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Comparative Study
. 2019 Oct 16;14(10):e0223770.
doi: 10.1371/journal.pone.0223770. eCollection 2019.

Comparison of corneal elevation and pachymetry measurements made by two state of the art corneal tomographers with different measurement principles

Simon Schröder  1 , Achim Langenbucher  1 , Jens Schrecker  2
Affiliations
Comparative Study

Comparison of corneal elevation and pachymetry measurements made by two state of the art corneal tomographers with different measurement principles

Simon Schröder et al. PLoS One. .

Abstract

Purpose: To compare corneal tomography measurements (elevation and pachymetry) as made by two corneal tomographers: Pentacam AXL and CASIA 2.

Material and methods: The devices were used in a standard measuring mode. 77 normal eyes were measured five times with both devices. The data maps for anterior and posterior corneal elevation and pachymetry were exported and analyzed. Repeatability and average values were calculated for each valid data point on the exported data maps. We also calculated a corrected repeatability of the elevation data maps by removing rotation, tilt, and decentration through realignment of the elevation measurement of each eye prior to analyzing the variations in the measurement usingthe same method as for the repeatability.

Results: Pentacam AXL offered the better (corrected) repeatability for anterior corneal elevation measurements. CASIA 2 offered better repeatability for the pachymetry measurements. The tomographers could not be used interchangeably. The central corneal thickness was measured 9 μm ± 3 μm larger when measured with Pentacam AXL compared to CASIA 2.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Difference between repeatability and corrected repeatability.
Sketch of a central cut through two corneal surface elevation measurements (first measurement in red, second measurement in black) of the same eye. The sketch is not to scale and differences are exaggerated for better visibility. (a) Differences in surface elevation between consecutive measurements define the repeatability. (b) The differences are partly due to alignment errors such as decentration, axial displacement, rotation, and tilt (misalignment). (c) After realignment of the surfaces, the differences are potentially reduced. The differences between the realigned consecutive measurements define the corrected repeatability.
Fig 2
Fig 2. Repeatability and corrected repeatability of anterior corneal elevation.
(a) Repeatability (red) and corrected repeatability (black) of anterior corneal elevation data maps obtained with Pentacam AXL and (b) CASIA 2 averaged along concentric rings ± standard deviation (shaded area) as a function of the radial distance r from the corneal apex.
Fig 3
Fig 3. Repeatability and corrected repeatability of posterior corneal elevation.
(a) Repeatability (red) and corrected repeatability (black) of posterior corneal elevation data maps obtained with Pentacam AXL and (b) CASIA 2 (right) averaged along concentric rings ± standard deviation (shaded area) as a function of the radial distance r from the corneal apex.
Fig 4
Fig 4. Repeatability of pachymetry.
(a) Repeatability of pachymetry data maps obtained with Pentacam AXL (left) and (b) CASIA 2 (right) averaged alongconcentric rings ± standard deviation (shaded area) as a function of the radial distance r from the corneal apex.
Fig 5
Fig 5. Systematic differences.
Systematic differences between the average elevation data maps obtained with Pentacam AXL and CASIA 2 (average elevation obtained with Pentacam AXL minus average elevation with CASIA 2). (a) The measurements are consistent for the anterior corneal elevation. (b) There were significant systematic differences between the posterior corneal elevation measured with Pentacam AXL and CASIA 2 and (c) between the pachymetry measurements.
See this image and copyright information in PMC

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