Why Do You Blink?

Step 1 of 5

Your eye is covered in a liquid film.

Three layers: watery in the middle, sticky underneath so it clings, and oily on top so it does not evaporate. Light passes through all of it before reaching you.

Step 2 of 5

That film breaks up in about ten seconds.

Left alone, it thins and tears into dry patches. Dry patches scatter light, which is why your vision goes fuzzy if you stare without blinking.

Step 3 of 5

A blink is a squeegee.

The lid sweeps from the outside inwards, pushing old fluid towards your nose and laying down a fresh layer behind it, in about a third of a second.

Step 4 of 5

Your brain hides the darkness.

You blink roughly fifteen times a minute, losing about half an hour of daylight a day — and never see a single flicker, because vision is suppressed as the lid moves.

Step 5 of 5

You blink more when you are thinking, less when you are reading.

Blink rate tracks attention, not dryness. Concentrating on a screen can halve it, which is exactly why screens leave your eyes feeling gritty.

Blinks are not random. In a group watching the same film, people tend to blink at the same moments — the dull bits.