Repeatability of curvature measurements in central and paracentral corneal areas of keratoconus patients using Orbscan and Pentacam

To determine the repeatability of curvature measurements in 5 corneal rings (1–5 mm from the corneal center) in keratoconus (KCN) patients using the Orbscan and Pentacam and to compare the values of these devices.

Forty-eight patients with a definite diagnosis of KCN were included in the study. Patients with any corneal scar or active disease or a history of ocular surgery were excluded from the study. The right eye of the patients was studied three times with the Orbscan and Pentacam. The repeatability of the curvatures of 5 corneal rings (1–5 mm from the corneal center) was evaluated using the Orbscan and Pentacam, and the agreement of their values was analyzed.

The intraclass correlation coefficient (ICC) of three measurements was at least 0.94 (P < 0.0001) for the Orbscan and at least 0.88 (P < 0.0001) for the Pentacam in all corneal rings. According to the grade of KCN, the Orbscan had a low ICC in the 2 mm ring in grades 2 and 3 (ICC = 0.750 and 0.298, respectively). Repeated measures ANOVA showed no significant difference between the repeated measurements of the Orbscan and Pentacam in all corneal rings. The paired t-test showed a significant difference in curvature measurements in all rings except for the 5-mm ring between the two devices (P < 0.0001). The Bland-Altman plot showed a week agreement between these two devices in 1–4 mm corneal rings in curvatures more than 45 D.

According to the results of this study, keratometry readings are highly repeatable in Pentacam and Orbscan devices in all corneal rings. Despite the high correlation between curvature measurements of the Orbscan and Pentacam, there was a significant statistical and clinical difference between the results of two devices in all corneal rings (except the 5-mm ring), and the curvature measurements of the Pentacam were steeper than Orbscan measurements.