When it comes to vision, humans are considered to have pretty good eyesight when compared to other terrestrial mammals. It's well-known that other animals, like birds of prey, have much better eyesight than humans - but what about our canine companions? You've probably heard that dog eyesight is poor, and maybe you've also heard that they only see in black and white. You might have questioned your dog's visual capabilities if you tossed a treat for them to catch and it hit them in the face instead. But what does science say about how well can dogs actually see?
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A dog's eyes
Though canine eyes have a design that is relatively similar to that of human eyes, there are some key differences that determine certain facets of their vision.
As a human, vision is your dominant sense, meaning that the primary way you absorb information is through your eyes. While dogs do rely on visual stimuli for information, their dominant sense is smell, followed closely by hearing, with eyesight coming in third. Dogs' brains are wired to support their strong sense of smell. Their olfactory bulb (the part of the brain responsible for processing scents) is 40 times larger than humans'. With eyesight taking a backseat to smell, dogs' brains contain a smaller number of neurons dedicated to processing visual information.
Both human and dog eyes contain a retina, which is the light-sensitive portion of the eye located in the back and inside the eyeball. The retina contains two kinds of photoreceptors (light-sensitive cells) called rods and cones. Rods provide vision and motion detection capabilities in dim light, while cones determine color perception and detailed vision in bright light. Compared to humans, dogs' retinas are rod-dominated, meaning they have better night vision than we do. When it comes to cones, human retinas are trichromatic and contain three types (blue, green, and red) while dog retinas are dichromatic and contain only two types (blue and yellow).
How do dogs see color?
Contrary to popular belief, dogs do not see the world in black and white. Their vision is actually most similar to that of a color-blind human. Color blindness is caused by a deficiency of one or more types of cones in an individual's eyes and causes them to be unable to distinguish between certain colors, depending on which cones are deficient. Since dogs have only two types of cones, their color perception is much more limited than humans'. Dogs are able to see shades of blue-violet and yellow and can also differentiate between shades of gray, but they are unable to see shades of green, orange, and red. Sunsets and rainbows would generally appear pretty unimpressive when viewed by a pup.
Dogs' field of vision
Dogs are very near-sighted compared to humans. Testing puts them at about 20/75 vision, meaning that what a human could barely see at a 75-foot distance is what a dog can just about make out at 20 feet. The way dogs' eyes are positioned in their heads also determines how well they can see. Both humans and dogs have eyes that are set close together, but while humans' eyes are forward-facing dogs' are set at about a 20-degree angle (though this angle can vary slightly across different breeds). This angle widens their field of view and therefore increases their peripheral vision. This increase in peripheral vision means that their binocular vision (where the field of view of each eye overlaps) is lacking, and in an adorable twist of fate, their long snouts also get in the way! This in turn reduces their depth perception and they cannot judge distances as accurately as humans can.
If you're curious to see some examples of dog vision, check out this fascinating set of photos that show how different scenes would look to a human versus a dog. The photos are run through a series of filters that remove colors dogs cannot see and alter other shades to reflect how they would be perceived by dogs, in addition to showing the differences of depth perception and sharp focus between humans and pups.
To sum it all up: dogs' eyes contain more rods than human eyes, making them superior at seeing in dim light. Dogs' eyes contain fewer cones than human eyes, meaning they don't perceive as many colors nor do they see in as great of detail. Dogs have better peripheral vision than humans, but they are near-sighted and their depth perception and binocular vision are lacking. Recent advances in science and research have shown that dogs have better vision than people had previously thought for decades. Dogs' eyesight is certainly different than humans', but as an animal whose dominant sense is smell, their brains have evolved to favor their noses over their eyes.