PURPOSE. To determine in patients with ocular hypertension (OHT) or early glau coma (EOAG) the change in blood flow measured at the neuroretinal rim of the opt ic disc in response to a 15-Hz diffuse green luminance flicker, a stimulus that activates predominantly the ganglion cell magnocellular pathway. METHODS. Thirt een patients with EOAG, 29 with OHT, and 16 age-matched control subjects, all w ith excellent fixation, were examined. Blood flow (Fonh) at the neuroretinal rim of the optic disc was continuously monitored by laser Doppler flowmetry before and during exposure to a 15-Hz, 30°field green luminance flicker. The response of Fonh to this stimulus (RFonh)-was expressed as percentage change in Fonh be tween baseline and the last 20 seconds of flicker. Two to three temporal sites o f the disc were tested, and the highest RFonh was considered for further analysi s. RF onh results in patients were correlated with morphologic (cup-to-disc ar ea ratio, cup shape neuroretinal rim area) and functional (perimetric mean devia tion and pattern electroretinogram amplitude) clinical parameters. RESULTS. In t he patients with OHT or EOAG, Fonh and RFonh were both reduced compared with the ir respective values in the control group. Both quantities decreased significant ly with neuroretinal rim area when the patients’data were pooled. No significan t correlation was found between Fonh or RFonh and the other morphometric and fun ctional parameters. The group averaged time course of RFonh was not significantl y different from that in the normal subjects. CONCLUSIONS. Luminance flicker-ev oked RF onh is abnormally reduced in patients with OHT or EOAG, indicating an im pairment of neurally mediated vasoactivity. The data suggest that PERG-derived neural activity and flicker-evoked RFonh can be independently altered early in the disease process. PURPOSE. To determine in patients with ocular hypertension (OHT) or early glau coma (EOAG) the change in blood flow measured at the neuroretinal rim of the opt ic disc in response to a 15-Hz diffuse green luminance flicker, a stimulus that activates METHODS: Thirteen patients with EOAG, 29 with OHT, and 16 age-matched control subjects, all w ith excellent fixation, were examined. Blood flow (Fonh) at the neuroretinal rim of the optic disc was continuous monitored by laser Doppler flowmetry before and during exposure to a 15-Hz, 30 ° field green luminance flicker. The response of Fonh to this stimulus (RFonh) -was expressed as percentage change in Fonh be tween baseline and the last 20 seconds of flicker. Two to three temporal sites of the disc were tested, and the highest RFonh was considered for further analysi. RF onh results in patients were correlated with morphologic (cup-to-disc ar ea ratio, cup shape neuroretinal rim are a) and functional (perimetric mean devia tion and pattern electroretinogram amplitude) clinical parameters. RESULTS. In t he patients with OHT or EOAG, Fonh and RFonh were both reduced compared with the ir values ​​values ​​in the control group. Both quantities decreased significant ly with the neuroretinal rim area when the patients’data were pooled. No significan t correlation was found between Fonh or RFonh and the other morphometric and funtion parameters. The group averaged time course of RFonh was not significantl y different from that in the normal subjects. CONCLUSIONS. Luminance flicker-ev oked RF onh is abnormally reduced in patients with OHT or EOAG, indicating an im pairment of neurally mediated vasoactivity. The data suggest that PERG-derived neural activity and flicker-evoked RFonh can be independently altered early in the disease process.