ONTOGENY OF THE PRIMATE FOVEA - A CENTRAL ISSUE IN RETINAL DEVELOPMENT

The formation of the primate fovea has fascinated a substantial number of histologists, pathologists, ophthalmologists and physiologists for more than a century. In this article, using data from the literature as well as our own observations, we identify events which we believe a re crucial in this process and present a developmental neurobiologist' s view of the formation of the primate fovea. The fovea is a region of the retina specialized for diurnal, high acuity functions which requi re a high spatial density of cone photoreceptors as well as a large nu mber of inner retinal cells in order to establish the distinct retinof ugal pathways (ganglion cell axons) receiving from individual cones in the foveal cone mosaic. A unique feature of the fovea is the displace ment of cells connected to the foveal cones onto the rim of the fovea. It is generally believed that this displacement counteracts the probl ems caused by the scattering of the incoming light by cells and blood vessels of the inner retina. We believe that one of the crucial events in the formation of the primate fovea is the early centripetal migrat ion of photoreceptors towards the central area (centripetal displaceme nt). Tnis process, initiated early in development, continues throughou t intrauterine life until some months or years postnatal. We propose t hat the displacement of cells from the inner layers is related to the earlier developmental accumulation of photoreceptors and inner retinal cells centrally. This, we propose, leads to metabolic ''starvation'' of the inner retina, resulting from the complete absence of retinal ve ssels from the vicinity of the incipient fovea. It is suggested that t hese factors in turn trigger centrifugal displacement of inner retinal cells towards the encroaching perifoveal capillary network and lead t o the formation of the foveal depression. (C) 1998 Elsevier Science Lt d.