Background literature was searched in PubMed using search terms such as ‘diabetic retinopathy’, ‘diabetic macular ischemia’, ‘diabetic macular edema’, ‘semaphorin 3a’, ‘neuropilin 1’, ‘retinal non-perfusion’, ‘vascular perfusion’, ‘anti-VEGF’, ‘corticosteroid’ and ‘laser photocoagulation’. The gene discussed is SEMA3A; the disease is diabetic macular edema.