Comparison of the combined placido disc. Scheimpflug and the Scheimpflug-only imaging systems for the assessment of anterior segment Yakov Goldich MD, Reut Singer MD, Cornelius Nasser MD, David Zadok MD, Isaac Avni MD Department of Ophthalmology Assaf Harofeh Medical Center Israel The authors have no conflicts of interest and no financial interest in the article’s subject matter or methods mentioned.
Background • Corneal topography and thickness are important in diagnosing and evaluating progression of corneal ectatic disorders.
Background • The Sirius topography system (CSO, Italy) is a new device that uses the combination of two, 360 -degree rotating Scheimpflug cameras and a Placido disk principles. • It provides, in a single scan, anterior segment imaging and measurements, anterior and posterior corneal topography, complete corneal pachymetry and wavefront analysis.
Purpose • The purpose of this study was to report our initial experience with the Sirius topography system, to assess repeatability of its measurements and to assess the agreement with Pentacam's (Oculus, Germany) measurements.
Methods • In this prospective study, we examined one eye of consecutive 45 healthy subjects (mean 40. 23 ± 10. 49 years, 21 male and 24 female). • The anterior and posterior corneal curvature (ACR, PCR) at 3 mm and 7 mm, anterior chamber depth (ACD) and minimal corneal thickness (MCT) were evaluated.
Methods • Evaluation of the repeatability of the Sirius was performed by calculating the coefficient of variation (CV). l l l • CV was defined as the SD of the difference from the mean of the repeat measurements divided by the mean response. For each measured parameter we calculated the coefficients of variation of each one of the subjects. The mean of these coefficients of variation was defined as the mean coefficient of variation of the specific parameter. Assessment of the agreement between the Sirius and the Pentacam was performed by calculating the 95% limits of agreement (Lo. A) and plotting Bland-Altman graphs.
Results • • Repeatability Mean coefficients of variation were as follow: l l l 0. 37% for anterior corneal radius at 3 mm 1. 32% for posterior corneal radius at 3 mm 0. 36% for anterior corneal radius at 7 mm 1. 28% for posterior corneal radius at 7 mm 1. 69% for the minimal corneal thickness 0. 56% for the anterior chamber depth
Results
Results FIGURE 1. Bland Altman plot for anterior corneal radius measured by Sirius and Pentacam. The dashed line represents the mean difference and the solid lines represent the 95% Lo. A. The 95% Lo. A were -0. 1 to 0. 12 mm (mean difference 0. 018 mm)
Results FIGURE 2. Bland Altman plot for posterior corneal radius measured by Sirius and Pentacam. The dashed line represents the mean difference and the solid lines represent the 95% Lo. A. The 95% Lo. A were -0. 54 to 0. 33 mm (mean difference 0. 1 mm)
Results FIGURE 3. Bland Altman plot for anterior chamber depth measured by Sirius and Pentacam. The dashed line represents the mean difference and the solid lines represent the 95% Lo. A. The 95% Lo. A were -0. 23 to 0. 09 mm (mean difference 0. 068 mm)
Results FIGURE 4. Bland Altman plot for thinnest corneal point measured by Sirius and Pentacam. The dashed line represents the mean difference and the solid lines represent the 95% Lo. A. The 95% Lo. A were -9. 61 to 33. 44 µm (mean difference 11. 91µm)
Conclusions • • The Sirius showed good to excellent repeatability for all measured parameters. The observed agreement with Pentacam for each parameter should be considered for each particular clinical application. The clinician should determine whether the difference between the two devices is clinically significant. We recommend these devices should not be used interchangeably. Correspondence: Yakov Goldich MD, E-mail: doctor. goldich@gmail. com
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