PURPOSE: To investigate the association of nailfold capillaroscopy, heart rate variability (HRV), and clinical characteristics of glaucoma with the plasma matrix metalloproteinase-9 (MMP-9) level in normal-tension glaucoma (NTG). MATERIALS AND METHODS: We conducted a prospective, cross-sectional study on 25 patients with NTG. Subjects with systemic diseases were excluded. The patients underwent a complete ophthalmic examination and were referred to the Rheumatology Department, where nailfold capillaroscopy and HRV assessment were performed. The patients were assigned to the lowest and highest HRV groups according to the standard deviation value of the qualified normal-to-normal intervals of the HRV assessment. Blood samples from all the subjects were assayed for MMP-9 concentrations. RESULTS: The systemic MMP-9 level was significantly associated with the nailfold capillaroscopy result (rho = 0.439, p = 0.032). Of the 25 patients, seven had optic disc hemorrhage (ODH). The mean MMP-9 concentration was 4375.6 +/- 2923.2 pg/ml in ODH patients and 5932.1 +/- 1265.4 pg/ml in patients without ODH. However, there was no significant association of HRV parameters or disc hemorrhage with the systemic MMP-9 level. CONCLUSIONS: The systemic MMP-9 level was associated with the nailfold capillaroscopy results in patients with NTG but had no direct association with ODH.