Abstract
PurposeTo investigate the choroidal circulation using the fat embolism model and electric circuit simulation.MethodsExperimental fat embolism was induced by infusing triolein emulsion into the internal carotid artery in cats. Video fluorescein angiography was recorded. The observations were interpreted by using a custom software developed to simulate the choriocapillaris as a schematic electric circuit; electric current for blood flow, voltage for intravascular pressure, and electric resistance for vascular resistance. A dual‐layered hexagon was designed to represent the choriocapillaris lobule. The anode and cathodes were connected to the center and periphery of each hexagon, representing the terminal arteriole and draining venules, respectively. Disconnecting the anode simulated choroidal embolism.ResultsPerfusion defects were observed in two categories. In the scatter perfusion defects suggesting an embolism at the terminal arterioles, fluorescein dye filled the non‐perfused lobule slowly from the adjacent perfused lobule. In the segmental perfusion defects suggesting occlusion of the posterior ciliary arteries, the hypofluorescent segment became perfused by spontaneous resolution of the embolism without subsequent smaller infarction. The findings could be simulated with an electric circuit. Although electric currents flowed to the disconnected hexagon, the level was very low compared with that of the connected ones.ConclusionsThe choroid appeared to be composed of multiple sectors with no anastomosis to other sectors, but to have its own anastomotic arterioles in each sector. Blood flows through the continuous choriocapillaris bed in an end‐arterial nature functionally to follow a pressure gradient due to the drainage through the collector venule.
Highlights
The choroid is a very special tissue, as it has the most abundant blood flow per weight in the human body and a highly complicated three-dimensional vascular structure
We investigated the choriocapillary circulation using fluorescein angiography (FA) in an experimental fat embolism model, and the angiographic findings were interpreted by using an electric circuit model simulating the choriocapillary bed
The perfusion defects of the choroid were observed in two categories (Fig. 1): (1) perfusion defects scattered among small choroidal patch fillings in 8 cats and (2) segmental perfusion and defects assumed to correspond to territories supplied by the posterior ciliary artery (PCA) in 4 cats
Summary
The choroid is a very special tissue, as it has the most abundant blood flow per weight in the human body and a highly complicated three-dimensional vascular structure. Postmortem corrosion cast studies revealed that choroidal circulation has anastomotic channels at various levels of capillaries, arterioles, and venules[6, 7] These characteristics are shared with various mammals including monkeys[6], horses[8], and cats[9]. The vascular channels are interconnected in the choroid, the blood will follow pressure gradient and will be observed as an end-arterial system in angiography. Observed in the occlusion of the posterior ciliary artery (PCA) cannot be explained by their theory, as the pressure gradient in the choroidal arterioles will be reversed when the PCA is occluded, and the non-perfusion would be resolved rapidly by perfusion via the anastomosing arterioles from the adjacent sectors. A triolein emulsion can have various particle sizes, which result in different findings, as vessels of various sizes were occluded This allowed the observation of both sectorial and lobular perfusion defects. The use of FA in feline eyes has the advantage of assessing the choriocapillaris circulation without interfering with background fluorescence
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