INVESTIGATIVE OPHTHALMOLOGY Retinal collateral vessel formation

Retinal vessels of 18 adult domestic cats were successfully embolized with graded glass microspheres, and the resultant vascular changes were monitored clinically by ophthalmoscopy. At specific times the cats were killed, their eyes were enucleated, and digest preparations of the vessels were made from each retina. The preparations were examined microscopically, and any alterations in vasculature were noted by at least two observers. Collateral retinal arterwles and venules were noted, and their numbers, sizes, and calibers were recorded. While collaterals were ophthalmoscopically evident within 24 hours of occlusion, none were identified histologically until seven days after occlusion. These collaterals developed from the pre-existing retinal capillary bed and often attained the same caliber as the occluded vessel.