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

To report a model of choroidal neovascularization feeder vessels that reconciles current histologic, angiographic, and clinical data, and to report experimental studies that investigate the potential of indocyanine-green-dye-enhanced photocoagulation to improve feeder-vessel treatment.

A model of choroidal neovascularization feeder vessels was conceived to account for current histologic and angiographic data. Based on that model, experimental studies of the efficacy of indocyanine green-dye-enhanced photocoagulation were performed, using pigmented rabbit eyes as a model system. A Zeiss fundus camera was modified to permit visualization of choroidal blood flow by high-speed indocyanine green angiography and to permit simultaneous delivery of 810-nm-wavelength diode laser photocoagulation pulses to specific choroidal vascular targets during indocyanine green-dye bolus transit.

Choroidal neovascularization feeder vessels appear to originate in the Sattler layer (that is, that portion of the choroidal vasculature consisting 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 experiments demonstrated that the presence of high indocyanine green dye concentration 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 eyes); and by application of laser energy during the initial transit of small-volume, high-concentration indocyanine green dye boluses, dye-enhanced photocoagulation of large diameter choroidal arteries can be accomplished with relatively little concomitant retinal tissue damage (three eyes).

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 delivery of 810-nm wavelength laser energy immediately upon arrival of a high-concentration indocyanine green dye bolus in a targeted feeder vessel. However, molecules of dye adhering to vessel walls or lying in tissue interstitial spaces appear to divert laser energy from the photocoagulation process, so efficiency of indocyanine green dye-enhanced photocoagulation gradually diminishes as the number of injected dye boluses increases.