The Third Eyelid Explained
Dogs have something you do not: a third eyelid called the nictitating membrane. It sits in the inner corner of each eye and sweeps horizontally across the eyeball like a windshield wiper. During waking hours, you rarely see it. But when your dog falls into a deep sleep and its muscles relax completely, the outer eyelids may not close all the way while the third eyelid slides partially across the eye.
What you end up seeing is a sliver of pinkish-white or gray membrane where you would expect to see the eye, or sometimes the white (sclera) of the eye with the pupil rolled upward or to the side. It looks eerie, like a horror movie extra, but your dog is not aware of it and is not uncomfortable.
The third eyelid serves an important protective function during waking hours: it helps produce tears, distributes them across the eye, and provides an extra layer of defense against debris. During sleep, it keeps the exposed portion of the cornea moist even when the outer lids are not fully shut.
REM Sleep and Eye Movement
Like humans, dogs cycle through stages of sleep, including REM (rapid eye movement) sleep -- the phase associated with dreaming. During REM sleep, you may notice your dog twitching, paddling their legs, whimpering, or making muffled barking sounds. Their eyes move rapidly behind their lids, and this is when the lids are most likely to part slightly.
Puppies and senior dogs spend more time in REM sleep than adult dogs, which is why you may notice the eyes-open sleeping more at those life stages. Puppies in particular seem to be champion REM sleepers, twitching and moving dramatically in their sleep as their developing brains process the flood of new information from their waking hours.
If your dog's eyes are only partially open during these active sleep phases and close fully during quieter sleep periods, this is entirely normal dreaming behavior.
Breeds That Do This More Often
Brachycephalic breeds -- dogs with short snouts and prominent eyes -- are significantly more likely to sleep with their eyes partially open simply because their eyelids have more surface to cover and the eyes protrude more. This includes:
- Pugs
- Boston Terriers
- Shih Tzus
- French Bulldogs
- Bulldogs
- Pekingese
- Cavalier King Charles Spaniels
Dogs with loose facial skin, like Bloodhounds, Basset Hounds, and Cocker Spaniels, may also show this tendency because the lower lid sags slightly during the total muscle relaxation of deep sleep.
If you have one of these breeds and your dog has always slept this way, there is nothing to worry about.
When It Might Be a Concern
In a small number of cases, sleeping with eyes open can indicate a medical issue. The key distinction is whether this is new behavior and whether it comes with other symptoms.
Lagophthalmos. This is the medical term for the inability to fully close the eyelids. If your dog's eyes are partially open not just during sleep but also when they blink while awake, and you notice redness, discharge, or the dog pawing at their face, the eyelids may not be closing properly due to nerve damage, scarring, or a structural issue. This needs veterinary attention because the cornea can dry out and develop ulcers.
Facial nerve paralysis. If one side of your dog's face seems droopy, with one ear hanging differently, drooling on one side, or one eye not closing fully, this could be facial nerve paralysis. It can be idiopathic (no known cause, similar to Bell's palsy in humans) or caused by an ear infection, trauma, or a growth. See your vet.
Cherry eye. If the third eyelid itself is protruding as a red, fleshy mass in the corner of the eye (not just visible as a membrane), your dog may have a prolapsed nictitating membrane gland, commonly called cherry eye. This is not an emergency but should be evaluated by a vet.
Seizure activity. In very rare cases, what appears to be sleeping with eyes open may actually be a seizure. If your dog is unresponsive to stimulation (calling their name, gentle touching), rigid, drooling excessively, or the episode lasts longer than a few minutes, seek veterinary care immediately.
How to Tell If Your Dog Is Just Sleeping Normally
Gently say your dog's name or make a quiet noise. A sleeping dog will typically twitch an ear, shift slightly, or wake up within a few seconds. If they respond normally -- even if just with an ear flick before going back to sleep -- they are fine. The eyes-open look is just how they sleep.
Should You Try to Close Their Eyes?
No. Touching your sleeping dog's eyelids will either wake them up (annoying for them) or, if they are in deep sleep, startle them in a way that could cause a reflexive snap. Their third eyelid is doing its job keeping the cornea protected. Leave them be.
If your dog sleeps in a drafty area or directly under a ceiling fan or heating vent, you might consider adjusting their bed placement so that moving air is not blowing directly across their partially open eyes for hours. This is more of a comfort consideration than a medical one.
The Short Version
Dogs sleeping with their eyes partially open is one of those things that looks deeply alarming and is almost always completely benign. The third eyelid is doing what it was designed to do. Your dog is dreaming, their muscles are relaxed, and the outer lids simply are not making a tight seal. Unless the behavior is new and accompanied by discharge, redness, facial asymmetry, or unresponsiveness, your dog is fine.
If your dog's sleeping habits concern you in other ways -- like panting at night without an obvious reason -- that is worth investigating separately, as nighttime restlessness can sometimes indicate pain or anxiety that the eyes-open sleeping does not.
Related: Dog Panting at Night but Not During the Day · Dog Reverse Sneezing Sounds Like Choking · Why Does My Dog Eat Grass Then Throw Up?
Written by Margaret O'Connor
Margaret writes about personal finance and money topics. She's passionate about making financial information clear and accessible.