Nettleship collaterals: circumpapillary cilioretinal anastomoses after occlusion of the central retinal artery.

In extremely rare cases, after occlusion of the central retinal artery, a complete ring of peripapillary anastomotic channels develops. One such case is described and a proposed term given to these channels--'Nettleship collaterals'--after the man who first described them. These collaterals are dilated pathways within the terminal capillary networks of the posterior ciliary arteries and the branches of the central retinal artery. Formation of the channels is believed to be promoted by prelaminar obstruction of the central retinal artery.