cat falls asleep with eyes open
Questions About Cats

Why Do Cats Sleep With Their Eyes Open?

Cats do many strange things, but one of their creepiest behaviors is when cats sleep with their eyes open. Not only is this alarming, but some owners worry that it’s a sign that something’s wrong.

It’s normal for cats to sleep with one or both eyes open. When they do, you’re likely to see the third eyelid (nictitating membrane). This protects the cornea from damage. Cats sleep with their eyes open when they’re in the lighter slow-wave sleep (SWS). They do this to protect themselves from danger, keeping a literal eye on what’s going on around them when they’re at their most vulnerable when sleeping.

However, it can also be a sign of a painful injury preventing cats from closing their eyes. While it’s common for cats to keep their eyes open, you need to look out for signs of an injury or illness.

Cat Sleep Stages

Adult cats sleep for up to 15 hours a day, while kittens sleep for up to 20. When they rest, they sometimes keep their eyes open, regardless of how deep they’re sleeping.

You might see both eyes open or just one. Either way, both instances are normal unless your cat displays signs of sickness. The main stages of cat sleep include:

Slow-Wave Sleep

Slow-wave sleep (SWS) is the shallowest form of rest. Brain Research describes how there are two different stages within slow-wave sleep: labeled light and deep slow-wave sleep.

While cats are in the slow-wave stage of sleep, their senses are still in tune with what’s going on in their environment. This is important for wild cats, who need to flee from predators and other dangers at short notice.

As a result, cats experiencing slow-wave sleep may keep one or both eyes open so that they can react immediately if they notice any abnormal sounds. These sounds sometimes signify that danger is close.

Rapid Eye Movement Sleep

The rapid eye movement of sleep (REM) is a deeper form of sleep. It’s when cats are most likely to dream. During this stage, cats lose muscle function, and their paws and ears will twitch. Your cat will seem active because the brain functions in the same way as when it’s awake. Sometimes, your cat will look like it’s running in its sleep.

However, while not as common, some owners notice that their cat’s eyes remain open during the REM stage of sleep. Sometimes, the cat’s eyes roll back when sleeping due to the loss of muscle function. They also twitch rapidly.

The reason a cat’s eyes remain open during REM is that its muscles are so relaxed. Open eyes are normal, and the cat’s brain and muscles need rest. By waking it, you’re ruining a cat’s sleep when it needed it the most.

do cats sleep with one eye open?

Why Do Cats Sleep with Their Eyes Open?

There are various reasons why cats fall asleep with their eyes open. The most common is that your cat has ingrained instincts to flee from danger.

This is part of a wild cat’s everyday survival, so it must keep its eyes open whenever it can. If the cat can’t flee quickly enough, it’s at risk of predation.

That being said, that’s not the only reason. Cats keep their eyes open when resting because:

Light Sleep

The most common reason your cat sleeps with its eyes open is that it’s in a light sleep. As already mentioned, this allows cats to react to danger.

If you notice your cat keeping one or both eyes open when it rests, it’s probably not in the deepest stage of sleep. As a result, it can be easily woken with light sound or touch.

These small bursts of sleep help cats conserve their energy for when they hunt at night. Cats also react to the weather, so when it’s cold and wet, they’re more likely to go into a lighter sleep more often. 

Noisy Environment

Domestic cats are less likely to worry about environmental dangers, but they’ll still keep their eyes open when it’s noisy and a lot is happening around them.

Particularly when the house is full of people (including strangers) during the day, cats will tuck themselves away to sleep while keeping at least one eye open. This allows them to literally keep an eye on dangers that they might need to run away from.

If your cat seems uncomfortable in its surroundings, provide access to a quiet, dark space where they can tuck themselves away to sleep. Place its blankets and toys in the area to let it know that they belong to your pet.

This should help your cat feel comfortable enough to doze off into a deep rapid eye moment of sleep.

Injured Eyes

Cats get into fights all the time, especially if they go out at night. If they encounter a territorial cat on their travels, they could easily end up with a nasty scratch across their eye or eyelid. As a result, closing them could be painful for the animal.

In particular, if the third eyelid is damaged, it can become lacerated. As described by Greenside Animal Hospital, this is a common injury seen in active cats involved in fights.

Scratches can also cause cornea ulceration, which is painful. Common symptoms of eye trauma include:

  • Redness
  • Inflammation
  • Watery eyes
  • Discharge
  • A noticeable scratch
  • Cloudiness
  • Pawing at the eye

These eye injuries can be treated with eye drops, but the eye may need suturing in the most severe cases.

Foreign Bodies

Besides eye trauma, foreign bodies within the eye, such as glass, sand, or thorns, can cause painful sores and ulcers that prevent the cat from sleeping with its eyes shut. If the foreign body isn’t treated quickly, it can lead to an eye infection.

Items that are only penetrating the surface of the cornea can be removed under local anesthetic. However, if the foreign body has gone in deep, it’ll need surgical removal. 

Dry Eye

Dry eye in cats is scientifically known as keratoconjunctivitis sicca (KCS). Dry eye occurs when the cornea becomes inflamed and the surrounding tissue dries out.

It’s caused by the inability to produce adequate amounts of tear duct film, which lubricates the eye and removes dirt and debris. According to VCA Hospitals, common causes of KCS include:

  • Weakened immune system, which is usually inherited
  • Feline herpes virus
  • Some medications
  • Nervous system effects from an inner ear infection

Cats with KCS usually have:

  • Red, irritated eyes
  • Excessive squinting and blinking
  • Dull appearance
  • Thick, yellow discharge

Some cats hold their eyes shut, while others can’t shut them at all because the eyes are too painful. As a result, they’ll sleep with the affected eye open to avoid discomfort.

Watching Out For Owners

Cats that have formed an intense bond with their owners sometimes can’t bear to be apart from them and like to know where they are at all times.

As described by a journal on Current Biology, cats attach themselves to their owners and use them as a sense of security.

Researchers discovered that cats that had developed a strong bond with their owners felt less stressed and become more relaxed as soon as the person returned from a brief absence.

This study indicates that some cats keep their eyes open while they sleep to monitor their owners’ movements. If their owner moves into another room, the cat will wake up and follow to remain close to them.

Waiting For Food

Hungry cats sleep little and often to conserve the energy they have. If they know food is nearby, or it’s nearly dinnertime, they’ll become more alert – even as they sleep – to ready themselves for food.

Similarly, greedy or opportunistic cats keep their eyes open to react as soon as their owner goes into the kitchen or area where food is stored. Here, they’ll follow in the attempt to win treats or food.

cats eyes roll back when sleeping

Why Do Cats Have A Third Eyelid?

When cats sleep with their eyes open, they expose their third eyelid. The first two eyelids occur on the top and bottom of the eye, meeting in the middle every time a cat closes its eyes. 

In comparison, the third eyelid, also called the nictitating membrane, is located in the eye’s inner corners. The third eyelid acts like a windshield wiper each time a cat blinks, clearing dust, pollen, debris, and other foreign bodies. It also produces up to 50% of a cat’s normal tears.

As previously mentioned, when cats are relaxed and go into a deep sleep, their eyes sometimes remain open. Similarly, if the eyes start closed, they gradually open as the cat’s muscles become more and more relaxed.

The third eyelid becomes more noticeable during the cat’s resting stages to protect the cornea and moisten the eye.

While it’s normal to see a cat’s third eye when it’s sleeping, it can be the sign of an illness when it shows when the cat’s awake and alert. Symptoms of an illness include:

  • Increased urination or thirst
  • Frequent trips to the litter box
  • Decreased or increased appetite
  • Increased vocalization
  • Weight loss or gain
  • Changes to grooming habits
  • Foul breath
  • Hiding away

Therefore, keep an eye on your cat’s third eyelid in case it remains visible when your cat wakes up. If it does, seek veterinary advice.

So, while it may look like cats have their eyes completely open when they sleep, their third eyelid keeps them protected from dirt and debris. Cats are closely related to their wild cousins. As a result, they have advanced instincts ingrained within them to protect themselves from harm, even if they’re safe inside their home.