Comparison of Posterior Corneal Curvature Measurements by Four Different Tomographers

To compare the posterior keratometry (PK) values obtained with three instruments based on optical coherence tomography (Anterion [Heidelberg Engineering], IOLMaster 700 [Carl Zeiss Meditec AG], and MS-39 [CSO]), and one Scheimpflug camera biometer (Pentacam AXL Wave; Oculus Optikgeräte GmbH). The average keratometry (Kave), total corneal power (TCP), anterior-to-posterior ratio (A/P ratio), and posterior corneal astigmatism (PCA) were also compared.

Measurements by the four instruments, expressed in diopters (D), were compared using repeated measures analysis of variance, when they were normally distributed, or Friedman's test, when they were not.

One hundred eyes (100 consecutive patients) scheduled to undergo cataract surgery were prospectively enrolled. Statistically significant differences among the Anterion, IOLMaster 700, MS-39, and Pentacam AXL Wave were detected for PK: Anterion: -6.08 ± 0.23 D, IOLMaster 700: -5.77 ± 0.23 D, MS-39: -6.15 ± 0.26 D, and Pentacam AXL Wave: -6.26 ± 0.26 D (P < .0001); for Kave: Anterion: 43.19 ± 1.50 D, IOLMaster 700: 43.35 ± 1.49 D, MS-39: 43.36 ± 1.53 D, and Pentacam AXL Wave: 43.22 ± 1.55 D (P < .0001); for the A/P ratio: Anterion: 1.19 ± 0.02, IOLMaster 700: 1.12 ± 0.02, MS-39: 1.20 ± 0.03, Pentacam AXL Wave: 1.22 ± 0.03 (P < .0001); and for TCP: Anterion: 42.69 ± 1.51 D, IOLMaster 700: 43.36 ± 1.49 D, MS-39: 42.92 ± 1.52 D, and Pentacam AXL Wave: 42.35 ± 1.55 D (P < .0001). PCA revealed significant differences for the KP(45) and KP(0) vectors (P < .0001).

The four instruments showed different PK values. The largest difference was observed with the IOL-Master 700, which provided the flattest PK and the lowest A/P ratio. The measurements cannot be considered interchangeable, and this should be considered when entering PK values into calculators using this parameter for IOL power.