<s>[INST] context: Fluorescein angiography is primarily used for retinal vasculature because:-
Fluorescein is readily bound to the albumin in the blood stream. The blood-retinal barrier, by preventing dye leakage in the physiological state facilitates the delineation of retinal vessels of all calibres. In the choroidal circulation, fluorescein passes freely across the endothelium of the capillaries to the extravascular space. Therefore fluorescein angiography is used primarily for retinal vasculature.
On the other hand, indocyanine green angiography is used primarily for choroidal vasculature because:-
Indocyanine green stays within the choroidal circulation and is stimulated by a longer wavelength of light than fluorescein dye. This provides a better resolution of the choroidal vasculature, especially choroidal neovascular membranes (CNVM).

 Therefore, ICG angiography is used for:-

The identification and delineation of poorly defined or occult choroidal neovasculorization.
Retinal pigment epithelium (RPE) detachments. [/INST] question: Indocyanine Green Angiography (ICG Angiography) is most useful in detecting – | options: A: Occult Choroidal Neovascularization (Occult CNV) B: Classic choroidal neovascularization(Calssic CNV) C: Angioid streaks with choroidal Neovascularization (CNV) D: Polypoidal choroidal vasculopathy | answer: A </s>