Measurements of Anterior and Posterior Corneal Curvatures with OCT and Scheimpflug Biometers in Patients with Low Total Corneal Astigmatism

Abstract

Background: Posterior keratometry measurements are evolving features of the optical biometers. The differences between devices have bigger impact for the low astigmatism values. The majority of adults present the corneal astigmatism below 1.5 D. Objectives: To compare the total corneal astigmatism measured with two different technologies in cataract patients with corneal astigmatism below 1.5 D. Material and Methods: Three automated exams were performed on each of the two devices: swept-source optical coherence tomography (SS-OCT) and Scheimpflug biometers. The anterior and total corneal astigmatism and power were analysed. Statistical comparisons were performed for within-subject standard deviation, repeatability, Bland−Altman and vector analysis. Results: Twenty-nine eyes of twenty-seven patients were included. The limits of agreement between anterior and total corneal astigmatism were narrower for the SS-OCT than for the Scheimpflug biometer (−0.16 to 0.29 D and −0.40 to 0.39 D, respectively). The >0.5 D difference between SS-OCT and Scheimpflug total astigmatism was noticed in 5 (17%) of cases. The difference between mean total keratometric power for both devices was statistically significant (0.2 D, p < 0.001). SS-OCT total corneal flat measurements had worse repeatability than Scheimpflug (p = 0.007). Conclusions: For the corneal astigmatism <1.5 D, the difference between anterior and total corneal astigmatism measured with SS-OCT was clinically not significant. The mean anterior and total keratometry values obtained with Scheimpflug and SS-OCT biometers are not interchangeable.

Keywords: astigmatism; keratometry; posterior cornea.

Figure 1

Bland–Altman plots of comparison between K and TK using (a) mean values, (b) astigmatism magnitude.

Figure 2

Bland–Altman plots of comparison between simK and TCRP using (a) mean values, (b) astigmatism magnitude.

Figure 3

Bland–Altman plots of comparison between K and simK using (a) mean values, (b) astigmatism magnitude and for TK and TCRP using (c) mean values, (d) astigmatism magnitude.

Figure 4

Bland–Altman plots for astigmatism vector analysis for K and simK (a) J0, (b) J45 and for TK and TCRP (c) J0, (d) J45.

Figure 5

Double-angle plots showing the astigmatism measured with (a) K, (b) simK, (c) TK, (d) TCRP. K—keratometry; simK—simulated keratometry; TK—total keratometry, TCRP—total corneal refractive power.