Experimental studies of indocyanine green dye-enhanced photocoagulation ofchoroidal neovascularization feeder vessels

PURPOSE: To report a model of choroidal neovascularization feeder vessels t hat reconciles current histologic, angiographic, and clinical data, and to report experimental studies that investigate the potential of indocyanine-g reen-dye-enhanced photocoagulation to improve feeder-vessel treatment. METHODS: A model of choroidal neovascularization feeder vessels was conceiv ed to account for current histologic and angiographic data. Based on that m odel, experimental studies of the efficacy of indocyanine green-dye-enhance d photocoagulation were performed, using pigmented rabbit eyes as a model s ystem. A Zeiss fundus camera was modified to permit visualization of choroi dal blood flow by high-speed indocyanine green angiography and to permit si multaneous delivery of 810-nm-wavelength diode laser photocoagulation pulse s to specific choroidal vascular targets during indocyanine green-dye bolus transit. RESULTS: Choroidal neovascularization feeder vessels appear to originate in the Sattler layer (that is, that portion of the choroidal vasculature cons isting of medium-diameter vessels) and enter the choriocapillaris in close proximity to the small capillary like vessels that penetrate Bruch membrane and communicate with the choroidal neovascularization, The rabbit eye expe riments demonstrated that the presence of high indocyanine green dye concen tration in circulating blood enhances uptake of near-infrared laser energy (three eyes); injection of sequential indocyanine green dye boluses results in gradually decreased efficiency of dye-enhanced photocoagulation (two ey es); and by application of laser energy during the initial transit of small -volume, high-concentration indocyanine green dye boluses, dye-enhanced pho tocoagulation of large diameter choroidal arteries can be accomplished with relatively little concomitant retinal tissue damage (three eyes). CONCLUSIONS: Although future trials will be necessary to substantiate these initial findings in the clinical arena, it appears that the efficiency of choroidal neovascularization feeder-vessel photocoagulation may be enhanced , while minimizing concomitant damage to overlying retinal tissue, by deliv ery of 810-nm wavelength laser energy immediately upon arrival of a high co ncentration indocyanine green dye bolus in a targeted feeder vessel. Howeve r, molecules of dye adhering to vessel walls or lying in tissue interstitia l spaces appear to divert laser energy from the photocoagulation process, s o efficiency of indocyanine green dye-enhanced photocoagulation gradually d iminishes as the number of injected dye boluses increases. (Am J Ophthalmol 2000;129:501-512. (C) 2000 by Elsevier Science Inc, All rights reserved.).