Retinol-binding protein (RBP) is a class of proteins responsible for transporting vitamin A (retinol). The RBP family mainly includes members such as RBP1, RBP2, RBP3, and RBP4. RBP4 is the major form in plasma, binding to and transporting retinol to tissues. RBP3, on the other hand, is a specific protein in the retinas of the eyes, involved in the visual cycle. These proteins are expressed in the liver, eyes, and other tissues, participating in the absorption, transport, and metabolism of vitamin A, affecting various physiological processes such as vision, reproduction, immunity, and cell proliferation. The specific expression and mutations of the genes are associated with various diseases, including night blindness, vitamin A deficiency, and metabolic disorders.