A Dogs Vision of His World
Did you ever wonder how your dog can navigate the back yard so well at night, but can't find the toy you just tossed right under his nose?
Dogs see the world from a different visual perspective than we do. Their vision is comparable to what we see at dusk. A dog's eye structure, while similar to humans, has its differences. The retina is why we see what we do. The retina contains two types of cells; rods and cones. While the rods detect motion and vision in dim light. Dogs have rod-dominated retinas that allow them to see well in the dark, they have superior night vision. Another useful difference it the layer of eye tissue called the tapetum lucidum, which reflects light into the retina. This boosts dog vision even more and why dogs' eyes shine in the dark.
Now, back to those cones. a dogs' retina contains
one-tenth of the number of cones that are present in the human eye. This prevents the dog from seeing colors the same as most humans. I say most, because a color-blind human may have a variation in the form of color-blindness; Trichromatic (3-color), or Dichromatic (2-color). Dog's vision is similar to the Dichromatic color-blindness in humans. A dichromatic human sees Red/Green colors, while a dog sees blue-violet and yellow, and can differentiate shades of gray. Dogs do not recognize orange, red, or green.
So, those dog toys that you were visually drawn to in the store, may have no appeal to your dog at all. In fact, your dog may not even be capable of visually distinguishing them from the grass.
That Red/Green deficiency brings up another question; how do seeing-eye dogs do their job? Such as assisting their human crossing the street at traffic lights. Dogs are trained to use their other senses. Rather than relying on color, they use smell, texture, brightness, and position. At the traffic light, they look for the brightness and position of the light. This along with the flow and traffic noise, clue them in on the safety of crossing at that time.
The set position of a dogs' eyes determines the field of vision and depth of perception. Humans and dogs have eyes that are set close together. Humans are positioned straight forward and most dogs' are set at a 20-degree angle. This angle increases the field of view and the peripheral vision for the dog.
Peripheral vision is comprised of binocular vision; the field where each eye vision overlaps. Binocular vision is necessary for depth perception. The wider set of the dogs' eyes cause them to have less depth perception. A dog's perception is best when they are looking straight ahead, but is hindered by their nose.
A dog's visual acuity is also less than a human. A human with 20/20 vision can distinguish letters or objects at a distance of 20 feet away. A dog typically has 20/75 vision, they must be 75 feet from an object to see the same as their human counterpart. There are exceptions, such as the Labrador Retriever, which are bred for better eyesight and have vision more closely resembling that of the humans' 20/20. Your dog cannot visually recognize you standing silently across a field until you display a familiar motion, he catches a familiar scent or he hears your verbal command. That is just another difference in the vision of a human and a dog.
Dog trainers use many different training techniques, depending on the purpose of training. Hunting dogs are trained to pick up on visual, verbal, or a combination of cues. For silent cue training, it is recommended that wide-sweeping hand and arm motions be used so that the dog has a clearer understanding of the cue. If you have ever watched a field trial or agility dogs at work, this is a very apparent technique all for the visual concept of the dog.
Just like humans, dog's eyes have problems too. As your dog ages, his eyesight changes. Dogs' nearsighted vision declines in middle age, making it difficult to catch a tossed treat, navigation of the stairs may become more difficult. Cataracts are a common disease among aging dogs, causing cloudiness of the lens and often lead to blindness. When dogs become blind, owners often wonder if their quality of life has diminished. Humans are more reliant on vision than dogs. Blind dogs can lead a comfortable happy life. Some environmental changes may need to be made such as fencing the yard, using leashes on walks, keeping pathways clear of stray objects, and limiting the need for stair navigation.
When dogs are in their home environment, most people don't know they are blind.
So that is just a small lesson on how our dogs see the world. How they can see that armadillos digging up the back yard when we see nothing. Why they prefer the multi-colored toy over the red ball. Why they turn their heads when looking at things. Why they sniff the air before heading off in a particular direction. Dogs use all their senses, not just the visual.