2012 - 3 Issue

Original article

Comparison of Central Corneal Chickness and Keratometric Measurements using the Scheimpflug HR Imaging System, Laser Interferometry, Automatic Keratometry and Ultrasound Pachymetry

Petra Pašová
Karolina Skorkovská – Jan Michálek

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Published in Czech and Slovak Ophtalmology: 2012 - 3

Published on website: 20.06.2012

Keywords: keratometry, pachymetry, CCT, Pentacam, BioGraph

Summary

Introduction: The aim of our study was to compare keratometry and central corneal thickness measurements obtained with three different ophthalmic devices and to decide if they can be used interchangeably in clinical practice.

Methods: 43 healthy persons were included in the study (29 women and 14 men, average age 25 ± 3.5 years). Central corneal thickness (CCT) was measured with the Scheimpflug HR imaging system (Pentacam), Allegro BioGraph and with ultrasound pachymetry (RXP OcuScan). Keratometry in two main meridians of the cornea (K1, K2) was measured with Pentacam, Allegro BioGraph and automated keratometry.

Results: The mean difference in K1-readings was 0.01 ± 0.31 D for BioGraph vs. automated keratometry, 0.06 ± 0.23 D for BioGraph vs. Pentacam and 0.05 ± 0.34 D for automated keratometry and Pentacam. The mean difference in K2-readings was 0.29 ± 0.45 D for BioGraph vs. automated keratometry, 0.11 ± 0.28 D for BioGraph vs. Pentacam and 0.19 ± 0.44 D for automated keratometry and Pentacam. The interdevice differences were in all cases statistically significant (p < 0.05). The mean difference in CCT was 4.57 ± 7.84 μm for BioGraph vs. ultrasound, 4.33 ± 7.55 μm for BioGraph vs. Pentacam and 8.90 ± 7.49 μm for ultrasound vs. Pentacam. The interdevice differences in CCT were also statistically significant (p < 0.05).

Conclusion: Our results suggest that the measurements of keratometry and CCT may differ significantly between the tested machines and therefore should not be used interchangeably in clinical practice.

References

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  7. Refai, T. A.: Agreement between pentacam and opd videokeratography in corneal power and axis assessment. Australian J Basic Appl Sci, 2010; 4: 5135–5143. sured by ultrasound were significantly higher than the values measured by Pentacam (average difference 5.54 ± 8 μm) [3]. The explanation for this finding is not yet clear. Most studies therefore engage in a comparison of measurement of CCT using Pentacam and ultrasound pachymetry. Few studies have been conducted on examination of pachymetry using laser interferometry (in our study on the instrument Allegro Biograph), despite the fact that this represents a relatively simple noncontact method of CCT measurement. Beutelspacher et al. retrospectively compared CCT measured using optical reflectometry and ultrasound in 50 patients, and determined a very good correlation of results between both (correlation coefficient r = 0.929) [1]. Further studies on this theme would undoubtedly be of benefit. Keratometry was always examined without cont