DCN and keratoconus: To understand whether differences in structural and extracellular proteins between normal and KC corneas could play a role in the etiopathogenesis of KC and ACH, we examined the presence and distribution of proteoglycans and ECM proteins—namely elastin, collagens I, IV, and VI, fibulin-2, and decorin—using immunohistochemical analysis in KC cases compared to normal corneas.