Astrocytes and blood vessels define the foveal rim during primate retinal development

PURPOSE. To investigate the relationship between development of the perifov eal blood vessels and formation of the foveal depression. METHODS. Retinal sections and flatmounts from monkeys aged between fetal da y (Fd)80 and 2 years of age were double labeled using antisera to CD31 or v on Willebrand factor to detect vascular endothelial cells and antiserum to glial fibrillary acidic protein to detect astrocytes. Sections were studied by fluorescence or confocal microscopy. RESULTS. From Fd88 to 115, vessels on the horizontal meridian were found on ly at the level of the ganglion cell layer (GCL)-inner plexiform layer (IPL ) border where they form the ganglion cell layer plexus (GCP). Stellate ast rocytes accompany GCP vessels and extend closer to the fovea than vessels. The foveal avascular zone was present within the GCP at Fd101, and at Fd105 a shallow foveal depression encircled by the GCP was present. The GCP fove al margin had the same dimensions as the adult foveal pit. Both blood vesse ls and astrocytes were excluded from the emerging fovea throughout developm ent. After Fd140, capillary plexuses in the outer retina anastomosed with t he GCP on the foveal slope to form a perifoveal plexus, but this plexus did not mature until a month or more after birth. After Fd142, astrocytes rapi dly disappeared from the GCP and most of central retina. CONCLUSIONS. An avascular area is outlined by the GCP before the foveal pit begins to form, suggesting that molecular factors in this region exclude b oth vessels and astrocytes. These factors may also guide neuronal migration to form the pit. Because the perifoveal plexus is formed during late gesta tion, both capillary growth and foveal development may be affected adversel y by prematurity.