 The main purpose of this project is to investigate the blood flow of the ophthalmic artery OA in patients with ocular hypertension, high tension glaucoma and normal tension glaucoma. It is also to study the influence of the intraocular pressure difference on OA blood flow in the two first groups. Furthermore, the investigators want to understand the relationship between ocular dynamics, blood flow and structural alternations of the optic nerve head ONH. The rationale behind the study is to improve knowledge of the pathogenesis of glaucoma. 