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J.V. Lovasik, H. Kergoat, M. Wajszilber; Flicker-induced Changes in the Choroidal Blood Flow and Electroretinograms . Invest. Ophthalmol. Vis. Sci. 2003;44(13):332.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The high metabolic activity of the human retina requires that adequate nutrients be available from the choroid to support phototransduction. In the present study, we measured the effect of increased flash frequency on choroidal blood flow (ChBF) by laser Doppler flowmetry (LDF), and retinal responsivity via the electroretinogram (ERG). Methods: Twenty healthy adults took part in this study. A new compact near IR (785 nm) confocal LDF was attached to the base of a slit-lamp for continuous measurements of the subfoveal ChBF. A dichroic mirror in front of the LDF and placed 45° to the visual axis directed diffuse 2.25 cd/m2 red flashes produced by an Espion Colorburst mini-ganzfeld at a frequency of 1, 30, and 60 Hz onto the test eye. A DTL electrode in the lower canthus of the test eye was referenced to a second DTL in the contralateral patched eye to detect the flash-induced ERGs. This arrangement permitted simultaneous recording of the subfoveal ChBF parameters (flow, volume, velocity) and the ERGs. Signal averaging for ERGs was performed by a Diagnosys Espion unit. The ChBF was measured in arbitrary units, and the fERG by the trough-to-peak amplitude in microvolts. To determine the effect of light on ChBF, all data were normalized to the ChBF in normal ambient light, while the 1Hz flashes were assigned a 100% value to evaluate the effect of flicker on ChBF. Results: The 1, 30 and 60 Hz flashes increased the baseline ChBF by 20, 28 and 58% respectively (p<0.05). This group average increase was associated with increased flow Volume (25, 37, 94%) but decreased flow Velocity (-0.2, -4, -12%). Relative to 1 Hz, the 30 Hz and 60 Hz flicker increased ChBF by 70% and 93%, while the ERG amplitude decreased by 30% and 93% (p<0.05). Conclusions: Higher flash frequencies increase the ChBF but elicit decreasing amplitude ERGs. Assuming the subfoveal blood flow measurements approximate blood flow changes in the portions of the retina responding to the flashes, it would be reasonable to conclude that the refractory period for the ERGs cannot be modified by increased perfusion of the RPE-photoreceptor complex.
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