Biology

The Science Of What Happens When You Blink

Turns out the thing you do 28,000 times per day is kind of mysterious

Biology
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Jan 25, 2017 at 11:27 AM ET

There’s a lot of coordination that goes into blinking, but the most amazing thing is that you don’t usually notice you’re doing it (except for right now. You’re going to be thinking about blinking a lot for the next few minutes). Scientists are still learning the details about what happens when you briefly close your eyes, and it’s more complicated than you’d imagine. They’ve answered some questions, but more remain.

The main reason we blink is to coat the cornea, the outermost tissue in the eye, with a layer of tears to keep it moist and free of irritants that might damage it. “You want your eyes to be wet but not too wet,” Baptiste Caziot, a postdoctoral fellow in vision sciences at the École Normale Supérieure in Paris, told Vocativ.

We do this a lot — about ever two to three seconds, or 28,800 times per day, each for 40 to 200 milliseconds at a time. Blinking is a reflex, so it’s hard to know what would happen if you never blinked again, but it seems likely that your corneas would get painfully dry and you might even develop vision problems.

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But a lot more is going on beyond the corneas when we blink. There are distinctive eye movements, called saccades, that only happen when you blink. The movements realign the eyeballs obliquely along the field of vision, each functioning independently depending on its positioning. A 2012 study found that your brain uses blinks to take mini-rests.

Perhaps what’s most striking, however, is what doesn’t happen when we blink. Light doesn’t dim or flicker. The image isn’t blurry or shadowy or shaky. And when you open your eyes after a blink, you’re probably still staring at the thing you were looking at before you blinked, despite the saccade that moved the eyeballs.

But the muscles that return our eyeballs to what we were looking at are slow, so there’s some error to that refocusing. That is the subject of a new study led by researchers from UC Berkeley and published in the journal Current Biology. In the study, the researchers used a classic experimental technique—they projected a white dot onto a wall in front of the participants in a dark room. Then, during a blink, when the participant’s eye was closed, the researchers would move the dot to the side just slightly. The participant’s eye would refocus on the new location with an extra motion—and after about 35 blinks, their eyes would refocus to the new spot automatically—but the participants didn’t notice that their eyes were working extra hard. Without that steadying and shift, the images we see after a blink would be dark and jittery, the researchers said.

“What it shows is you have a system that is dedicated to making sure there is no offset between where you look after and before the blink. You don’t notice the target moved, your visual system is making that adjustment,” says Caziot, who was uninvolved in the research.

Believe it or not, scientists still have questions about blinking. Caziot says other teams are looking into the coordination that happens between the muscles that physically close and open the eyelid, called the orbicularis oculi and levator palpebrae superioris muscle respectively, and the three sets of muscles that move the eyeball. There’s also debate about the role of blinking in how our brains process the passing of time.

“You do have quite a lot of processing going on to make you feel like you live in a coherent world,” Caziot says. “That’s most of your visual processing—making sure everything around you is making sense.”