Effects of Indocyanine Green on Retinal Ganglion Cells

Recently, indocyanine green (ICG) has been used to visualize the internal limiting membrane during vitrectomy. After intraocular administration, ICG accumulates at the optic disc. In this study, the effects of ICG on retinal ganglion cells (RGCs) were examined. In vitro, rat RGCs were purified by a two-step immunopanning procedure, briefly exposed to ICG (2.5 x 10(3) mg/L), and irradiated with an endoilluminator for 15 minutes or incubated in the presence of ICG (concentration: 2-250 mg/L) without irradiation. The number of viable RGCs was counted after 3 days in culture. In vivo, after rats received an intravitreal injection of 3 micro L ICG (0.25 and 2.5 mg/L), the distribution of ICG was observed with a fundus camera, and the number of viable RGCs was examined by a DiI (1,1'-dioctadecyl-1-3,3,3',3'-tetramethylindocarbocyanine perchlorate)-retrolabeling technique. In vitro, a brief exposure to ICG and light did not affect RGC survival. However, ICG reduced the number of viable RGCs in a dose-dependent manner when the cells were exposed for 3 days. In vivo, the dye was initially distributed on the retinal surface and around the optic disc. At day 7, the fluorescence became invisible in the 0.25-mg/L group, whereas the staining of the optic disc contour was evident in the 2.5-mg/L group. The number of viable RGCs decreased significantly in the 2.5-mg/L group 14 days after the injection. ICG showed an inherent toxicity to RGCs in a dose-dependent manner. Lower concentration and shorter staining time of ICG should be used for dye-assisted vitrectomy.