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C. Haritoglou, A. Gandorfer, M. Schaumberger, A. Kampik; Light-absorbing Properties and Osmolarity of Indocyanine-green Depending on Concentration and Solvent Medium . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4052.
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Purpose: To evaluate the absorption spectrum and osmolarity of three currently used indocyanine green (ICG) products at different concentrations and using different solvent mediums. Design: Experimental investigation. Methods: The absorption spectrums of 3 different ICG products (Pulsion, Munich, Germany; Akorn, IL, USA; Laboratoires S.E.R.B., Paris, France) were analysed. Each ICG powder was first dissolved in fluids provided by the manufacturer and then further diluted using balanced salt solution (BSS or BSS plus, Alcon Inc., Fort Worth, Texas, USA) or glucose 5%. Four different concentrations were evaluated: 0.005%, 0.0025%, 0.001% and 0.00025%. The absorption spectrum was measured between 400 to 1000 nm at 2 nm intervals. Furthermore, the osmolarity of each sample was measured as well as the emission spectrum of our light source. Results: Independently from the manufacturer, 0.005% and 0.0025% ICG diluted in BSS or BSS plus showed two maxima, one at approximately 700 nm and a second one at 780 nm. There was an increase from zero to maximum absorption between 600 and 700 nm and a decrease back to zero between 800 and 900 nm. At lower concentrations of 0.001% or 0.00025%, the peak at 700 nm decreased forming a "shoulder", while the peak at 780 nm remained stable. Osmolarity was in the range of 302 to 313 mOsm. In contrast, absorption between 600 and 700 nm decreased, when the ICG products were diluted with glucose 5%. The osmolarity of glucose 5% diluted ICG was lower and ranged between 292 and 298 mOsm. Our light source emitted between 380 nm and 760 nm. Conclusion: Dilution of ICG using BSS or BSSplus results in a steep increase of absorption starting at 600 nm. In clinical practice, there is an overlap between the absorption band of ICG and the emission curve of the light source resulting in a possible photodynamic effect, especially at higher ICG concentrations. This effect becomes less likely with decreasing ICG concentrations or when glucose 5% is used as a solvent medium.
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