Reproducibility of Scheimpflug Tomography Measurements Regarding Corneal Front and Back Surface Power

Background and Purpose: The Oculus Pentacam (R) is one of the most commonly used devices in ophthalmology for assessment of the anterior eye segment. The purpose of this study was to determine the reproducibility of the corneal power as measured by the Pentacam (R) in a normal population. Methods: We enrolled 25 eyes of 25 subjects aged between 13 and 68 (46.7 +/- 21.7) years, within a spherical equivalent from - 4 D to + 4 D and refractive cylinder up to 5 D and without notable pathologies or history of surgery. A sequence of 5 measurements was performed using the Pentacam (R), the Zeiss IOLMaster (R) as well as an autorefractometer after (re-)positioning the patient's head and the measurement device. From the Pentacam (R) we collected power data for the corneal front and back surfaces, apical corneal thickness at apex and internal anterior chamber depth. From the IOLMaster (R), we extracted corneal power data, and from the autorefractometer we obtained refractive power data of both cardinal meridians. For statistical analysis, we used Cronbach's a as a measure of reproducibility and Spearman's rank correlation test for correlation of data. Results: Pentacam (R) yields highly reproducible power data for both corneal surfaces, with Cronbach's a of greater than 0.97 for primary parameters (e.g. radii of curvature) and 0.9 for secondary parameters (e.g. vector components of astigmatism). Central corneal thickness and eccentricities of both surfaces as well as anterior chamber depth yielded highly reproducible values, with alpha of >= 0.97. Corneal power derived from IOLMaster (R) and objective refraction extracted from the autorefractometer yielded a values of around 0.9. Mean corneal power of Pentacam (R) and IOLMaster (R) correlated well, but there was no correlation to spherical equivalent. Astigmatism values from Pentacam (R) and IOLMaster (R) correlated well with each other and with refractive cylinder. Conclusion: Our results indicate that measurements of anterior segment using the Pentacam (R) yield highly reproducible results in a normal population without major pathologies of the anterior eye segment.