Development of the eye of the chick embryo.

Vertebrate eye development begins with the formation of the optic vesicles as outgrowths of the forebrain. These initial pouches grow laterally and can be subdivided into optic stalk and optic vesicle. The axis of growth then shifts to produce optic vesicles that enlarge dorsally to lie alongside the expanding diencephalon. Concomitant invagination of the optic vesicles and the overlying ectoderm produces the optic cup and lens. During later stages, the lens detaches from the surfaces ectoderm and the optic cup forms the neural retina and the pigmented epithelium. Experimental analysis of eye development has revealed an intimate relationship between invagination of the lens and optic cup. The primordia of the lens and neural retina become adherent, as a result of changes in the extracellular matrix, before invagination commences. Interference with matrix synthesis causes abnormal development of the optic cup, and subsequent abnormalities of the lens. The forces that control invagination are under investigation. Lens formation may result from internal contractile forces as well as from forces exerted by surrounding cells. Characteristic changes in cell shape and cytoplasmic organization occur during invagination of the neural retinal primordium. These and the effects of inhibitory drugs suggest the involvement at least in part of a contractile mechanism during optic cup formation.