Repeatability and reproducibility of Keratograph 5M corneal topography

Background Corneal topography is an important diagnostic tool and highly repeatable and reproducible topographic devices are essential in eye care practice. Placido disc-based topography is one of the most widely used methods because of its high resolution and accuracy. The aim of this study was to analyse the intrasession repeatability and intersession reproducibility of measurements obtained with a Keratograph 5M in a sample of healthy subjects. Methods Three consecutive measurements were performed with a Keratograph 5M during two sessions in 24 healthy subjects to calculate the within-subject standard deviation (Sw), repeatability and reproducibility limits, coefficient of variation (CoV), and intraclass correlation coefficient (ICC) of corneal curvature (K1, K2 and Max-K), eccentricity, corneal diameter, and corneal aberration (6-mm pupil; coma, trefoil, spherical aberration, secondary astigmatism and quadrafoil). Results No statistically significant differences were found between the three measurements in either session (P ≥ 0.06). The corneal parameters that demonstrated the best repeatability were corneal curvature and corneal diameter with a CoV, and the ICCs ranged from 0.41% and 0.990 (corneal diameter) to 0.28% and 0.998 (K2). Eccentricity and corneal aberrations had lower repeatability results, with CoVs and ICCs ranging from 3.88% and 0.992 (spherical aberration) to 40.21% and 0.643 (quadrafoil), respectively. In the case of reproducibility, excellent results were obtained for corneal curvature and diameter measurements (CoV ≤ 0.36% and ICC ≥ 0.987), with moderate reproducibility for corneal eccentricity (CoV ≥ 2.03% and ICC ≤ 0.986), secondary astigmatism (CoV = 20.05% and ICC = 0.787), and quadrafoil (CoV = 23.55% and ICC = 0.696). Conclusions The Keratograph 5M demonstrated excellent repeatability and reproducibility in measuring corneal curvature and corneal diameter in healthy subjects. Corneal eccentricity shows moderate accuracy, whereas corneal aberrations (except coma, trefoil, and spherical aberrations) exhibit moderate measurement reliability and should be interpreted with caution in clinical practice.