Primary open-angle glaucoma (POAG) is a syndrome with bilateral progressive optic neuropathy with consecutive visual field damage. Patients experience retinal ganglion cell death that leads to a localized or diffused loss of nerve fibers and thinning of both the nerve fiber layer and the neural retinal rim of the optic disc. This rim loss, together with tissue remodelling induced especially by reactive astrocytosis, leads to typical glaucomatous optic nerve head excavation. Risk factors include increased intraocular pressure (IOP), disturbed autoregulation of ocular perfusion, myopia, and race. The cause of IOP increase is not well understood. An increased outflow resistivity, induced by tissue remodelling of the trabecular meshwork, seems to play a major role. The main cause of disturbed autoregulation is primary vasospastic syndrome, rendering the eye more sensitive to IOP increase or blood pressure decrease. Recent studies have shown elevated ET-1 levels in the blood and aqueous humor of patients with NTG or POAG. The effects of such ET-1 increases are significant: ET-1 may play a role in tissue remodelling of the trabecular meshwork and the optic nerve head; ET-1 induces a constriction of the trabecular meshwork and increases IOP; and ET-1 may be involved in the pathogenesis of vascular dysregulation. Conclusion: Evidence suggests that the pathological increase of ET-1 is involved in tissue remodeling of the anterior and posterior part of the eye and in the pathogenesis of dysregulation of IOP and blood flow.