In a double-blind randomized clinical trial, 79 non-insulin-dependent diabetic subjects with early retinopathy and open-angle glaucoma received orally either three 500-mg capsules of Doxium (calcium dobesilate) daily for 6 months (41 patients) or three placebo capsules daily for the same period (38 patients). At the end of the study statistically significant differences in the Doxium group compared with the placebo group were recorded: intraocular pressure, visual field defects, surface area of retinal hemorrhages, and whole blood and plasma viscosity were reduced (p less than 0.001). Coefficient of outflow facility and serum albumin concentration were increased (p less than 0.001 and p less than 0.02, respectively). These results suggest that increased whole blood viscosity is a risk factor for diabetic retinopathy and for glaucomatous optic nerve damage. They further suggest that Doxium reduces blood hyperviscosity and lowers intraocular pressure, with a beneficial effect on retinal state and visual fields.