Inclusion Criteria:  glaucoma and/or ocular vascular disease in at least on eye abnormal SSpERG RVP measured using an ophthalmodynamometer at least 15 mmHg higher than intra-ocular pressure (IOP), fasting serum Hcy level > 12 µmol/l stable and well-controlled IOP (with or without IOP-lowering treatment)  Exclusion Criteria:  starting other systemic or ocular medications with potential impacts on RVP within a month before entering the study or during the course of the study starting or changing the dosage of other medications with potential impact on SSpERG within 3 months before entering the study or during the course of the study non-adherence to the follow-up schedule inability to perform a proper RVP measurement using ophthalmodynamometry.