Comparison of anterior and posterior elevation map measurements between 2 Scheimpflug imaging systems

Purpose

To compare the anterior and posterior elevation measurements above the best-fit sphere (BFS) between the Galilei (dual-Scheimpflug) and Pentacam (single-Scheimpflug) systems in candidates for refractive surgery.

Setting

Poostchi Ophthalmology Research Center, Shiraz, Iran.

Methods

In this prospective study, both eyes of consecutive patients were examined with the 2 imaging systems. The anterior and posterior BFS and the central and maximum elevation measurements in each of 4 quadrants were compared between the dual-Scheimpflug system and the single-Scheimpflug system. Bland-Altman plots were used to evaluate the agreement in the measurements between the imaging systems.

Results

The study comprised 31 patients (62 eyes). The mean radius of the anterior BFS measurement was 7.72 mm ± 0.21 (SD) with the dual-Scheimpflug system and 7.83 ± 0.21 mm with the single-Scheimpflug system. The mean radius of the posterior BFS was 6.37 ± 0.18 mm and 6.47 ± 0.19 mm, respectively. On the anterior and posterior elevation maps, the single-Scheimpflug system led to statistically significantly higher measurements than the dual-Scheimpflug system in the central, inferior, and temporal elevations (P<.001). Bland-Altman plots showed more agreement between the systems in anterior elevation measurements than in posterior elevation measurements.

Conclusion

In refractive surgery candidates with healthy eyes, the elevation map measurements with the single-Scheimpflug system were significantly different from those with the dual-Scheimpflug system in most aspects and therefore may lead to misinterpretation of clinical data that could alter clinical decisions if the 2 imaging systems are considered interchangeable.