In vivo Analysis of Choroidal Circulation by Continuous Laser-targeted Angiography in Rat

Abstract

Abstract: : Purpose: High quality angiograms of the rat choriocapillaris were achieved by continuous laser-targeted angiography (LTA). By studying the patterns of those images, we assessed the choroidal circulation system in vivo. Methods: We developed a modified slit lamp by installing two kinds of lasers (argon and diode). Carboxyfluorescein was encapsulated in heat-sensitive liposomes and injected intravenously. Encapsulated carboxyfluorescein was released locally by applying continuous heat beam provided by diode laser (810nm) in various powers. Video angiograms were generated with excitation illumination provided by argon laser (488+514nm) to observe highly selective images of choriocapillaris. Results: Three distinct phases (filling, plateau and draining) of fluorescent images of choriocapillaris were observed by applying the diode laser continuously. In the plateau phase, a lobe-shaped area of choriocapillaris peripheral to the laser site was illuminated and this finite area did not change in size while continuous laser was applied to the same spot. By increasing laser power, a larger area of choriocapillaris was illuminated in the plateau phase. The filling and draining phases demonstrated the flow patterns of choriocapillaris lobules, which filled from a central spot and drained along a peripheral ring. Conclusions: This study showed that the choriocapillaris is divided into an independent functional unit and that the choroidal circulation is segmental under normal conditions. The results implied that in LTA, diode laser warms up a choroidal artery and released fluorescein flows downstream to an area of choriocapillaris fed by the same artery. LTA appeared to be a powerful method to analyze choroidal circulation in vivo.

Keywords: choroid • blood supply • laser