Tonometry is the measurement of pressure or tension within the eye. It is advisable for adults, particularly individuals over 40 to have their intraocular pressure (IOP) measured routinely as elevated IOP’s can lead to optic nerve damage. The optic nerve is a crucial part of the visual system; it collects all the visual information gathered by the photoreceptors of the retina and transmits this information to the brain where the signals are interpreted as vision. Optic nerve damage can lead to decreased peripheral vision (tunnel vision) and loss of nerve tissues. Elevated IOP’s can commonly occur without symptoms, meaning like many other eye conditions the individual may be unaware there is a problem. Elevated IOP’s is associated with glaucoma; as a result tonometry is important in diagnosing and monitoring glaucoma.
Non-contact tonometry, more commonly known to patients as the ‘puff of air test’ allows the optometrist to quickly measure IOP’s in millimeters of mercury (mmHG). The non-contact tonometer works on the principle of a time interval; measuring the time it takes from the initial generation of the puff of air, to were the cornea is flatten by the air, to the point where the timing device stops as the cornea returns to its normal shape. It takes less time for the puff of air to flatten an eye with low IOP’s than it does in eye with high pressures.
In normal individuals the pressure is commonly between 10-21mmHg. In individuals with elevated IOP’s the measurements will be repeated on a separate day at a different time of day to account for fluctuations in IOP at different times of day. The procedure is completely painless, takes only a few seconds to perform and will not affect vision meaning driving afterwards is safe.