Tired eyes, remedies: clear sight until the evening.

For tired eyes from screens, the remedies that help most are simple: blink fully, look into the distance every twenty minutes, keep the screen 50-70 centimetres away and slightly below eye level, and make the air less dry. If stinging and blurry vision last for weeks, get your eyes tested.

It's six o'clock. You reread the same line of the contract, the letters blur and your eyes sting. I see it often in the people I work with: they blame their age, rarely the day they've put their eyes through.

Tired eyes: what are the symptoms?

Stinging, blurry vision, heavy eyelids and a stiff neck. It's digital eye strain, which doctors also call computer vision syndrome, and it usually builds with your hours at the screen.

• Grit under your eyelids. Dry eyes you rub without noticing.
• Fuzzy letters. You zoom in and check the same figure twice.
• Lead eyelids. In meetings it's hard to follow the slides.
• A stiff neck. Your head pushes towards the screen and your neck carries that weight for hours.

Why do your eyes get tired at a computer?

Mainly because you blink less at a screen, and often only halfway. Then posture, dry air and sight that isn't corrected for that distance add to it.

Your blinking slows down. Normally you blink about fifteen times a minute; at a screen it can drop to five or seven. The brake seems to come more from concentration than from the monitor: it happens on paper too. The screen adds incomplete blinks, which don't close the eye fully and let it dry out.

Posture. Your eyes are one of the sensors your body uses to hold itself upright. If your sight is working hard, your head moves forward to chase the screen, and your neck and shoulders take the load.

Tired eyes from screens: what can you do?

Twenty, twenty, twenty. Every twenty minutes, for twenty seconds, look at something at least twenty feet away, about six metres: out of the window or down the corridor. It's a rule of thumb, sensible and free, though few studies have put it to the test. The mistake nearly everyone makes is spending the break on their phone, eyes back up close.

Full blinks. When the work gets hard, now and then close your eyes on purpose, all the way, without squeezing. The evidence is still thin, but it takes two seconds.

The screen at the right distance. 50-70 centimetres from your eyes, roughly an arm's length. Top edge at eye level, so the centre sits 10-13 centimetres lower: your gaze drops slightly and your eyelid covers a little more of the eye. No window or lamp reflected on the screen. On a laptop, a stand and a separate keyboard.

Less dry air. Air conditioning and heating can dry your eyes: move the vent that blows in your face, and open the window every day, winter included.

Pick the easiest habit and start today: your eyes are the work tool you use most.