Written by Raymond Nakamura
Once upon a time, Raymond earned his doctorate studying the hydrodynamics of sand dollars. Nowadays, when he’s not employed as personal assistant to his lovely and demanding daughter, he enjoys creating fun and educational experiences in science and history using facts and fiction, words, pictures and whatever else is handy. Follow him on Twitter @raymondsbrain


air puff non contact tonometry

Created date

Sunday, March 27, 2016 - 9:00am

Ever Wonder About Air Puff Eye Tests?

When I visit the eye doctor, I can understand what most of the tests are for, like: "Which one is clearer, A or B?" or "Can you see the dot? How about this one?" But, "Hold still while I puff air at your eye"? I wondered what that one was for.

The device, I found out, is the air puff tonometer, which measures introcular pressure (IOP)—the pressure in your eyeball. It had not occurred to me that eye pressure was a thing to measure, but if something blocks the aqueous humour fluid flow to your eye, it is not funny. High eye pressure can damage your optic nerve and be a sign of glaucoma—So, not a good thing—especially for those who are more at risk, including those with a family history of glaucoma.

The air puff tonometer releases air over a range of pressures at your eye. At the same time, an infrared beam of light is shone off your cornea. When the cornea flattens out under the pressure of the air, the beam of light reflects at a different angle. When this occurs, the device records the pressure of the air that was required, measured in millimetres (mm) of mercury (Hg), a quaint unit of measurement that lingers like an after image of an earlier time. The test is usually repeated to account for variations in eye pressure.

So-called normal eye pressure ranges from 12–21 mmHg. Individuals vary, so repeated measurements over time helps establish what is normal for an individual. This air puff method is not as accurate as other tonometer methods and tends to give higher readings. But it is easier to administer and less invasive, so optometrists use it as a screening method. If a problem is indicated, then the eye doctor will resort to a more precise method involving anesthetizing your eye and pressing a small plate against it. 

Some people don't like this air-puff test and other methods are being used as well. If you've had your eye pressure measured, let us know in the comments what method was used and how you felt about it.
 

If you're a curious type, like Raymond, you might have wondered about Epsom Salts—what's the buzz about Epsom baths? Speaking of buzz, you might also have wondered about Fly Swarms. So did we! 

 

Comments

Thanks for clearing up the

Thanks for clearing up the confusion! I hated those machines as they startled me!!

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