An in depth analysis of histopathological characteristics found in keratoconus.

AIMS The aims of this study were to re-assess the histopathology of the disease by introducing more modern measuring techniques and to determine if axial stromal thinning, which is the most apparent change, is related to the other alterations observed. METHODS Recipient keratoconic corneas from 36 patients following corneal transplantation were studied. Haematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) staining were used to identify breaks in Bowman's layer and Descemet's membrane. Thickness of corneal layers was measured by Leica QWin software. Epithelial and stromal thickness were measured in each sample at the periphery of the corneal button and at the area of maximal stromal thinning. The presence of apoptotic cells in Bowman's layer breaks was detected by terminal deoxynucleotidyl transferase mediated dUTP-X nick end labelling. RESULTS In all 36 corneal samples the central stroma, at the apex of the cone, was thinner than the peripheral. There was a negative correlation between central stromal and central epithelial thickness (p = 0.009). Bowman's layer breaks were found in 92% of corneas. Apoptotic cells were detected at the level of Bowman's breaks membrane. We found a positive correlation between epithelial thickness and the number of Bowman's layer breaks (p = 0.009 for central epithelial thickness and p = 0.003 for peripheral epithelial thickness). Descemet's membrane deformities were observed in 19% of corneas and central stromal thickness of these corneas was significantly less than corneas without breaks (p = 0.006). CONCLUSIONS There are various different histopathological features associated with keratoconus and some of them are very subtle and not very well studied. Accurate measurements also suggest some correlations between them. Stromal thinning is associated with the number of breaks in Descemet's membrane, but it is the thickening of the epithelium which is associated with breaks in Bowman's layer.