Glaucoma is the second cause of blindness in industrialized countries. One of the principal risk factors for open angle glaucoma, the most prevalent form of the disease, is an increase in intraocular pressure (IOP). An excessive drop in nocturnal blood pressure (so called dipping) can be harmful by increasing ischemic damage to the optic nerve. In case of progression of glaucoma despite well controlled IOP, 24h BP monitoring is recommended. The relationship between IOP and systemic blood pressure has been the subject of several studies that are reviewed in this article. The influence of antihypertensive drugs on IOP is also discussed.