Comparison of Corneal Tomography: Repeatability, Precision, Misalignment, Mean Elevation, and Mean Pachymetry

ABSTRACT

Purpose: To compare corneal tomography and its statistical uncertainty for measurements obtained by three clinically used corneal tomographers: A Scheimpflug camera (Pentacam HR), a swept source optical coherence tomography system (CASIA SS-1000), and Placido ring imaging (TMS-5).

Material and Methods: Repeated measurements with all three devices on 34 normal eyes were used to estimate the repeatability, precision, and mean values of corneal elevation and pachymetry within 8 mm diameter. The repeatability (standard deviation) was calculated for each data point of the corneal elevation data-maps of anterior and posterior cornea as well as for the pachymetry data-maps. Uncertainty on the position of the eye at each measurement might contribute to the differences between elevation data-maps. To take this into account, we defined the precision as the standard deviation for the elevation data-maps of anterior and posterior cornea after correction of misalignment-effects (rotation, translation). The mean elevation and pachymetry data-maps were fitted with Zernike polynomials for interdevice-comparison.

Results: Pentacam HR offered the best repeatability and precision for the anterior corneal elevation (<3 and <1.6 μm, respectively). CASIA SS-1000 offered good repeatability and precision with high resolution for posterior corneal elevation, and the best repeatability for pachymetry (<3 μm). TMS-5 measured anterior elevation with similar repeatability to CASIA SS-1000 (<6 μm). The data-maps of the three tomographers could not be used interchangeably. The largest differences were observed for pachymetry and posterior corneal elevation data-maps.

Conclusions: Misalignment limited the repeatability of TMS-5 and Pentacam HR, but had little influence on the repeatability of CASIA SS-1000.

KEYWORDS:

• Corneal shape
• corneal height
• interdevice comparison
• corneal diagnostics
• corneal thickness

Supplementary material

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Declaration of interest

The authors report no conflicts of interest.

Additional information

Funding

This research was funded through a research grant of the Federal Ministry of Economic Affairs and Energy (BMWi). It was presented at the ESCRS meeting in Lisbon 2017. Simon Schröder received a bursary from the meeting’s organizers for his participation and presentation of the poster. There are no conflicts of interest.