['To test the hypothesis that retinochoroidal collateral veins (RCVs), or alternatively, retinociliary or optociliary shunts/collaterals/veins or opticociliary anastomoses, act protectively against the development of anterior segment neovascularization (ASN) following central retinal vein occlusion (CRVO).', 'Case-control retrospective medical record review of patients with CRVO.', 'We identified 107 patients with CRVO, of whom 34 had developed ASN, by reviewing their medical records. After applying exclusion criteria, a case group and an age-, sex-, and visual acuity-matched control group were selected. We analyzed these groups for the presence or absence of RCVs and noted the time course involved in their development.', 'Anterior segment neovascularization (including neovascularization of the iris and/or anterior chamber angle), neovascular glaucoma, and RCV development.', 'Only 1 (5.4%) of 19 individuals who developed ASN did so in the presence of RCVs. In contrast, 11 (57.9%) of 19 individuals in the control group developed RCVs. Statistical analysis revealed that patients who developed ASN were roughly 25 times less likely to have had RCVs than individuals who never developed ASN (odds ratio = 24.74; P =.001).'] Do retinochoroidal collateral veins protect against anterior segment neovascularization after central retinal vein occlusion?