ObjectiveTo study the changes the changes of cytokine expression the aqueous humor of patients with macular edema secondary to branch retinal vein occlusion (BRVO-ME) before and after intravitreal ranibizumab (IVR). MethodsA prospective clinical study. From June 2018 to June 2021, 31 eyes of 31 patients with non-ischemic BRVO-ME diagnosed by ophthalmic examination in Department of Ophthalmology, Beijing Hepingli Hospital were included in the study. Among them, 15 males had 15 eyes, and 16 females had 16 eyes. Age was 70 (65, 72) years; the course of disease was 10 (9, 15) days. All of them were first-time patients. All eyes were treated with IVR once a month for 3 consecutive months. At the end of each IVR treatment, 0.1 ml aqueous humor was extracted immediately. The concentrations of vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in aqueous humor were detected by flow cytometry. The concentrations of cytokines in aqueous humor before and after treatment were compared by Kruskal-Wallis or Wilcoxon signed-rank test. Spearman correlation analysis was performed on the correlation between VEGF and MCP-1 expression level in aqueous humor before treatment. ResultsThe concentrations of VEGF and ICAM-1 in aqueous humor were significantly lower at 1 month after treatment compared with that before treatment, and at 2 months after treatment compared with that at 1 month after treatment (Z=4.03, 3.25, 2.50, 3.48; P＜0.05); the concentrations of IL-6 and VCAM-1 increased and the concentration of MCP-1 decreased, but there was no significant difference (Z=－0.21, 1.42, 0.86, －0.53, 0.92, －1.57; P＞0.05). Spearman correlation analysis showed that there was a strong positive correlation between VEGF and MCP-1 in aqueous humor before treatment (r=0.78, P＜0.001). ConclusionThe concentrations of VEGF and ICAM-1 in aqueous humor significantly decrease after IVR treatment in BRVO-ME; the concentrations of IL-6, MCP-1 and VCAM-1 do not obviously change.