The human retinal vascular network is composed of multiple layers of vessels and capillaries,
1,2 supplying oxygen and nutrients as well as disposing metabolic byproducts for the inner retinal layers.
3 The fovea vascular network, in contrast, consists of a single layer of interconnected capillaries that perfuse the inner retinal layer.
1,2,4 This foveal capillary network forms a ring at the margin of the fovea, producing a capillary-free region called the fovea avascular zone (FAZ). Clinically, the assessment of retinal vasculature perfusion typically requires intravenous injection of fluorescein dye.
5–7 Owing to the invasive nature of fluorescein angiography, these studies are seldom performed on healthy controls. Noninvasive visualization of the foveal capillary network and foveal pit architecture are now provided by advances in retinal imaging, offering the opportunity to examine the foveal vasculature and pit development in healthy and diseased retina.
8–14 Several research groups that used entopic perception,
15,16 optical coherence tomography,
9,17 and adaptive optics ophthalmoscopy
11,12,14 have shown that the size of FAZ varies considerably in healthy subject. Previous studies
12,14,18 have reported that larger FAZ is associated with a broader foveal pit in healthy controls. It has also been demonstrated that patients with a history of retinopathy of prematurity have smaller FAZs and narrower foveal pits when compared to full-term controls.
19,20 Despite the extensive investigations of the correlations between the FAZ and foveal pit morphology, considerable individual variation of FAZ dimension and foveal pit architecture limits understanding of the relation between the vasculature, the neural and glial components of the retina, and how they interact during foveal development. In addition, previous data from both ex vivo and in vivo studies show that a high density of cones extends out to a greater eccentricity in the horizontal than the vertical meridian.
21,22 Thus, if the FAZ develops to provide clear vision in the region of relatively high cone density, it might be expected that the FAZ would extend further laterally than vertically. Conversely, there are presumably physiological penalties for extending cone axons and glia too far from the inner retinal blood supply. To examine the interplay of these factors, we measured the shape and size of the FAZ and the retinal thickness measured at the edge of the FAZ in 32 healthy subjects by using an adaptive optics scanning laser ophthalmoscope (AOSLO) and spectral-domain optical coherence tomography (SDOCT).