I’ve been known to claim that I’m “just resting my eyes” while watching a movie at night, when I know full well that I’m exhausted and, in reality, just a couple seconds away from conking out. But, as it turns out, your eyes actually do need rest, and “resting your eyes” isn’t just a euphemism for taking a nap. After prolonged or intense use, the eyes themselves can get tired, which, in medical terms, is called eye fatigue or eyestrain (aka asthenopia).

The main symptoms of tired eyes are the ones you’ll know well, if you’ve ever stared at a computer screen for hours: pain and discomfort, itchiness, dryness, squinting, blurry vision, twitching, and even headache. You may even have red eyes when you wake up from a restless night. Much like any other muscle in the body, the muscles in the eyes can become fatigued when they’re overworked, which is what triggers these symptoms, says Anita Mistry, optician at contact-lens brand WALDO. “Over time, if your eyes are tired, and you’re experiencing a few of these symptoms, it can also become difficult to concentrate,” she says.

What causes tired eyes?

In short, focusing your eyes for an extended period of time is what causes tired eyes. And that can happen in a few different ways.

One of the most common is staring at a digital screen for several hours, whether it’s a computer screen, tablet, or phone. This can cause a particular kind of tired eyes called digital eye strain, which happens due to the tendency for a person to blink less often and blink “incompletely” (that is, not fully closing the eyes with each blink) while looking at a screen.

Though it isn’t fully understood why this change in blinking happens with screen use, researchers speculate that “it’s likely caused by a neural feedback loop,” says Brian Boxer Wachler, MD, ophthalmologist and medical reviewer at All About Vision. Additionally, the concentration involved in doing an active cognitive task on a screen—like work or reading versus passively watching a movie—can independently reduce a person’s blink rate, too.

“Blinking less often causes more exposure of the eyes and makes them dry,” says Dr. Wachler. Over time, that lack of lubrication can lead to the pain, soreness, and blurry vision typical of eyestrain.

“The muscles in the eyes that focus up close can become fatigued when you look at something too closely for too long.” —Brian Boxer Wachler, MD, ophthalmologist

In the case of digital eye strain, there’s also the glare from the screen, the blue light, and the tendency to lean your face toward a screen, all of which can be hard on the eyes. “The muscles in the eyes that focus up close can become fatigued when you look at something too closely for too long, which happens often with screens,” says Dr. Wachler.

Aside from screen use, however, it’s also possible for the eyes to get tired from any prolonged visual task (like reading a book or driving), playing video games that require you to move your eyes back-and-forth quickly, and straining to see something in dim lighting, says Mistry. “Concentrating your focus on something like small text or print or simply overusing your eyes without resting them can also lead to tired eyes,” she adds.

You’re also more at risk for eye fatigue from the get-go if you’re sleep-deprived (and therefore not physically closing the eyes for long enough each night), have dry eyes, or have uncorrected vision, which can cause you to strain the eye muscles in order to see or read, according to Dr. Wachler.

What can you do to prevent tired eyes?

If you know you’ll be doing visually taxing work or looking closely at a screen for several hours, Dr. Wachler recommends practicing the 20/20 rule, which involves closing your eyes for 20 seconds every 20 minutes in order to rest and naturally re-lubricate them. It may also be helpful to maintain good posture and avoid leaning toward your screen, as focusing too closely can set off eyestrain in the first place.

It’s also important to wear your glasses or contacts, if you’re near- or farsighted, and to use prescription reading glasses if you need them, adds Dr. Wachler. This way, you’re less likely to find yourself straining to see or read in a way that can tire the eyes more quickly.

How is eyestrain treated?

In most cases, eyestrain will dissipate on its own once you identify the activity that’s triggering it—close reading, screen use, or the like—and give yourself a brief break from that activity. “Ensure that the room is light enough to read comfortably, close your eyes for a few seconds, and give yourself a light massage to help relax the eyes,” says Mistry.

If dryness is your primary eyestrain symptom, or having dry eyes is contributing to your eyestrain, you can also use artificial tears (which can be purchased over-the-counter) or take oral flax oil capsules, which Dr. Wachler says are “systemically absorbed, helping nourish mucous membranes [which contribute to eye wetness].”

While discomfort is the most common health risk of frequently tired eyes, if you already have advanced dry eyes, regularly exhausting the eyes can lead to complications such as corneal abrasions and infections, says Dr. Wachler: “If the tear film poorly covers the cornea (as can be the case with tired eyes), it can cause breakdown of the epithelium, or the cornea’s top layer, allowing it to tear or for bacteria to gain access.” Both scenarios are rare, but should either happen, you would need to seek medical treatment from an ophthalmologist.

In most cases, however, tired eyes are nothing more than a temporary nuisance that you can resolve with an eye break.