Functional end-arterial circulation of the choroid assessed by using fat embolism and electric circuit simulation
Abstract
Purpose
To investigate the choroidal circulation using the fat embolism model and electric circuit simulation.
Methods
Experimental 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.
Results
Perfusion 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.
Conclusions
The 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.
