Repeatability of corneal tomography and the impact of misalignment
Session Details
Session Title: Presented Poster Session: Glaucoma and Imaging
Venue: Poster Village: Pod 3
First Author: : S.Schroder GERMANY
Co Author(s): : S. Maurer T. Eppig B. Seitz K. Rubly A. Langenbucher
Abstract Details
Purpose:
To compare statistical uncertainty of corneal tomography measured with three corneal tomographers: A Scheimpflug imaging system (Pentacam HR, Oculus Optikgeräte GmbH, Wetzlar, Germany), an anterior segment optical coherence tomography system (CASIA SS-1000,Tomey Corp., Nagoya, Japan), and a combined system using Placido disk- combined with Scheimpflug imaging (TMS-5, Tomey Corp., Nagoya, Japan).
Setting:
Institute of Experimental Ophthalmology, Homburg/Saar, Germany
Department of Ophthalmology, Saarland University Medical Center, Homburg/Saar, Germany
Methods:
In this comparative study we performed repeated (5-8) measurements on 34 normal eyes to estimate repeatability, and precision. The repeatability (standard deviation) was measured for each point of the exported corneal elevation of anterior and posterior cornea as well as the pachymetry. Differences between elevation data can partially be explained by positioning variability of the eye at each measurement (misalignment). The Precision was calculated from the elevation data of anterior and posterior cornea after correction for misalignment (displacement, tilt, rotation) as standard deviation from the corrected elevation. Correction for misalignment was applied to the anterior and posterior surface independently.
Results:
The Pentacam offers best repeatability and precision for the anterior cornea (<3µm and <1.6µm within 8mm diameter,respectively). Unlike the Pentacam, the precision and repeatability with CASIA are almost identical, misalignment plays a minor role. The CASIA offers good repeatability/precision for posterior corneal elevation, and the best pachymetry-repeatability (<4µm). Although, the Placido disk mode of the TMS-5 measures the curvature of the cornea, the derived elevation data show a repeatability comparable to the elevation data of CASIA. Merging ring and slit calculations in the TMS-5 worsens its repeatability for anterior corneal elevation, but reduces the impact of misalignment.
Conclusions:
The three devices are capable of assessing the cornea with good repeatability. Pentacam has its strength in measuring the elevation of the anterior cornea, while CASIA provides most excellent repeatability for pachymetry.
Financial Disclosure:
NONE
