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Fundus Photography, Wide-Field & Fluorescein Angiography Technique
Ultra-Widefield Fundus Imaging
A standard fundus camera captures roughly 30–50° of the retina. That is enough for the posterior pole, but it falls well short of the far periphery, where much of the retina's degenerative and vascular pathology actually lives. Ultra-widefield (UWF) imaging solves that problem by using a scanning laser system rather than a conventional flash camera: it can capture up to roughly 200° of the retina in a single image, with or without pupillary dilation, a field of view no conventional camera can match.
That expanded reach is what makes UWF valuable for peripheral degenerative lesions: peripheral retinoschisis, lattice degeneration, and peripheral retinal breaks or detachments that would otherwise need a slow, piecemeal indirect ophthalmoscopy exam to document fully. Most UWF systems also offer autofluorescence and angiography modes. A single UWF color/autofluorescence composite is now a standard way to track peripheral pathology across serial visits.
Fluorescein Angiography Technique
Fluorescein angiography (FA) works by injecting sodium fluorescein dye intravenously, then photographing the retina in rapid sequence as the dye circulates through the retinal and choroidal vasculature. The camera illuminates the fundus with a blue excitation filter and captures only the fluorescent light returned by the dye through a yellow-green barrier filter. That filter pairing isolates the dye's signal from ordinary reflected light, producing the high-contrast, black-and-white angiogram images read for filling pattern, leakage, and blockage.
The angiogram unfolds in a predictable sequence of timed phases after injection:
- Choroidal (pre-arterial) phase: beginning roughly 10–15 seconds after injection, seen as a patchy, lobular pattern of choroidal filling as dye leaks from the fenestrated choriocapillaris.
- Arterial phase: following within a second or two, as dye first fills the retinal arteries.
- Arteriovenous (mid) phase: the retinal capillary bed fills completely and dye begins entering the veins, typically visible as laminar flow along the venous walls before the full lumen fills.
- Venous phase: complete filling of the retinal veins, with peak overall fluorescence around 30 seconds post-injection.
- Late/recirculation phase: occurring several minutes after injection as dye recirculates and gradually washes out of the retinal vasculature, which is when true leakage (as opposed to normal transit) becomes most apparent as an area that keeps accumulating dye rather than clearing it.
Reading an angiogram comes down to tracking a lesion across these phases. A finding that is hyperfluorescent early and stays exactly the same size and shape throughout, such as an RPE window defect, behaves very differently from one that starts small and progressively brightens and enlarges into the late phase: true leakage, as from choroidal neovascularization or an inflamed vessel wall.
- UWF imaging reaches up to ~200° of retina in one capture: the tool of choice for documenting peripheral pathology like retinoschisis or lattice degeneration.
- FA uses a blue excitation filter + yellow-green barrier filter to isolate the fluorescent signal from the injected dye.
- Phase order: choroidal flush → arterial → arteriovenous → venous → late/recirculation, spanning roughly 10 seconds to several minutes post-injection.
- True leakage keeps intensifying into the late phase; a static hyperfluorescent spot that doesn't change is more likely a window defect than active leakage.
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