When dogs look up at us imploringly with those big, soulful eyes, they are pretty irresistible. It’s easy to assume that what they see when they look at the world is the same as what we see. But actually, it isn’t.
Dogs see fewer colors than most humans (yellows and blues), recognize objects only at much shorter distances (perhaps why your own dog barks at you when you’re in the driveway), and their depth perception is poorer than ours (30-60 degrees compared to 140 degrees in humans). However, when it comes to seeing in the dark, dogs definitely have us beat.
The eyes of animals, including dogs’ eyes, function much like ours do, according to an article in the Merck Veterinary Manual. “The eye is an active organ that constantly adjusts the amount of light it lets in and focuses on objects near and far. It produces continuous images that are quickly relayed to the brain.”
- Visual perspective
- Field of view
- Depth perception
- Visual acuity (Dogs typically have 20/75 vision.)
- Perception of color and form
- Ability to perceive light and motion
The place to start to understand what dogs see in the dark is with our pets’ evolution from wild canines. Wild canines were crepuscular, derived from the Latin word for twilight, meaning they were active primarily at dusk and dawn. They needed to be able to spot movement in dim light in order to track and catch their dinner or breakfast. As dogs evolved, they retained this advantage to see in the dark, while adapting to function in broad daylight.
The Structure of the Canine Eye
When you take your dog out at night, do you ever notice how he alerts to objects more quickly than you do? Obviously, his stronger sense of smell is useful, but it’s also because dogs can see movement and light in the dark, and other low-light situations, better than humans.
They are assisted by the high number of light-sensitive rods within the retina of their eyes. Rods collect dim light, supporting better night vision. In contrast, the human retina is dominated by cones that detect color and function in daylight.
But a dog’s secret weapon in his ability to see in the dark is the part of the canine eye called the tapetum lucidum. The tapetum is a special layer of reflective cells behind the retina that acts as a mirror within the eye, reflecting the light that enters it, and giving the retina another opportunity to register that light. This magnifies and enhances visual sensitivity under low light conditions and increases the dog’s ability to detect objects. Human eyes don’t have the tapetum.
An animal’s ability to see in the dark is also influenced by Flicker Fusion Frequency (FFF), or the rate at which intermittent frames of light are perceived as a steady, continuous picture. Generally speaking, the faster a species moves through its environment, the higher its FFF. “Dogs have a higher flicker fusion threshold than humans, so a television screen that appears to show continuous motion to humans might appear to flicker to a dog, while this sharpened ability to see flickering light allows the dog to detect slighter movements in the dark,” says Dr. Jerry Klein, AKC chief veterinary officer.
Most dogs, depending on breed, have eyes situated more on the side of their heads than we do, which also gives them a wider range of view than humans – allowing them to scan their environment more quickly.
Why Do Dogs’ Eyes Glow in the Dark?
You’ve no doubt seen that eerie, greenish-yellow glowing look of a dog’s eyes when light hits them at night from headlights or a flashlight, and in photos (caused by the camera flash). What you’re seeing comes from the tapetum.
The color of the tapetum as it reflects light back and forth can vary from a green, blue, orange, or yellow hue. This coloration often changes over the first 3 months of life, according to the American College of Veterinary Ophthalmologists.
Some dogs, most commonly those with blue eyes, don’t have a tapetum. So, when you take a picture of these dogs, rather than getting the greenish-colored reflection from the tapetum, you instead often get red eyes – coming from the red blood vessels in the back of the dog’s eyes.
Why Do We Care About What Dogs See?
Information about what and how dogs see can help us understand how vision works and is affected by the environment for dogs and for humans. It also helps us breed and train working dogs for specific tasks that are dependent on different types of vision, as the authors of an article in the Journal of Vision discussed.
For example, a Labrador Retriever must visually track and mark the places where birds fall in the field or the water. Border Collies must detect the smallest movements of their sheep. And guide dogs need excellent peripheral vision to keep their partners safe.
If you’d like a more visual sense of a dog’s night vision, you can experience the spectrum of vision dogs possess at Dog Vision, which has an image processing tool that allows users to upload a photo that can be modified to show the difference between how humans and dogs see it.
And here’s a video that gives another perspective on canine vision: