Alterations in NO activity and increased ET-1 expression, which could promote the weakening of the blood retinal barrier (BRB), have been observed in patients with glaucoma (Noske et al., 1997; Tezel et al., 1997; Tunny et al., 1998; Nicolela et al., 2003; Polak et al., 2007). Here, EDN1 is linked to glaucoma.