The Foveal Avascular Region of Developing Human Retina

Abstract

The adult human fovea has a unique structural organization. Its most obvious feature is a shallow pit in which the ganglion cell, inner plexiform, and inner nuclear layers are displaced peripherally, forming a thick rim or slope around the pit (Figure 1A). In the center of the fovea, or foveola, only the photoreceptor layer remains and this consists of tightly packed, elongated cones and Müller cell processes. Rods are excluded from the foveola, forming a central rod-free zone where cone density reaches more than 200 000/mm², the highest in the retina.¹ All adult primate foveae contain a central avascular region known as the foveal avascular zone (FAZ) (Figure 1B), because blood vessels are found on the slope (Figure 1A) but not in the foveola. Studies from our laboratories have shown that the foveal pit and the peak cone density are a product of complex developmental processes that occur during the last half of gestation and the early postnatal years.^2-5 Using a combination of finite element analysis and quantitative morphology, Springer and Hendrickson^6,7 have developed a model of primate foveal development in which they suggest that the presence of an FAZ is a critical requirement for formation of the foveal pit. Furthermore, several studies using optical coherence tomography now indicate that absence of the FAZ is associated with absence of a foveal depression and reduced uncorrectable visual acuity.^8-13