Insulin and insulin-like growth factor-1 (IGF-1) are abundant in ocular tissues. They may act as messengers, coding for differentiation in the eye, may be directly or indirectly involved in the visual process in the adult animal or control other important processes such as outer segment renewal. Equally important, receptors for these messengers are highly concentrated in developing retina, pigment epithelium, and sclera, and may play a role in differentiation of these tissues. All the components of an IGF-1 system are present in the retinal interphotoreceptor matrix (IPM). The photoreceptor region thus possesses an IGF-I autocrine-paracrine system. Abnormal ocular growth during early retinal degeneration and experimental myopia, for example, could be associated with changes in insulin and IGF-1 concentrations, or possibly with binding to receptors and/or binding proteins.
