Normal cornea. A, The cornea is composed of epithelium (Ep), Bowman layer (B), stroma (S), Descemet membrane (D), and endothelium (En). B, On higher magnification, periodic acid–Schiff (PAS) stain highlights the epithelial basement membrane (EBM), distinguishing it from Bowman layer (B). Because of dehydration of the tissue during processing for paraffin embedding, multiple areas of separation (clefts) of the stromal lamellae are evident (arrows). If the stromal clefts are absent, corneal edema or fibrosis is suspected (the former if the cornea is thick, and the latter if thin). This is an example of a meaningful artifact. C, Higher magnification (hematoxylin-eosin [H&E] stain) also delineates Descemet membrane (D), endothelium (En), and a thin, acellular stromal pre–Descemet membrane layer (arrowheads). The keratocyte nuclei (arrow) are apparent. (Note that PAS stain also highlights Descemet membrane.)