Shunt Vessels and Outcomes in Patients With CRVO Treated With Bevacizumab

C entral retinal vein occlusion (CRVO) is second only to diabetic retinopathy as a vascular cause of vision loss.1 Visual morbidity and blindness are most commonly due to macular capillary nonperfusion and persistent macular edema, as well as macular hemorrhage, vitreous hemorrhage, retinal detachment, and neovascular glaucoma.1,2 As the precipitating event in CRVO is thought to be intravascular venous thrombosis,3,4 restoration of venous flow occurs by recanalization of the central retinal vein,3 or by the development of collateral vessels.3,4 Optociliary shunt vessels are known to develop in CRVO,5 and studies have shown that they significantly drain the retinal venous circulation into the choroidal vasculature, then into the vortex veins.5-7 Collateral veins have also been shown to be negatively associated with anterior segment neovascularization after CRVO7 and with better visual acuity outcomes and accelerated resolution of retinal edema in CRVO eyes treated with radial optic neurotomy.8 Concentrations of vascular endothelial growth factor (VEGF) are elevated in the aqueous fluid of eyes with CRVO, with highest concentrations in the presence of iris neovascularization.1,9-11 VEGF promotes angiogenesis by increasing endothelial cell migration and proliferation, and it increases vascular permeability through breakdown of the blood retinal barrier.12-14 Prospective studies using anti-VEGF therapy in the form of bevacizumab (Avastin, Genentech, Inc.) have shown significant improvements in visual acuity and mean central retinal thickness in patients with CRVO.1,2 However, as VEGF is required for vasculogenesis, its presence may be necessary for the formation of optociliary shunt vessels, in which case VEGF inhibition would actually prove to be detrimental.2 We performed a study to investigate the impact of intravitreal bevacizumab on the development of optociliary shunt vessels in patients with macular edema secondary to CRVO and to evaluate the functional and anatomical outcomes in patients who developed shunt vessels vs patients who did not.