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Central retinal vein occlusion (CRVO) may lead to the spontaneous formation of shunt vessels running over the optic nerve head.1 This may contribute to improve retinal venous drainage. The occurrence of shunt vessels elsewhere in the fundus in these patients has not been reported yet. We report here a case of retinochoroidal venous anastomosis through a peripheral chorioretinal scar that revealed itself after the occurrence of CRVO, suggesting that elevated retinal venous pressure triggered the creation of the venous bypass.
A 70 year old man presented in our department with loss of vision in the left eye which had started 2 months previously. At presentation, visual acuity was 20/200. Fundus examination showed the presence of dilated veins and scattered haemorrhages in four retinal quadrants associated with macular oedema. In addition, in the superotemporal area a large atrophic chorioretinal scar underlying the superotemporal retinal vein was present (Fig 1, left). The patient had no history of eye trauma, inflammation, or photocoagulation. Fluorescein angiography showed that within the scar there was no detectable connection between the arterial and choroidal circulations (Fig 1, right). At a control examination 1 month later, the superotemporal vein overlying the scar was interrupted (Fig 2, left). ICG videoangiography demonstrated that the superotemporal retinal vein was anastomosed to the underlying choroidal vein, with drainage of upstream but not downstream venous blood (Fig 2, right). At that time, rubeosis iridis was present, associated with widespread capillary non-perfusion. Retinal panphotocoagulation was performed which led to regression of rubeosis. Final visual acuity was 20/200.
Shunt vessels over the disc are frequently observed after CRVO.1 They are possibly caused by the elevation in capillary pressure that dilates pre-existent retino-opticociliary capillaries. Shunt vessels occurring outside of the disc have been reported in association to a chorioretinal scar,2 but to our knowledge not during CRVO. In our case, pre-existing retinochoroidal anastomosis or choroidal new vessels may have been present within the scar before CRVO until the increased retinal venous pressure due to CRVO increased the retinochoroidal flow through the scar. However, on the first fluorescein angiogram, there is no evidence of pre-existing anastomosis or new vessels. We therefore cannot conclude on the precise mechanism relying the anastomosis to the CRVO. The anastomosis did not appear to have significantly improved upstream or downstream venous drainage. Moreover, there was occlusion of the venous segment downstream of the anastomosis site. This indicates, as observed after laser induced chorioretinal anastomosis, that anterograde and retrograde drainage is not always present together in the anastomosis site. This may be because a higher difference in pressure between retinal and choroidal veins is needed to promote retrograde drainage.
The authors have no proprietary interest in the present study.