Comparability and repeatability of corneal astigmatism measurements using different measurement technologies

To determine the comparability and repeatability of corneal astigmatism measurements obtained with different devices and determine the interobserver variability of a new automated keratometer.

University Eye Clinic Maastricht, the Netherlands.

Prospective cohort study.

The right eye of healthy subjects was examined with the following 6 devices: IOLMaster (automated keratometry), Lenstar (automated keratometry), SMI Reference Unit 3 (automated keratometry), Javal (manual keratometry), KR-1W (corneal topography), and Pentacam (Scheimpflug imaging). An experienced operator obtained 3 repeated measurements. An inexperienced operator obtained additional measurements with the SMI Reference Unit 3. Astigmatism vector analysis was used to determine the comparability, repeatability, and interobserver variability.

Corneal astigmatism vectors measured by automated, manual, or simulated keratometry were comparable except for the Pentacam equivalent keratometry (K) (P<.001, repeated-measures analysis of variance [ANOVA]). The mean difference between the equivalent K and other K values was 0.18 to 0.29 diopter (D) (P<.05, Hotelling trace multivariate ANOVA). The mean differences between automated, manual, and simulated keratometry were small (≤0.12 D). The within-subject standard deviation ranged from 0.05 D @ 21 degrees (KR-1W) to 0.18 D @ 23 degrees (Lenstar). The SMI Reference Unit showed small mean differences and comparable repeatability between the experienced operator and the inexperienced operator.

Vector analysis showed comparable corneal astigmatism measurements using automated, manual, and simulated keratometry. Pentacam equivalent K values were not comparable with those of the other keratometers. The repeatability of astigmatism magnitudes was acceptable; however, the repeatability of astigmatism meridians was moderate. The SMI Reference Unit showed good interobserver variability.