NOS3 and snowflake vitreoretinal degeneration: In light of the fact that aging per se is a prominent risk factor for SVD, it is intriguing that eNOS-dependent vasodilation of cerebral arterioles is impaired in aged rats, as contrasted to adult rats; treatment with tempol, or the NADPH oxidase inhibitors apocynin and DPI, restored normal vasodilation in these aged rats [18].