Gold standard for IOP measurement possible during pandemic, but alternatives available
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Goldmann applanation tonometry for IOP measurement is still possible during the SARS-CoV-2 pandemic with additional steps for safety, but alternative IOP measurement devices are gaining in popularity.
“Disinfection is more important than ever. Disposable [GAT] tips have their quirks, but they can be overcome,” Philip Chen, MD, said at the virtual American Glaucoma Society annual meeting.
Some methods of IOP measurement have become contraindicated during the COVID-19 pandemic. Air puff tonometry, the Ocular Response Analyzer (Reichert) and pneumotonometer all use compressed air, which may cause aerosolization of the tear film.
Goldmann applanation tonometry (GAT) is still the gold standard for IOP measurement, but the method requires anesthetic, fluorescein, the sterilization of tips after each use and the required close proximity of patients and testers, Chen said.
Disposable GAT tips are available to reduce the constant need for disinfecting of reusable tips. Studies have shown a strong agreement between the reusable and disposable tips, but the disposable tips have quirks that must be worked around to acquire an accurate reading, he said.
“You need to turn the prism to an angle. If the prism is kept to 180°, you have a lot of glare, which makes it difficult to read the pressure. In some cases, there are some quality control problems, and there is a small discontinuity in the center of the prism, which affects measurement,” he said.
One alternative to GAT, the Tono-Pen XL (Reichert), operates on the Mackay-Marg principle of applanation. A recent study found a high correlation of 0.76 between the Tono-Pen and GAT. The 95% confidence limits were also high, at nearly 7 mm Hg, Chen said.
The iCare ic100 rebound tonometer is another IOP measurement alternative. It does not require drops and does not require the test to be as close to a patient as GAT. However, the tonometer tips are expensive, and it requires careful positioning for IOP accuracy, he said.
Correlation with GAT outcomes is highest with the Tono-Pen XL compared with the iCare device, he said.
“In glaucoma clinics at the [University of Washington], we are using the disposable Goldmann tips, which are unfortunately fairly expensive, which we make up for by having the retinal and corneal clinics using Tono-Pen. Most of the comprehensive clinics also use Tono-Pen, except for their glaucoma patients,” Chen said during a live discussion at the meeting.
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Chen P. Keeping it safe: How to measure IOP in the era of COVID-19. Presented at: American Glaucoma Society annual meeting; March 4-7, 2021 (virtual meeting).
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