Abstract
Purpose :
Our purpose was to use optical coherence tomography angiography to evaluate the intra-retinal course of collateral vessels occurring in eyes with branch or hemispheric retinal vein occlusion (RVO) in order to demonstrate a previously proposed serial organization of retinal vascular flow with venous outflow originating in the deep vascular complex (DVC).
Methods :
Eyes with branch or hemispheric RVO displaying collateral vessels in the macula, as identified with color fundus photography and fluorescein angiography, were retrospectively analyzed with OCT angiography. Meticulous segmentation at the level of the supercial capillary plexus and deep vascular complex was performed in each case. The course of collateral formation that did not involve the perifoveal vascular ring was analyzed using two dimensional OCT angiographic study as well as three dimensional volume rendering in order to determine whether they coursed through the superficial vascular plexus, deep vascular complex, or both.
Results :
From 23 eyes (21 branch, 1 hemispheric RVO) of 23 patients (mean age 73 ± 11 years), 101 collateral vessels were identified and analyzed (mean of 4.4 ± 2.0, range: 2-9 collaterals per eye). On OCTA, the collaterals appeared as curvilinear dilated flow signals that connected veins across the horizontal raphe or veins on opposite sides of an occluded venous segment within the same retinal hemisphere. Of the 101 collaterals analyzed, nearly all demonstrated substantially greater flow signal in the DVC, and all collateral vessels had some portion of their course identified within the DVC. Three dimensional projection resolved volume rendering of the OCT angiograms, to simultaneously visualize the superficial and deep retinal vascular complex, demonstrated the course of the collateral vessels through the DVC where the bulk of their flow was identified.
Conclusions :
Collateral vessels associated with branch or hemispheric retinal vein occlusion and identified outside the perifoveal capillary ring were all found to course through the deep vascular complex. The absence of collaterals confined to the SVP supports a serial organization of retinal vascular flow with venous drainage originating a DVC showing specialized structure adapted for this function. A model of retinal venous outflow is proposed.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.