Comparison between the CASIA SS-1000 and Pentacam in measuring corneal curvatures and corneal thickness maps

Abstract

Purpose: To compare the intra-device repeatability and inter-device reproducibility between two anterior segment imaging instruments, the CASIA SS-1000 (Tomey Corp., Nagoya, Japan) and Pentacam (OCULUS, Arlington, WA) in measuring anterior segment parameters.

Methods: Single-center, prospective clinical trial. Participants ≥20 years of age were included. One eye was randomly selected, each imaged by three CASIA SS-1000 devices and three Pentacam devices by three different examiners. Each photographer operated a pair of devices, one CASIA SS-1000 and one Pentacam. The image order for each participant was determined by a random permutation table. Three images were taken from each device. A total of 18 images were taken for each eye. Ratios of the standard deviations, referenced as (CASIA/Pentacam), were calculated to compare the repeatability and reproducibility of the two imaging instruments.

Results: In all, 66 participants with a mean age of 46.4 years (±21.7) were enrolled in the study. All repeatability ratios and intra-device variability were less than 1 (anterior corneal curvature: flat = 0.86, steep = 0.85; posterior corneal curvature: flat = 0.43, steep = 0.61; and map: thinnest = 0.22; central = 0.24, 2 mm = 0.26, 4 mm = 0.27, and 6 mm = 0.30). All reproducibility ratios, which measure the inter-device variability, were less than 1 (anterior corneal curvature: flat = 0.58, steep = 0.73; posterior corneal curvature: flat = 0.25, steep = 0.31; and pachymetry map: thinnest = 0.20; central = 0.20; 2 mm = 0.20; 4 mm = 0.19; and 6 mm = 0.22). A ratio of less than 1 indicates that the CASIA SS-1000 has more consistent measurements.

Conclusions: The CASIA SS-1000 was found to have better repeatability and reproducibility compared to the Pentacam for both corneal curvature and pachymetry maps. This greater consistency may require further study to determine whether the decreased variability can be translated into improved clinical results.

Keywords: CASIA SS-1000; Corneal curvature; Laser refractive surgery; Pentacam.

Fig. 1

Bland-Altman plots: Red line indicate CASIA SS-1000 and Pentacam are identical (difference = 0); Blue lines = limits of agreement (LOAs); Black dots connected with grey lines are the measurements from the same subject. AKf = anterior curvature flat axis; AKs = anterior curvature steep axis; PKf = posterior curvature flat axis; PKs = posterior curvature steep axis; TCT = thinnest corneal thickness; TCP(X) = horizontal distance from the apex to the thinnest corneal point; TCP(Y) = vertical distance from the apex to the thinnest corneal point; CCT = central corneal thickness; PCT = peripheral corneal thickness

Fig. 2

Deming Regression plots: Red line indicate CASIA SS-1000 = Pentacam; Blue line = Deming regression line; Black circles are the measurements. AKf = anterior curvature flat axis; AKs = anterior curvature steep axis; PKf = posterior curvature flat axis; PKs = posterior curvature steep axis; TCT = thinnest corneal thickness; TCP(X) = horizontal distance from the apex to the thinnest corneal point; TCP(Y) = vertical distance from the apex to the thinnest corneal point CCT = central corneal thickness; PCT = peripheral corneal thickness