Why Do Optometrists Blow Puffs of Air Into Your Eye?

I’m basically blind without my contacts, so every year I dutifully schlep to the optometrist to get my eyes tested and outfitted for a new prescription. And every year, I dread it—not just because of the pressure to read the tiniest lines without squinting (just me?), but because of the part of the exam where the doctor has me sit in front of a machine and blasts two puffs of air into each eye. I recently sat through the torturous puffs of air again, and I asked my optometrist: Is this necessary? Can I skip it next time?

Unfortunately for me, this part of the eye exam helps the doctor determine the fluid pressure inside my eyeball, and is therefore totally necessary. High pressure in the eye can cause glaucoma, or vision loss due to damage to the optic nerve. So the doctor asks me to put my chin on the chin rest, stare at a green light, and then uses a machine called a non-contact tonometer to administer two gentle (but totally startling) puffs of air onto the surface of my eye. The machine measures the air that bounces back and then calculates my intraocular pressure. No one likes this part of the test; it was even the subject of an episode of Friends:

There are other ways to test for glaucoma, but many optometrists opt for the air puff test because it’s quick and painless for the patient. So I guess next year, I'll just have to open my eyes up wide and bear it.

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