Scanning and transmission electron micrographs of a normal human corneal endothelium. (A, B) The endothelial cells are hexagonal, have tight junctions, and contain numerous mitochondria. Acute pseudophakic bullous keratopathy (C, D). There is loss of endothelial cells and tight junctions (C). The stressed endothelial cells have laid down a diffuse, banded posterior collagenous layer (D).