In a previous article we looked at how dogs see colors, today instead we will take a peek at how dogs see in the dark. While humans detect colors much better than dogs, when it comes to night vision, dogs come out as winners. A dog's ability to see in the dark may not beat the night vision of cats, but they aren’t too far behind. Interestingly, this ability to see in dim light is courtesy of several evolutionary adaptations meant to help dogs see in low-light conditions.
A Matter of Conformation
While dogs can't appreciate our same visual acuity and same color palette as us, when it comes to night vision, dogs are blessed with characteristics that make them see far better than humans.
Dog eyes have a larger lens and thus a larger corneal surface, than humans, explains Dr. Randy Kidd.
Why they see better than us in dim light, isn't surprising. Animals have larger pupils than humans and this allows more light to reach the retina, which is why they have superior night vision, claims Dr. Lynsey Wagner, a board-certified veterinary ophthalmologist working for South Texas Veterinary Ophthalmology.
While a dog's night vision is superior to humans, it can't beat though the night vision of cats. Cats are nocturnal animals par excellence and their incredible night vision comes courtesy of the vertical shape of their pupils and their larger cornea.
"Compared to the human eye, the dog has a larger lens and a correspondingly larger corneal surface, enhancing its ability to capture light and thus see in reduced lighting conditions. " ~Randy Kidd, DVM, PhD
Light Sensitive Rods
While the human retina has more cone cells, which allow a better ability to distinguish colors, dogs' retinas have a higher concentration of rods, special light-and-motion-sensitive cells that help distinguish light from shadow. This allows dogs to see better than humans in semi-darkness.
Additionally, these rods help the dog detect small movements, which came helpful for hunting prey animals at night, or, in the case of our domesticated companions, catching a ball tossed on a summer evening.
There's a trade-off though for these advantages. The price to pay for seeing in dim light and detecting small movements, appears to be less visual acuity during the day.
"The dog's retina is like a high speed photographic film with a high ISO or ASA number; great in dim light but 'grainy' with less detail (visual acuity) in bright light." ~Dr. Kerry L Ketring, board-certified veterinary ophthalmologist.
A Bright Tapestry
The dog's tapetum lucidum, a mirror-like membrane lined with a layer of highly reflective cells, further helps dogs see better when the lights go out. How? This membrane reflects back any light entering the eye which enables dogs to see better.
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According to Dr. Steven M. Roberts, a board-certified veterinary ophthalmologist, it is thanks to the tapetum lucidum, along with the greater corneal and pupil diameter, that dogs can see "a low-light world that's two to ten times brighter than what we see."
Ever wondered why dogs get "Halloween eyes?" The reason why dog eyes glow at night in an eerie way is because the unabsorbed light reflects off the tapetum lucidum.
This also explains why a dog's eyes glow in pictures when taken with flash. Humans, unlike dogs, do not have a tapetum lucidum.
"Dogs, can probably see in light five times dimmer than a human can see in." ~Paul Miller, clinical professor of comparative ophthalmology at University of Wisconsin—Madison.
Dogs Cannot See in Total Dark
Dogs see in total darkness the same way us humans do. The reason why they see better in dim light is simply because they make better use of the light they have.
The secret behind a dog's night vision therefore relies on our companion's ability to make better use of whatever source of light is available to them. So turns out, it's a myth that dogs are able to see in total pitch black darkness.
Dogs have an advantage though over us humans when it comes to navigating in the dark that's worthy of mentioning. They can rely on their "feeler" whiskers which prevents them from bumping into things and allows them to navigate around a room in dim light with a good level of ease.
On top of that, they have an uncanny ability to memorize the layouts of their homes. Perhaps this is why the myth of dogs seeing in the dark got popular!
“Dogs and cats are very good at memorizing their environment. We see lots of patients that have pretty advanced visual dysfunction without their owners being aware of it simply because the layout of their home never changed.”~ Christopher Pirie, board-certified veterinary ophthalmologist.
Did you know? That eerie green-yellowish glow that is emanated from the eyes of animals at night is known as "eye shine."
- Tufts Now, Spotting Eye Problems in Pets, retrieved from the Web on February 18th, 2016
- South Texas Veterinary Ophthalmology, The Ghostly Glow, Why do Animal's Eyes Shine? by Dr. Lynsey Wagner, retrieved from the Web on February 18th, 2016
- What Do Animals Really See, by Kerry L Ketring, DVM DACVO, All Animal Eye Clinic Whitehall, MI 4946, retrieved from the Web on February 18th, 2016