The model treats only one cytokine, a single VEGF isoform without consideration of other larger VEGF isoforms, PEDF, PDGF, erythropoietin, angiopoetin-1, angiopoetin-2 or angiopoetin-like 4, all of which likely play at least some role in vascular changes in diabetic retinopathy [117, 140–142]. This evidence concerns the gene EPO and diabetic retinopathy.