Comparison of central corneal thickness in healthy eyes using ultrasound pachymetry, non-contact specular microscopy and a high-resolution Scheimpflug camera.

PURPOSE: To compare and analyze the interchangeability in measuring central corneal thickness (CCT) using ultrasonic pachymetry (USP, PACHMATE 2, DGH, Inc, Exton, PA, USA), non-contact specular microscopy (NCSM, CEM-530, Nidek CO, LTD, Gamagori, Japan) and a high-resolution Scheimpflug Camera (Pentacam HR, OCULUS, Wetzlar, Germany). METHODS: An observational, cross-sectional study was performed recruiting 216 volunteers, for a sample size of 216 eyes with no ocular abnormalities other than refractive errors. All subjects underwent pachymetric measurements obtained by USP, NCSM and Pentacam HR. Examinations were performed by the same examiner with USP always following the noncontact examinations. RESULTS: The mean CCT (± SD) was 560.30 ± 38.80 µm, 556.76 ± 36.83 µm and 547.31 ± 35.28 µm for USP, NCSM and Pentacam HR, respectively. The Bland-Altman analysis showed that the highest concordance was found between USP and NCSM, with differences between - 13.18 µm and 20.26 µm. For the differences between measurements obtained with Pentacam HR and USP, the differences at Bland-Altman plot were between - 28.25 and 13.57 µm. The lowest concordance was found for the CCT values measured with Pentacam HR and NCSM, with differences between - 25.67 and 6.86 µm. The intraclass correlation coefficient (ICC) between all pairs of measurements was between 0.979 and 0.987, suggesting that the mean measurements were strongly correlated. CONCLUSION: Measurements obtained with all three devices had high correlation. USP and NCSM were found in good agreement and high concordance, too. The above results indicate that these two devices are interchangeable in clinical practice. Pentacam HR may be a useful alternative for measuring CCT; however, it significantly underestimates CCT and cannot be used interchangeably with the other devices that we studied.

Corneal Densitometry Assessed With Scheimpflug Camera in Healthy Corneas and Correlation With Specular Microscopy Values and Age.

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.