The vasculature in the developing eye (Figure 125.1A) has been an excellent model system to study both normal angiogenesis and remodeling, as well as unique aspects of the central nervous system (CNS) vasculature. Like the rest of the CNS, microvasculature of the retina consists of endothelial cells (ECs), pericytes, and glial cells that form a barrier to tightly regulate transport from the blood into the tissue. In the retina, it is called the blood–retinal barrier (BRB). But other vascular beds in the eye are also useful for the study of developmental mechanisms (Figure 125.1B). For example, the first vasculature to form in the developing eye is the hyaloid vasculature, which feeds the early lens and spontaneously regresses as the retinal vessels form and become competent to supply the nutritional needs of the growing and metabolically demanding retina. Another specialized vasculature in the eye is the choroidal vasculature, which feeds the back of the retina through diffusion throughout the retinal pigmented epithelium. This vascular bed, like that of the retina proper, often is compromised in ocular diseases such as retinopathy and macular degeneration. This chapter, however, focuses on the study of the retinal and hyaloid vasculatures, because they have been especially useful in the elucidation of basic molecular and cellular mechanisms of vascular development.

In rodents, the hyaloid blood vessels form during embryogenesis but regress in the first week of postnatal development. During that time, the first retinal blood vessels form a primitive network of capillaries that progressively spread from the optic disc outward toward the periphery of the retina.