FUNDUS FLOURESCEIN ANGIOGRAPHY
Interpret fundus fluorescein angiography ( FFA ) abnormalities and defects on angiograms.
Diagnose the retinal vascular disease on the nature of blood flow through the retinal artery and veins with the help of FFA.
• Fluorescein is an organic dye commonly used in Ophthalmic test.
• When blue light is flash on fluorescein dye, it fluoresces yellow-green.
• We do this commonly when looking at the cornea after instilling fluorescein. The same dye can be injected intravenously.
• A blue light camera can take pictures of the retinal circulation, and the emitted fluorescence is then passed through a yellow-green filter and sent to the camera for the final image.
• In a normal eye, fluorescein can not permeate through the endothelial cells of the retinal blood vessels nor can it pass through tight junctions in the retinal pigment epithelium (RPE).
• The yellow-green wavelength is also heavily absorbed by the RPE so the choroidal fluorescence is blocked.
• This makes FFA good for evaluating the retinal vasculature, not the choroidal vasculature.
• In contrast with FFA, indocyanine green (ICG) dye is great for evaluating the choroidal circulation.
• Almost all of the ICG molecules are protein bound, so they do not readily produce retinal leakage or staining.
• ICG fluoresces in the infrared wavelength and readily passes through the RPE (retinal pigment epithelium).
Phases of the FFA
Choroidal phase (AKA pre-arterial phase):
• 9-15 seconds- The choroidal hyperfluorescence is present. A cilioretinal artery if there is one will fill in this phase.
• Delayed choroidal filling time happens in ocular ischemic syndrome (OIS).
Arterial phase:
• 1-3 seconds later - Arteries are bright, but the veins remain dark.
Arteriovenous phase:
• Laminar flow in the veins – the walls of the veins are bright while the center of the vein is still dark.
Venous phase:
• By 30 seconds - Complete filling of the veins.
Late phase:
• 30 seconds – 10 minutes - Dye has recirculated. Things that are going to leak or pool will have done so already.
Types of hyperfluorescence defect
• There are 4 different types of hyperfluorescence abnormalities (brightness) in FFA:
Leakage:
• Hyperfluorescence progressively enlarges with fuzzy borders.
• The dye permeates out of leaky, incompetent blood vessels in the setting of neovascularization, retinal vasculitis, vascular malformations, tumors, or disc edema (dye leaks from prepapillary capillaries).
Pooling:
• Hyperfluorescence progressively enlarges to fill the fluid cavity and then becomes fixed in size.
• Usually the dye fills a cavity like the subretinal space or sub-RPE space (in a PED).
Staining:
• Late hyperfluorescence due to accumulation of fluorescein dye.
• The hyperfluorescence gradually gets brighter, but the size stays the same.
• Usually a mild amount of fluorescence is seen, but it is never very bright.
• The optic disc always stains. Additionally, drusen and fibrosis will stain.
Window defect:
• Defect in the RPE allows transillumination of the choroidal hyperfluorescence.
• Remains static in size and brightness and becomes fluorescent with the choroidal phase before the arteries even fill in the early frames.
Types of hypofluorescence defect
• There are 2 major types of hypofluorescence:
Blocking:
• Blood or other opacities block the fluorescence.
• Blockage of the retinal fluorescence can happen due to preretinal or vitreous hemorrhage.
• Blockage of the choroidal fluorescence can happen due to nevi or melanomas, Stargardt’s disease (lipofuscin blocking choroidal flush leading to a “dark choroid”), or subretinal blood.
Filling defect –
• lack of retinal perfusion due to capillary dropout, retinal artery occlusion and other causes.
Conclusion
• Fluorescein angiography (FA) is a great way to evaluate retinal circulation.
• Nowadays, OCT has greatly reduced the number of FAs performed, though FA still remains a very important modality for assessing many circulatory dysfunctions of the retina.
• FAs can be evaluated based on distinct phases of dye circulation.
• Various pathology can cause structures to be hyperflourescent or hypoflourescense. It is important to know generally what pathology correlates with what FA appearance.