MMP2 and keratoconus: Degradation of collagen components of the extracellular matrix in keratoconus corneas favours changes in the expression of ECM enzymatic regulators, that is, gelatinase A and matrix metalloproteinase 2 (MMP-2), which digest the main structural elements of the ECM, namely, collagen IV, collagen V, fibronectin, and laminin [47, 48], and MMP-2 inhibitor, that is, tissue inhibitor metalloproteinase 1 (TIMP-1).