A traditional tonometer must make contact with the eye in order to obtain a pressure measurement. The air puff test emits a gentle puff of air onto the eye, then measures the time it takes for the air to flatten a small area of the cornea and return to the instrument.
The air puff test is advantageous to traditional tonometry in that it can be performed with less skill and can be done by a technician. Also, it does not touch the eye, so there is no concern with contamination. Furthermore, no eye drops are needed before the test.
Some clinicians feel that the air puff test is not as accurate as a traditional tonometer that actually touches the eye. However, this may depend more on the actual brand of NCT and the properties of a patient’s own eye tissue.