What’s up with the air puff?

No one likes the air puff test, however it does provide a very useful screening test for glaucoma. The air puff, or non-contact tonometer, measures the pressure within the eye without touching the eye. Other instruments can be used to measure the pressure, but they must actually touch the eye to do so, requiring the eye to be numbed first. Being able to measure the pressure without numbing the eye or touching the eye makes the test much more convenient.
How does it work? Think about an inflated balloon held in your hand, and blow a stream of air at it. A small indention will be temporarilly created where the air stream hits the balloon surface. The lower the pressure within the balloon, the larger will be the resulting indentation. Higher pressure will result in a smaller indentation. Now think about your eye. When the air puff hits the surface of your eye, a momentary indentation is created on the eye. The air puff instrument watches the surface of the eye, and measures the change on the surface of the eye caused by the puff of air. The pressure in the eye is then immediately displayed, even if you blinked! Amazing.