Objective:To observe the clinical features of collateral circulation in different types of retinal vein occlusion.Methods:A retrospective clinical study. A total of 360 patients with monocular retinal vein occlusion diagnosed by ophthalmic examination in Department of Ophthalmology of Yunnan University Affiliated Hospital from December 2021 to December 2023 were included in the study. Among them, 157 males had 157 eyes and 203 females had 203 eyes. Age were (61.0±5.9) years. The duration of the disease from the onset of symptoms to the time of treatment was 3 days to 6 months. Macular branch vein occlusion (MBRVO), retinal branch vein occlusion (BRVO) and central retinal vein occlusion (CRVO) were observed in 67, 187 and 106 eyes, respectively. 210 eyes were with macular edema. All patients with macular edema were treated with anti-vascular endothelial growth factor (VEGF) by intravitreal injection. All eyes were examined by scanning source optical coherence tomography. The incidence, location, morphological characteristics, formation time of retinal collateral circulation and the effect of anti-VEGF drug on the formation of collateral circulation were observed. A short circuit in which blood vessels originating from the optic disc in the form of a blood loop return to the optic disc after the disc has been deformed for some time is defined as a short-circuited collateral circulation of the ciliary vessels of the optic disc.Results:After 1 week of disease course, MBRVO and collateral circulation of BRVO affected eye were established. By 1 to 2 months, a relatively abundant and stable collateral circulation had been established. In the course of 2 to 3 months, the short-circuit collateral circulation of ciliary vessels in the optic disc of the affected eye gradually formed. At 6 months, collateral circulation was established in 36 eyes (53.7%, 36/67) in 67 MBRVO patients. Collateral circulation was observed in 187 eyes of BRVO patients (100.0%, 187/187). In 106 eyes with CRVO, collateral circulation was established in 29 eyes (18.1%, 29/106). In 36 eyes with MBRVO, collateral circulation was established at the vertical horizontal slit between the blocked area and the non-blocked area. In 187 eyes of BRVO patients, collateral circulation was established in the vertical horizontal slit between the blocked and non-blocked areas in 102 eyes; 54 eyes were blocked the most central bypass to the collateral circulation on normal blood vessels. The collateral circulation of 19 eyes was established through nasal and temporal side. Collateral circulation through the fovea was established in 12 eyes. Its morphology is straight out of shape, spiral sinuous and flower cluster. CRVO established collateral circulation in 29 eyes, all of which had short-circuit collateral circulation of ciliary vessels. In 210 eyes treated with anti-VEGF drugs, collateral circulation was established in 160 eyes. Among them, 32 eyes were MBRVO (50.7%, 32/63), BRVO 119 eyes (100.0%, 119/119), CRVO 9 eyes (32.1%, 9/28).Conclusions:The incidence of collateral circulation of MBRVO, BRVO and CRVO is 53.7%, 100.0% and 18.1%, respectively. The forms of MBRVO were varied and the course of disease is about 2 months. Anti-VEGF therapy did not inhibit the establishment of collateral circulation.