Michaelson1 showed that embryonic retinal capillaries developed entirely from veins and stated that the retinal capillaries and veins should be considered one vascular unit. He proposed that all retinal vascular development occurred in response to some unknown tissue factor present in areas of relative retinal anoxia. As the capillary bed developed, nearby arteries with their higher oxygen environment had an inhibitory influence on the production of this unknown tissue factor and thus an inhibitory influence on capillary extension in their vicinity. At term retinal vascularization became complete; a state of equilibrium was reached, and further vascular formation ceased. Finally, Michaelson stated that the capacity of veins and capillaries to form new vessels did not disappear at birth but simply became dormant.
In a previous article2 it was proposed that some degree of capillary or vein obstruction in the fully developed retina initiated the reawakening of Michaelson's dormant embryologic
WISE GN. Coats' Disease. AMA Arch Ophthalmol. 1957;58(5):735–746. doi:10.1001/archopht.1957.00940010757013
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