When we drive a motor-vehicle in bad weather, it is very important to have the windscreen wiper working efficiently. Yet the best windscreen wiper ever made for any car can’t compare with the “windscreen wiper” nature has given us for our eyes!

The lids of our eyes, which move up and down when we blink, are our built-in windscreen wipers. The lids are made up of folds of skin, and they can be raised and lowered by certain muscles. But they move so rapidly that they don’t disturb our vision in any way.

A curious thing about our lids is that they work automatically, just as windscreen wipers do on motor-cars when they’re turned on. We blink our eyes every six seconds! This means that in the course of a lifetime, we pull them back and forth about 250 million times!

Why is blinking important to us? How does it protect our eyes? One reason has to do with our eyelashes. These are the short curved hairs which are attached to each lid. Their job is to catch dust which might go into our eyes. When you walk through rain or a sandstorm, the lids automatically drop down and the eyelashes keep out foreign matter. The eyebrows, by the way, carry off rain or perspiration to a side, so that the drops won’t run into the eyes.

But the chief benefit of blinking is that this provides automatic lubrication and irrigation of the eyes. Along the edge of each lid there are twenty or thirty tiny sebaceous glands. These glands have their opening between the lashes. Every time our lids close, these glands go to work and a secretion comes out. This secretion lubricates the edge of the eye lid and the lashes, so that they won’t become dry.

Here is how blinking provides “irrigation” for the eye. In each eye we have a tear gland, where the liquid that makes tears is stored. Every time we blink, the eyelid applies suction to the opening of the tear gland and takes out some of the fluid. This prevents the eye from drying out. We might say that we “cry” every time we blink our eyes!