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Background: Cataract surgery in keratoconic patients is challenging because of the corneal distortion, which can lead to inaccurate keratometry readings. This study is a comparison of the accuracy of keratometry readings by two types of devices in a tertiary hospital. Purpose: To evaluate the comparability of corneal power measurements, anterior chamber depth (ACD), and white-to-white (WTW) distance between Scheimpflug-based tomography (Pentacam AXL; OCULUS GmbH, Wetzlar, Germany) and swept-source optical biometry (IOLMaster 700; Carl Zeiss Meditec AG, Jena, Germany) in patients with keratoconus. Methods: This pilot, prospective, interinstrument reliability study included 30 keratoconic eyes of 15 individuals who had not undergone any kind of corneal surgery. Standard K and total refractive power (TK®) of the flattest and steepest axes of the IOLMaster 700 were compared with the standard keratometry (SimK), true net power (TNP), equivalent keratometer readings (EKR), and total corneal refractive power (TCRP) of the Pentacam. The Bland–Altman analysis was used to evaluate the agreement between the measurements of both devices. The paired-samples t-test and the Wilcoxon signed-rank test were performed to compare the mean values of the variables obtained with the devices. Results: The K1 value of the IOLMaster 700 was significantly higher from EKR K1 along the 3-mm (mean difference: 0.79 diopters, p = 0.01), 4-mm (mean difference: 1.01 D, p = 0.01), and 4.5-mm zones (mean difference: 1.20 D, p = 0.01) and TNP K1 along the 3-mm (mean difference: 0.88 D, p < 0.001) and 4-mm zones (mean difference: 0.97 D, p < 0.001). The TK1 value was significantly higher from EKR K1 along the 2-mm (mean difference: 0.42 D, p = 0.04), 3-mm (mean difference: 0.83 D, p = 0.003), 4-mm (mean difference: 1.05 D, p = 0.004), and 4.5-mm zones (mean difference: 1.24 D, p = 0.005) and TNP K1 along the 3-mm (mean difference: 0.92 D, p < 0.001) and 4-mm zones (mean difference: 1.01 D, p < 0.001). The K2 value of the IOLMaster 700 was significantly higher from TK2 (mean difference: 0.11 D, p = 0.04) and all the corresponding variables of the Pentacam device. The TK2 value was significantly higher from all the corresponding variables of the Pentacam device. The Pentacam also yielded significantly lower values for the WTW distance (mean difference: 0.31 mm, p < 0.001) and no significant difference in terms of ACD values ( p = 0.9). Conclusion: The IOLMaster measured significantly greater keratometry readings in the steep axis for all the variables studied. The keratometry and WTW measurements of the investigated devices cannot be used interchangeably in keratoconus.

Purpose: To investigate correlations between specular microscopy endothelial parameters and age with corneal densitometry values, as they are presented from a Scheimpflug device, in different levels of the cornea.Methods: Two hundred eighty-four eyes of 142 healthy subjects were included in this observational, prospective study. Corneal densitometry was evaluated with Scheimpflug imaging system in the central 0-to 2-mm annular zone of the cornea, whereas the endothelial cell properties were assessed with the use of a noncontact specular microscope. Results:Corneal densitometry values of all corneal layers were statistically significant and positively correlated with age. In univariate linear regression analysis among corneal densitometry values and the endothelial parameters, only endothelial cell density (CD) was statistically significant and inversely correlated with densitometry values in all corneal layers. In stepwise multivariate linear regression analysis, after adjustment for age, hexagonality was statistically significant and inversely correlated with posterior densitometry values, whereas coefficient of variation was positively and significantly correlated with the anterior densitometry values. When repeating stepwise multivariate linear regression analysis without adjusting for age, CD was negatively and significantly correlated with corneal densitometry values of all layers, whereas coefficient of variation was positively and significantly correlated with anterior and total corneal densitometry values.Conclusions: Corneal densitometry increases with age. It is also inversely correlated with CD, and this might be used as an indirect way to assess the status of the corneal endothelium.

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