Later, a recent metanalysis revealed that KC patients showed elevated levels of inflammatory factors (e.g., IL1A, IL1B, IL6, TNF), a collagen-degrading enzyme (MMP9), and an apoptosis-related protein (SFRP1), while the expression levels of extracellular matrix -related proteins (e.g., LOX, MRC2, FMOD, and KERA) were reduced. Here, MMP9 is linked to keratoconus.