Gravity-induced homeostatic reactions in the macular and choroidal vasculature of the human eye.

We quantified the changes in macular and choroidal blood flow during body inversion to elaborate their hemodynamic attributes and relate them to our previously reported effects of inversion on visual neural function. Ten healthy subjects took part in the study. The intraocular pressure (IOP) was altered through graded body tilts. Macular and choroidal pulsatile ocular blood flow (POBF) were measured with an Oculix BFS 2000 and a Langham OBF system, respectively. Body inversion caused a systematic decrease in the POBF for all subjects. Systematic changes in macular leukocyte velocity and density were also found with inversion. Six of ten subjects showed a reciprocal relationship between the leukocyte density and velocity as a function of body orientation, while parallel changes in the leukocyte density and velocity were seen during inversion for the remaining subjects. Our results may reflect individual strategies for autoregulation within the macular circulation and an absence of autoregulation in the pulsatile component of the choroidal circulation.