Susceptibility to pressure amaurosis was measured in young research subjects before and during blood pressure elevation induced by intravenous infusions of phenylephrine. Intraocular pressure elevations were produced by paralimbal suction; we measured the highest level to which intraocular pressure could be raised without obliterating perception of a slowly flickering stimulus in the nasal field of vision. Elevation of systemic blood pressure was accompanied in all subjects by a corresponding increase in the highest "safe" level of intraocular pressure. This observation confirms the commonly held hypothesis that pressure amaurosis is the result of pressure-induced neuroretinal ischemia.