Myopia is increasing in prevalence world-wide, nearing epidemic
proportions in some populations. This has led to expanded research efforts
to understand how ocular growth and refractive errors are regulated. Eye
growth is sensitive to visual experience, and is altered by both form
deprivation and optical defocus. In these cases, the primary targets of
growth regulation are the choroidal and scleral layers of the eye that
demarcate the boundary of the posterior vitreous chamber. Of significance
to this review are observations of local growth modulation that imply that
the neural retina itself must be the source of growth-regulating signals.
Thus the retinal pigment epithelium (RPE), interposed between the retina
and the choroid, is likely to play a critical role in relaying retinal
growth signals to the choroid and sclera. This review describes the ion
transporters and signal receptors found in the chick RPE and their
possible roles in visually driven changes in eye growth. We focus on the
effects of four signaling molecules, otherwise implicated in eye growth
changes (dopamine, acetylcholine, vasoactive intestinal peptide (VIP), and
glucagon), on RPE physiology, including fluid transport. A model for
RPE-mediated growth regulation is proposed.
Critical Role of TrkB and Brain-Derived Neurotrophic Factor in the Differentiation and Survival of Retinal Pigment Epithelium