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From a Dogs perspective
 
Dogs, animals that once roamed the jungles and still do, are efficient predatory animals. They have acute sense of smell and hearing... and how about sight? A dog can see things in the dark but is unable to differentiate colors. Yet there are dogs who work as a pair of eyes for the blind. How do they know when the light is green so that they can safely lead their owners across the street? It is a known fact that a dog sees differently than we do, but just how different?
 
The differences begin with the structure of the eye. The retina, which covers the back of the inside of the eyeball, contains cones and rods-two types of light-sensitive cells. Cones provide color perception and detailed sight, while rods detect motion and vision in dim light. The retinas of a dog are rod-dominated and hence they can see better in the dark than humans do and have motion-oriented vision. However, because they have only about one-tenth the concentration of cones that humans have, dogs do not see colors as humans do. However, dogs can pick out two colors-blue-violet and yellow-and they can differentiate among shades of gray. Dogs are unable to distinguish among green, yellow, orange, and red. They also have difficulty differentiating greens and grays. So when a seeing dog helps his blind owner cross the street, he relies on at the brightness and position of the light not the color. This and the flow and noise of traffic to will tell the dog that it is the right time to cross the street.
 
The second difference between human eyes and that of dogs is the setting of the eyes. We have eyes that are set straight forward while dog eyes, depending on the breed, are usually set at a 20 degree angle. This angle increases the field of view and therefore the peripheral vision of the dog. However, this increased peripheral vision compromises the amount of binocular vision. Where the field of view of each eye overlaps, we have binocular vision, which gives us depth perception. The wider-set eyes of dogs have less overlap and less binocular vision. Dogs' depth perception is best when they look straight ahead, but is blocked by their noses at certain angles. Although the area of binocular depth perception available to our dogs is smaller than that available to us, it is obvious to all of us with hunting retrievers that they can clearly judge distances very well.
 
In addition to having less binocular vision than humans, dogs also have less visual sharpness. Humans with perfect eyesight are said to have 20/20 vision-we can distinguish letters or objects at a distance of 20 feet. Dogs typically have 20/75 vision-they must be 20 feet from an object to see it as well as a human standing 75 feet away. So an object a human can see clearly may appear to be blurred to a dog looking at it from the same distance. However, certain breeds like the Labrador have been bred for better eyesight and may have closer to 20/20 vision.
 
Although the canine visual system may be considered inferior to the human visual system in such aspects as degree of binocular overlap, color perception, accommodative range, and visual acuity, the canine visual system is superior to the human visual system in other aspects, such as functional ability in low light conditions, field of view, ability to differentiate shades of gray, and possibly the ability to detect motion.

 
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