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Table 2 Definition of vessel types

From: Grading fluorescein angiograms in malarial retinopathy

Vessel type Description
Capillary Smallest vessel visible on a well focussed angiogram image
Post-capillary venule Formed by the confluence of two or more capillaries, and extends up to the point where it is joined by a second post-capillary venule or other larger venular segment
Pre-capillary arteriole Extends upstream from the divergence of two or more capillaries to the point where it branches from another pre-capillary arteriole or other larger arteriolar segment
Post-capillary venule complex Extends approximately 1/3 of a disc diameter (~500 μm) downstream from the capillaries along venular segments
Pre-capillary arteriole complex Extends approximately 1/3 of a disc diameter (~500 μm) upstream from the capillaries along arteriolar segments
Small venule Extends from the edge of the post-capillary venule complex downstream to the point of confluence with another venule of similar or larger caliber
Small arteriole Extends from the edge of the pre-capillary arteriole complex upstream to the point of branching with another arteriole of similar or larger caliber
Large venule Extends downstream from the point of confluence that defines the upper caliber boundary of small vessel segments to the edge of the optic disc
Large arteriole Extends upstream from the branching point that defines the upper caliber boundary of small arteriolar segments to the edge of the optic disc