VASCULAR DEVELOPMENT IN PRIMATE RETINA - COMPARISON OF LAMINAR PLEXUSFORMATION IN MONKEY AND HUMAN

Purpose. The temporal and spatial sequence of development of laminar v ascular plexuses was determined qualitatively and quantitatively in mo nkey and human retina. Methods. Histologic and cytochemical methods we re used to study Macaca monkey eyes from fetal day 55 (F55d; birth = F 168d) to 17 years, and human retina from fetal 21 weeks to adult. Resu lts. In monkey retina, spindle-shaped, presumed vascular precursor, ce lls appear at F55d in the nerve fiber layer (NFL) adjacent to the opti c nerve. The vascular plexuses in the NFL-ganglion cell layer appear f irst and form in the presence of spindle cells. Nerve fiber layer vess els extended radially to reach the temporal ora at F95d and nasal ora at F110d. The capillary plexus at the inner border of the inner nuclea r layer (INL) appears at F120d near the optic disc, whereas the plexus at the outer INL border appears at F130d. Both reach their final posi tion before birth. The INL plexuses form by endothelial budding from m ore vitread vessels in the absence of spindle cells. In the NFL, vesse l growth to match retinal growth at the ora also involves endothelial budding. The growth rate of all plexuses was approximately 225 mu m/da y. The central fovea and the most peripheral retina adjacent to the or a serrata remained avascular throughout development. Differences betwe en humans and monkeys include: Human vessels complete maturation after birth; human vessels reach the nasal ora earlier than the temporal er a; and spindle cells are more abundant and dispersed over a greater ar ea within human NFL. Growth rates of human plexuses were comparable to those in monkeys. Conclusion. In both primates, deeper capillary plex uses form only by extension from existing vessels (angiogenesis). In t he NFL, early vessel formation involves spindle precursor cells (vascu logenesis). The main difference between monkey and human in these proc esses is that the mature monkey vascular pattern is established well b efore birth.