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John Vincent Lovasik, Helene Kergoat; A comparison of subfoveal to parafoveal choroidal blood flow dynamics. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):692.
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© ARVO (1962-2015); The Authors (2016-present)
Due to photoreceptor density differences at the fovea and parafovea we hypothesized a difference in the choroidal blood flow in these regions. Consequently, we measured the Laser Doppler Flowmetry parameters of choroidal blood flow (ChBF), volume (ChBVol) and velocity (ChBVel) at the fovea and parafovea and compared their respective pulsatility index (PI) before and during diffuse flicker. The PI is a measure of resistance to blood flow such that a lower PI equals an increase in blood flow facility.<br />
20 young healthy adults (25 ± 3 yrs) took part in this study. The probing laser was a 785 nm beam with a power of 65μW at the cornea. The blood flow parameters and their respective PIs were recorded first for the fovea without flicker and then throughout a 60 sec interval of 12Hz blue flicker. The same test sequence and measurements were made for an eccentric site about 7 degrees nasal to the fovea. Recordings were time-averaged over a 5 sec interval prior to flicker (baseline) and over the last 10s during the flicker period.
At the fovea, the group-averaged ChBF, ChBVol, and ChBVel with their respective PIs were unchanged by flicker (p> 0.05). At the eccentric test site, while none of the blood flow parameters changed during flicker (p> 0.05), the PI for choroidal blood Volume decreased during flicker (p< 0.05).
At the fovea, the absence of change in both the PI and blood flow parameters suggest that the subfoveal-choroid has properties of a resistive vasculature. In the periphery, the decrease in PI would have been accompanied by an increase in ChBVol in a fully resistive vasculature. The fact that this was not the case suggested that the foveal and peripheral choroid differ in resistive forces to flow. The increased blood flow facility at the eccentric site may correlate with topographic changes in the metabolic demands of the resident photoreceptor population.
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