Do you ever get jealous of your dog? If so, you aren’t the only one! Sure, they have their set of problems to deal with. But on a long, hard day at work, I know I’m not the only one who thinks “must have been nice to be my dog today.” They never have to cook their own food, they don’t have to go to work, and they sleep up to 16 hours per day!
Speaking of sleeping, that’s another reason I get jealous of my dog…I toss and turn all night, meanwhile my dog can fall asleep on command. If you’ve ever watched your dog sleep, you may have noticed that sometimes it looks like their eyes are open when they sleep…
…but can dogs actually sleep with their eyes open? The answer to this is technically no, dogs can’t sleep with their eyes FULLY open. The reason it might look like your dog’s eyes are open is because of something called the nictitating membrane. The nictitating membrane is transparent, which makes it look like the eyes are open.
We will go into more detail on the nictitating membrane below. For now, remember that it’s completely normal for dogs to give the appearance that their eyes are open while sleeping. Your pup isn’t the only weirdo in town!
What is The Nictitating Membrane
Here’s a fun fact about dogs…they have three eyelids! The nictitating membrane is a transparent, third eyelid that acts as a windshield wiper to keep dirt and debris out of your dogs eye.
Dogs aren’t the only animal that has the third eyelid. Many mammals, birds, reptiles, and even sharks all have the third eyelid. We’ve just never noticed it because it’s transparent. It’s like someone wearing contacts…you can’t tell they’re wearing contacts until you get up close and look closely.
Where is it?
If you just looked closely at your dog’s eyes to try to find the third eyelid, you probably couldn’t see it no matter how carefully you looked. That’s because it’s in the medial canthus (the corner of the eye closest to the nose where the upper and lower eyelids meet). When it’s not covering the eyes, only about 10% of it is visible.
How Does it Work?
When dogs blink or close their eyes, the upper and lower eyelids move up and down (although the upper eyelids do most of the moving). The nictitating membrane moves horizontally across the eyeball. Usually, it only moves when a dog closes their eyes or blinks, which is why you’ve probably never seen it.
What’s The Purpose?
The purpose of the third eyelid is to protect the eyes from getting dry and to protect the eyes from dirt and debris. Humans have hands we can use to rub dirt and debris out of our eyes. Dogs don’t have this ability, so the third eyelid comes to the rescue. Think of it like a windshield wiper. It sweeps across the eyeball horizontally and clears the eye from any irritants.
So Dogs Aren’t Actually Sleeping With Their Eyes Open?
Nope! When it looks like your dog is sleeping with their eyes open, that means their upper and lower eyelids are open, but their third (transparent) eyelid is closed.
This leads to the next logical question…why would a dog do this? If they’re going to sleep, why not close all three eyelids instead of keeping two of them open?
That’s a great question, and we have five possible answers for you.
5 Reasons a Dog Would Sleep With 2 Eyelids Open
The first two reasons below are likely the answer. The final three reasons are medical conditions that should be addressed with the vet. However, the three medical reasons are rare, so there’s a good chance you have nothing to worry about.
1) Self Defense While Sleeping
When is an animal most vulnerable to becoming someone else’s lunch? When they’re sleeping. A predator is more likely to attack their prey when the prey is asleep. If the predator notices the dog’s eyes are open, they’re less likely to attack.
Obviously, your dog has nothing to worry about at home. When they go to sleep at night, they don’t have to worry about a predator attacking them. But that doesn’t change the fact that dogs will still act on their instinct, and when they sense there could be danger, they might choose to sleep with the two eyelids open.
2) Dog’s Sleep LIghtly
Even though dogs sleep for most of the day (up to 16 hours), that doesn’t mean they spend all day in a deep sleep. In fact, most of the time they spend asleep is in a lighter sleep phase.
Most scientists will agree that the reason dogs need so much sleep is that they don’t spend much time in REM when they do sleep. Sleeping more often throughout the day helps them make up for lack of REM.
During those times of light sleep, dogs may choose to sleep with two eyelids open, so they can still be aware of what’s going on around them. Have you ever had one of those moments where you’re half asleep, half awake? Some people call this lucid dreaming. Although a dog isn’t lucid dreaming, they do spend most of their sleeping time half awake/half asleep.
Next time you see your dog sleeping with their eyes open, they’re probably in a very light stage of sleep and will immediately run to you when you call their name.
3) Cherry Eye
Cherry eye is a condition in which the nictitating membrane falls out of place and protrudes from the dog’s eye. The first time you see this, it can be alarming. Not only is the membrane out of place, but it comes red and swollen (hence the name cherry eye).
The good news is the fact that it causes absolutely zero pain for your dog. There will likely be discomfort, but your dog isn’t in pain. The bad news is the fact that if it’s not treated, it can cause severe long term damage to the eye.
Part of the reason it can cause long term damage is that the eye will dry out. The protruding membrane (along with the swelling) will make it impossible for your dog to close their eye. That’s why dogs with cherry eye will sleep with their eye open; they literally can’t close it. However, this time the nictitating membrane won’t be covering the eye, which is a severe problem.
If you notice a red lump in the corner of your dog’s eye, it’s important you take them to the vet ASAP. There’s a chance the vet will be able to fix the issue by performing a massage around the eye. If that doesn’t fix it, they will provide you with a topical treatment that will fix things in a matter of days.
Along with the topical treatment, they might give you eye drops to place in the dog’s eye every few hours to prevent dryness.
4) Lagophthalmos
Lagophthalmos is a rare condition in dogs (but more common in short-nosed breeds). This condition prevents a dog from fully closing their eyes. Although many dogs are born with it, it can be developed over time.
The reason this needs medical attention is for the same reason cherry eye needs medical care…it can cause the eyes to dry out, which can result in permanent damage.
The leading cause of lagophthalmos is an extremely shallow orbit in the eye, which causes the eye to protrude further than it should.
There’s a chance a vet may be able to reverse the condition with surgery. If it can’t be reversed, the vet will provide you with lubricating ointment, which you’ll need to apply to the eyes daily.
5) Seizures
The fifth reason your dog might appear to be sleeping with their eyes open is that they’re having a seizure. Seizures are common in dogs, although you’ll likely already know if your dog suffers from seizures or not.
There’s a clear difference between a dog that’s sleeping with eyes open and a dog that’s having a seizure. If the dog is simply sleeping, they’ll be completely still (might twitch every once in a while). If a dog is seizing, their eyeballs will likely roll back and their body will become extremely tense and start shaking.
Dogs Technically Can’t Sleep With Their Eyes Open
Although it may seem like your dog has fallen asleep with their eyes open, they’re most likely just resting while the nictitating membrane (the third eyelid) is covering the eyes. If the dog’s eyes were truly open, they would dry out in a matter of minutes.
Next time you see your dog sleeping with their eyes open, take a closer look and you’ll be able to see the third eyelid protecting their eyes.
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