FAG and ICGA in the diagnosis of AMD

L'imaging of AMD is currently based on three examinations:

1) Retinal fluorangiography (FAG - Fluorescein Angiography)
2) Angiography with Indocyanine Green (ICGA or ICG examination - Indocyanine Green Angiography)
3) Optical Tomography with Coherent Light (OCT - Optical Coherence Tomography)

These examinations have different and complementary properties; therefore, in order to examine the macular region in a complete manner, it is recommended to perform all three.

FAG and ICGA are angiographic examinations which exploit the fluorescence principle of dyes, fluorescein for FAG and indocyanine green for ICGA respectively, and allow macular lesions to be examined dynamically, as opposed to OCT which detects them statically.

The FAG is ideal for examining the retina, while the IGCA is used to study the choroid; in both examinations, the images obtained are black and white and the presence of the dye (fluorescence) appears white.

The FAG is the oldest examination (1960s) and is still the gold standard in the assessment of macular lesions. In fact, under normal conditions, fluorescein injected intravenously, once it reaches the retina, cannot (due to its physical-chemical properties) cross the internal blood-retinal barrier and remains inside the retinal capillaries, from which it escapes (leakage) only in the presence of pathological conditions that cause it to rupture.

The fluorangiographic examination also includes the collection of photographic documentation with the execution of colour retinographs, aneritre retinographs e autofluorescence images.

The limitation of the FAG is related to the impossibility of accurately detecting what occurs at the level of the thin vessels of the choriocapillaris, where free fluorescein (not bound to serum proteins) is able to diffuse into the extravascular spaces, even though it cannot cross the Bruch's membrane - EPR complex (outer blood-retinal barrier).

L'ICG examination, introduced in the 1970s and fully developed in the 1990s, uses indocyanine green as a dye, which, unlike fluorescein, binds integrally to serum proteins and thus, under normal conditions, remains confined to the lumen of the choriocapillary vessels, which are impermeable to these proteins.

Because of all its properties, the ICGA is the ideal examination for studying the choroidal circulation and, therefore, for detecting the pattern of neovases in the DMLE exudative. Moreover, it is the only diagnostic means that allows the differentiation of different subtypes of vascular anomalies (CNV, RAP and PCV) with certainty, but also to exclude their presence, such as in drusenoid and serous retinal pigmented epithelium (DEP) detachments.