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Flicker-Evoked Response Measured at the Optic Disc Rim Is Reduced in Ocular Hypertension and Early Glaucoma

¹From the Institut de Recherche en Ophtalmologie, Sion, Switzerland; and ²Istituto di Oftalmologia, Università Cattolica del S. Cuore, Rome, Italy.

PURPOSE. To determine in patients with ocular hypertension (OHT) or early glaucoma (EOAG) the change in blood flow measured at the neuroretinal rim of the optic disc in response to a 15-Hz diffuse green luminance flicker, a stimulus that activates predominantly the ganglion cell magnocellular pathway.

METHODS. Thirteen patients with EOAG, 29 with OHT, and 16 age-matched control subjects, all with excellent fixation, were examined. Blood flow (F_onh) 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 F_onh to this stimulus (RF_onh) was expressed as percentage change in F_onh between baseline and the last 20 seconds of flicker. Two to three temporal sites of the disc were tested, and the highest RF_onh was considered for further analysis. RF_onh results in patients were correlated with morphologic (cup-to-disc area ratio, cup shape neuroretinal rim area) and functional (perimetric mean deviation and pattern electroretinogram amplitude) clinical parameters.

RESULTS. In the patients with OHT or EOAG, F_onh and RF_onh were both reduced compared with their respective values in the control group. Both quantities decreased significantly with neuroretinal rim area when the patients’ data were pooled. No significant correlation was found between F_onh or RF_onh and the other morphometric and functional parameters. The group-averaged time course of RF_onh was not significantly different from that in the normal subjects.

CONCLUSIONS. Luminance flicker-evoked RF_onh is abnormally reduced in patients with OHT or EOAG, indicating an impairment of neurally mediated vasoactivity. The data suggest that PERG-derived neural activity and flicker-evoked RF_onh can be independently altered early in the disease process.

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