Histological Proof of Indocyanine Green Angiography: Healthy Eyes

Abstract Purpose: To determine the histological localization of indocyanine green (ICG) in the healthy rat eye and to correlate this with ICG angiographic findings. Methods: After intravenous ICG dye injection, the rat eyes were enucleated and processed by freeze-substitution fixation with acetone. The tissue sections were stimulated with an 805-nm diode laser and observed with an infrared microscope with an intensified charge coupled device camera. The histological examinations of ICG localization were correlated with the ICG angiographic images. Results: ICG dye did not leak from the retinal and iris vessels. However, in the choroid, extravasation of ICG from the choriocapillaris was observed. The extravascular ICG from the choriocapillaris slowly diffused to the choroidal stroma but did not diffuse to the neurosensory retina through the retinal pigment epithelium. Conclusion: Change in the localization of ICG in ocular tissue was demonstrated in the ICG angiographic findings. These results help to interpret clinical ICG angiographic findings.