Microhemodynamics of retinal collateral vessel formation.

Retinal collaterals are a common clinical occurrence after branch vascular occlusions in humans and laboratory animals, yet the etiology and functional significance of these vessels is uncertain. A hypothesis is presented which attempts to explain the difficult problem of retinal arterial collateral circulation. This theory is consistent with microcirculatory hemodynamic research which demonstrates that microcirculatory flow determinants are primarily guided by resistance factors and vascular geometry. Testing with a simple mathematical model and SPICE simulation of a circuit model suggests this theory can be applied to cases of both arterial and venous collaterals. While the underlying determinants of flow can be described, the exact mechanisms of vascular remodelling into large caliber vessels must be primarily cellular.