[About the frequency of excessive epithelial basement membrane thickening in keratoconus]

In spite of a huge amount of morphological and biochemical findings the aetiology of keratoconus (KC) is still unclear. While the primary changes are seen and found mainly within the anterior corneal stroma, some authors believe that the corneal epithelium plays the major role in KC formation. Consequently, the epithelial basement membrane (BM) has become a matter of interest in KC research.

The study included 55 consecutive patients who had a perforating keratoplasty performed because of KC. The corneal explants were processed for light microscopy in the usual manner. Slides were stained with PAS. The whole explant was investigated although the focus of interest was put on the epithelial BM. 10 normal corneas of eyes which had to be enucleated because of a choroidal melanoma served as a control.

In 3 patients (5.5 %) there was a significant linear thickening of the BM (thickness of the BM more than 5 % but less than 30 % of the thickness of Bowman's layer). Only in one patient (1.8 %) there was an excessive BM thickening (thickness of the BM more than 30 % of that of Bowman's layer) with focal (central) BM warts directed against the epithelium ("inverse cornea guttata"). In general, thickening of the BM was most pronounced paracentrally. None of the control corneas had a significantly thickened BM.

A massively thickened epithelial BM can be occasionally observed in KC but is rare on the whole. It is most likely an unspecific secondary phenomenon and not a prerequisite for KC development. The "inverse cornea guttata" was a unique finding.