Visual system development in vertebrates

The development of a functional visual system involves a complex series of inductive and signalling interactions essential for the formation of the eye and its central connections with the brain. Outpouchings from the forebrain, together with the overlying surface ectoderm and neural crest cells give rise to the major structures of the eye (neural retina, pigmented epithelium, lens and cornea). Central connections between the eye and brain regions that receive direct connections from the eye (visual targets) are formed by the axons of retinal ganglion cells. Attractive and repulsive cues in the extracellular environment guide the retinal axon along specific pathways in the brain. Gradients of signalling molecules, together with spontaneous neural activity, drive a point-to-point mapping of retinal axons in visual targets, ensuring accurate reconstruction of the visual image. The cellular, molecular and inductive mechanisms that sculpt each of these key developmental processes essential for normal visual system development are beginning to be understood.