What is first seen (recorded) in fluorescein angiography?

Fluorescein angiography is a photographic technique used to visualize the blood vessels in the retina and choroid by injecting a fluorescent dye. The first phase that is recorded during this procedure is known as the choroidal flush. This occurs shortly after the fluorescein dye is injected into the bloodstream and indicates the dye's initial passage through the choroidal circulation, which is characterized by a brisk influx of dye into the choroid, illuminating the choroidal vascular structures.

The choroidal flush can be observed as the dye rapidly fills the large choroidal vessels, creating a rich display of fluorescence that is visually captured in the angiographic images. This phase is essential because it sets the stage for the subsequent visualization of the retinal and capillary phases, showing the progression of dye circulation through the various vascular territories.

The arterial phase follows the choroidal flush, marking the arrival of dye into the arteries supplying the retina. The capillary phase reflects the filling of the retinal capillaries. Finally, the venous phase indicates the return of blood flow through the retinal veins. Each of these phases has its significance, but the primary and initial observation in fluorescein angiography is indeed the choroidal flush.