Anterior Surface Measurements Correlation and Agreement Between Rotational Scheimpflug and Placido Disc-based Devices in Primary Eyes

PURPOSE: To evaluate the inter-device agreement between Placido -based topography (Topolyzer Vario, WaveLight, Alcon Laboratories, Inc., Ft Worth, Texas, USA) and rotational Scheimpflug tomography (Oculyzer II, WaveLight, Alcon Laboratories, Inc., Ft Worth, Texas, USA) for measuring anterior corneal surface parameters. METHODS: Fifty eyes from 50 subjects with no ocular disease were included in this study. The main outcome measurements were keratometric readings and anterior surface irregularity metrics derived from Fourier analysis (decentration, decentration axis and irregularity). Inter-device correlation and agreement between the two devices were assessed. RESULTS:No statistically significant differences were detected among the parameters obtained by both devices (paired t test; p > 0.05). The 95% LoA between instruments were within the clinically relevant margins of discrepancy for the keratometric parameters. Seven (14%) and five (10%) eyes presented a difference greater than 0.5 D for the flat meridian (K1) and steep meridian (K2) parameters, respectively. Regarding corneal astigmatism, only three eyes (6%) presented a difference greater than 0.5 D between both devices. All the parameters selected from the Fourier analysis showed a lower level of correlation and a more extensive range of LoA compared to the keratometric variables. CONCLUSION: Placido topography and Scheimpflug tomography showed good correlation and agreement for keratometric measurements, including corneal astigmatism. Based on the data derived from the Fourier analysis, the results recommend caution when selecting the data to plan the topography-guided customized ablation, especially in primary eyes, which calls for prospective studies, possibly using simulated models.