Corneal graft failure. A, PAS stain of failed penetrating keratoplasty (PK) graft with diffuse endothelial cell loss, fibrous retrocorneal membrane (F), secondary stromal edema with bullous keratopathy (arrowhead), epithelial basement membrane thickening (arrow), and thick fibrous pannus (asterisk). B, Clinical appearance of fibrous downgrowth (arrows). C, PAS stain of a failed graft following Descemet-stripping automated endothelial keratoplasty (DSAEK). The abnormally positioned donor lenticule (L) with donor Descemet membrane (arrowheads) faces the recipient’s Descemet membrane (arrows). Note the endothelial attenuation and marked stromal edema. D, Clinical appearance of epithelial downgrowth in a PK graft (arrowheads). E, Histology of an explanted donor lenticule from a failed DSAEK graft (different patient) shows full-thickness cornea with Bowman layer (arrowheads) on the right and partial-thickness cornea on the left. Retention of donor epithelium led to the epithelial ingrowth (red arrowheads).