Anchoring fibrils form a complex network in human and rabbit cornea.

Anchoring fibril distribution, depth of penetration into the stroma, and pattern of histochemical localization of type VII collagen (the anchoring fibril collagen) were studied in normal human and rabbit corneas. Electron micrographs of cross sections and sections taken parallel to the basement membrane demonstrate that anchoring fibrils insert into the basal lamina and then splay out laterally. They are more readily seen in sections taken parallel to the basal lamina, where they are observed to form a complex branching and anastomosing network below the basal lamina. Distal to the basal lamina, anchoring fibrils appear to insert into patches of dense extracellular matrix termed "anchoring plaques." Average depth of penetration of anchoring fibrils into stroma is 0.60 and 0.54 microns for human and rabbit, respectively. Monoclonal antibodies to type VII collagen localize only to the basement membrane-anchoring fibril zone of both human and rabbit corneas. No obvious differences in anchoring fibril structure or distribution were observed between human corneas, which have a Bowman's layer, and rabbit corneas, which do not.