Concomitantly, vasoconstriction-induced microcirculatory dysfunction in the optic nerve head exacerbates ischemic injury to retinal ganglion cells (RGCs), with experimental data showing a significantly higher RGC apoptosis rate (P<0.001) in glaucoma animal models (27), closely associated with Matrix Metalloproteinase-9 (MMP-9)-mediated extracellular matrix degradation and mitochondrial dysfunction (25, 28). This evidence concerns the gene MMP9 and glaucoma.