Axon-tracing properties of indocyanine green.
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.


CONCLUSIONS
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.
Paques
Michel
M
Laboratoire d'Etude de la Microcirculation, Hôpital Fernand Widal, Paris, France. michel.paques@laposte.net
Genevois
Olivier
O
Régnier
Angélique
A
Tadayoni
Ramin
R
Sercombe
Richard
R
Gaudric
Alain
A
Vicaut
Eric
E
D000818:Animals; D001369:Axons / Q000502:physiology*; D002452:Cell Count; D004396:Coloring Agents; D004058:Diffusion; D005829:Geniculate Bodies / Q000502:physiology; D007208:Indocyanine Green; D007267:Injections; D008297:Male; D009900:Optic Nerve / Q000166:cytology; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D012165:Retinal Ganglion Cells / Q000166:cytology*; D014795:Visual Pathways / Q000166:cytology* / Q000502:physiology; D014822:Vitreous Body / Q000378:metabolism
D004396:Coloring Agents; D007208:Indocyanine Green