Local response of the primate retinal microcirculation to increased metabolic demand induced by flicker

Purpose. To study the response of the macular circulation to a local increase in metabolic demand created by a flickering source of illumination. Methods. Laser-targeted angiography (release of a fluorescent dye from heat- sensitive liposomes using a laser pulse) was used to study, in subhuman primates, changes in hemodynamic parameters of the retinal circulation that were induced by a flickering source of illumination. Changes in the macular macrocirculation were compared with those in the macular microcirculation and were evaluated at various distances from the foveola. Results. In response to monochromatic light flicker, the blood flow in retinal arteries increased by 30%. The response of the microcirculation was not homogeneous. It showed a maximum increase in the mid-perifoveal region where there is an increase in ganglion cells and nerve fibers. Interestingly, the maximum change in the index representing capillary blood flow exceeded the blood flow change in the artery (P < 0.08). Conclusions. A stimulus expected to cause increased metabolic demand results in a regulatory response by the retinal microcirculation. This response shows spatial variations that correspond with known variations in retinal anatomy. The authors propose that a redistribution of blood can occur between the capillary layers to fulfill high metabolic demands by neuronal tissue remote from the choroid.