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H. Kawano, E. Piazza, B. Khoobehi; Microsphere Imaging of Retinal and Choroidal Circulations Following Photodynamic Therapy . Invest. Ophthalmol. Vis. Sci. 2003;44(13):344.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To evaluate the effect of photodynamic therapy (PDT) on retinal and choroidal hemodynamics using FluoSpheres® (Molecular Probes) with the argon laser (retina) and TransFluoSpheres® (Molecular Probes) with the He-Ne laser (choroid). Methods: The photosensitizer SnET2 (0.5 mg/kg) was injected intravenously into an African Green monkey, and the fundus was irradiated with a diode laser (spot size, 600 nm; power, 10 mW; duration, 20 msec; fluence, 17.7 J/cm2; wavelength, 664 nm). Spots were made nasal to temporal, inferior to the optic nerve head, as well as over the macula. Four weeks after PDT, a suspension of 2-µm-diameter microspheres was injected intravenously. Blood flow in the retinal microcirculation over the treated spots was evaluated using 488/514 nm microspheres (FluoSpheres) and the argon laser of the scanning laser ophthalmoscope (SLO); blood flow in the choroidal circulation over the treated spots was studied using 633/755 nm and 633/825 nm microspheres (TransFluoSpheres) in conjunction with the He-Ne laser of the SLO. TransFluoSpheres contain several dyes (up to seven) selected to permit an efficient resonance energy transfer cascade from an absorbance donor dye to a series of acceptor dyes. TransFluoSpheres excited with the 633 nm beam of the He-Ne laser fluoresce at the near infrared part of the spectrum. Results: In the retinal circulation, images of circulating particles (488/544 nm microspheres) were observed; blood flow velocity was not significantly different in areas subjected to PDT, compared with untreated areas. In the choriocapillaris, blood flow velocity measured with the TransFluoSpheres was significantly different in the treated vs. non-treated areas. Additionally, the circulating TransFluoSpheres showed that only the superficial layer of choroidal vessels was occluded; circulation remained intact in the deep layers of the choroid. Conclusions: Incorporation of several dyes into TransFluoSpheres allows a wide range of separation between excitation and emission spectra which, in turn, allows easy filtering of excitation wavelengths at the detector of the SLO. Thus the TransFluoSpheres are capable of assessing the hemodynamic parameters of the choroid after photodynamic treatment in animal model. This technology can be used to study the effectiveness of treatment for choroidal neovascularization.
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