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C. Linden, P. Hallberg, K. Santala, A. Eklund; Clinical Evaluation of Applanation Resonance Tonometry . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4432.
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Intraocular pressure (IOP) is most commonly determined by applanation tonometry, where the force needed to flatten a certain area of the cornea is measured. Different sources of error such as corneal thickness and corneal curvature has been shown to influence the accuracy of measurements. This suggests that new methods are needed, and the research in this area have met increasing interest. A new technology, applanation resonance tonometry (ART) was recently introduced for IOP–measurements. The corneal contact area is measured with a resonator sensor device. The sensor produces a frequency shift which is shown to be proportional to the contact area. A force transducer mounted in the same device measures simultaneously the contact force. The purpose of this study was to evaluate the new ART system in a clinical setting with Goldmann applanation tonometry (GAT) as the reference.
An open randomised study included measurements on totally 153 eyes evenly distributed in three pressure intervals; below 16 mm Hg, between 16 and 23 mm Hg and above 23 mm Hg. The ART sensor was mounted on a biomicroscope. A quick applanation against the cornea was performed with the ART sensor. Linear regression was used to analyse continuous force increase against continuous frequency shift during the applanation. The slope in the frequency interval (–30 to –180 Hz) was determined and interpreted as proportional to IOP. Mean (n=6) ART was compared with mean (n=6) GAT readings.
The correlation between IOP according to ART and GAT was R= 0.95 (p<0.01, n=153). The SD was 2.1 mm Hg with a significant dependence of age and measurement order.
The resonator sensor technology is introducing a new methodology for measuring intraocular pressure. The method is, to our knowledge, the first to combine simultaneous, continuous sampling of both force and area. The precision was within the limits set by ISO–standard for eye tonometers.
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