Comparison of corneal tomography measurements using Galilei, Orbscan II, and Placido disk-based topographer systems

To evaluate agreement in keratometry readings and anterior and posterior elevation map measurements among the Galilei V4.01 (Ziemer), Orbscan IIz (Bausch & Lomb), and Corneal Map topographer (Costruzione Strumenti Oftalmici) systems.

This prospective comparative study comprised 184 eyes of 92 consecutive refractive surgery candidates who were simultaneously examined with the Galilei (dual Scheimpflug), Orbscan II (scanning-slit), and Corneal Map topographer (Placido disk-based) systems. Keratometry readings and anterior and posterior elevation map measurements were compared using analysis of variance and paired t test, respectively.

Mean keratometry reading was 44.30 ± 1.49 diopters (D), 44.11 ± 1.47 D, and 44.60 ± 1.56 D with the Galilei, Orbscan, and Corneal Map topographer, respectively. Despite a significant difference in mean keratometry (P<.001), the correlation among these three systems was strong. The maximum mean difference between two sets in simulated keratometry and astigmatism was <0.50 D. In the evaluation of anterior best-fit-sphere (BFS) and posterior BFS, the correlation between Galilei and Orbscan II was found to be 0.960 and 0.947, respectively. Maximum anterior central elevation measured by Orbscan II and Galilei was 9.2 ± 5.1 μm and 3.2 ± 1.8 μm, respectively. Maximum posterior central elevation by Orbscan II and Galilei was 33.8 ± 9.3 μm and 6.8 ± 3.8 μm, respectively.

Despite significant differences in mean keratometry readings and anterior and posterior elevation measurements among the three systems, the keratometry readings can be used interchangeably, as this difference is not clinically significant.