Adrienne is a certified dog trainer, behavior consultant, former veterinarian assistant, and author of Brain Training for Dogs.
Interested in discovering some facts about dog eyes? As the saying goes, "the eyes are the window to the soul," but in this case, they are also the window that will allow you to gain a deeper understanding of your canine companion.
Let's face it: Dogs often behave in ways that leave us wondering what's going on in their minds. By getting more acquainted with our canine companions and seeing the "world through their eyes," we can gain a deeper understanding of their perceptions.
It's time to learn more about dog eyes so that we can better understand how dogs perceive the world around them—and why they sometimes do the odd things they do. Whether you own a German Shepherd, a Chihuahua, or a Beagle, these fun and fascinating facts will leave you in awe.
30 Eye Facts Your Dog Wants You to Know
1. Dog retinas have a larger density of rods compared to cones than people.
Rods and cones are special cells known to carry out several important functions. Rod cells help dog eyes detect and follow movement. Rods also allow dogs to see better in dim light compared to humans, but there are some tradeoffs for good vision at night and a keen perception of movements: a poor ability for distinguishing fine details (dogs have a visual acuity of 20/75 while humans with excellent vision have 20/20) and issues with the perception of colors.
Cones, on the other hand, allow for the detection of colors, but do not help in low light conditions. Human retinas have lots of cones because a human's evolutionary history required them to have a deeper need for distinguishing colors due to the fact that humans depended a lot on distinguishing ripe fruits.
2. Dogs see the world as deuteranopes.
Dogs are known for having two types of functioning cone cells in the eye which allows them to see color. This makes dogs dichromates. Humans, on the other hand, have three and that makes them trichromats.
One may compare a dog's perception of color as being roughly similar to that of a person who is red-green color blind (a deuteranope).
Just like a deuteranope, dogs have a hard time discriminating between red and green, however, they have a much better time detecting yellow and blue. This explains why in the sport of agility, you often see many agility obstacles featuring the colors blue and yellow.
So next time you are picking a toy for your dog, skip the red toys and look for a blue one instead.
3. Dogs see better in the dark because they have a history as crepuscular hunters.
It is estimated that dogs are capable of seeing in light that is five times dimmer than what a human can see. Dogs see better in dim light because of their evolutionary past as crepuscular hunters. A dog's ancestors indeed fed on critters that were mostly active during crepuscular times, at dusk and dawn.
4. The tapetum lucidum is what creates "eyeshine."
The tapetum lucidum is a mirror-like layer that is found just behind the dog's retina. This special structure helps dogs make the most out of small amounts of light. The term tapetum lucidum indeed derives from the Latin words for "carpet of light."
Basically, what happens is that, once light enters the eye, it hits the retina and then reflects off the tapetum, providing the cells of the retina with a second chance to sense it, explains John Bradshaw in the book Dog Sense: How the New Science of Dog Behavior Can Make You A Better Friend.
It is due to the presence of the tapetum lucidum that dogs show that eerie Halloween-like eyeshine seen when the glare of a flashlight or a car's headlight hits this area. This is referred to as "eyeshine." The green color is simply due to the layer of shiny cells lining the tapetum lucidum.
5. Humans "borrowed' this marvel for safety purposes.
Mother Nature's creation of the tapetum lucidum is so ingenious that humans decided to borrow the idea for the purpose of manufacturing those raised pavement markers seen at night on roads. These markers are referred to as "cat eyes" considering that cats are another species known for sharing with dogs this amazing reflective structure.
6. Bullmastiffs kept "an eye" on poachers.
Bullmastiffs are nicknamed the "Gamekeeper's Night Dog" for a good reason. Their job was to help gamekeepers protect large extensions of land from poachers who would hunt for fish, birds and wildlife in the lands of the nobles who had exclusive rights over game within their properties.
A good gamekeeper's dog had to pay a lot of attention to his surroundings in dim light. Bullmastiffs back then were required to feature a specific coat color which helped them camouflage and hide in the dark. This explains why many bullmastiffs back then were bred to have a typical fawn coat color.
7. Keeshonds are known to "wear glasses."
A hallmark of this breed is its "spectacles." Keeshonds indeed, feature dark lines running from the outer corner of the eye to the base of their ears making these dogs appear as if they're wearing glasses!
8. Sighthounds are blessed with a visual streak.
The eyes of sighthounds are known for boasting a special feature that's known as a "visual streak." The visual streak is a horizontal area in the retina that's lined up with ganglion cells. This streak came extra handy back in time when sighthounds spent most of their days spotting prey over the wide-open lands in the desert.
9. The blue eye color in huskies (or any other dog or person) is just an optical illusion.
It may sound quite odd, but when you gaze into pretty blue eyes, there’s really no blue pigment. The blue color is due to the way light enters and exits the eye, creating the appearance of blue. This phenomenon is similar to the way the sky looks blue when we know that in reality, that outer space is not blue at all, explains geneticist Kristopher Irizarry.
10. Border collies are known for "giving eye."
Border collies stalk and stare intently at sheep, a behavior that's known as "giving eye." The purpose of this stare, it to control the flock. By lowering their bodies and staring at sheep, border collies exert a sort of psychological pressure to get the sheep moving. Sheep apparently respond naturally to the border collie's posture and stare because it somewhat mimics a wolves' hunting tactic of selecting a victim from the herd by catching its eye before chasing.
11. Your dog's pupil is just a black hole.
When you look into your dog's eye, the pupil looks like a black circle, but in reality, the pupil is just a black hole that appears to be black due to the presence of special light-absorbing pigments located in the interior portions of the eye. The same applies to the pupils of humans and other animals.
12. Brown eyes in dogs are due to melanin.
Dogs with brown eyes are known to have a greater concentration of melanin in their iris compared to dogs with lighter colored eyes.
13. A study has revealed that dogs see in ultraviolet.
According to a study, dogs along with cats, ferrets, hedgehogs and okapi, share the fact that they are equipped with special lenses that make them UV sensitive, allowing them to detect a wider spectrum of wavelengths. The exact function of this is not clear.
14. Dogs don't have eyebrows like humans do.
Dogs do not have eyebrows in the real sense of the word for the simple fact that they don't need them. Eyebrows in humans are there for one main reason: preventing salty sweat from falling down the forehead into the eyes. Imagine if that would happen, ouch!
Indeed, if you look at your eyebrows' arched shape with a slant to the side, you'll notice how they allow sweat or rain to flow sideways towards the nose and sides of the face safely away from the eyes.
Dogs do not need eyebrows because they don't sweat as humans do, explains Stanley Coren in the book How to Speak Dog.
15. Dogs have whiskers over their eyes for an important purpose.
Those whiskers above your dog's eyes are known as supraorbital whiskers and they play a very important role: protect your dog's eyes from being poked and injured by sticks, brush, debris and even an owner's fingers.
Upon detecting something making contact with these whiskers, indeed, the dog's "blink reflex" will jump into action eliciting the eyes to close so to prevent them from getting accidentally scratched or poked.
16. Humans love dogs with large eyes.
Many humans find large eyes in dogs far more attractive than smaller ones. They seem to make dogs look like babies. Due to this preference, several dogs breeds were selectively bred to have prominent eyes. There is a tradeoff though that comes with changes in eye size: increased risk of eye diseases and trauma to the cornea. Pugs, in particular, are known to possibly develop what's called "eye proptosis" causing the eye to literally pop out of its socket.
17. Humans love eyebrow movements in dogs, too.
According to research by Waller et al., the more dogs made facial movements that resulted in raising their inner eyebrows, the quicker the dogs were rehomed. Again, this is likely due to the fact that, by raising the eyebrows, the upper facial muscle contractions cause the eyes to appear bigger and more infant-like.
18. Dogs enjoy gazing into human eyes.
According to a study, dogs established eye contact with humans for an average of 40 seconds, dingoes for less than 3 seconds, whereas wolves rarely established any eye contact with humans at all.
19. and they dedicate left eyebrow movements exclusively for their owners.
According to research conducted by Nagasawa et al, upon noticing their owners' arrival, dogs moved their left eyebrows for about half a second. The studied dogs though failed to move their eyebrows in response to attractive toys or when strangers greeted the dog. This seems to suggest that the left eyebrow movement denotes a positive social emotion.
20. Those dots above a dog's eyes are known as "pips."
Those pigmented markings over a dog's eyes that sometimes are referred to as "eyebrows" are really known as "pips." Breeds of dogs featuring pips include Rottweilers, German shepherds, Bernese mountain dogs, Doberman pinschers, Gordon setters, miniature pinschers, English toy spaniels and the black and tan coonhounds.
21. Newborn puppy eyes open only at 10 to 14 days old.
This is because dogs are an altricial species and puppies are born in a helpless state. Unlike precocial species such as horses, cows and sheep, dogs depend on their moms entirely for several weeks after being born.
On top of being unable to regulate their body temperatures and being unable to eliminate without mother dog's assistance, newborn puppies are also born deaf and blind.
Because their neural system is not ready for processing visual information yet, the eye-opening process is therefore delayed. This is likely the price to pay for a shortened gestation time (63 days on average in dogs compared to 11-12 months in horses).
22. Dogs are blessed with a third eyelid.
This third eyelid is not much visible as it stays tucked in a corner when the dog is awake and alert. When your dog is sleeping though, you may see it sometimes making the dog appear as if sleeping with his eyes opens. A dog's third eyelid may also be sometimes seen in dogs who are not feeling well.
According to the American College of Veterinary Ophthalmologists, the purpose of the third eyelid is the production of 40 to 50 percent of the dog's tears. When it is drawn across the dogs' eyes while sleeping, it helps protect the eyeball and keeps it moist.
23. The fight or flight response in dogs causes dilated pupils.
When dogs feel threatened, their fight or flight response is activated and triggers a surge in adrenaline. The adrenaline is meant to help save the dog's life. The heart pumps faster so to send more blood to the dog's legs so to spring quickly in action. A dog's senses also sharpen.
In the case of the eye's dilating, the goal is to allow more light to enter the eyes so that the dog's brain can process any information fast. Taking in as much visual information as needed acts as an "eye opener" which comes handy at a time when the dog's life may be in peril and every second counts.
Those eye pupils may also dilate when the dog is in the mood of hunting or playing. In this case, the purpose of the adrenaline rush is to to help dogs see better and detect the slightest movements in order to succeed in "catching their dinner."
24. Dogs use their eyes in communication.
Pay attention to what your dog's eyes are saying. When dogs are super satisfied with something, they'll show squinty eyes almost as if daydreaming.
When dogs are worried about something, they may show the white of the eyes (whale eyes). Whale eyes are often seen in dogs who turn their heads but want to keep an eye on what is going on as they do this.
25. Dog's have a blind spot under their noses.
Ever wondered why your dog may fail to see that treat that is right in front of him? Well, here's why. Let's face it: Dogs are equipped with quite a cumbersome nose. Unlike the nose in humans which is discreetly placed in the middle of the face, dogs have rather prominent noses which can block some vision and cause a blind spot right in front of them. Of course, this doesn't apply to dogs with smushed-in noses such as pugs.
26. Aging causes cloudiness in a dog's eyes.
As dogs age, the eyes may appear hazy. Cloudy changes in an older dogs’ eyes are due to an age-related connective tissue change of the lens called lenticular sclerosis. Also known as nuclear sclerosis, lenticular sclerosis in dogs is often found in dogs over the age of nine and can cause signs of nearsightedness.
27. Certain dog breeds with heavy hair covering their eyes are prone to problems.
With hairs in the eyes, the eyes are prone to being continually irritated putting affected dogs at risk for tearing, redness, chronic conjunctivitis, corneal ulceration and several other ophthalmic problems, explains Michael W. Fox.
28. Eyelashes in dogs sometimes grow abnormally and cause problems.
Some eyelash problems found in dogs include ectopic cilia, trichiasis and distichiasis. What causes these eyelash disorders are hair follicles located in abnormal places and causing irritation and even scratches to the dog's cornea.
29. Swelling under a dog's eye may be due to a tooth problem.
Dogs are equipped with large upper carnassial teeth which have long roots that reach below the eye. An abscess of a dog's carnassial tooth has been known to cause swelling under a dog's eye which is sometimes confused with an eye problem.
30. PRA may cause dogs to act anxious at night.
Some dog breeds are known to develop an eye disorder known as progressive retinal atrophy (PRA). This inherited condition affects both eyes and leads to the rod cells dying. Since the rod cells are responsible for causing dogs to see in dim light, affected dogs may act anxious at night, refusing to enter dark rooms or bumping into objects.
If your dog shows any changes in his eyes or you notice any vision problems in your dog, see your vet sooner than later. Some eye conditions can progress to blindness quickly if left untreated.
This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
© 2019 Adrienne Farricelli
Adrienne Farricelli (author) on May 12, 2019:
Weird indeed! Perhaps worthy of informing the vet just to exclude any abnormalities. He or she may see if there's anything odd using the ophthalmoscope. If it's always been this way though and your dog had vets examine the eyes in the past with no problems were seen, perhaps it's just some normal variation of the eye.
Heidi Thorne from Chicago Area on May 10, 2019:
Adrienne, the weirdest thing is that they both have brown eyes! I've never seen the green thing until we got our cattledog mix last year. I'm still trying to figure it out. Maybe it's the angle at which the light is hitting her eyes. But it is funny, freaky, weird. :)
Adrienne Farricelli (author) on May 03, 2019:
Heidi Thorne, that's interesting! If I recall well, I think that dogs with blue eyes may show a red eye shine. Now that I think about it, I think I have a picture of me and a husky and his eyes were red and he had pretty blue eyes. Does your dog by any chance have blue eyes?
Heidi Thorne from Chicago Area on May 03, 2019:
Super interesting! What's very strange with our current two, is that when our outdoor garage light is on at night, the one's eyes appear red, while the other one's appear green, perfect horror story imaging. :) Both of their eyes appear brown in daylight, but, obviously, have different makeup.
Thanks for sharing your knowledge with us, as always!