What’s the point of the puff of air test?

For lots of people, the puff of air test is the most memorable part of the sight-test, but why is it so important?

The optometrist uses the ‘puff of air’ in order to measure the eye pressure, in a procedure called ‘non-contact tonometry’. The ‘tonomoter’ produces a rapid air puff which temporarily changes the shape of the front of the eye or cornea. A light source and receiver within the instrument measure how quickly the cornea returns to the normal round shape and uses this to calculates the pressure inside the eye.

The test is painless, but the puff of air can make one jump a little! The best result is achieved when the patient is relaxed and sitting still with eyes wide open. The optometrist can demonstrate the feel of the air puff on a hand for re-assurance


The reason this test is important is that having an abnormally high (or low) eye pressure can indicate a risk of certain eye conditions, such as glaucoma. Conditions such as glaucoma might have no symptoms until the disease is quite advanced. By having regular sight tests, including a pressure test, eye problems can be identified and managed earlier, leading to better outcomes for the patient.