Repeatability and comparability of the Galilei-G4 and Cassini in measuring corneal power and astigmatism in normal and post-refractive surgery eyes

Abstract

To assess the repeatability and comparability of the Galilei G4 versus the Cassini topographer in post-refractive eyes and in normal eyes, including older patients representative of an initial cataract evaluation. Simulated keratometric (simK), total corneal and posterior corneal power and astigmatism were evaluated in both post-refractive and normal eyes. Repeatability was measured by calculating within-subject standard deviation (Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Vector analyses and Bland-Altman plots were employed to assess agreement between devices. We studied 32 subjects with a history of refractive surgery and 32 subjects without a history of refractive surgery undergoing cataract surgery. The mean age was 55 ± 18.5 years and the age range was 21.5-91.5 years. In non-refractive and post-refractive eyes, the ICC was > 0.9 (P < 0.001) for all corneal powers and for simK and total corneal astigmatism for both analyzers. The ICC for posterior corneal astigmatism magnitude using the Galilei was 0.62 and 0.67 and for the Cassini 0.55 and 0.38 in normal and post-refractive eyes, respectively. In both post-refractive and normal eyes, the Galilei G4 and Cassini analyzers have high repeatability in simK, total, and posterior corneal power and low repeatability for posterior corneal astigmatism.

Figure 1

(A) Galilei and (B) Cassini, for normal eyes, double-angle plots showing intrasubject differences in simulated keratometric (SimK) (top row), total (middle row), and posterior corneal astigmatism (bottom row) measurements. Each ring represents 0.25 diopters (D), and the outer ring represents 1.0 D.

Figure 2

(A) Galilei and (B) Cassini, For post-refractive eyes, double-angle plots showing intrasubject differences in simulated keratometric (SimK) (top row), total (middle row), and posterior corneal astigmatism (bottom row) measurements. Each ring represents 0.25 diopters (D), and the outer ring represents 1.0 D.

Figure 3

Bland–Altman plots showing differences in corneal power and astigmatism for repeated measurements in normal eyes. The differences were taken between the first and second measurements for each subject. The mean difference is represented by the solid line, and 95% limits of agreement (LoA) are represented by dotted lines. (Top left) total corneal power, (top right) total corneal astigmatism, (bottom left) posterior corneal power, and (bottom right) posterior corneal astigmatism.

Figure 4

Bland–Altman plots showing differences in corneal power and astigmatism for repeated measurements in post-refractive surgery eyes. The differences were taken between the first and second measurements for each subject. The mean difference is represented by the solid line, and 95% limits of agreement (LoA) are represented by dotted lines. (Top left) total corneal power, (top right) total corneal astigmatism, (bottom left) posterior corneal power, and (bottom right) posterior corneal astigmatism.