This Is Why You Can’t Keep Your Eyes Open When You’re Tired
Surely you’ve experienced the phenomenon of feeling like you can’t possibly keep your eyes open for one second longer when you’re tired — in the predawn hours feeding a newborn or while attempting to stay up and watch your favorite show. Why does this eyelid heaviness happen?
There are a multitude of reasons. Eyelids are made of muscles, and these muscles are at work all day, keeping the eyelids open and blinking. Like all muscles, says Dr. Kelsey Kleinsasser, an eye specialist based in Lee’s Summit, Missouri, they need rest. “During waking hours [our eyelids] are continuously blinking,” Kleinsasser says. “It’s analogous to being on your feet all day.” (One thing to note: Heavy eyelids are different than droopy or sagging eyelids, which can be caused by inflammation — think allergies — or ptosis, a condition where the upper eyelid droops due to muscle weakness that occurs with age.)
“During waking hours [our eyelids] are continuously blinking. It’s analogous to being on your feet all day.”
Aside from fatigue, dry eye is another cause of eyelid heaviness, says Kleinsasser. When eyes are open for an extended time (in other words, all day long) it can lead to dry eye, even for people who are not overly susceptible to dry-eye symptoms, he says. The tired, “heavy” feeling is a “protective mechanism” that forces people to close their lids and lubricate the eye’s sensitive outer layer, or cornea. What’s more, that overwhelming urge to rub your eyes when you’re tired also has a biological purpose — it can help alleviate dryness by stimulating the lacrimal glands to produce more tear fluid.
Hormones can play a role as well, says Dr. Jack Parker, an ophthalmologist and corneal specialist based in Birmingham, Alabama. “Each day, as the morning progresses into the afternoon and then the evening, your body’s circulating adenosine, and melatonin levels rise, specifically to prepare the body for sleep,” he explains.
“As a result of these circulating chemicals, your core body temperature drops as does your heart rate and blood pressure. This is accompanied by a feeling of tiredness, which may be thought of as a ‘hunger’ or ‘appetite’ for sleep.” Since it’s difficult to sleep with your eyes open, this tired feeling corresponds with a desire for the eyes to close — hence the heavy eyelids. Interestingly, coffee works in part by blocking adenosine, which explains why you often feel less heavy-lidded after a cup or two.
For heavy, tired eyes, there’s only one thing that will help: sleep. The next time you find yourself struggling to stay awake, do yourself a favor and stop fighting the feeling. Your eyes will thank you.