Reproducibility and Repeatability of Central Corneal Thickness Measurement in Keratoconus Using the Rotating Scheimpflug Camera and Ultrasound Pachymetry

doi:10.1016/j.ajo.2007.07.021

American Journal of Ophthalmology

Volume 144, Issue 5, November 2007, Pages 712-718.e1

https://doi.org/10.1016/j.ajo.2007.07.021 Get rights and content

Purpose

To assess repeatability, reproducibility, and agreement of rotating Scheimpflug camera (Pentacam Oculus, Wetzlar, Germany) and ultrasound pachymetry in measuring central thickness of keratoconic corneas.

Design

Method-comparison study.

Methods

In 33 patients with keratoconus (one eye per patient), two examiners each used both pachymetric methods to measure central corneal thickness (CCT); in the same session, measurements then were repeated by examiner 1 (A.M.). The difference between two examiners, and between first and second measurements by examiner 1, with both methods and the difference between the two pachymetric methods in measuring central thickness of keratoconic corneas were noted.

Results

With the rotating Scheimpflug camera, interexaminer correlation was higher (intra-class correlation coefficient [ICC], 0.98 vs 0.76) and inter-examiner variability was lower (95% limits of agreement [95% LoA], −14.8 to 13.8 μm vs −18.0 to +49.5 μm) than with ultrasound pachymetry. Both methods showed close first- to second-measurement correlation (ICC, > 90), but the rotating Scheimpflug camera had lower variability (95% LoA, −14.5 to 14.2 μm vs −27.4 to 26.0 μm). Mean CCT was 478.9 ± 34.6 μm with the rotating Scheimpflug camera and 486.6 ± 30 μm with ultrasound pachymetry. Although the mean difference was small (−7.8 μm), the 95% LoA (−43.8 to 28.2 μm) showed that the difference between the two methods can be considerable.

Conclusions

In keratoconic corneas, the rotating Scheimpflug camera provides measurements of central thickness that are more reproducible and repeatable than those obtained with ultrasound pachymetry. The rotating Scheimpflug camera seems to be suitable for disease staging and follow-up, when corneal thickness measurements may be repeated over time by different examiners.

Section snippets

Methods

CCT was measured with the rotating Scheimpflug camera and ultrasound pachymetry in 33 patients with previously diagnosed keratoconus (22 men, 11 women; mean age ± standard deviation [SD], 37 ± six years; range, 19 to 61 years). The initial diagnosis of keratoconus was based on clinical slit-lamp findings and associated characteristic Placido-based topographic patterns. Slit-lamp findings included one or more of the following signs: stromal thinning, conical protrusion, Fleischer ring, Vogt

Reproducibility and Repeatability of the Two Methods in Central Thickness Measurement of Keratoconic Corneas

Analysis of inter-examiner reproducibility revealed a lower ICC, higher coefficient of repeatability, and wider 95% LoA for ultrasound pachymetry compared with the rotating Scheimpflug camera (Table 1). The 95% LoA for ultrasound pachymetry indicated that differences between examiners could be of clinical significance with this method. Figure 1 graphically illustrates the difference between the two examiners in measuring each individual CCT, with both methods, through Bland-Altman plots.

Discussion

In Keratoconus, the cornea tends to be thinner than normal, both centrally and peripherally,25, 26 so that reproducible, repeatable, and accurate measurements of corneal thickness are required for the diagnosis, staging, and follow-up of this disease, as well as for planning surgical procedures. Although a comprehensive clinical examination plus Placido-based topography have good accuracy in detecting keratoconus, measurement of corneal thickness may provide useful corroborative evidence for

Ugo de Sanctis, MD, PhD, completed the post-graduate training in Ophthalmology, and the post-graduation doctorate in Cornea and External Diseases at the Ophthalmology Institute, University of Turin, Italy. Currently, Dr de Sanctis is an Assistant Professor of Ophthalmology and Head of Cornea Service at the Medical University of Turin. His clinical and research interests include corneal and external diseases, refractive surgery, and cataract surgery.

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The purpose of this study was to compare central corneal thickness (CCT) values and evaluate the agreement obtained with three different devices in healthy eyes.
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The mean patient age was 28 ± 5.73 years (18–40 years). The mean CCT values obtained by AL-Scan, UP, and SD-OCT were 532.4 μm ± 29.7, 549 μm ± 30.4, and 547 μm ± 30.6, respectively. The mean differences in CCT were 15.30 ± 9.52 μm between AL-Scan and OCT (P < 0.01), 17.15 ± 8.42 μm between AL-Scan and UP (P < 0.01), and 1.85± 8.78 μm between UP and OCT (P = 0.067). All three methods of CCT measurement were closely correlated with each other.
The present study results suggest that, despite good agreement between the three devices, AL-Scan significantly underestimated CCT compared to UP and OCT. Therefore, clinicians should be aware that different results can be obtained using different devices for CCT measurements. It would be a better approach not to use them as interchangeable in clinical practice. CCT examination and follow-up should be performed using the same device, especially for patients who will undergo refractive surgery.
Le but de cette étude était de comparer les valeurs d’épaisseur centrale de la cornée (central corneal thickness [CCT] en anglais) et d’évaluer la correspondance obtenue avec trois dispositifs différents pour des yeux sains.
Un total de 120 yeux de 60 individus sains (36 hommes et 24 femmes) ont participé à cette étude rétrospective. Les mesures CCT ont été effectuées à l’aide d’un biomètre optique (AL-Scan), d’une tomographie par cohérence optique dans le domaine spectral (SD-OCT) (Topcon 3D) et d’une pachymétrie ultrasonique (UP) (Accupach VI) et les résultats ont été comparés. L’analyse de Bland–Altman a été utilisée pour démontrer l’accord entre les méthodes.
L’âge moyen des patients était 28 ± 5,73 ans (entre 18 et 40 ans). Les valeurs moyennes de CCT obtenues par AL-Scan, UP et SD-OCT étaient 532,4 μm ± 29,7, 549 μm ± 30,4 et 547 μm ± 30,6, respectivement. Les différences moyennes de CCT étaient de 15,30 ± 9,52 μm entre AL-Scan et OCT (p < 0,01), 17,15 ± 8,42 μm entre AL-Scan et UP (p < 0,01), et 1,85 ± 8,78 μm entre UP et OCT (p = 0,067). Les trois méthodes de mesures CCT étaient étroitement en corrélation les unes aux autres.
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Original articleReproducibility and Repeatability of Central Corneal Thickness Measurement in Keratoconus Using the Rotating Scheimpflug Camera and Ultrasound Pachymetry

Purpose

Design

Methods

Results

Conclusions

Section snippets

Methods

Reproducibility and Repeatability of the Two Methods in Central Thickness Measurement of Keratoconic Corneas

Discussion

Surv Ophthalmol

Surv Ophthalmol

J Cataract Refract Surg

J Cataract Refract Surg

J Cataract Refract Surg

Am J Ophthalmol

J Cataract Refract Surg

Am J Ophthalmol

J Cataract Refract Surg

J Cataract Refract Surg

Ophthalmology

Ophthalmology

J Cataract Refract Surg

Ophthalmology

Deep lamellar keratoplasty using viscoelastic dissection

Arch Ophthalmol

A quick surgical technique for deep, anterior lamellar keratoplasty using visco-dissection

Cornea

Original article
Reproducibility and Repeatability of Central Corneal Thickness Measurement in Keratoconus Using the Rotating Scheimpflug Camera and Ultrasound Pachymetry