FFA and ICGA Interpretation: Phases, Patterns and Classic Images

For an angiography image, begin with three things: when was it taken, what is the fluorescence doing, and which mechanism explains that behaviour? In fundus fluorescein angiography (FFA, often called FA), a bright lesion may represent transmission, leakage, pooling or staining. A dark lesion may be blocked fluorescence or a filling defect. Those mechanisms are more reliable starting points than a reflex disease label.

Indocyanine-green angiography (ICGA) uses a different dye and near-infrared imaging, so it is particularly useful for choroidal vascular information in selected settings. Both investigations must be interpreted alongside clinical findings and other imaging. This article is examination education for doctors, not a patient-specific investigation or treatment guide.

The reporting grammar: time → behaviour → mechanism

Use this one-sentence frame in every image station:

“This is a [phase] [FFA/ICGA] image showing [hyper/hypofluorescence] at [anatomical location], which [increases/remains fixed/decreases] in [intensity/area]; the appearance most likely represents [mechanism]. In the supplied clinical context, the differential includes [condition].”

It forces the observation to come before interpretation. It also makes you differentiate increasing intensity from increasing area. A lesion can become brighter without enlarging; that is not the same behaviour as leakage spreading into surrounding tissue.

The AAO’s angiography education materials are useful for revising the modality distinction.¹² In a timed answer, avoid false precision about a phase occurring at an identical number of seconds in every study. State the sequence and phase shown; acquisition technique and circulation vary.

FFA phases: learn the sequence, then identify the frame

FA begins after intravenous fluorescein administration and is photographed serially. Traditional descriptions include a choroidal flush, arterial phase, arteriovenous/capillary transit, venous phase and late phase. The exact labels may overlap in teaching sets; a normal image series is not a stopwatch examination.

Choroidal flush

In an early frame, choroidal fluorescence appears in a patchy background pattern through the RPE before complete retinal arterial filling. If the question asks for the first visible phase, use “choroidal flush” when that is what the frame shows. Do not call a background choroidal signal “leakage.”

Arterial phase

Retinal arteries fill while venous filling is limited. In a vaso-occlusive question, this phase can make delayed or absent arterial filling relevant. Your answer should be anatomical: “retinal arterial filling is delayed/absent in the supplied image,” not “this proves a particular systemic diagnosis.”

Arteriovenous (capillary transit) phase

Arterial filling continues as laminar venous flow begins. The venous leading edge can create a classic laminar appearance. In ischaemia questions, this is where capillary non-perfusion, microaneurysm-related leakage patterns or abnormal vascular networks may be assessed, depending on image quality and supplied context.

Late phase

The late frame tells you whether a lesion has enlarged, intensified, pooled within a defined space or stained with fixed margins. It is the phase that separates many look-alike early hyperfluorescent lesions. Never interpret “late bright” without comparing it with an earlier frame.

Hyperfluorescence: four mechanisms, four different answers

Hyperfluorescence means more fluorescence reaches the camera. It does not mean one thing has happened to the retina. Ask what has changed: an absent screen, escaping dye, retained dye, or dye collected in a space.

Transmission/window defect

In a transmission defect, reduced RPE pigment or attenuation permits more of the normal underlying choroidal fluorescence to be seen. It appears early and maintains a relatively fixed configuration. The important negative statement is that there is no progressive spread characteristic of leakage. If a stem uses older terminology, “window defect” is acceptable; explain the mechanism instead of merely naming it.

Leakage

Leakage shows increasing intensity and increasing area, often with blurred edges. It is a behaviour, not a diagnosis. Microaneurysms, disc inflammation, retinal neovascularisation and other lesions can leak in particular contexts. An answer such as “late hyperfluorescence with expansion beyond the initial lesion, consistent with leakage” earns more than “bright spot equals DMO.”

Pooling

Pooling is fluorescein collecting in an anatomic space. In central serous chorioretinopathy (CSCR), a focal leakage point may be followed by subretinal pooling, and classic descriptions include ink-blot and smoke-stack patterns. The words “classic” and “may” matter: do not require one pattern in every CSCR question, and do not diagnose CSCR from subretinal fluid without context.

Staining

Staining becomes more intense late but generally retains its boundaries. Scar tissue and the optic disc are standard teaching examples. If an image shows persistent late disc hyperfluorescence, say whether it is leakage or staining only after comparing early and late images and using the clinical context. A normal disc appearance and pathological disc leakage should not be conflated.

Hypofluorescence: blocked signal or absent filling?

Darkness in angiography has two core explanations. The distinction is simple but important: is fluorescence present behind an obstacle, or did dye fail to arrive?

For a pre-retinal or subretinal haemorrhage, blocked fluorescence is usually the first mechanism to consider because blood attenuates the signal. For capillary non-perfusion in diabetic retinopathy or vein occlusion, the problem is lack of perfusion rather than a physical screen. Do not write “hypofluorescence due to blockage” without identifying something capable of blocking the light. Likewise, do not call every dark choroidal region “non-perfusion” in an ICGA frame.

What ICGA adds: ask choroidal questions deliberately

Indocyanine green binds strongly to plasma proteins and its near-infrared fluorescence permits imaging through pigment, blood and fluid better than visible-light FA in relevant circumstances. That does not make it universally superior. It makes it a different modality whose answer often focuses on choroidal vasculature.

In a viva, say: “ICGA is particularly useful when the question is about a choroidal vascular pattern or when FA detail is limited by pigment, blood or fluid.” This is a modality-level statement, not an indication checklist for a real patient.

Polypoidal choroidal vasculopathy (PCV)

In the appropriate clinical and imaging setting, ICGA may demonstrate polypoidal lesions and a branching vascular network. The International PCV Study Group report is a useful source for revising the historical imaging terminology.³ The safe exam sequence is: identify the modality; describe the early/late choroidal vascular pattern; then state that the pattern supports PCV in the supplied context. Do not call every focal late hyperfluorescent lesion a polyp.

AMD, MNV and historical labels

Older FFA questions may use “classic” and “occult” choroidal neovascularisation language. Contemporary writing often uses macular neovascularisation (MNV) and multimodal imaging. For an exam, answer in the terminology asked, then show that you understand the image behaviour. The AAO AMD Preferred Practice Pattern places angiography among the tools used in AMD assessment; it does not make a single image a complete classification.⁴

CSCR and choroidal imaging

FA is classically used to demonstrate a leakage point and pooling pattern in CSCR. ICGA can add choroidal information in selected discussions. Avoid reducing this to a treatment algorithm. The educational point is the morphology: a focal point of increasing fluorescence that can spread, followed by fluid in a defined subretinal space.

Pattern cards: connect a disease stem to behaviour, not to a photograph

Diabetic macular oedema (DMO)

The relevant FA observations can include focal microaneurysm-associated leakage, diffuse leakage and capillary non-perfusion. These are separate findings. An image with cystic change on OCT and leakage on FA does not allow you to omit the perfusion assessment. The AAO diabetic-retinopathy guidance is a useful source for keeping imaging within the broader disease-assessment context.⁵

Retinal vein occlusion

Expect a stem to test leakage, masking from haemorrhage and non-perfusion. Do not assume that extensive retinal haemorrhage proves non-perfusion; it can block fluorescence. Describe what the angiogram shows and distinguish the two mechanisms.

Optic disc hyperfluorescence

Late disc hyperfluorescence can be an important clue, but the word “disc leakage” should not be used casually. Compare phase, margin and context. State “late disc hyperfluorescence with [fixed/increasing] margins” before committing to staining or leakage.

Inflammatory lesions

Inflammatory conditions can generate diverse FA/ICGA patterns. When you do not know the named entity, a correct mechanism-first answer remains valuable: “early hypofluorescence with late staining/leakage,” or “a persistent blocked lesion,” as shown. The answer must follow the supplied sequence, not a memorised disease list.

The 30-second viva answer

“This is a [early/mid/late] [FFA/ICGA] image. The lesion is [hyper/hypofluorescent] at [location]. Compared with the earlier frame, it [increases in intensity only / increases in area and intensity / remains fixed / is persistently blocked]. I would therefore describe the mechanism as [transmission defect, leakage, pooling, staining, blocked fluorescence or filling defect]. In the clinical context provided, this supports [differential], and I would correlate it with fundus examination and OCT/OCTA where relevant.”

This is better than a stream of eponyms because it proves you read the image. It also prevents a common verbal error: saying “leakage with well-defined fixed margins,” which is internally contradictory unless the sequence supports some other mechanism.

If the image sequence is incomplete

Some stations provide a single late frame and deliberately withhold the early image. Do not manufacture the missing time course. State the limitation: “This late hyperfluorescent lesion could represent staining, leakage or pooling; comparison with early and intermediate frames is needed to distinguish the mechanism.” A conditional answer is not a weak answer when the data are conditional. It is stronger than declaring an unseen expansion of margins.

Apply the same discipline to an apparently dark lesion. If a photograph shows haemorrhage over the corresponding site, blocked fluorescence is plausible. If there is no visible blocker and the lesion respects a vascular distribution, a filling defect becomes more plausible. “Plausible” is the correct word until the angiographic sequence and clinical setting complete the pattern.

Seven exam traps to eliminate

1. Hyperfluorescence equals leakage. False: transmission, pooling and staining are alternatives.
2. Late brightness proves active disease. False: staining can be late and bright with stable margins.
3. Every dark area is non-perfusion. False: blood, pigment and exudate can block fluorescence.
4. Window defect equals RPE leakage. False: it reflects increased transmission through reduced RPE pigment.
5. Pooling and leakage are interchangeable. False: pooling is constrained by a defined anatomic space.
6. ICGA is “FFA but deeper.” Too crude. State its near-infrared, choroidal-information role.
7. One angiogram image confirms a final diagnosis. Unsafe. The phase series and clinical context matter.

A memory drill for image papers

Make six flashcards labelled: transmission, leakage, pooling, staining, blocked, filling defect. On the reverse, draw only the time-course: early/late, fixed/spreading, bright/dark. Next, take an angiography sequence and force a single mechanism sentence before reading the caption. Finally, pair FA and OCT: ask whether OCT contributes fluid compartment, interface or RPE morphology, while FA contributes fluorescence behaviour. This trains modality selection rather than visual guessing.

For broader context, study from the verified retina study guide. For structured report/test revision, see Read Ophthalmology Reports & Tests. Use high-yield free MCQs for timed recall and the verified ophthalmology glossary when consolidating terminology. These are revision resources; local protocols and supervised judgement govern clinical angiography use.

Sources

All sources were checked on 18 August 2026. Re-check current society guidance before publication.

Footnotes

1. American Academy of Ophthalmology: Fluorescein Angiography ↩

2. American Academy of Ophthalmology: Indocyanine Green Angiography ↩

3. International PCV Study Group report ↩

4. American Academy of Ophthalmology: Age-Related Macular Degeneration Preferred Practice Pattern ↩

5. American Academy of Ophthalmology: Diabetic Retinopathy Preferred Practice Pattern ↩