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How well can dogs see?:
Dogs can see color, but not nearly as well as we can. The reason is
because the dog's eye has considerably smaller ratio of cones to rods
in their retinas. Cones enable color vision; rods are useful for
black and white vision in dim light.
Dogs, therefore, can see far better in dim light than we can. This
makes sense because dogs originated from animals that hunted in the
dawn and dusk when there is little light and it is important
to make the most of what light there is.
The dog's eye also possesses a light-reflecting layer called the
tapetum lucidum that acts as an image-intensifying device.
This reflection makes an object seen in dim light more clear. And
the tapetum lucidum also causes dogs eyes to shine in the dark.
Dogs perceive motion better than we do, but see detail less. If an
object is far off and is stationary, it will be nearly invisible to
a dog; tests have shown that a dog cannot see its owner when the owner
stands a mere 300 yards away, but is not moving. However, a dog can
easily detect someone a mile away waving his arms! Again, the dog's
vision is a result of its ancestry as a hunter that needs to track
fleeing prey.
Finally, dogs have a wider field of view than humans do. A greyhound
has a visual range of 270 degrees. Typical dogs have about 250
degrees. Humans have only 180 degrees.
Source: Illustrated Dogwatching, by
Desmond Morris, Crescent Books, New York, 1996, p. 84.
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