not tend to look directly into the eyes of other individuals. In humans, this is a friendly and polite behavior, but in dogs it is rude and even threatening. Dogs can be taught to look at a person directly on cue, but it is not generally a natural behavior. Looking away with their head down is generally considered a deferential gesture, whereas looking away with the head turned up is used as a social signal that means the one performing this behavior is not currently available for social interaction. (For more information on look aways, review the August 20, 2007 blog entry.)
One last interesting note about dogs' eyes is that many old timers in the field of dog training think there is some truth to the saying, "Beware the dog with amber eyes." In my clinical practice with aggressive dogs, I have seen many dogs with amber eyes. Some, but not all, of them require caution, just like dogs with every other eye color. So, while I'm not convinced that there is any truth to the saying, I do always think of it whenever I meet a dog with amber eyes.