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R Jorge, JA Cardillo, RA Costa, LS Quirino, ME Farah, SM T Nunes, AC Tedesco; Modified Indocyanine Green For Experimental Choriocapillaris Photodynamic Therapy . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1298.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To compare the potential of indocyanine green (ICG) photodynamic therapy in occluding the albino rabbit choriocapillary layer using a modified ICG formulation (mICG) with a regular ICG in aqueous solution (aICG). Methods:A new ICG using a lipid polymeric emulsion was developed (mICG). Determination of singlet oxygen yield, aggregation capability and blood clearance of both aICG and mICG were determined by photobleaching and spectrophotometry. Fundus photography, fluorescein angiography, and light and transmission electron microscopy were used to compare the efficiency of PDT-induced phothrombosis using mICG, and aICG as the photosensitizer, and to assess the resultant collateral damage to the albino rabbit retina. The delivery system consisted of a modified infrared diode laser tuned to 810nm. Results:The mICG clearance process was slowed down as compared to the aICG. The incorporation of ICG in emulsion enhanced the yields of triplet formation in two times and inhibited the drug aggregation capability. Using a 10 mg/ml ICG dose, choriocapillary occlusion of the albino rabbit was achieved at a radiant exposure of 28J/cm2 with mICG and 56 J/cm2 with aICG. Damage to the neural retina was minimal. Only inner photoreceptor segments showed degeneration, probably secondary to choroidal ischemia. Bruch's membrane remained intact. Retinal pigment epithelium was invariably damaged, as seen with other photosensitizers. Conclusion:The use of mICG resulted in a higher half-time of ICG in blood, a lower aggregation capability, and a higher singlet oxygen quantum production when compared to aICG. The lower irradiance and fluence required to obtain choriocapillaris occlusion with this new formulation may prevent from collateral thermal damage and the confinement of ICG in the vascular compartment may enhance membrane targetability. These combined considerations point towards further study of PDT using mICG for the treatment of choroidal vascular disease.
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