Microvascular remodeling after occlusion-recanalization of a branch retinal vein in rats.

PURPOSE To describe the time course of microvascular changes after transient branch retinal vein occlusion (BRVO) in rats. METHODS BRVO was induced in pigmented rats by focal laser photocoagulation. The subsequent changes in the retinal angiogram were followed up, both in vivo by confocal scanning laser ophthalmoscopy and ex vivo by confocal microscopy. RESULTS At day 1, capillary closure affected the three microvessel layer differentially, the intermediary layer being the most affected. Collateral veins, which were initiated by the dilation of deep-layer venules, pursued their course below adjacent arteries. These microvascular changes peaked between days 1 and 3. After recanalization at day 3, microvascular changes regressed gradually but incompletely, and at day 30 capillary closure and venule dilation persisted. CONCLUSIONS Transient occlusion of a retinal vein in rats leads to short- and long-term microvascular remodeling upstream of the occlusion site. This study describes a model for the tridimensional arrangement of retinal microvessel that accounts for the topography of the early capillary closure and collateral vessel formation that occur after BRVO. In the long term, these changes regressed incompletely, with recanalization of the occluded vein, suggesting that after a short period of occlusion, microvascular changes may become at least partially independent of flow. Despite the intrinsically limited applicability of this model to human vein occlusion, the results suggest that even if therapeutic decompression of an occluded vein is performed early, it may not reverse capillary dropout completely.