HMOX1 and diabetic retinopathy: Artery or vein occlusion, as seen in CRAO or in diabetic retinopathy, leads to oxidative stress in both retinal endothelial cells and retinal neural cells (RGCs) through the decreased activities of several antioxidant enzymes, including superoxide dismutase (SOD), glutathione peroxidase, catalase, hemeoxygenase-1 and thioredoxins (Trx1 and Trx2), and has been implicated in promoting RGC death [34,35,36].