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MH Geiser, A Longo, D Fournier, CE Riva; Postural Changes And Choroidal Blood Flow . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3288.
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Purpose: To evaluate the effect of postural changes on sub-foveal choroidal blood flow (ChBF) in the human eye. Methods: ChBF was measured during postural changes by laser Doppler flowmetry in 11 healthy volunteers between 17 and 61 years of age (mean ± sd: 33 ± 11). The subjects were maintained on a mechanically driven radiology table that was tilted from 90° (standing position, 1) to –8° (supine position, 2) and back to 90° (standing position, 3) with respect to the horizontal. ChBF and heart rate (HR) were continuously measured as subjects were tilted from the position 1 to 2 in 20 sec., remained at this position for 3 min and returned to position 3 in 20 sec. Systemic brachial artery blood pressure (BP) was measured at positions 1, 2, 3. The experiment was repeated to measure the intraocular pressure (IOP) at these positions. The mean ocular perfusion pressure (PPm) was defined as MOABP - IOP, where MOABP is the mean ophthalmic artery blood pressure. Results: BP did not change significantly throughout the experiment. PPm was 55 ± 6% (mean ± sd) higher (p<0.001), HR 16 ± 8% lower (p<0.05) and ChBF 11 ± 11% higher (p<0.001) in position 2 than in position 1. During the tilting from position 2 to 3, PPm, HR and ChBF all returned to values not significantly different from their initial values. The change in ChBF was predominantly due to the change in blood velocity rather than to that of blood volume. Conclusion: In the human eye, ChBF increases when the body is tilted from the standing to the supine position by an amount that is markedly smaller than the increase in PPm. This suggests that an active regulatory mechanism increases the choroidal vascular resistance to limit the increase in ChBF to a value well below that which would be reached with a constant resistance. The site where the change in resistance takes place remains to be determined.
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