The 20-20-20 rule says: every 20 minutes at a screen, look at something about 20 feet (6 metres) away for at least 20 seconds. The American Academy of Ophthalmology and the American Optometric Association both recommend it for digital eye strain: the tired, dry, sometimes blurry eyes you get after hours at a screen. A short look into the distance lets the eye's focusing muscle relax and gets you blinking again. Studies show the breaks can ease symptoms while you take them. They don't show much more than that, and the hard part is remembering to take them at all.
What digital eye strain is
The AOA defines computer vision syndrome, also called digital eye strain, as "a group of eye- and vision-related problems" from prolonged screen use. The usual symptoms are eyestrain, headaches, blurred vision, dry eyes, and neck and shoulder pain. A 2018 review in BMJ Open Ophthalmology puts the prevalence at "50% or more among computer users".
Two reassurances from the AAO: devices "will not damage your eyes permanently", and the discomfort "is not caused by blue light" (Digital Devices and Your Eyes).
Why screens tire your eyes
Focusing. To see something close, a ring of muscle inside the eye, the ciliary muscle, contracts so the lens becomes rounder and stronger. Reading at 20 cm asks for about 5 dioptres of that effort (StatPearls). Hold it for hours and the system tires. Looking far away is the moment the muscle can let go.
Blinking. We normally blink around 15 times a minute; the AAO says that rate "can be cut in half when staring at screens". A 1991 study measured "an average 5-fold drop in blink rate" during computer work. Fewer blinks means the tear film dries out between them, which is where the stinging, gritty feeling comes from.
Where the rule comes from
The rule is credited to Jeffrey Anshel, an optometrist, who told Optometry Times he came up with it around 1991 as part of a "blink, breathe, and break" approach. It is simple advice from clinical practice, not the result of a trial. The AOA adds a longer one: rest the eyes for 15 minutes after two hours of continuous computer use.
What the studies show
The evidence is thin and mixed:
- A trial of reminders. Talens-Estarelles and colleagues (2023) put software on the laptops of 29 people with symptoms. It reminded them to follow the 20-20-20 rule for two weeks. Dry eye and eye strain symptoms went down, and the eyes refocused faster. But "this improvement was not maintained one week after discontinuation", and the tear film didn't measurably change.
- A trial of breaks. Johnson and Rosenfield (2023) had 30 young adults read on a tablet for 40 minutes, with 20-second breaks every 5, 10, 20 or 40 minutes. The breaks made "no significant effect" on symptoms. The authors note there is "relatively little peer-reviewed evidence to support this rule."
So: breaks are cheap, they help some people while they keep taking them, and they don't fix anything for good. Blinking on purpose, a screen at arm's length and slightly below eye level, and treating dry eye are part of the same toolkit.
Breaks and myopia
Myopia (nearsightedness) means distant things look blurry. In children, more near work goes with a little more myopia: a 2015 meta-analysis of 27 studies found the odds rose 2% for each extra dioptre-hour of near work a week. The AAO notes that time outdoors, especially in early childhood, "can slow the progression of nearsightedness" (Screen Use for Kids).
No study shows that the 20-20-20 rule prevents myopia or reverses it.
There is also a temporary kind of blur. After sustained near work, some people see slightly less clearly at a distance for a while, called near-work-induced transient myopia. It is small, a fraction of a dioptre, and usually fades within minutes, though one study found it hadn't fully gone two minutes after reading in up to 46% of myopes. Whether it leads to lasting myopia is still an open question (Ciuffreda and Vasudevan, 2008).
If distant things stay blurry, or the blur is new, see an optometrist or an ophthalmologist. A reminder app is not an eye exam.
One person's experience
I'm Jo, and I make Toolnotch, so read this as one person's story and nothing more:
"Before, I used to see blurry in the distance. That's no longer the case since I started taking a break every 20 minutes with Bodybreak; it lets my body and my eyes rest."
It may be the temporary blur described above, or something else entirely. One person's experience proves nothing, and it's no reason to skip an eye exam.
The body side
Sitting still for hours has costs of its own. The WHO's 2020 guidelines say that replacing sedentary time with activity "of any intensity (including light intensity) provides health benefits". In a 2012 lab study, 19 overweight adults who stood up for a two-minute light walk every 20 minutes had lower blood sugar and insulin after a meal than when they sat without a break. That's a short-term result in a small group. A Cochrane review found one low-quality study where short breaks every half hour cut sitting at work by about 40 minutes a day.
A 20-second eye break won't get you walking. A longer break every hour or so, where you stand up and move, covers that side.
Making it happen on a Mac
macOS has no break reminder. Screen Time can schedule downtime and limit apps, and its Screen Distance alert works only on iPhone and iPad. You can run a timer by hand, or use an app; the break reminder app guide compares the options.
Here is how Bodybreak, the break tool in Toolnotch, runs the rule:
- A heads-up first. 30 seconds before a break, an island under the notch says « Break soon · Tap to snooze 5 min » with a countdown.
- It waits for a pause in your typing. A break that comes due mid-sentence waits until your hands rest, a minute at most.
- The break. By default a small card drops from the notch: « Look at something 20 feet away » (« 6 meters » on a metric Mac) and a 20-second ring. Nothing dims, and Skip is on the card.
- Done. The card folds back and the notch says « Break done · 3 today ».
It also pauses itself during calls (the microphone or a camera is in use), presentations in full screen, videos, screen recordings and games. It only checks whether the microphone or camera is in use; nothing is recorded. If you leave the Mac for two minutes, that counts as your break.
Every 90 minutes of work, a five-minute long break walks you through standing up, neck rolls, shoulder shrugs, looking out a window and drinking water. You can change the interval (15 to 60 minutes), the length (10 to 60 seconds), and choose a stricter mode in Settings › Bodybreak.
Its limits: it can't tell whether you actually looked away. Recording detection covers known recorders only. And no app replaces an eye exam.
Toolnotch runs on macOS 15 or later. See pricing, or try the break card in the demo on the home page.
FAQ
Does it have to be exactly 20 feet?
No. The point is to look at something far enough that your eyes stop focusing close: out of a window, down a hallway, across the room. About 6 metres is the usual figure.
Do blue light glasses prevent eye strain?
The AAO says digital eye discomfort is not caused by blue light. Breaks, blinking and a comfortable screen distance do more.
Can the 20-20-20 rule cure nearsightedness?
No. There is no evidence that breaks prevent or reverse myopia. Lasting blurry distance vision needs an eye exam.
How long should a screen break be?
For the eyes, 20 seconds every 20 minutes. The AOA also suggests 15 minutes of rest after two hours of continuous computer use. Standing up and moving every hour or so helps the rest of the body.
This article is general information, not medical advice. If your eyes hurt, your vision changes or a symptom lasts, see an optometrist or an ophthalmologist.