ENDOTHELION Study Group: Effect of Bosentan in NAION Patients

Inclusion Criteria: * Non arteritic ischemic optic neuropathy (NAION) with onset \< 21 days * Age ≥ 50 years old * Signed informed consent form * Patients affiliated with a national health insurance scheme or beneficiaries of such a scheme Exclusion Criteria: * Pregnant women, women in labour or breast-feeding mother * Patients with other acute or chronic intercurrent ocular pathology interfering with visual acuity or visual field (diabetes, drug-induced or other retinopathy, other optic neuropathy including uni- or contralateral glaucoma and/or intraocular pressure \> 30 mmHg, advanced cataract, corneal opacities, amblyopia \< 5/10, severe myopia \> -6 diopters, retinal disease) * Simultaneous bilateral NAAION, 1 month apart or less * Signs that may raise suspicion of other inflammatory neuropathy: arterial NAAION (Horton's disease), pain on eye movement or any signs suggestive of optic neuritis, known diagnosis of multiple sclerosis, history of inflammatory optic neuropathy (homo- or ipsi-lateral). A temporal artery biopsy should be performed if there are symptoms suggestive of Horton's disease, or if there is pale and/or diffuse edema, or obliteration of the associated central retinal artery. * Patients with systolic blood pressure below 100 mmHg * Patient with orthostatic hypotension (20 mmHg drop in SBP and/or 10 mmHg drop in DBP when moving to a standing position) * Neurological history of vascular or tumour-related changes to the visual field or other optic neuropathy * Systemic inflammatory disease * Known allergy to bosentan * Patients with moderate to severe hepatic impairment (Child-Pugh class B or C), biliary cirrhosis (serum levels of liver aminotransferases, aspartate aminotransferases (ASAT) and/or alanine aminotransferases (ALAT), greater than three times the upper limit of normal, bilirubin greater than twice normal) * Estimated glomerular filtration rate (GFR) \< 30 ml/min/1.73 m2 * Patients treated with drugs whose efficacy may be reduced by activation of cytochrome P450, 2C9, 3A4 and 2C19 isoenzymes * Patients treated with amiodarone * Patient treated with systemic corticosteroids (background treatment or treatment initiated at the time of NAAION diagnosis) * Person deprived of liberty by judicial or administrative decision, adult protected by law, hospitalized person * Ongoing participation in another clinical research study or in the exclusion period of another clinical study