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Axon-Tracing Properties of Indocyanine Green
Michel Paques, MD, PhD;
Olivier Genevois, MD;
Angélique Régnier, MS;
Ramin Tadayoni, MD;
Richard Sercombe, PhD;
Alain Gaudric, MD;
Eric Vicaut, MD, PhD
Arch Ophthalmol. 2003;121:367-370.
Objective It has been shown recently that the application of indocyanine green (ICG) over the retinal surface is followed by prolonged staining of the optic disc. This study was performed to analyze the diffusion of ICG in the optic tract.
Methods Anterograde diffusion of ICG was evaluated after injection into the vitreous of rabbits. Retrograde diffusion was evaluated after microinjection into the lateral geniculate nucleus of rats.
Results Anterograde and retrograde diffusion occurred along the axons at a rate of about 2 mm per hour when ICG was injected. Anterograde staining of the visual pathway persisted for several weeks. After injection into the lateral geniculate nucleus, fluorescent retinal ganglion cells could be visualized for at least 7 days in conscious rats by conventional infrared photography. Microscopic examination findings of retrograde-labeled retinas showed the presence of ICG vesicles inside the axons, cytoplasm, and dendrites of retinal ganglion cells. No evidence of toxic effects was detected by optical microscopy.
Conclusions Indocyanine green is a fast bidirectional axonal tracer. Injection into normal vitreous results in long-term staining of the visual pathway. In vivo counting of ICG-labeled retinal ganglion cells in rats can be performed for several days after injection. Indocyanine green is therefore potentially of interest for use in experimental neurophysiological studies.
Clinical Relevance The present results suggest that in humans, epiretinal application of ICG results in prolonged staining of the visual pathway. Therefore, additional studies of long-term toxic effects of ICG on neural cells are warranted before recommending its use in humans as an intraoperative tool for vitreoretinal surgery.
From Laboratoire d'Etude de la Microcirculation, Hôpital Fernand Widal (Drs Paques, Genevois, Tadayoni, Sercombe, and Vicaut); Ophthalmology Department, Hôpital Lariboisière (Drs Paques, Tadayoni, Gaudric, and Vicaut); Laboratoire de Recherches Cerebrovasculaires (Ms Régnier and Dr Sercombe), Centre National de la Recherche Scientifique (CNRS), Unité 646; Université Paris 7 and Assistance Publique-Hôpitaux de Paris, Paris, France. Dr Paques is now with the Fondation Ophtalmologique Rothschild, Paris. The authors have no relevant financial interest in this manuscript.
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