EDN1 and glaucoma: Topical IU has been used to treat glaucoma and ocular hypertension for many years, but clinical studies have shown that topical IU use can increase retinal and choroidal blood flow.[16,17] One study demonstrated that human choroidal blood flow improved after ocular instillation of 1 to 4 drops of 0.12% IU, q30 min for a total of four doses, after the blood flow was decreased by an injection of endothelin 1 (ET-1) intravenously.[17]