Why Do Dogs Sleep With One Eye Open

Have you ever walked past your dog and, thinking they’re awake and looking right at you, reached out to pet them? Then they snore, or twitch, or don’t react to your hand, and you realize that your dog is fast asleep! But their eyes are open, or at least one eye is. It might be staring right at you, or their eye might be rolled up so that all you see is the white, but your dog’s eye is definitely open! Is your dog a wizard, sleeping with one eye open at all times? Why do some breeds have a higher chance of doing this than others? If you’ve ever wondered why your dog sleeps with one eye open, we’re going to talk about that. 

While it may look as though your dog is sleeping with one eye open, the truth is that your dog’s eye is not really open. If your dog’s eye was open with no protection, it could cause the eye to dry out, causing something called exposure keratitis, or dry eye syndrome, requiring tear stimulation, medicated eye drops, and visits to the vet to manage. What you are actually seeing is a dog’s nictitating membrane or third eyelid. Much like cats, dogs have a third eyelid that aids in tear production and protecting the eye, working like a windshield wiper to clear the eye of any sort of debris and keep it healthy and moist. Your dog’s nictitating membrane and the gland attached to it is responsible for up to 50% of their tear production, so it is important that it is functioning properly. Unlike cats, however, a dog’s third eyelid is a passive membrane, triggered by the dog’s natural eye motions – like when your dog is deeply asleep, and their eyes roll back!

Not all dogs will have a visible nictitating membrane or appear like they are sleeping with their eyes open, though. Dogs with longer faces or more bulbous eyes, like the Greyhound or the Pug, may be more likely to show their eyes when they’re sleeping. So if you have never noticed your dog sleeping with one or both eyes open, do not worry – it is likely that they are just a breed which does not have that trait. There is also a train of thought that suggests that dogs evolved their third eyelid as a form of self-defense; sleeping while appearing to be awake is thought to have deterred predators from attacking because the dogs appeared alert and ready to defend themselves. Even though your dog has nothing to defend themselves from except for your affection (and perhaps playtime with other pets), the defense mechanism is hard-wired through generations of evolution and won’t wear off easily.

Because this behavior is not typically damaging and is based on evolution and physical characteristics, there’s not really a reason to either encourage or discourage it. As a naturally occurring behavior, you may actually cause harm or stress to your dog if you try to force them to sleep with both eyes closed, especially if their body is unable to do so. However, there are times when your dog sleeping with one or both eyes open could be cause for concern. While dogs will normally twitch slightly in their sleep, your dog’s eyes being wide open and staring blankly, paired with involuntary noises or movements, could be signs that your pet is suffering a seizure. If this is the case, your first goal is to make sure your dog is safe until the seizure is over. Then you should get your pet to a vet immediately, to hopefully prevent such stressful situations in the future.

It is normally fairly easy to distinguish between typical twitching during dreaming and a seizure. When your dog wakes up, are they disoriented and confused? Do they have difficulty “waking up” all the way? Do they seem unstable? These are all signs that your dog’s twitching wasn’t normal. While this behavior isn’t one you can train, it’s one that’s important to pay attention to. If your dog suddenly starts sleeping with their eye or eyes showing when they haven’t before or starts suffering from more extreme twitching and seizure-like behaviors, it’s time to get them to the vet!

In addition to seizures, your dog’s eye being open while sleeping can be indicative of other issues, like cherry eye or Lagophthalmos. Cherry eye is a disease that occurs when the cartilage supporting your dog’s eyelid falls over, exposing their gland and preventing their third eyelid from being able to protect them. Your dog might not be able to properly close their eye all the way, resulting in the appearance of sleeping with one eye open. Lagophthalmos occurs in short-faced dog breeds like Shih Tzus, Pekingese, and Pugs, and is characterized by your dog’s inability to close their eyes completely. Again, this can result in dryness and irritation of the eye, which could lead to other issues in the future. With either of these conditions, you should take your dog to the vet immediately, so that the problem doesn’t get worse.

No, your dog is not a ninja, sleeping with one eye open to keep a watch on your home – though it is a nice thought! Your dog’s eyes are closed and they are sleeping peacefully, and the “open eye” you see is their third eyelid protecting their eyes from harm. Unless you have noticed strange behavior, your pup is likely content dreaming away, and you should let him!