Fundus Fluorescein Angiography (FFA)
June 05, 2023
Fundus Fluorescein Angiography (FFA)
Fundus fluorescein angiography is a type of angiographic photography that does not rely on ionizing radiation or iodine-based contrast. After the intravenous injection of a fluorescein solution (usually in a hand or arm vein), a rapid sequence of photographs is taken using a camera with spectral excitation and barrier filters. Fluorescein sodium absorbs blue light, with maximum absorption and excitation at wavelengths of 465 to 490 nm. Subsequently, fluorescence occurs at yellow-green wavelengths of 520 to 530 nm. The fluorescein molecule is 80% bound to proteins and does not penetrate the tight junctions of a healthy blood-retina barrier (the RPE and retinal capillaries are impermeable, while the Bruch's membrane and choriocapillaris lack tight junctions and are freely permeable).
It is particularly helpful in detecting and assessing the following conditions:
Macular Edema: FA can detect and evaluate the presence of swelling in the macula, the central part of the retina responsible for sharp vision. Macular edema can occur due to various causes, such as diabetes, and can lead to distorted vision.
Diabetic Retinopathy: FA is effective in detecting and monitoring abnormal blood vessels in the retina caused by diabetes. It helps determine the extent of damage and aids in planning appropriate treatment strategies.
Macular Degeneration: This age-related condition affects the macula and can lead to vision loss. FA is instrumental in identifying and classifying the type and severity of macular degeneration, assisting in treatment decisions.
Vein Blockage (BRVO or CRVO): When veins inside the eye become blocked, it can result in vision problems. FA helps identify the location and extent of the blockage, providing crucial information for planning treatment, such as laser therapy.
Macular Pucker: Sometimes, a wrinkle or scar tissue can form on the surface of the macula, causing distorted vision. FA aids in visualizing the pucker and determining its impact on retinal function.
Ocular Melanoma: FA can play a role in the diagnosis and evaluation of ocular melanoma, a type of eye cancer. By assessing the blood flow within the tumor, FA helps determine the size and characteristics of the melanoma.
Phases of Fundus Fluorescein Angiography:
- Choroidal filling (background fluorescence): Begins 8 to 15 seconds after the injection. The choroid becomes completely filled within 5 seconds of dye appearance in the tissue.
- Arterial phase: Begins 1 to 2 seconds after choroidal filling.
- Arteriovenous phase (laminar flow).
- Venous phase: Arteriovenous transit time is the time from the first appearance of dye in the retinal arteries of the temporal arch to the corresponding veins becoming fully filled, usually <11 seconds.
- Recirculation phase: Occurs 45 to 60 seconds after the arterial phase.
- Late phase: Occurs 10 to 30 minutes after the injection.
Description of an Abnormal Study:
Hypofluorescence:
Leakage: Fluorescein penetrates the blood-retina barrier and accumulates subretinally, intraretinally, or preretinally. Hypofluorescence increases in size and intensity as the study progresses (e.g., choroidal or retinal neovascularization, central serous chorioretinopathy [CSCR], cystoid macular edema [CME]).
Staining: Mild fluorescence appears in the late phase while its edges remain fixed (e.g., scar).
Pooling: Fluorescein accumulation in fluid-filled spaces in the retina or choroid. The margins of the fluorescein-trapping space are distinct (e.g., retinal pigment epithelium detachment [PED], CSCR).
Window defect or transmission defect: Focal area of hypofluorescence without leakage, usually due to RPE atrophy, appearing early and remaining stable in intensity (e.g., geographic atrophy, RPE tear, laser scar).
Autofluorescence: Naturally fluorescing structures can be captured on film before intravenous fluorescein injection (e.g., optic nerve drusen and lipofuscin).
Hyperfluorescence:
Blockage: Due to an optically dense material such as blood, pigment, or fibrous tissue interposed between the camera and the choriocapillaris.
Nonperfusion: Unfilled vessel(s) causing relative or absolute hypofluorescence (e.g., central retinal artery occlusion). Applies to both capillaries and larger vessels.
Uses in Ophthalmology:
- Used to capture images of retinal, choroidal, optic disc, iris vasculature or a combination thereof. Used for diagnosis and therapeutic planning (e.g., retinal lasers).
- Transit times between injection and appearance of dye in the choroid, retinal arteries, and veins can also be used to evaluate vascular flow. Arm-to-retina time is less precise than intraretinal circulation times.
- Suspected retinal ischemia (capillary nonperfusion) and neovascularization in various conditions (e.g., diabetes).
- Suspected choroidal neovascularization (CNV) in various diseases (e.g., AMD).
Guidelines for Requesting the Study:
Side effects of intravenous fluorescein include nausea (10%), vomiting (2%), urticaria, pruritus, and vasovagal response. True anaphylaxis is rare. There may be 1 death per 220,000 injections. Extravasation into the extracellular space at the injection site may cause local necrosis. Treat with cold compresses. Excretion in urine occurs within 24 to 36 hours. Urine will be brightly colored yellow; remember to warn all patients about this.Because it is a photographic method, moderately clear media is required for visualization.
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