A comparison of Scheimpflug imaging simulated and Holladay equivalent keratometry values with partial coherence interferometry keratometry measurements in phakic eyes

Abstract

Objective: To evaluate the interchangeability of a Scheimpflug camera (Pentacam, Oculus) and a partial coherence interferometry keratometer (IOLMaster, Zeiss) for measures of keratometry and anterior chamber depth (ACD). A particular focus was to determine which Pentacam keratometry value best correlates with the IOLMaster and if these results can be used interchangeably in clinical practice. Study Design: Retrospective comparative study using data from the GRMC Vision Centre and ImagePlus Laser Eye Centre. Participants: Fifty-two eyes from 27 patients (11 male, 16 female) of normal general health with no history of ocular disease. Methods: Each eye was assessed by an IOLMaster as part of a complete eye examination, and later by the Pentacam, prior to laser in situ keratomileusis (LASIK) surgery. Results: The differences in the mean keratometry readings of the IOLMaster and those of the simulated and equivalent Pentacam measurements were 0.35 D and 0.23 D, respectively. The Bland-Altman plots showed 95% limits of agreement (LOA) of 0.92 D and 1.68 D for the same parameters. A comparison of ACD measurements revealed a 0.03 mm difference in mean measurements with a 95% LOA of 0.33 mm. Conclusions: The interdevice variability was significantly lower than that reported previously but still warrants caution if the 2 instruments are to be used interchangeably. With an appropriate correction for mean differences, the Pentacam's simulated keratometry values would be within 0.46 D of the IOLMaster, 95% of the time. When the Holladay equivalent keratometry values were compared with the IOLMaster, a greater interdevice variability was seen.