Investigation and Assessment of Normal Control Values Using the Cornea Module of the HRT II

Abstract

Abstract: : Purpose: Various corneal abnormalities can be visualized with the Rostock cornea module combined with the Heidelberg Retina Tomograph II (HRT II), a new method of confocal cornea microscopy. No control values for the clinical routine application exist. The purpose of this study was to establish and evaluate control data for validation of pathological findings. Methods:/b> 30 healthy individuals (age 25 ± 3 years) were examined with the Rostock cornea module of the HRT II (Heidelberg Engineering), the Pentacam (Oculus), and the IOL–Master (Zeiss). With a specially designed lens attachment, the imaging level of the HRT II system can be focused from the retina to the anterior segment. It generates homogeneous, undistorted images of the cornea with up to 600 × magnification. The densities of epithelial cells, keratocytes, and endothelial cells were measured. Corneal thickness, corneal radii, and axial bulbus length were evaluated and correlations between different parameters and methods were performed. Results: The mean epithelial cell count was 5385 ± 1135 cells/mm². The density of keratocytes showed values of 1055 ± 205 cells/mm² in the anterior stroma and 535 ± 98 cells/mm² in the posterior stroma. Endothelial cell counts revealed means of 2840 ± 404 cells/mm². The mean central corneal thickness evaluated by the cornea module was 496 ± 30 µm and evaluated by the Pentacam 530 ± 27 µm. The correlation coefficient between both thickness measurements was 0.68. A positive correlation betweeen endothelial and epithelial cell count (r= 0.64) was found, however there were no correlations between cell counts and corneal thickness, radii, or axial bulbus length. As expected, a significant correlation between axial length and anterior chamber depth was calculated (r=0.78). Conclusions: This new technique of confocal microscopy allows for quantitative and careful in vivo histology of the cornea including exact depth analysis. Normal control values could be established for the cell counts in different corneal layers. The pachymetry with the cornea module measures lower values than the pentacam, in which the tear film is included.

Keywords: cornea: clinical science • imaging/image analysis: clinical • clinical research methodology