What Is Fluorescein Angiography?
Fluorescein angiography (FA) is a diagnostic imaging procedure that documents the blood flow through the retinal and choroidal vasculature. A fluorescent dye is injected intravenously, and sequential photographs are taken as the dye circulates through the ocular blood vessels. FA reveals vascular abnormalities, leakage, ischemia, and neovascularization that may not be visible on clinical examination or standard photography.
The Procedure
- Preparation: Dilate the patient's pupils fully. Position the patient at the fundus camera. Take baseline color and red-free photographs.
- IV access: Establish a peripheral IV line (usually in the antecubital fossa).
- Injection: Inject 5 mL of 10% sodium fluorescein rapidly (a bolus injection).
- Sequential photography: Begin capturing photographs approximately 10-15 seconds after injection and continue at regular intervals through the various angiographic phases.
- Late photos: Capture final images at 5-10 minutes to document late leakage or staining.
Angiographic Phases
The dye passes through the ocular circulation in a predictable sequence:
| Phase | Timing | What You See |
|---|---|---|
| Choroidal flush | ~10-12 seconds | Patchy filling of the choroidal circulation (appears before retinal vessels fill) |
| Arterial phase | ~12-15 seconds | Retinal arteries fill with dye |
| Arteriovenous (AV) phase | ~15-20 seconds | Capillary filling, veins begin to show laminar flow |
| Venous phase | ~20-30 seconds | Veins fully opacified, arteries begin to fade |
| Late/recirculation phase | ~5-10 minutes | Dye fading, residual staining or leakage documented |
Key Angiographic Findings
Hyperfluorescence (Brighter Than Normal)
- Leakage: Dye escaping from abnormal or damaged vessels. The hallmark of active choroidal neovascularization in wet AMD. The area of fluorescence expands and intensifies over time.
- Staining: Late-phase fluorescence from dye absorbed into tissue (drusen, scar tissue). Does not expand over time.
- Pooling: Dye accumulating in a defined anatomical space (subretinal fluid, pigment epithelial detachment).
- Window defect: RPE atrophy allows underlying choroidal fluorescence to show through. Appears early and fades with the background.
Hypofluorescence (Darker Than Normal)
- Blockage: Blood, pigment, or other material blocks the fluorescence from underlying vessels (hemorrhage covering the retina).
- Nonperfusion/ischemia: Vessels are occluded and do not fill with dye. Appears as dark areas where vessels should be visible.
The distinction between leakage and staining is timing. Leakage expands and intensifies in late frames because dye continues to escape from vessels. Staining remains the same size because the dye is fixed in tissue. This distinction is critical for identifying active disease (leakage) versus inactive scarring (staining).
Adverse Reactions
The ophthalmic assistant must be prepared for adverse reactions to intravenous fluorescein:
Common (Mild)
- Nausea (most common, usually brief)
- Temporary yellow skin discoloration and yellow urine for 24-48 hours
- Vomiting (have an emesis basin ready)
Uncommon (Moderate)
- Urticaria (hives)
- Pruritus (itching)
Rare (Severe)
- Anaphylaxis
- Bronchospasm
- Cardiac arrest (extremely rare)
Not having emergency supplies readily available during fluorescein angiography. Although severe reactions are rare, epinephrine, oxygen, and resuscitation equipment must be immediately accessible. Always ask about allergies and previous reactions before the procedure.
Key Takeaways
- Fluorescein angiography documents blood flow through retinal and choroidal vessels using injected fluorescent dye
- The five phases (choroidal flush, arterial, AV, venous, late) follow the predictable path of dye through the circulation
- Leakage (expanding hyperfluorescence) indicates active vascular pathology; staining (stable hyperfluorescence) suggests inactive tissue
- Nausea is the most common adverse reaction; anaphylaxis is rare but preparation is mandatory
- Patients should be warned about yellow skin and urine for 24-48 hours after the test