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Can You Trust the Accuracy of Intraocular Pressure Measurements?

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Although Goldmann applanation tonometry remains the gold standard for determining IOP, several factors leave eye care professionals wondering whether they can truly trust the accuracy of intraocular pressure measurements?

Due to different corneal parameters and technique factors, the Goldmann applanation tonometry method can be flawed. Let's take a closer look at some of the most commonly-known factors affecting the accuracy of tonometry as well as a few simple ways you may be able to improve the accuracy of your intraocular pressure measurements.  

Corneal Thickness Affects IOP Measurements

It's well-known and accepted that corneal thicknesses has an effect on accuracy of intraocular pressure measurements. While people with thicker corneas have traditionally received higher readings; patients with thinner corneas have received lower readings. Even though there has been a lot of work dedicated to creating a nomogram to account for corneal thickness, none of the work has been notably fruitful.

Why? Because there is much more involved than simply corneal thickness. Specifically, the accuracy of intraocular pressure measurements is also impacted by corneal rigidity.

Previous Corneal Surgery Affects IOP Measurements

High levels of astigmatism and previous corneal surgery can also affect the accuracy of intraocular pressure measurements. If a patient has had the LASIK surgery performed, you can expect challenges with getting an accurate measurements.

If possible, you may be more effective at getting measurements prior to LASIK and then compare it with post-LASIK measurements to understand the differences. Others have suggested attempting to get peripheral measurements.

IOP Measurements Fluctuate During the Day

In addition to the other previously mentioned factors, your patient's intraocular pressure measurements are likely to fluctuate throughout the day. For many patients, their IOP reading will be the highest in the morning — but this isn't the case for everyone. As a matter of fact, an increasing amount of evidence points to the possibility of spikes in pressure outside of the normal business hours.

To counteract this, it may be more helpful to take pressure readings as late and as early in the day as you can. You should also consider things happening between office visits or outside of office hours you may not be aware, such as the use of marijuana, alcohol, and drinking large amount of liquid.

Additional Factors Affecting IOP Measurements

If your patient has corneal scarring, it's important to know they may have a higher IOP measurement; while those with corneal edema can have lower readings. In addition, you may have difficult getting an accurate intraocular pressure reading on patients who hold their breath during the measurement or those who squeeze their eyelids shut.

You may also have difficulty keeping a patient's droopy eyelid out of way of the tip of the tonometer. In some instances, patients who are large and/or need to lean forward too far can cause your reading to be thrown off.

Your technique can affect the accuracy of your patient's intraocular pressure measurements. For instance, if you're accidently applying pressure to the eye, it will render a higher pressure reading.

Simple Methods for Improving the Accuracy of Intraocular Pressure Measurements

The accuracy of your intraocular pressure measurements are nothing short of critical. These clinical and trusted measurements drive a vast range of decisions in glaucoma management. You'll use IOP levels to determine which patients are at risk for glaucoma and identify which patients you should treat.

Once you've administered treatment, you'll then use IOP measurements to determine the efficacy of your treatment. Needless to say, your ability to attain the most accurate IOP measurements is of unparalleled importance. While some factors affecting the accuracy of intraocular pressure measurements are out of your control, there are techniques you can use to improve the accuracy of your IOP measurements.

  1. Your technique is of the utmost importance. When you're taking a patient's pressure, make sure you do not touch their eye at all. If you need to provide assistance in holding the patient's eye open, do not put any pressure on the globe — it will increase IOP.

  2. If your patient is leaning forward significantly, try to position them so they're not leasing as far forward.

  3. If your patient has a tight collar around their neck, ask them to loosen their collar or unbutton their shirt.

Contact Keeler for Reliable Ophthalmic Instruments

We get it — Goldmann applanation tonometry isn't perfect. Even so, most experts see it continuing to be the gold standard for the foreseeable future. The fact that Goldmann is connected to the slit lamp makes it cheap, convenient, accessible, and an essential piece of equipment for every ocular exam room.

Since we introduced the Pulsair in 1987, Keeler has led the filed in tonometry. We're home to multiple generations of cutting-edge tonometry products and a world-class line of non-contact and contact tonometers.

Contact Keeler Ophthalmic Instruments today to learn more.

About the Author Eugene VanArsdale

Eugene is the Director of Marketing Communications at Keeler Instruments. He has been with Keeler since 1982 and is co-holder of two patents for the company. Eugene has a true passion for the eye care industry and has dedicated himself to understanding the ins and outs of the optometric and ophthalmic equipment market.