Repeatability of Posterior and Total Corneal Curvature Measurements Using Point-Source Color LED and Dual-Scheimpflug Placido Topographers
To evaluate the repeatability and comparability of the Cassini topographer (i-Optics) and the Galilei tomographer (Ziemer) in measuring posterior and total corneal astigmatism and curvature in normal and post-refractive surgery eyes.
In this prospective comparative study, a single observer performed three consecutive measurements in one eye of each subject using the Cassini and Galilei. The mean posterior and total corneal astigmatism was measured in both normal and post-refractive surgery eyes. Repeatability was assessed by calculating the within-subject standard deviation (SD), coefficient of variation (COV), and intraclass correlation coefficient (ICC). The Bland and Altman plots were used to assess agreement in measurements between devices. Vector analysis was used to compare astigmatism values.
The study will enroll 32 patients. Our preliminary results are as follows: in normal (n=18) eyes, the SDs for posterior corneal astigmatism were 0.14 diopters (D) and 0.05 D for the Cassini and the Galilei, respectively; the SDs for total corneal astigmatism were 0.31 D and 0.17 D for the Cassini and the Galilei, respectively. In post-refractive (n=8) eyes, the SDs for posterior corneal astigmatism were 0.08 D and 0.07 D for the Cassini and the Galilei, respectively; the SDs for total corneal astigmatism were 0.22 D and 0.13 D for the Cassini and the Galilei, respectively.
Additional patients are currently being enrolled, and final results and conclusions will be presented. The performance of these two devices will be discussed.