Have you ever wondered what your eyes do when you finally close them after a long day of visual processing and stimulation? Let’s take a closer look at what happens behind your closed lids when your head hits the pillow.
What Do Your Eyes Do When You Sleep?
During sleep, our closed eyes function in a limited fashion with the ability to sense light. This explains why switching on a bright light or the sun rising in the morning can wake you up while lying in a dark room will help you sleep.
While asleep, your eyes don’t send visual data or information about images to your brain. In fact, it takes almost 30 seconds for the connection between your eyes and your brain to reboot when you wake up. This is why it’s often difficult to see complete and clear images when you first wake up.
When your eyelids are closed during sleep, the body perceives darkness which helps melatonin production, a hormone necessary for sleep and circadian rhythm.
The Stages of Sleep and Eye Movement
Our bodies pass through five phases of sleep known as stages 1, 2, 3, 4, (which together are called Non-REM) and REM (rapid eye movement) sleep. During a typical sleep cycle lasting around 90-110 minutes, you progress from stage 1 to 4, then REM, and then start over. As the night goes on, you’ll have longer REM sleep and less deep sleep.
Only 20% of our total sleep time is spent in REM sleep, and about 50% is spent in light sleep (stage 2). The remaining 30% of our total sleep is spent in the other stages (1, 3, and 4).
During stage 1 of non-REM sleep, your eyes open and close slightly while slowly rolling back. When sleep is deeper during stages 2-4, your eyes no longer move.
- Stage 1: You begin to fall asleep and can be awakened easily. Your eyelids begin to close, and your eyes start to roll slowly underneath your eyelids.
- Stage 2: Light sleep when your heart rate begins to slow. Eye movement will stop, body temperature will drop, and your breathing will regulate during this phase of sleep.
- Stage 3: The first stage of deep sleep when the body relaxes even more; muscle tone, pulse, and breathing rate decreases. (This is the stage when sleepwalking, sleep talking, or night terrors tend to occur.)
- Stage 4: The deepest phase of sleep, when there is no muscle activity and the most restoration occurs. If awakened from this stage, you may feel disoriented for a few minutes before fully waking.
What Happens During REM Sleep?
REM sleep is the last phase of sleep before looping back to Stage 1 sleep, and when most dreams occur. The eyes move rapidly while closed during this phase, which is thought to play an essential role in learning and forming memories. A person’s breathing, heart rate, blood pressure, and brain activity increase during this phase, while muscles are temporarily unable to move.
Do Your Eyes Roll Back When You Sleep?
When you start to fall asleep, your eyes may slowly roll back and outward. This movement is known as Bell’s phenomenon. Once in a deeper sleep, eye movements stop for a while until entering REM (rapid eye movement) sleep later in your sleep cycle.
Do Your Eyes Twitch While You Sleep?
An eyelid twitch is an involuntary, uncontrollable spasm of the eyelid. This movement typically lasts a few minutes throughout the day and often disappears while you’re asleep.
Potential causes of eye twitching include:
- Fatigue or lack of sleep
- Stress or major life changes
- Too much caffeine
- Dry or irritated eyes
- Eye strain
- Certain medications
- Problems with either of the eyelid muscles that close or open your eyelid
Do Your Eyes Clean Themselves When You Sleep?
Though your eyes don’t technically clean themselves when they sleep, your eyelids are hard at work, providing a protective barrier to keep debris out of the eyes and keep moisture from our natural tears on our eyes. This helps to prevent dryness and irritation throughout the night.
Why Do I Wake Up With Eye Gunk in the Morning?
Many people wake up with eye gunk or eye crusties (less commonly known as “rheum”) in the corners of their eyes, which is typically an aftereffect of the eye’s normal protective process. When awake, regular blinking helps keep our oily tears from our meibomian glands on our eyes and also flushes out debris and normal mucus produced by the conjunctiva. When asleep, most people’s eyelids remain closed, and blinking no longer occurs. With the help of gravity, eye discharge collects along our eyelashes and in the corners of our eyes, resulting in hard crusts or sticky, wet gunk in our eyes in the morning.
What Happens When You Sleep in Contacts?
Our corneas need oxygen from their external environment to function properly, remain clear, and stay healthy. When our eyes are open during the day, oxygen reaches the cornea directly through our natural tears on the eye. However, suppose someone sleeps with contact lenses in their eyes. In that case, the contacts form a barrier between the cornea and our natural tears which limits the amount of oxygen available to the cornea. The term for this is known as “corneal hypoxia,” and can result in several contact lens-related complications.
Although there are certain brands of contact lenses approved by the USA Food and Drug Administration (FDA) for overnight wear, sleeping in contact lenses significantly increases the risk of painful eye infections and the following:
- Conjunctival inflammation and redness (conjunctivitis)
- Corneal swelling (edema) and inflammation (keratitis)
- Corneal neovascularization (new and abnormal blood vessel growth)
- Corneal opacity and scarring
- Permanent vision loss
If you do accidentally sleep in your contact lenses, you should remove them as soon as you wake up and not wear contacts for 24 hours. By giving your eyes a break from contact lens wear, your corneas will have greater access to oxygen and your natural tears again.
If you are consistently sleeping in your contacts or experience any redness or pain after removing them, you should contact your eye doctor to discuss the possible need for medical evaluation and alternative contact lens options that may better suit your eye health.
Why Do Some People Sleep With Their Eyes Open?
Nocturnal lagophthalmos is the term for sleeping with your eyes open or incomplete eyelid closure when asleep and occurs in about 5% of the population.
There can be many causes for sleeping with your eyes open, including:
- Damage to the facial nerves (i.e., Bell’s palsy) or eyelid muscles
- Bulging eyeball (proptosis)
- Eyelid disease
- Chemical burns
- Physical trauma
- Sedatives (i.e., sleeping pills)
- Excessive alcohol
- Thyroid eye disease (which can cause swelling and inflammation of the muscles around the eyes)
- Infections (less common, but may result from Lyme disease, Mumps, Chickenpox, Polio, Diphtheria, Botulism)
- Very thick eyelashes
- Certain cosmetic procedures (ex: Botox injections, eyelid-tightening surgery)
Potential side effects from nocturnal lagophthalmos may include:
- Dry eyes upon waking
- Sore or painful eyes
- Red eyes
- Watery eyes
- Blurry vision
Take Care of Your Eyes With a V-Eye-P Exam
In short, while your eyes do move around during sleep, they are not actively processing visual imagery. Closing your eyelids and sleeping essentially gives your eyes a break. Shut-eye helps recharge your eyes, preparing them to help you see the next day.
If you have any concerns about blurry vision, dryness or irritation, or excessive eye crust or discharge upon waking, schedule an eye exam with us today.