The Hemorheological Mechanisms in Normal Tension Glaucoma

PURPOSE: To investigate the differences in hemorheological parameters between patients with normal tension glaucoma (NTG) and normal controls. METHODS: Twenty patients with NTG and 21 age-matched normal controls were included in the study. Hemorheological parameters of the venous blood samples, including blood viscosity at the shear rates of 500, 250, and 5 s(-1), and viscoelasticity were measured using a rotational rheometer; erythrocyte deformability and aggregation were measured using a ektacytometer; and erythrocyte rigidity and the oxygen transport efficiency of blood were calculated. RESULTS: Higher blood viscosities at the high (p < 0.01), medium (p < 0.01), and low (p < 0.01) shear rates were found in the NTG group than in the control group. Significantly higher erythrocyte aggregation index (p < 0.01); lower index of erythrocyte deformability at medium (p < 0.01) and high shear rates (p < 0.05); and lower oxygen transport efficiency of blood at low (p < 0.01), medium (p < 0.01), and high shear rates (p < 0.05) were obtained in the NTG group. CONCLUSIONS: The higher blood viscosity of the NTG patients at the high shear rate may be related to impaired erythrocyte deformability associated with a change in erythrocyte rigidity. Higher blood viscoelasticity and blood viscosity of NTG patients at the low shear rate was due to increased erythrocyte aggregability. Also, the impaired erythrocyte deformability of NTG patients is susceptible to developing abnormalities of the distal microcirculation. Furthermore, the increased blood viscosity and low oxygen transport efficiency of blood may result in hypoperfusion of optic nerve in NTG patients.