Comparative analysis of anterior corneal curvature and astigmatism measurements obtained with three different devices

Background: The objective of this study was to compare the central corneal curvature and astigmatism measurements obtained with three different systems in healthy eyes and to assess the level of interchangeability between them.

Methods: This was a comparative study examining 30 healthy eyes of 30 patients (age 15-53 years). A complete eye examination was performed in all cases including analysis of anterior corneal curvature and astigmatism with three devices: the colour-LED topography system Cassini (i-Optics) (CAS), the Scheimpflug-based system Pentacam (Oculus Optikgeräte) (PTC) and the optical biometer IOL-Master 500 (Carl Zeiss Meditec) (IOLM). Differences between devices in terms of curvature in the flattest (flat K) and steepest meridians (steep K) as well as in the magnitude (AST) and power vector components of astigmatism (J₀ and J₄₅ ) were evaluated. The interchangeability between devices was evaluated with the Bland-Altman method.

Results: Statistically significant differences between devices were found in steep K and flat K (p < 0.001). No statistically significant differences between devices were found in AST (p = 0.057) and J₀ power vector (p = 0.185). However, differences between devices in J₄₅ did reach statistical significance (p = 0.039). Ranges of agreement for curvature measures ranged from 0.123 (flat K, CAS-PTC) to 0.165 mm (steep K, CAS-PTC). Ranges for the magnitude of astigmatism were 0.868, 1.059 and 0.739 D in CAS-IOLM, PTC-IOLM and CAS-PTC comparisons, respectively. For J₀ and J₄₅ , ranges of agreement were below 0.522 D.

Conclusions: Measurements of central corneal curvature and astigmatism obtained with the three devices evaluated cannot be used interchangeably.