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Retinal ganglion cells toxicity caused by photosensitising effects of intravitreal indocyanine green with illumination in rat eyes

¹ Department of Anatomy, The University of Hong Kong, Pokfulam, Hong Kong SAR, People’s Republic of China
² Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, Hong Kong SAR, People’s Republic of China
³ Department of Ophthalmology, Hong Kong Sanatorium and Hospital, Hong Kong SAR, People’s Republic of China

Correspondence to:
Correspondence to:
Dr Alvin K H Kwok
MD, FRCS, Department of Ophthalmology, Hong Kong Sanatorium and Hospital, 2 Village Road, Happy Valley, Hong Kong; alvinkwok{at}hksh.com

Aim: To investigate the effects of indocyanine green (ICG) with or without illumination on rat retinal ganglion cells (RGC) and retinal morphology.

Methods: Intravitreal injections of 1.0 mg/ml ICG solution were performed in rat eyes with or without subsequent illumination for 5 minutes. Eyes in the control group had intravitreal injections of balanced salt solution with illumination. Retrograde labelling of RGC with 6% Fluoro-Gold was performed 1 month later and RGC densities were compared between the three groups. Light microscopy with measurements of outer nuclear layer (ONL) and inner nuclear layer (INL) thicknesses were also performed and compared.

Results: Eyes with ICG without illumination showed insignificant reduction in RGC density compared with the control group (p = 0.28), whereas a significant decrease in RGC density was found in eyes that had ICG injection with illumination (p = 0.036). A significant increase in ONL thickness was also observed in the ICG with illumination treated eyes compared with the ICG without illumination and the control groups (p<0.001). No significant difference in INL thickness was observed between the three groups.

Conclusions: Intravitreal injection of 0.1 mg/ml ICG in rat eyes followed by illumination resulted in photosensitising toxicity to RGC. Lower ICG concentration or illumination level should be considered when performing ICG assisted macular surgery.

Abbreviations: BSS, balanced salt solution; ICG, indocyanine green; ILM, internal limiting membrane; INL, inner nuclear layer; ONL, outer nuclear layer; PBS, phosphate buffered saline; RGC, retinal ganglion cells

Keywords: indocyanine green; retinal ganglion cell; photosensitising toxicity; rat

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