Patients with primary open-angle glaucoma are characterized by levels of MMP-1, MMP-2, MMP-3, MMP-9, and MMP-12 protein in aqueous humor, and by upregulated mRNA expression of MMP-1, MMP-9, and MMP-12 in the blood (peripheral blood lymphocytes) compared to the subjects without any type of glaucoma, suggesting that these changes may be considered as a risk factor for the development of primary open-angle glaucoma. Here, MMP9 is linked to glaucoma.