Q: Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.
Abstract: Beading of a retinal vein draining a choroidal melanoma is reported, showing that the endothelial proliferation producing the beading is a response to some blood borne factor(s) traversing the vein and that retinal capillary non-perfusion adjacent to the beaded vein is not a necessary part of the process.
A:
Capillaries