Do you face those times so often that you can’t help but ask yourself why do dogs sleep with their eyes open?

This is actually a common mystery to most dog owners and only a few have discovered its secrets. Watching my dog sleeping with their eyes open worries and scares me. It makes me think that there could be something wrong like is he okay? Is he having eye problems? Or is he dreaming? Sometimes I even end up waking him up to double check things. But now, I have learned that some things are not always as they seem.

Sleeping with their eyes open? Think again…

As our dogs sleep, we expect them to have their eyes closed all the time like we do when we are sleeping. But are they really sleeping with their eyes open? Then again, maybe not!

Opening their eyes while they sleep may be risky for them. There are tendencies to which they could develop eye diseases. This is because their eyes are being exposed to all sorts of elements or bacteria. Their eyes could also become dry and open to damages like exposure keratitis.

Getting to Know the “Third Eyelid”

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What we are seeing when they are “opening their eyes” as they sleep is not as noticeable. It is actually a pinkish white flesh called the third eyelid. At first, this may seem quite shocking. But believe me, it’s there, alright.

The third eyelid is also known as a nictitating membrane, palpebra tertia or haw. Like the name itself, it is a membrane that covers up your dog’s whole eye. Because of it, you won’t be able to see much color of your fur baby’s eyes. Its purpose is to protect your dog’s eyes from harmful elements as well as keep it from drying up.

How the Third Eyelid Works

The Third Eyelid has many functions when it comes to eye works. It lubricates your dog’s eye and retracts when your dog is at their “idle mode”.

Its movements are quite passive and surprisingly, has no muscles attached to it. For instance, when a dog starts to retract their eyes, this triggers their third eyelid to passively glide across the eye’s surface which is being explained by the famous Christine C. Lim, a veterinary ophthalmologist in her book called “Small Animal Ophthalmic Atlas and Guide”.

It has also become a fact that the dog’s breed matters when it comes to the visibility of the third eyelid. Whether it be that the dog is sleeping or not. There are specific breeds that have their third eyelids more visible than the rest.

Dogs with smaller eyes in the dolichocephalic breeds (long heads) are often known to have their third eyelids more noticeable. The brachycephalic breeds (short heads) on the other hand, are quite the opposite.

Why do Dogs have this capability?

This ability started all the way back from their wild heritage. Long ago, your dog’s ancestors used this “eye opening while sleeping” trick as a defense mechanism. This is because of the other beasts that roam as they take a rest. They wouldn’t want to be off-guard even while they are sleeping. Your dog may not be part of those tough and dangerous times like their ancestors, but they have inherited this trick until now.

When you see your dog having these times as they sleep, don’t worry. This is quite normal for them. No need to go and call the vet. Unless of course, your dog has been showing signs other than the fact they are “opening” their eyes as they sleep.

Are dogs the only ones who have the Third Eyelid?

Some people wonder if dogs aren’t the only species who have a third eyelid. You are probably wondering too. Well, the answer is no. Dogs are not the only species with a third eyelid. In fact, study shows that even camels, cats, fishes, birds and certain reptiles have this as well.

The third eyelid is very useful for the wildlife as they are used for hunting and defending themselves. But then again, the third eyelid is not present in the other animals the way we see them in our dogs.


Were you able to get the answers to your questions? I hope you did! To sum it up…

  • Dogs aren’t really opening their eyes when sleeping.
  • The third eyelid is what covers the whole eye to prevent any harmful elements from ever touching it.
  • The third eyelid’s visibility depends on the breed.
  • Dogs are not the only ones who have third eyelids.
  • Dogs have defense mechanisms using the third eyelid.

This brings you to the end of the article. Thank you for reading!

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