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M. E. Iliev, M. Egli, D. Goldblum, A. Kipfer-Kauer, K. Rohrer, C. Tappeiner, M. Abegg, L. Berger; Assessment of a New Goldmann Applanation Tonometer. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2044.
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The classic Goldmann applanation tonometer (GAT) has been further developed by Haag-Streit Int., Koeniz, Switzerland. The applanation principle has been retained, while the internal force transmission and the pressure gauging have been optimized, the display of results digitized, and an internal measurement control integrated. The new device is claimed to offer an increased stability, less variability of results, and intraocular pressure (IOP) readings within 0.5 mmHg. The study purpose was to compare the standard GAT AT900 with the new version of the device (GAT digital), to test the variability of consecutive measurements, and the device safety.
Patients at the Ophthalmology Dept. were included after informed consent, and protocol approval by the local ethical committee. Study criteria were aimed at excluding participants with corneal abnormalities that might influence the applanation method (e.g., corneal surgery, keratoconus, sicca, cormeal edema, etc). Central corneal thickness was measured with a non-contact method. IOP measurements were taken with a pair of two tonometers (GAT and GAT digital) in random order. Four tonometer-pairs were used throughout the study. For each eye, three measurements in a row were taken with one device, and, after an interval of three minutes, three measurements with the second device. Mean values and standard deviation (SD) were calculated. Analysis was performed separately for the right and left eyes.
111 patients were included. Mean IOP for the right eyes (OD) was: GAT 17.53±6.74 mmHg, range 5.33-52.33; GATdigital 17.45±6.99 mmHg, range 6.30-52.70 (p=0.88); and for the left eyes (OS): GAT 18.69±9.14 mmHg, range 6.0-60.0; GATdigital 18.42±9.19 mmHg, range 5.80-59.43 (p=0.82). Trend line: OD: y = 1.0222x - 0.4714; OS: y = 1.0004x - 0.2548, for a range of pressures between 5 and 60 mmHg. Pearson correlation coefficient: OD: 0.985; OS: 0.994. Bland-Altmann analysis: Compared with GAT, GATdigital readings showed almost no skew: mean difference OD: -0.08 (SD 1.19); OS: -0.24 (SD 1.03). The 95% confidence interval (SD 1.96) was OD between -2.42 and +2.25 mmHg; and OS between -2.33 and +1.91.
The new GATdigital is safe, and shows a very good correlation with the standard GAT. No skewness trend of readings was noticed. The correlation was preserved in eyes with low and with high pressures. The display of IOP up to the first decimal digit is not necessarily assocciated with a more precise measurement, but may offer an additional comfort compared with the 2 mmHg scale of the classic GAT.
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