Fluorescence characteristics of indocyanine green in the normal choroid and in subretinal neovascular membranes.

Indocyanine green angiography with scanning laser ophthalmoscopy is a new supplementary method studying subretinal neovascular membranes. However, it is still controversial as to whether of not exudation of this dye occurs from regular choroidal vessels or such membranes. Fluorescence of the macula area, a parapapillary retinal vein, and of venous blood and plasma was therefore measured with a picture analysis system in five healthy young volunteers. Furthermore, the angiograms of 150 subretinal neovascular membranes were reviewed. Membrane fluorescence was measured in ten exemplary cases and compared with the background fluorescence. The results show that macula fluorescence is detectable much longer than the fluorescence of retinal vessels. However, a comparison with the fluorescence of blood and plasma samples revealed that this late fluorescence must be caused by retinal and choroidal capillaries with a significantly reduced hematocrit. It is not caused by apposition or exudation of indocyanine green. The same was true for the majority of subretinal neovascular membranes. Exudation was rarely detected in membranes that were regularly surrounded by exudates but could be induced by laser coagulation. These observations indicate that exudation occurs only after massive destruction of the endothelial barrier. The results are important for the interpretation of indocyanine green angiograms and for possible photodynamic therapy with this dye.