Embryology of Retina and Choroid

Abstract

The retina is a part of the brain. At the end of the first month in the development of the human embryo, two optic vesicles develop at the lateral surfaces of the embryonic forebrain. The lumina of the optical vesicles are continuous with the primitive ventricular system. At the end of the fourth week, the optical vesicles collapse and form optic cups. The ventricular space is reduced to a capillary cleft between two sheaths of neuroectodermal epithelium. The optical cups, connected to the forebrain by the optical stalks, induce the formation of the eyes in a complicated sequence of events (see for example: Starck 1975). In the adult, the anterior part of the retina, covering the ciliary body and iris, retains the original structure of two epithelial sheaths; the apical poles of their cells face each other. In the posterior part of the retina, the outer neuroectodermal sheath of the eyecup remains a single layer. It becomes the retinal pigment epithelium, whereas the inner sheath transforms into the nervous tissue of the neuroretina. The former optical ventricle remains a distinct extracellular compartment between the neuroretina and pigment epithelium: It is commonly termed subretinal space. A summary of recent research on vertebrate retinal development can be found in Barnstable (1987).