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N. Schaedle, J. D. Unterlauft, T. Klink, G. Geerling; Evaluation of Dynamic Contour Tonometry in Keratoconus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4348.
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The gold standard for measuring intraocular pressure (IOP) is until now Goldmann applanation tonometry (GAT), which depends on the central corneal thickness (CCT) and curvature. In patients with keratoconus who have an abnormal corneal geometry and thickness, measurement of pressure with GAT is often difficult and not very reproduceable. We compared the dynamic contour tonometry (DCT), a digital method to measure IOP which is adapted to the corneal geometry, with GAT .
IOP was measured in 66 patients (26 men and 40 woman, mean age of 35 ± 10,57 years) with GAT and DCT in randomised order. All patients had a keratoconus which was assured by topography. In addition central corneal thickness (CCT) was measured with the Pentacam. For statistical analysis the Pearson-Correlation was calculated and a Bland-Altman diagram plotted.
Mean corneal thickness was 488,7 ± 44,9 µm. DCT measured the IOP at a mean value of 14,8 ± 2,7 mmHg and GAT at 13,1 ± 2,9 mmHg. With a mean difference of 1,7 ± 2,5 mmHg DCT measured significantly higher than GAT (p≤0,05) Neither IOP measurements with GAT (r=-0,01, p>0,05), nor those with DCT (r=0,14, p>0,05) showed a significant correlation to central corneal thickness .
The example of keratoconus confirms that IOP measured by GAT is lower than if measured by DCT. Because both methods are independent of the CCT they are equaly convenient for IOP follow-up in eyes with keratoconus, which may result in progressive corneal thinning in the longterm.
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