A comparative study of total corneal power using a ray tracing method obtained from three different Scheimpflug camera devices.

PURPOSE: To assess the agreement of ray-traced corneal power values by three Scheimpflug tomographers and construct the corresponding arithmetic adjustment factor in comparison with an automated keratometer (IOLMaster) and a conventional Placido-based topographer (Allegro Topolyzer). DESIGN: Prospective reliability analysis. METHODS: A total of 74 eyes from 74 healthy subjects, who underwent corneal power measurements using Pentacam, Sirius, Galilei, IOLMaster, and Allegro Topolyzer were included. Ray-traced corneal power values, such as (total corneal refractive power (TCRP), mean pupil power (MPP), total corneal power (TCP), mean keratometry (Km), and simulated keratometry (SimK) were recorded respectively and analyzed using one-way analysis of variance (ANOVA) and Bland-Altman plots. RESULTS: Among the three ray-traced corneal power values, TCRP and MPP did not differ significantly (P=0.81), whereas TCP presented a slightly significant larger value (P<0.001). Compared to Km or SimK, corneal power measurements by the ray tracing method exhibited significantly lower values (P<0.001). Bland-Altman plots disclosed that the three Scheimpflug tomographers showed similar 95% Limit of agreement (LoA) after arithmetic adjustment as compared to Km (-0.40 to 0.40 D, -0.39 to 0.39 D, and -0.35 to 0.36 D) or SimK (-0.50 to 0.51 D, -0.43 to 0.42 D, and -0.46 to 0.46 D). CONCLUSIONS: Ray-traced corneal power values obtained using three Scheimpflug tomographers with default diameter settings were similar, indicating that they could be used interchangeably in daily clinical practice. The three Scheimpflug tomographers were satisfactory in agreement after arithmetical adjustment as compared to conventional automated keratometer or Placido-based topographer.