SUCNR1 and retinopathy of prematurity: G protein-coupled receptors 91 and 81 (GPR91and GPR81), localized in ganglion cells and Muller cells respectively, are involved in the pathogenesis of diabetic retinopathy (DR) and hypoxic retinal diseases such as retinopathy of prematurity (ROP), inner vascular network development and restoration of the vasculature in response to injury (152, 164).