Interestingly, recent studies have shown decreased levels of IRBP in the vitreous in the early stages of diabetes.8 The source and turnover of vitreous IRBP is unknown although its mRNA has been detected in the ciliary epithelium.9 Finally, in the retina, IRBP is not restricted to the IPM as was commonly assumed, but is internalized avidly by the RPE (see below). The gene discussed is RBP3; the disease is diabetes mellitus.