*5.4. Diabetic Retinopathy*

Diabetic retinopathy is a vision-threatening complication of diabetes a ffecting approximately 93 million in the middle-aged and elderly populations [146]. Chronic hyperglycemia causes progressive damage to retinal cells and to the retinal capillaries, leading to ischemia, VEGF-mediated retinal vascular abnormalization, and neovascular vessels that leak and bleed into the retina. Macular edema is also a major cause of vision loss in diabetic retinopathy [1]. Clinical reports have shown the link between iron levels in the vitreous and proliferative diabetic retinopathy [124,147]. A strong iron label was observed in the RPE and outer plexiform layer of patients with diabetic retinopathy [148]. In a mouse model of diabetic retinopathy, higher iron concentrations in the retina led to an increased expression of renin by a mechanism dependent on the GPR91 receptor [106].
