EDN1 and glaucoma: In addition, the association of lower end-diastolic velocity with higher impendence indices found in our study may indicate that autoregulation related to an imbalance of endothelium-derived vasoregulatory factors (nitric oxide and endothelin-1) cannot maintain a constant blood velocity despite changes in IOP in GODA and glaucoma subjects; this does not happen in the healthy control group.