[Dark rim around choroidal neovascularization in indocyanine green angiography]

Experimentally produced choroidal neovascularization (ChNV) surrounded by a dark rim in indocyanine green (ICG) angiography was studied histopathologically. Dark rims were seen in 28% of ChNVs which were detected with ICG angiography 2 weeks after photocoagulation. During the developing stage of ChNV, the dark rim around it was seen in the early phase of ICG angiography, but in the late phase, the dark rim became unclear because of extravascular dye leakage. During the regressive stage, the dark rim was seen in all phases of angiography. It was especially clear in the late phase. Histopathologically, at the site of the dark rim the retinal pigment epithelial cells proliferated to surround the ChNV in the subretinal space during both stages. These results show that proliferated retinal pigment epithelium surrounding ChNV blocks the fluorescence of the choroid, and causes the dark rim. The dark rim is helpful for diagnosis of ChNV.