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Raksha Urs, Timothy J Archer, Marine Gobbe, Michael Ha, Michele D Lee, Dan Z Reinstein, Ronald H Silverman; Comparison of Ultrasound and Scheimpflug Corneal Pachymetric Maps in Normal and Keratoconic Eyes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2450.
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© ARVO (1962-2015); The Authors (2016-present)
Ultrasound pachymetry has long been regarded as the gold standard for corneal thickness determination. Our aim was to compare measurements of corneal thickness from pachymetric maps obtained by the Pentacam Scheimpflug system with those obtained from the Artemis immersion scanning high-frequency ultrasound system and to assess the agreement between the two devices.
Corneal pachymetric maps of 28 normal and 28 keratoconic (KC) eyes (one per subject) were obtained from Artemis and Pentacam. For each map, the minimum corneal thickness (MCT) and mean corneal thickness in 0.5 mm-wide annuli of up to 3 mm radius around the location of MCT were determined. Thickness progression rate (TPR) was calculated as the slope of the mean annuli thickness as a function of distance from location of MCT.
The MCT of normal eyes from Artemis and Pentacam corneal pachymetric maps were 493.7 ± 32.3 µm and 507.9 ± 32.6 µm respectively and 450.1 ± 55.8 µm and 469.8 ± 52.3 µm for KC eyes. There was high correlation between the MCT readings by the two methods (R = 0.95 for normal eyes and R = 0.96 for KC eyes). Bland-Altman analysis showed that Pentacam values of MCT exceeded Artemis values by 14.3 µm in normal eyes and 19.7 µm in KC eyes. Mean corneal thickness values in each of the 0.5 mm annuli were also highly correlated (R>0.94 for normal eyes and R>0.92 for KC eyes). At the outermost annulus, Pentacam values were thicker by approximately 27 µm in both normal and KC eyes. The average TPR in normal eyes were 17.2 ± 2.5 µm/mm and 21.9 ± 2.5 µm/mm for Artemis and Pentacam, and 33.8 ± 13.1 µm/mm and 35.7 ± 13.3 µm/mm respectively in KC eyes.
While Artemis and Pentacam corneal thickness measurements are highly correlated in both normal and KC eyes, Pentacam values were systematically thicker, with a larger difference at the periphery.
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