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J. R. Lewis, A. M. Mahmoud, C. J. Roberts; Comparison Between Placido Disc and Scheimpflug Surface Topography Measurements. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4022.
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To compare Placido disc and Scheimpflug topographic devices for agreement and repeatability of surface topography measurements on calibrated test surfaces.
A comparison of Placido disc (Keratron Scout, Optikon, Rome, Italy) and Scheimpflug (Pentacam, Oculus Optikgerate GmbH, Wetzler, Germany) surface topography measurements was performed. Topography data were collected on six spherical test surfaces with curvatures ranging from 40.04 D to 45.70 D. The surfaces were positioned to allow best alignment and focus. Five consecutive scans were acquired for each surface using the Keratron Scout and Pentacam. The Pentacam was set to 3-D scan mode with 50 images. The Sim K values were recorded from each device and statistically analyzed. Repeated Measures ANOVA and two-tailed T-tests were performed to test repeatability and to compare the devices’ computed values to the calibrated test surfaces’ values.
Repeated Measures analysis showed that the Pentacam K1, K2, Kave and Cyl values were repeatable (P> 0.05). The Keratron K1, K2, Kave and Cyl were also repeatable (P>0.05). T-test comparisons of the mean Keratron values versus theoretical values showed a nonsignificant difference in mean K1_diff = 0.07 D (P>0.05), however significant differences in mean K2_diff = 0.25 D, mean Kave_diff = 0.16 D, and mean Cyl_diff = -0.19 D (P<0.05). However, these differences were clinically insignificant. The mean Pentacam values versus theoretical values showed a clinically significant difference for all values, mean K1_diff = -1.16 D, mean K2_diff = -0.46 D, mean Kave_diff = -0.81 D, and mean Cyl_diff = -1.06 D (P<0.05). All measures were significantly different (P<0.05) when comparing Pentacam to Keratron.
Both Placido disc and Scheimpflug topographic devices acquired repeatable surface topography values. However there were significant differences between the two devices in terms of accuracy and relative direction of difference in the measured topography values.
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