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H Kergoat, JV Lovasik, E Bitton; Reduction in Choroidal Blood Flow in the Foveal and Perifoveal Area During Dark Adaptation . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3300.
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Purpose:The retinal cone and rod receptors allow the eye to see under various lighting conditions. The cones predominate in the central retina and are responsible for daylight-like vision whereas the rods are found in highest density in a concentric band located some 10-15 degrees from the fovea and are more active during nighttime-like vision. The objective of the present study was to determine whether changes in photoreceptor function could be coupled with changes in ocular blood flow. For this objective, we measured the choroidal blood flow (ChBF) perfusing the central cones as they were systematically desensitized during dark adaptation (DA). Methods:Twelve healthy adults (mean age: 26.5 ± 8.2 years) volunteered for testing. ChBF at the fovea and at 8 equally spaced retinal sites 1 mm away and concentric to the fovea was measured by Laser Doppler Flowmetry (LDF). The retina was first light adapted for 2 minutes to a uniform white light presented in Maxwellian view via a fundus camera through a dilated pupil. Then all room lights were turned off and the subject's head and the front of the LDF covered with a black light tight cloth to maximize the level of dark adaptation. The only light visible to the subject during DA was the dim 811 nm probing laser, and the series of 8 very dim pinpoint fixation targets that are illuminated one at a time. ChBF was sampled for some 10 seconds at each retinal location every 2 minutes over 24 minutes of DA. Results:Group averaged data revealed that the baseline foveal (6.08 ± 0.63 arbitrary units - AU) and perifoveal (5.49 ± 0.39 AU) ChBF did not differ (p= 0.2363) and that the overall ChBF (foveal plus perifoveal) decreased biphasically by a total of 17% (p= 0.0024) during DA. Conclusion:Our data suggest that the ChBF was redirected by some mechanism to zones with increasing metabolic demands, such as those populated by the rods in the mid-periphery. This interaction between altered blood flow and a shift from cone to rod function provides additional support for the notion of a coupling between blood flow and neural function.
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