On the basis of ocular perfusion pressure a new method was suggested for determining an individually endurable intraocular pressure (IOP), i.e. pressure of target. A total of 390 eyes (232 patients with primary open-angle and normal-tension glaucoma) were examined before and after conservative and surgical treatment. The pressure of target was found, in a progressing worsening of visual functions, to be significantly lower versus the stabilized glaucoma, which was due to a low ocular perfusion pressure. The maximally tolerable IOP in a progressing glaucomatous optic neuropathy concomitant with a normalized IOP amounts to 13-15 mm Hg; while, in the stabilized glaucoma it can exceed the mean statistic norm. The pressure of target was shown to be a non-permanent value, which changes depending on the dynamics of the ophthalmic perfusion pressure and IOP. The sensitivity of the suggested method is 77.4%. It can be used in prognosticating the glaucomatous-process clinical course and in choosing an optimal tactics for the treatment of open-angle and normal-tension glaucoma.