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Berthold Seitz, Berit Elzer, Corinna Spira-Eppig, Achim Langenbucher, Elena Zemova, Nóra Szentmáry, Timo Eppig; Repeatability of Scheimpflug imaging and anterior segment optical coherence tomography parameters in keratoconus is decreasing with increasing severity. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3436.
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© ARVO (1962-2015); The Authors (2016-present)
The indication for corneal crosslinking in keratoconus (KC) is typically based on the progression of tomographic parameters. Definition of progression, however, requires knowledge about measurement repeatability. The purpose of this study was to assess the repeatability of tomographic parameters in keratoconus depending on KC severity comparing two different devices.
A total of 129 eyes with keratoconus stages from 0 (normal) to 4 according TKC (Topographic Keratoconus Classification) were examined five times repeatedly with the Scheimpflug tomographer Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) and the anterior segment optical coherence tomographer (AS-OCT) Casia 2 (Tomey Corp., Nagoya, Japan). Main outcome measures included (1) mean anterior (KA) and (2) mean posterior power (KP), (3) mean astigmatism (KAST) and (4) corneal thickness at thinnest point (TCT). Results were compared between severity stages of KC, and in the same stage between two devices using Wilcoxon’s test. P-values <0.05 were considered statistically significant. In addition, the standard deviation (SD) of repeated measurements was compared between severity stages and within the severity stages between two devices.
The number of eyes in TKC groups 0|1|2|3|4 was 25|20|24|27|33, respectively. TCT was measured significantly thicker (from 10 µm with TKC 0 to 28 µm with TKC 4) with the Pentacam HR. The SD of repeated measurements of KA, KP, KAST and TCT increased from (AS-OCT | Pentacam) 0.11 D | 0.08 D, 0.01 D | 0.03 D, 0.14 D | 0.09 D and 1 µm | 5 µm for eyes with TKC 0 to 0.98 D | 0.73 D, 0.12 D | 0.19 D, 1.00 D | 1.03 D and 11 µm | 12 µm for eyes with TKC 4. There were significant differences regarding keratometric and pachymetric data between the two devices for eyes with the same KC stage.
Repeatability of tomographic indices in keratoconus is decreasing with increasing severity of KC using Pentacam HR and AS-OCT Casia 2. None of the devices proofed to be consistenly more repeatable than the other. The tomographic results of both devices cannot be used interchangeably. Therefore, identification of KC progression should be performed with the same device. The magnitude of change for identifying progression should be adjusted according to the KC stage.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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