Reproducibility of corneal topographic data derived from anterior segment spectral-domain OCT

1. Rosachiara Leaci, Alberto Neri, Patrizia Scaroni, Claudio Macaluso Ophthalmology, University of Parma, Parma, Italy The authors have no financial interest in the subject matter of this poster Reproducibility of corneal topographic data derived from anterior segment spectral-domain OCT

2. Purpose: To evaluate the reproducibility of corneal curvature measurements entirely derived from OCT scan data, and to compare them to measurements obtained by means of a conventional Placido disc topographer.

3. Methods: • 101 kERATOCONuS patientsand 40 normal subjects were examined in their right eye with two instruments: • a spectral domain OCT, dedicated to anterior segment examination (Casia SS-1000, Tomey Co., Japan) • a conventional Placido-disc topographer (Keratron Scout, Optikon, Italy) • Examinations were carried out in the same session twice with each device, in order to assess reproducibility. • Statistical analysis was performed with the SPSS 18.0 software.

4. Casia SS-1000 (Tomey Co., Japan) is an OCT dedicated to the anterior segment that is equipped with a fully automated topography routine, deriving curvature data by fitting OCT data scans along 16 meridians Immagine riconoscimento profili topo casia

5. The software automatically identifies outer and inner corneal boundaries on each of the 16 B-scan. The operator is asked to check that the position of the boundaries is correct before to visualize topographic data.

6. The OCT shows maps of anterior, posterior corneal curvature and pachimetry.

7. Results: validity of OCT keratometry Curvature measurements obtained with the two instruments showed excellent agreement both in the normal and in the patients group, with Intra-Class Correlation Coefficients (ICC) of 0.959 and 0.985, respectively. A B Pathologic eyes ICC = 0.985 D C Normal eyes ICC = 0.959 A, C: scatter plots of the average corneal curvature values obtained by Casia AS-OCT (x-axis) and Keratron topographer (y-axis). B, D: Bland-Altman plots of Casia-Keratron comparison, representing the differences of corresponding measurements (y-axis) in relation to their means (x-axis). Corneal curvature is expressed in Dioptries.

8. Results: reproducibility In the normal group reproducibility (ICC) of curvature measurements was 0.988 for the OCT and 0.976 for the conventional topographer, while in the patients groupICC for OCT and topographer was 0.997 and 0.989, respectively. Scatter plots of test (x-axis) vs. re-test (y-axis) average corneal curvature values are shown below. CASIA AS-OCT KERATRON TOPOGRAPHER ICC=0,997 ICC=0,989 Pathologic eyes ICC=0,988 ICC=0,976 Normal eyes

9. Results: reproducibility Further analysis of reproducibility with Bland-Altman plots revealed a higher variability with the conventional topographer as compared to the OCT in the patients group (p<0.01), but not in the normal group (p=0.085). ICC and Coefficient of Repeatability(CR) are reported in the figures below. [CR = 1,96 x SD of the differences between repeated measures]. CASIA AS-OCT KERATRON TOPOGRAPHER CR=0,62D CR=1,07D Pathologic eyes ICC=0,997 ICC=0,989 CR=0,35D CR=0,46D Normal eyes ICC=0,988 ICC=0,976

10. Conclusions: Corneal curvature measurements entirely derived from OCT scan data showed excellent reproducibility and were found comparable to measurements obtained by means of a conventional Placido disc topographer.

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