Most of us have never heard of a tonometer or the science of tonometry.  But most people visit an optometrist or ophthalmologist every year or two, especially those of us who wear contact lens or eye glasses.  Nearly everyone over the age of 30 who has visited an optometrist has been exposed to a tonometer but did not know the name of the machine.

Tonometers are used by ophthalmologists and optometrists to measure intraocular pressure (IOP) in the eyes; the pressure should be between 10-21 mmHg.  The readings refer to the millimeters (mm) of mercury (Hg) used in measuring pressure.  Readings higher than 21 mmHg can indicate a detached retina or the early stages of glaucoma.