Here we investigated the level of VEGF-A protein and free drug concentration of ranibizumab in serum and breast milk following intravitreal injection of ranibizumab in a young woman suffering from branch retinal vein occlusion (BRVO).<h4>Case presentation</h4>A 30-year-old female, who was nursing her six-month-old son, was treated by intravitreal injection of ranibizumab (IVR) for cystoid macular edema owing to BRVO of her right eye. The gene discussed is VEGFA; the disease is Cystoid macular dystrophy.