The central area of the retina, or macula, measures approximately 5.5 mm in diameter and is centered between the optic nerve head and the temporal vascular arcades. On histologic examination, this area features 2 or more layers of ganglion cells, accounting for half of all the ganglion cells in the retina. Oxygenated carotenoids, in particular lutein and zeaxanthin, accumulate within the central macula and contribute to its yellow color.
The central 1.5 mm of the macula, which is called the fovea (or fovea centralis), is specialized for high spatial acuity and color vision. The fovea has a margin, a downward slope, and a floor known as the foveola, a 0.35-mm-diameter region where cones are slender, elongated, and densely packed. At the very center of the foveola is a small depression, 150–200 µm in diameter, known as the umbo. Within the fovea is a region devoid of retinal vessels known as the foveal avascular zone (FAZ). The geometric center of the FAZ is often taken to be the center of the macula and thus the point of fixation; it is an important landmark in fluorescein angiography. Surrounding the fovea is the parafovea, a ring 0.5 mm in width where the ganglion cell layer, inner nuclear layer, and outer plexiform layer (also known as Henle fiber layer) are thickest. Surrounding this zone is the perifovea, a ring approximately 1.5 mm wide (Table 1-1). Thus, the umbo forms the center of the macula, and the periphery of the perifovea forms its margin, which is sometimes referred to as the area centralis (Fig 1-2).
The retina outside the macula, sometimes referred to as the extra-areal periphery, is commonly divided into a few concentric regions, starting with the near periphery, a 1.5-mm ring peripheral to the temporal major vascular arcades. The equatorial retina is the retina around the equator, and the region anterior to the equatorial retina is called the peripheral retina. In the far periphery, the border between the retina and the pars plana is called the ora serrata. The posterior border of the vitreous base is typically located between the ora serrata and the equator of the eye. This region is where most retinal tears occur. Jetties of retinal tissue, called dentate processes, extend anteriorly into the pars plana. These processes are more prominent nasally. Ora bays are posterior extensions of the pars plana toward the retina. On occasion, dentate processes may wrap around a portion of an ora bay to form an enclosed ora bay. A meridional fold is a radially oriented, prominent thickening of retinal tissue that extends into the pars plana. When aligned with a ciliary process, such folds are known as a meridional complex (Fig 1-3).
Figure 1-2 Anatomical macula, also called area centralis or posterior pole. The anatomical fovea and foveola are contained within the center of the anatomical macula. Letters indicate borders of: a = umbo; b = foveola; c = fovea; c to d = parafoveal macula; d to e = perifoveal macula; e = macula.
(Courtesy of Hermann D. Schubert, MD.)
Table 1-1 Anatomical Terminology of the Macula (Area Centralis)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.