Dynamic examinations of 78 patients with a primary diagnosis of glaucoma with low intraocular pressure and 25 persons without disturbances in intraocular pressure regulation, using up-to-date adequate methods--ultrasound dopplerography, rheography, fluorescence angiography, electron tonography, as well as other traditional methods, allow to make a conclusion that glaucoma with low intraocular pressure is a variant of the development of a typical open-angle glaucoma complicated by involutional changes in the body in a form of chronic vascular deficiency (chronic ischemic neuropathy of the eye). Glaucoma with low pressure should be differentiated from ischemic neuropathy or its outcome. The criterium for a diagnosis of low pressure glaucoma is the presence of changes in hydrodynamic and their progression (intensification of retention in reduced level of intraocular fluid outflow), positive results of unloading tests. A term "primary open-angle glaucoma, chronic vascular deficiency" is proposed.