Though many researchers have proposed that abnormal stromal metabolism is the primary site of corneal dysfunction in KC, various histopathological studies have highlighted the epithelial abnormalities and postulated that insults to the epithelium cause a release of proteolytic enzymes (such as MMP9, IL6 and LOX) to degrade the stromal collagen and matrix components1,53,69,70. Here, MMP9 is linked to keratoconus.