Theoretical investigation of the role of choriocapillaris blood flow in treatment of subfoveal choroidal neovascularization associated with age-related macular degeneration.

PURPOSE: To investigate the relationship between choriocapillaris blood flow and blood flow through an overlying choroidal neovascularization, as it relates to photocoagulation-induced changes in the choriocapillaris circulation. METHODS: A theoretical model that simulates the blood flow in the choriocapillaris and choroidal neovascularization of the human eye was developed, based on histologically determined vascular geometry and experimentally measured blood pressure gradients. The choriocapillaris blood pressure and blood flow were examined before and after simulated photocoagulation of various Sattler layer vessels entering the choriocapillaris in the vicinity of the choroidal neovascularization. (The Sattler layer is the inner layer of medium-sized choroidal vessels that includes both arterioles and venules that supply the choriocapillaris.) RESULTS: The theoretical model showed that both partial and complete occlusion of either Sattler arteriole or venous vessels in the vicinity of the capillary-like vessels connecting a choroidal neovascularization to the underlying choriocapillaris results in significant choroidal neovascularization blood flow reduction. These theoretical results are similar to clinically observed changes induced by laser photocoagulation of feeder vessels. (In this discussion, the term "feeder vessels" refers to those vessels in an indocyanine green angiogram image that appear to supply blood to a choroidal neovascularization; these vessels appear to be Sattler layer vessels, rather than the histologically demonstrated short, capillary-like vessels that form choriocapillaris-choroidal neovascularization communications.) CONCLUSIONS: Reduction of choriocapillaris blood flow underlying a choroidal neovascularization may be sufficient to reduce the blood flow rate in the choroidal neovascularization and thereby reduce the associated retinal edema. The results also suggest that reduction of choriocapillaris blood flow may be the common hemodynamic event associated with the successful application of several currently practiced methods of choroidal neovascularization treatment, including feeder vessel photocoagulation, photodynamic therapy, transpupillary thermotherapy, and prophylactic drusen photocoagulation. Ultimately, this model may be useful in determining optimal placement of laser photocoagulation burns to achieve a desirable perturbation in choroidal blood flow distribution and thereby reduce choroidal neovascularization blood flow to the extent necessary to obliterate associated retinal edema.