During fundus fluorescein angiography (FFA), the 'transit time' from arm to retina is normally about 10–15 seconds. In which phase of FFA do arteriovenous shunts (retinal arteriovenous malformations) characteristically appear to fill?

• A Choroidal flush (pre-arterial phase)
• B Arteriovenous (capillary) phase ✓
• C Arterial phase
• D Late venous phase

Explanation

Retinal AVMs (racemose haemangiomas) shunt blood directly from arteries to veins, so they fill prominently in the arteriovenous/capillary phase when laminar flow in veins becomes visible. Choroidal flush precedes retinal arterial filling; arterial phase shows arteries only; late venous phase shows staining/leakage. AVMs are notable for lack of leakage in any phase despite large calibre vessels.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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