Tonometry: Can You Really Trust Those Readings?

Written by Michael Vu

OCT montage showing cross-section of a human eye. Credit: Jon Brett. CC BY-NC

Although visits to an ophthalmologist become more frequent with age, regular eye check-ups are an important aspect of a healthy lifestyle. If you’ve ever been to an ophthalmologist, you might be able to draw many similarities between ophthalmologists and optometrists. And in more ways than one, they are pretty similar; however ophthalmologists play a larger role within your holistic health.

One important test performed during regular ophthalmic check ups is tonometry. Tonometry is the measurement of your eyeball’s intraocular pressure. More specifically, it is the fluidic pressure inside your eye, usually measured in mmHg. As society progresses both technologically and medically, there has been increasingly more ways to measure this pressure. However, certain methods are definitely more efficient and accurate than others, and this article will encompass those methods [4].

Why should you care? Well, tonometry measurements can provide information on possible health issues that may have gone undetected. For example, a high intraocular pressure demonstrates to the doctor that you are at a really high risk of glaucoma. Glaucoma is an eye disease that leads to optic nerve damage and loss of vision. Therefore, it is of great importance that these tests yield results as accurate as possible, so doctors can target and address these health issues before they elevate in severity [1,2].

There are multiple methods of performing tonometry exams. The first and most common is the Tono-Pen. The Tono-Pen requires the doctor to first numb your eye with some anesthetic drops, and then lightly tap the flat tip of an electronic pen, on the middle of your eyeball. Although results are instantaneous and the test can be performed virtually anywhere, because the skill level and technique of the person providing the exam will play a factor, inconsistent application of the test will yield results that are not as reliable [3].

Another tonometry method that is also widely practiced is non-contact tonometry. This procedure involves resting your head on a chin rest, while having a light shined directly into your eye. After prepping, the doctor administers a slight puff of air, and the machine measures how the light reflections change in response to this. This method is a more accurate in a sense that the administrator’s skill level does not really influence the results of the exam. However, this exam is immobile, and other varying health factors such as corneal thickness and eyeball shape can play a role in results [3].

To this day, the most accurate method has to be Dynamic Contour Tonometer. Similarly to the Tono-Pen, a measuring device is physically placed on your eyeball. However, unlike the Tono-Pen, this device is connected to a large apparatus, and the tip is rested on your eyeball. This takes the administrator’s inconsistent application out of the factors list, and will also render corneal thickness and elasticity effects uninfluential. Furthermore, unlike the Tono-Pen, the tip of the measuring device is not flat and blunt, instead it is curved to compensate for the curvature of the eyeball. By addressing little issues like curvature and corneal thickness, the vision of more accurate tonometry readings are within reach [5].

However, in today’s society, with such fast paced lifestyles, most people prefer the mobility of Tono-Pens, over the accuracy provided by immobile machines. Maybe in the near future, Dynamic Contour Tonometry could be provided at more reasonable costs, and in smaller sizes, so that it will become to the go-to method, for it is a test of great importance [6].

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