Staring at a fixed near distance locks the ciliary muscle that focuses the lens; over hours it fatigues like any held muscle. Blink rate also drops from ~15 to ~6 a minute at a screen, which dries the tear film — the gritty, sand-in-the-eyes feeling by 4 pm. Looking far away releases the focusing muscle; the long blink and the walk to a window re-wet the surface.

Set the desk up once: screen an arm’s length away (50–70 cm), top of the monitor at or just below eye level, brightness matched to the room rather than maximum, and no glare from windows behind or in front. Fonts a size larger than comfortable is a tax worth paying — it survives every busy day.

When to stop self-managing: persistent blurring at any distance, double vision, headaches that start behind the eyes, or dry-eye that misses no day of the week deserve an optician, not another timer. Prescription “computer distance” lenses exist for exactly this.

Based on the 20-20-20 guidance publicised by optometry bodies (e.g. the AOA and NHS eye-care advice). Not medical advice. Last reviewed 2026-09-21.