The 20-20-20 rule: what it is and how to make it stick

If your eyes feel gritty by mid-afternoon, or the words on screen start to swim a little after a long stretch of email, you have probably met the 20-20-20 rule already. Every 20 minutes, look at something 20 feet away for 20 seconds. It is the advice eye doctors give most often to people who work at screens, and it is easy to understand.

It is also very easy to forget. This post covers what the rule actually does for your eyes, what it does not do, and how to turn it into something that happens without you having to remember it.

What the rule asks you to do

The rule has three parts, and each one has a reason behind it.

• Every 20 minutes. Long, unbroken stretches of close work are what tire the eyes. Twenty minutes is short enough that the strain never builds up very far.
• Look 20 feet away. That is about six meters: the far side of a room, a window, the end of a corridor. At that distance the focusing muscles inside your eyes can almost fully relax.
• For 20 seconds. Long enough for the focusing muscles to let go, and long enough to blink properly a few times.

The rule is usually credited to Jeffrey Anshel, a California optometrist who wrote about computer eye strain in the 1990s. Today it shows up in advice from the American Academy of Ophthalmology and the American Optometric Association, among others.

Why close work tires your eyes

When you look at something near, a ring of muscle inside each eye, the ciliary muscle, tightens to change the shape of the lens and bring the text into focus. Your eyes also turn slightly inward so that both point at the same spot. Holding those two efforts for hours is a bit like holding a light weight at arm's length. Nothing hurts at first. Then it does.

Screens add a second problem. When people concentrate on a screen, they blink less often, and many of the blinks they do make are partial ones that don't sweep fully across the eye. The surface of the eye dries out between blinks, which is why screen days so often end with eyes that sting, burn or feel full of sand.

Looking far away answers both at once. The ciliary muscle relaxes, the eyes stop converging, and with nothing to read you tend to blink normally again.

What the 20-20-20 rule does not do

It helps to be honest about the limits, because the rule is sometimes sold as more than it is.

• It does not damage-proof your eyes. Digital eye strain is uncomfortable, but for most people it is temporary. The rule eases the discomfort. It is not protecting you from lasting harm, because in adults screen use is not known to cause any.
• It is not a treatment. Headaches that don't go away, blurred vision that stays blurred, double vision or eye pain are reasons to see an optometrist or a doctor. An out-of-date glasses prescription is one of the most common reasons screen work feels hard, and no break schedule fixes that.
• The numbers are a rule of thumb. Nobody has shown that 20 minutes is better than 25, or that 20 seconds is the magic length. Research on breaks for screen workers is fairly small, and it mostly suggests that regular short breaks ease symptoms. The value of 20-20-20 is that it is memorable.

Why it's hard to keep up

Almost everyone who hears the rule agrees with it, and almost nobody follows it for more than a day or two. The reason is simple: the moment you need a break is the moment you are most absorbed. You don't notice 20 minutes passing when you are deep in a spreadsheet, and when you do notice, you are in the middle of something.

Setting a timer helps for a while, but a timer that interrupts with a sound or a banner starts to feel like a nag. Most people turn it off within a week. The trick is a prompt that is easy to act on, easy to put off for a moment, and gentle enough that you don't resent it.

Ways to make it a habit

Here are a few approaches that work better than willpower.

Tie it to things you already do

Use natural pauses as triggers. Every time you send an email, glance out of the window before you open the next one. Every time a file is uploading or a build is running, look across the room until it finishes. Every time you take a sip of water, look up. You will not hit exactly 20 minutes, but you will look away far more often than you do now.

Give your eyes somewhere to go

The rule is easier when there is something worth looking at 20 feet away. If you can, put your desk so that a window or a long view is just off to one side of your screen, not behind it. A plant or a picture on the far wall gives your eyes a target in rooms without a view.

Pair it with a few slow blinks

While you are looking far away, close your eyes slowly and fully three or four times. This spreads the tear film back over the surface of the eye and takes care of the dryness half of the problem in the same 20 seconds. Blinking more at the computer has more on why screens cut your blink rate.

Let something else keep count

Your attention is the scarce resource here, so hand the counting to your Mac. In Notchpals, eye breaks belong to the Eyes characters, Blip, Bill and Blush, and Blip comes with every copy of the app. Whichever one is in your crew slides down from the notch every so often and asks you to look across the room. It goes by the time you actually spend at the Mac, so a long lunch away from the desk doesn't count as screen time.

BlipLook twenty feet away for twenty seconds! What do you see? Is it amazing?

Press Done when you have looked away, or Later if you are in the middle of a sentence, and it comes back once, 20 minutes on. Notchpals doesn't try to match the strict rule. Eye breaks come out of one daily allowance that every repeating reminder in your crew draws from: 4 on Calm, 8 on Normal and 12 on Chatty, and even Chatty keeps them at least 40 minutes or so apart. That is fewer prompts than one every 20 minutes, on purpose, so the notch never turns into an alarm clock. The habits above fill the gaps, and the visits keep the habit alive.

The rest of the picture

The 20-20-20 rule is one piece of a comfortable screen day. A few other changes do as much or more:

• Put the screen at the right distance. About an arm's length away, with the top of the screen at or a little below eye level, so that you look slightly down at it. How far your screen should be from your eyes covers the details for laptops and larger displays.
• Match brightness to the room. A screen much brighter or darker than its surroundings is harder work. On a Mac, turn on automatically adjust brightness in System Settings under Displays, if your Mac offers it.
• Make text bigger. If you lean in to read, the text is too small. Use a larger scaled resolution, or zoom in with Command and the plus key in most apps.
• Blink on purpose. Slow, full blinks a few times an hour keep the surface of the eye comfortable.
• Keep your glasses up to date. Many people who struggle at screens need a small change in prescription, or glasses made for the distance of a screen.

Taken together, these turn the 20-20-20 rule from a chore you forget into one part of a working day that is kinder to your eyes. Start with the breaks, because they are the easiest to fix, and let something other than your memory keep the time.