Comparison of keratometry versions in patients with corneal astigmatism

Purpose: to compare the corneal power at main meridians, the magnitude and the axis of corneal astigmatism and the reproducibility of measurements taken three times with different types of biometers. Material and methods. 22 subjects (24 eyes) with regular corneal astigmatism 1.89–8.02 D were given three biometry tests using IOL Master 500, Lenstar LS 900, IOL Master 700, Pentacam and Galilei G6. Results. The data were divided into groups depending on the principle of mathematical modeling of the corneal surface: group I involved the material processed by IOL Master 500, Lenstar LS 900, IOL Master 700; group II contained maps of the anterior corneal surface; and group III, those of the posterior surface. In group I, Lenstar showed the highest values of keratometry. In group II, the values of K1 , Kave in the 6 mm area were lower than in the pupil diameter area and than any values of K in the 4 mm area; the lowest values of K in this area were obtained on the Pentacam SimK. In group III, in the pupil diameter area (4.0–4.5 mm), all K values obtained with diverse equipment were different whilst in the 6 mm area the values differed only in the flat meridian. Astigmatism within groups I, III showed no difference while in group II the SimK data were different. The astigmatism axes obtained on IOLMaster 500 differed from the respective data provided by other devices. The devices of group I, 6 mm area, were the most stable. Conclusions. The highest values of keratometry are obtained when only the anterior surface of the cornea is taken into account, the lowest values are characteristic of the posterior surface. The stability of the parameter registered grew with the increase of the measured zone diameters. The biometers of group 1 showed the highest values of astigmatism with the maximum repeatability of the measurements