Purpose: To investigate the ultrastructure of advanced Salzmann nodular degeneration (SND) and to correlate it to confocal in vivo findings.
Methods: The corneal degenerative nodules from four patients with SND were examined with confocal microscopy and then removed and processed for light microscopy (LM) and transmission electron microscopy (TEM).
Results: The confocal examination revealed elongated basal epithelial cells and activated keratocytes in the anterior stroma near the nodules. Occasional subbasal nerves and tortuous stromal nerve bundles were observed. With LM and TEM, five zones were described: one internodular and four pertaining the nodule, each characterized by peculiar aspects of the epithelium and stroma. As also confirmed by the morphometry, in the zones corresponding to the nodules, the epithelium was lower and with fewer cell layers than the peripheral zones. Over the nodules, the basement membrane was discontinuous or absent and the Bowman's layer, when present, had a granular-filamentous appearance. The nodular stroma was formed by many activated keratocytes and irregular lamellae. Subbasal nerves were always isolated and had degenerative changes in the center of the nodule.
Conclusions: This work illustrates the confocal microscopic findings associated with LM and TEM observations in patients with advanced SND. Our data revealed milder changes of the epithelium together with more pronounced changes of the basement membrane and Bowman's layer, which are aspects of increased keratocyte activity and an altered nerve pattern. All of these structures seem to contribute to the characteristic corneal disorganization of SND.