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Assessment of True Intraocular Pressure

Submitted by dave on Mon, 06/09/2008 - 6:47pm

"This may be the beginning of the end of the GAT as the gold standard for measuring IOP." -- Etsuo Chihara, MD, PhD

This quote comes from the author of the following paper, published in Survey of Ophthalmology (Surv Ophthalmol. 2008 May-Jun;53(3):203-18): Assessment of true intraocular pressure: the gap between theory and practical data

The paper includes a discussion of my three favorite tonometers: the Tiolat iCare rebound tonometer, the Pascal dynamic contour tonometer and the Reichert Ocular Response Analyzer.

In my opinion, every glaucoma patient should be examined by their doctor with both the Pascal dynamic contour tonometer and the Reichert Ocular Response Analyzer. Your doctor will probably want to use the Goldmann applanation tonometer (GAT) for historical reasons, but there is no longer any good reason for not examining glaucoma patients with the best tonometers available. Intraocular pressure remains the number one risk factor for glaucoma and it is the only risk factor that is the target of approved treatments. Therefore, the combination of self-tonometry at home (with the Reichert AT555 or the Tiolat iCare) and in-office IOP examinations with both the Pascal dynamic contour tonometer and the Reichert Ocular Response Analyzer makes sense.

Here is the abstract of the paper I mentioned above:

A precise assessment of the intraocular pressure (IOP) is crucial for diagnosis and decision making regarding treatment modalities in patients with glaucoma. Recent epidemiologic studies show that a difference of only 1 mm Hg in the mean IOP may be critical enough to determine the visual field prognosis in patients with glaucoma. However, the Goldmann applanation tonometer, which is current gold standard, is not precise enough to measure the true IOP within an error of 1 mm Hg. There are many clinically proposed correction algorithms to correctly measure IOP. However, corrections using only the central corneal thickness and curvature may not be sufficient in each individual case. In this article, previously reported theoretical equations about the effects of corneal topography, modulus of elasticity, and tear film on Goldmann applanation tonometric IOP readings were reviewed, and their discrepancies with clinical or experimental data were analyzed. Thereafter, new tonometers such as the dynamic contour tonometer, the rebound tonometer, and the ocular response analyzer were compared with the Goldmann applanation tonometer and other popular tonometers. 

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