Repeatability and Agreement of Orbscan II, Pentacam HR, and Galilei Tomography Systems in Corneas With Keratoconus

Purpose: To assess the repeatability and agreement of keratometry and pachymetry measurements obtained using 3 tomographers in eyes with keratoconus.

Design: Reliability analysis.

Methods: setting: Institutional.

Study population: Fifty eyes of 50 participants with keratoconus. observational procedure: Steep keratometry, flat keratometry, central corneal thickness (CCT), and thinnest corneal thickness (TCT) measurements using Galilei, Orbscan II, and Pentacam HR.

Main outcome measures: Repeatability was assessed using within-subject standard deviation (S_W), coefficient of variation (CV), and intraclass correlation coefficient (ICC). Bland-Altman plots and 95% limits of agreement (LoA) were used to evaluate agreement between device pairs.

Results: For all studied parameters, ICC was >0.97 with the least repeatable measurements obtained using Orbscan II. Mean steep keratometry values were similar while mean flat keratometry values were significantly different between all devices. The Galilei and Pentacam HR had the lowest 95% LoA for both CCT and TCT. There were no significant differences in mean CCT between Galilei and Pentacam HR. Mean Orbscan II CCT measurements were not significantly different overall but had wide 95% LoA with Pentacam HR (-47.95 to 58.09 μm) and Galilei (-43.70 to 53.91 μm). Mean Orbscan II CCT measurements were significantly lower when an acoustic factor of 0.92 was applied (-33.6 μm vs Pentacam HR, P < .001; -33.6 μm vs Galilei; P < .001).

Conclusions: Keratometric and pachymetric measurements of keratoconic eyes obtained by Galilei, Orbscan II, and Pentacam were disparate. Measurements were less repeatable with Orbscan II compared with Pentacam HR and Galilei, although overall repeatability was high for all instruments.