The idea that numbers never lie is a lie unto itself. Numbers can obfuscate, they can mislead, and they can be the results of faulty equations—garbage in, garbage out, as they say in the computer science field. In the field of ophthalmology, one of the most evident instances of numbers’ less-than-truthfulness lies in the measurement of intraocular pressure, or IOP. Measuring IOP is integral to screening for glaucoma—the loss of vision due to damage of the optic nerve. This damage most often occurs when insufficient drainage of fluid in the eye places pressure upon the nerve. To detect the likelihood of this damage, eye doctors use tonometers to measure this pressure, but due to instrumental error or patient variation, the numbers can, in some sense, lie. While getting the perfect tonometer reading may not be possible, these ways to improve intraocular pressure measurement accuracy help ophthalmologists get closer to the truth.
Use Goldmann When Possible
The Goldmann applanation tonometer is the gold standard of IOP measurement. The Goldmann tonometer works by making direct contact with the surface of the eye and measuring the resistance of the probe while the patient is seated before the tonometer. Goldmann tonometers provide the highest accuracy and should be the first choice of ophthalmologists to seek the most accurate reading. However, placement before a Goldmann tonometer is not for everyone, and for those patients, a handheld tonometer, such as the Tono-Pen, is an alternative, albeit a less accurate one.
Account for Corneal Thickness
The thickness of the cornea can vary from person to person, which affects intraocular pressure readings. Abnormally thick corneas, despite no effect on the person’s vision, do have an effect on IOP measurements. With more resistance to the probe from a thicker cornea, a tonometer will report higher pressure than the eyes may actually have. Ophthalmologists can counter the inaccuracy that corneal thickness supplies by complementing a tonometer with a pachymeter—a measurement of thickness. (Compare with pachyderm, the term for the thick-skinned elephant.) By determining thickness in conjunction with IOP, eye doctors can get a clearer picture of the pressure.
Improper Tono-Pen Calibration
The Reichert Tono-Pen provides a useful alternative to the Goldmann tonometer and its limitations. However, the Tono-Pen, which already has a lower accuracy than the gold-standard Goldmann, can be further compromised if an ophthalmologist does not cover the tip of the probe. If you’re using the Tono-Pen as an alternative or adjunct, proper care is one of the best ways to improve intraocular pressure measurement accuracy. Not only is skipping the tip cover unsanitary, but it also decalibrates the tonometer, which accounts for the presence of the cover on the probe. Tono-Pen tip covers will not only keep your Tono-Pen safe but also functioning as best it can to deliver such important readings.