Electron microscopic studies on Fuchs ' combined dystrophy

Anterior portions of the central corneas of Fuchs' combined dystrophy were studied with the electron microscope, with the use of the same corneal buttons as in Part I of this study, in which changes of the posterior portions were reported. The epithelium showed various grades of cellular edema, mostly in the basal layer. Some of the edematous cells appeared to burst and coalesce to form subepithelial bullae. Possibly as a result, together with proliferation of epithelial cells, marked undulations of the epithelial base and "epithelial quasi islands" toith fissures were formed. Intercellular spaces with desmosomes were usually closed and tight •junctions of the surface layer could be seen as in the controls. Alterations of the subepithelial region paralleled or followed the epithelial changes. Cells appeared in this region at an early stage. Serial sections showed these to come from the anterior stroma. Later, active fibroblasts and collagen fibrils increased, forming large subepithelial masses of connective tissue. These filled all spaces between the irregular epithelial base mentioned above and Bowman's layer, including the fissures separating the epithelial quasi islands. At a later stage fibroblasts became inactive and fewer and the collagen fibrils became thicker. Alterations of Bowman's layer and stroma were less marked, although some changes were seen in the stroma as compared with normal controls. All this indicates that the changes in the anterior cornea in Fuchs' dystrophy are secondary to the involvement of the posterior portions tohich were discussed in Part I, and that the subepithelial alterations are to form a subepithelial connective tissue. Development of anterior bullous changes may be largely dependent upon the balance between the barrier function of the posterior banded region of Descemet's membrane and dysfunction of the altered endothelium.