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In fluorescein angiography, the early venous phase is characterized by the fluorescence of the arteries and capillaries. During this phase, the fluorescein dye, injected into the bloodstream, travels through the retinal arteries, illuminating the capillaries as it reaches them. It highlights the vascular details and allows for the assessment of blood flow and the integrity of retinal vessels.

In this phase, the arteries are typically the first to show fluorescence as they are filled with the dye shortly after the injection, allowing for the visualization of their structure and any potential abnormalities. Following this, the capillaries become visible as the dye continues to circulate, providing critical information about the capillary perfusion and presence of any defects within the retinal circulation.

This phase is distinct from other phases, such as the arterial phase, which focuses primarily on the arteries immediately after dye injection, and later phases, where fluorescence from veins and potential leakage of the dye occurs. The pre-arterial phase involves the time before the arteries are fully filled with dye, which does not capture the fluorescence of the arteries or capillaries effectively.