If dogs wore glasses, they'd all have bifocals that were as thick as Coke bottles! They can see fairly well at a distance, but reading would be beyond them (if they could read of course). Most dogs can't focus at all on objects closer than 1 1/2 feet away. That's why a seemingly smart, highly sensitive dog can lose a rubber cheeseburger that's lying directly under his nose.

The reason for this canine farsightedness lies in their paws: Dogs don't have opposable thumbs the way people do. They don't need to be able to closely examine things at an arm's length. As they've evolved, they've needed to be able to catch sight of prey at a distance and keep it in view while they try to run it down. Objects that are just a paw's length away aren't likely to get up and run away, and dogs don't need to see them clearly.

Even if dogs had 20/20 vision, they might not bother looking at things close-up. A large portion of a dog's brain is devoted to processing smells. They depend on smell far more than their other senses, including sight. A dog who is frantically searching for a toy that he knows was right there a minute ago isn't using his eyes very much. All of that head turning and body positioning is an attempt to pull in scent molecules from all directions. It's his sense of smell, not his eyes, that will lead him to the prize. Finding things by smell probably isn't as fast as seeing them clearly, but in the long run, it's just as accurate.

Blurry vision isn't the only reason dogs lose things that are right in front of them. Unlike people, they have a small (or not so small, depending on the breed) anatomical disadvantage: a very big nose. It's rather like a blind spot in the car - they just can't see around it. The bigger the nose, the bigger the blind spot.

Once again, this wasn't a disadvantage in the evolutionary scheme of things. Dogs who hunted needed to know what was happening off to the sides and far in front of them. Their eyes are set far apart, which allows them to see an area that encompasses 240 degrees. (Humans, by contrast, can see about 180 degrees.) A tennis ball may disappear when it's right under a dog's nose, but he'll spot it in an instant when it's off to the side.

Dogs see moving things even better. Their eyes are exquisitely sensitive to motion, whether from a rabbit rustling the bushes or a tennis ball rolling across the lawn. Things that are motionless, however, might as well not even be there. Dogs just can't see them as easily.