NutriSource Blogs

How do dogs see?

November 17, 2020

Almost every dog owner in existence has had the same, singular question cross their mind at some point: What does my dog see? It’s a simple-enough question on the surface, but it turns out a dog’s sight is quite complex and different from that of humans. Understanding those differences can help us better understand why our canine companions do the quirky things they do.

Basics of Vision

In mammals, there are two basic structures in the retina that make seeing possible. These are called rods and cones, and they each handle a different aspect of vision. Rods are responsible for low-light vision and are especially light sensitive. Cones, on the other hand, are responsible for seeing color and need more light to work effectively.

Humans and dogs both have rods and cones in their eyes. However, they’re present in different amounts, and dogs are missing one type of cones entirely.

How Do We Study Dog Vision?

There are unique challenges to trying to study animal vision. They cannot tell us anything directly, and we can’t look through their eyes to see for ourselves. However, some clever experiments have been developed over the years that can overcome the dog-to-human language barrier.

These experiments have largely focused on answering four key questions about dog vision.

  • What colors can dogs see?
  • Are dogs nearsighted?
  • What do dogs see at night?
  • How do dogs see human faces?

To get at the answers to these questions, researchers will ask dogs to perform various tasks. For example, one experiment had dogs look at three blocks of color on a touch screen. Two were the same color but the third was different. Dogs were trained to touch the color that was different in order to receive a treat (no word on if they kept to healthy treat limits, but a little overindulgence may be worth it for science).

What Does the Research Tell Us?

Thanks to the hard work of dog-loving scientists, we can now say with pretty high certainty what and how a dog sees. Of course, there is always a chance that new research will change our understanding. After all, it wasn’t too long ago that people widely believed that dogs only saw in black and white.

How dogs see color

That black and white vision myth persisted because dogs do, in fact, see less color than humans. This is because they have fewer types of color-sensing cones in their eyes — two instead of three. However, there are still plenty of colors that can be perceived with just two types of cones.

A dog’s vision is similar to a human who has red-green colorblindness, meaning they cannot pick out red and green. Researchers found that when they showed a dog two red blocks and one green on the touchscreen, they only picked the green one correctly one third of the time. In other words, they appeared to be guessing randomly. However, when blue and yellow were used instead, the dogs almost always got the answer right[1].

There are a lot of theories about why some animals can see red and green and others do not. For dogs, many suspect it has to do with the behavior of their ancestors. When hunting at night, seeing in full color just isn’t that important.

How dogs see details

To test nearsightedness in dogs, one experiment had canine participants look at two patterns side by side. One was made up of black and white vertical stripes, while the other one was uniformly gray. If the dog identified the striped pattern, once again they received a treat. As the test progressed, the width of the stripes got narrower and narrower. Eventually, the striped pattern blurred together, and the dog could only see two identical solid gray patterns.

Scientists took the width measurement at which the stripes disappeared for a dog and converted that into the conventional 20/20 visual acuity scale. Dogs received a final acuity result of around 20/75. That means a dog sees at 20 feet what a person with healthy vision would see at a full 75 feet away. In other words, dogs are extremely nearsighted[2].

Once again, evolution for hunting at night seems to be the explanation behind this. A reflective membrane, called the tapetum, enhances the amount of light that reaches a dog’s eyes. However, it also causes some of that light to scatter, making their eyes less able to focus on fine detail.

How dogs see at night

It’s more than just the tapetum that enhances dog vision at night. Compared to humans, dogs have more rods in their eyes, which allow them to see in far dimmer conditions than we ever could.

Dogs also have larger pupils than humans. Pupils dilate automatically to control the amount of light admitted. When it’s dark, human pupils will dilate as wide as possible to admit any light that’s available. Dogs’ pupils do the same thing. However, their widest possible dilation is much greater.

These adaptations make dogs incredibly skilled at tracking movement in low light. By sacrificing some colors and fine details, they’re able to catch sight of rustling prey by just the light of a waning moon. It was an effective trade-off, allowing their wolf-like ancestors to better survive in the wild.

How dogs see human faces

Putting aside all the interesting bits of dog biology and eyeball mechanics, there’s one more facet of fascination that people have always had with their dogs. How do they recognize people? More importantly, how do they see a person’s face?

Generally speaking, dogs are good at learning human faces. They can even read your emotions in your facial expressions. This includes when it’s just the face, with no scent or sound clues to aid in identification. When asked to pick out a specific face on a screen, most dogs were able to nail the task.

Seeing the whole face is best for dogs. They appear to recognize the configuration of the eyes, nose and mouth together. However, when faces were broken down into just one component, dogs were best at discriminating between pairs of eyes[3]. Which makes sense when you consider some dogs can learn to take direction just from where a person points their gaze.

Maintaining Healthy Vision in Dogs

While dogs have excellent smell and hearing, their eyes are clearly also vital to living a normal life. Supporting healthy vision in a dog often comes down to simply providing them a nutritious diet.

If you’re looking for a safe snack, consider carrots. Just like how they help human eyes, carrots can help our dogs’ eyes as well. They are a great source of beta-carotene, provitamin A, vitamins B, C, D, E, K and many other micronutrients.

Other important nutrients for vision are omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Food that features cold water fish is a great way to ensure there is abundant EPA and DHA in your dog’s diet.

All of NutriSource’s recipes include ingredients that are beneficial for your dog’s eyes. It’s part of ensuring your dog’s food is the best they can eat for health and nutrition. You can find NutriSource dog foods at your local, independent pet store.