The insufficiency of the autoregulation at the optic nerve's head may cause the glaucoma optic neuropathy (GON). If the long-term stressing exists and an additional endurance arises, the autoregulation may fail and significant changes of the resistance index (RI) at the central retinal artery (CRA) and at the posterior ciliar artery (PCA) can be detected by color flow ultrasonography. Resistivity index represents peripheral resistance. It is displayed in numerical value 0-1. 0 indicates none peripheral resistance, 1 indicates maximal peripheral resistance. The goal of this paper was to determine a risk value of the RI at the CRA and PCA that could suggest possible damaging of the optic nerve. Two groups of the patients were evaluated in the course of 4 years duration of the study. In the I. Group were 72 patients (144 eyes) with GON and with intraocular pressure (IOP) 14-24 mm Hg. The II. Group consisted of 25 healthy men (48 eyes) without diagnosis of GON and with IOP values 14-20 mm Hg. There were RI measurements at all patients at the CRA and CPA at the idle mode and immediately after ordinary addition endurance (performing squatting--Master test). The statistical analysis by T test was evaluated with value: 0.05.According to our findings, the difference between RI: 0.12 +/- 0.03 at the CRA at the idle mode and immediately after ordinary addition endurance is significant for damaging of the autoregulation at the optic nerve's head. For assessment of the insufficiency of the autoregulation at the optic nerve's head RI from PCA is not significant.