Why we blink less in front of a screen
When we stare at a screen, we blink about half as often as usual. Normally it is around fifteen to twenty blinks a minute, but during focused work that number can fall to eight or ten. On top of that, many blinks are incomplete: the lid drops only halfway, and the tear film is not fully renewed.
The tear film is a thin layer of fluid that keeps the cornea moist and smooth. When it is not renewed for a long time, it starts to evaporate, the surface of the eye becomes uneven, and vision blurs slightly. The eye then burns, itches, or feels as if there were sand in it. Discomfort most often sets in toward evening, after several hours in front of a monitor.
A blink itself lasts roughly one to two tenths of a second. During that time the lid spreads the tear film across the cornea, and glands along the edge of the lid release a thin layer of oil that slows evaporation. When blinks are rare or incomplete, that layer is renewed less well, and the lower part of the cornea stays more exposed to the air.
Blinking is not just mechanical cleaning. The brain also uses it to mark small pauses: we blink at the end of a sentence, when we turn a page, or when we finish a thought. That is why deep concentration and infrequent blinking go hand in hand.
People also blink reflexively. A touch to the cornea, a sudden bright light, or something flying quickly toward the face triggers a blink without any decision on our part. It seems that during deep focus spontaneous blinking weakens while the reflexes remain, and that is exactly what this test relies on.
The well-known 20-20-20 rule advises that, every twenty minutes or so, you look for about twenty seconds at something about twenty feet (six meters) away. This relaxes the focusing muscles and, along the way, usually prompts a few full blinks as well.
Evaporation is also affected by the humidity of the air, the airflow from an air conditioner or fan, and the position of the monitor. When we look upward, the eye opens wider and more of its surface is exposed, so a monitor placed slightly below eye level usually means less evaporation.
If your eyes regularly feel dry or burn, or your vision blurs toward the end of the day, it is worth talking to an eye doctor. Artificial tears and good habits help, but the cause is not always just the screen.
While you read, do not hunt for cues with your eyes and do not try to control your blinking. The aim is for your eyes to behave the way they normally do while you work.