HISTOLOGIC LOCALIZATION OF INDOCYANINE GREEN-DYE IN AGING PRIMATE ANDHUMAN OCULAR-TISSUES WITH CLINICAL ANGIOGRAPHIC CORRELATION

Objective: This study aimed to histologically localize indocyanine gre en (ICG) dye in the geriatric primate and human eye and to correlate t hese findings with clinical ICG angiography. Design: The study design was a clinicopathologic correlation. Participants: Six eyes of three g eriatric monkeys (Maccaca mulatta) with macular drusen, 19 to 29 years of age, housed at the California Primate Research Center and an enucl eated human eye from a 66-year-old patient with choroidal melanoma wer e examined. Intervention: All six monkey eyes and the human eye underw ent clinical ICG angiography. Five monkey eyes were enucleated at vary ing intervals after intravenous ICG dye injection for histologic exami nation. One monkey eye was removed without prior ICG injection as an a ge-matched control. The human eye was enucleated after intravenous inj ection of ICG dye. Main Outcome Measures: Infrared fluorescence micros copy of freeze-dried tissue sections was performed to detect ICG fluor escence. Histologic sections were stimulated with an 810-nm diode lase r, and the fluorescence emitted was detected with a Hamamatsu infrared camera. The images were digitally recorded. The distribution of fluor escence on histologic examination was correlated with the fluorescence of the clinical ICG angiogram. Results: Infrared fluorescence microsc opy of monkey sections localized fluorescence within retinal and choro idal vessels early after injection of ICG dye. The ICG fluorescence wa s seen in the extravascular choroidal stroma within 10 minutes after i njection. The stromal fluorescence persisted in sections obtained 50 m inutes after injection of ICG. The retinal pigment epithelium (RPE)-Br uch's membrane complex was brightly fluorescent in the middle-and late -stage histologic sections. Drusen deposits were brightly fluorescent at all timepoints examined. Similar findings were observed in freeze-d ried tissue sections of the human eye. The fluorescence detected on hi stologic sections correlated closely with the fluorescence of the clin ical ICG angiograms for the same interval.Conclusions: The ICG dye doe s not remain solely within the choroidal intravascular space but extra vasates into the choroidal stroma and accumulates within the RPE. Extr avascular ICG binds to drusen material. These findings will enhance th e interpretation of clinical ICG angiography.