By 3 PM every workday, my eyes felt like they had sand in them. Dry, gritty, hard to focus. I tried those blue-light glasses everyone was pushing — spent forty dollars on a pair — and they did approximately nothing for me. Eye drops helped for about ten minutes.

An optometrist I saw for a routine checkup asked how much screen time I logged. When I told her, she said: “Try the 20-20-20 rule before you spend more money on products. It is free and it actually works.” Six months later, I still do it every day. My eyes feel normal again.

What the 20-20-20 rule is

Every 20 minutes, look at something at least 20 feet away for 20 seconds. That is the entire rule. Three numbers. No equipment, no subscriptions, no special glasses.

The science behind it is straightforward. Your eye muscles — the ciliary muscles — contract to focus on close objects like screens. Holding that contraction for hours causes fatigue, the same way holding a bicep curl for eight hours would wreck your arm. Looking at a distant object relaxes the ciliary muscles completely. Twenty seconds gives them enough time to reset.

Why 20 feet specifically

At 20 feet, the light rays entering your eyes are essentially parallel — your focusing muscles do almost zero work. Anything beyond 20 feet works, but 20 feet is the minimum distance for full relaxation. Looking across the room or out a window both qualify.

How to actually remember to do it

Nobody remembers to check the clock every 20 minutes. I tried. Lasted about an hour. What worked for me was using a free browser extension that dims the screen every 20 minutes as a reminder. There are several — search for “20-20-20 timer” in your browser’s extension store. The screen dim is impossible to ignore but not disruptive.

If you do not want an extension, set a recurring timer on your phone. Or just make it a habit: every time you finish a task or send an email, look out the window. The exact interval matters less than the habit of regularly breaking near-focus.

What else helps

Blink consciously. People blink half as often when staring at screens — about 7 blinks per minute instead of the normal 15. Blinking spreads tear film across your eyes. Less blinking = dry spots. Make a point of fully closing your eyes a few times during each 20-second break.

Position your screen so the top edge is at or slightly below eye level. Looking downward at a screen exposes less eye surface area to the air, reducing tear evaporation. This one adjustment cut my dry-eye symptoms noticeably within a few days.