Fovea centralis

The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina.Illustration showing main structures of the eye including the foveaStructures of the eye labeledThis image shows another labeled view of the structures of the eyeSchematic diagram of the macula lutea of the retina, showing perifovea, parafovea, fovea, and clinical maculaA fundus photograph showing the macula as a spot to the left. The optic disc is the area on the right where blood vessels converge. The grey, more diffuse spot in the centre is a shadow artifact. The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina. The fovea is responsible for sharp central vision (also called foveal vision), which is necessary in humans for activities where visual detail is of primary importance, such as reading and driving. The fovea is surrounded by the parafovea belt, and the perifovea outer region. The parafovea is the intermediate belt, where the ganglion cell layer is composed of more than five rows of cells, as well as the highest density of cones; the perifovea is the outermost region where the ganglion cell layer contains two to four rows of cells, and is where visual acuity is below the optimum. The perifovea contains an even more diminished density of cones, having 12 per 100 micrometres versus 50 per 100 micrometres in the most central fovea. This, in turn, is surrounded by a larger peripheral area that delivers highly compressed information of low resolution following the pattern of compression in foveated imaging. Approximately half of the nerve fibers in the optic nerve carry information from the fovea, while the remaining half carry information from the rest of the retina. The parafovea extends to a radius of 1.25 mm from the central fovea, and the perifovea is found at a 2.75 mm radius from the fovea centralis. The term fovea comes from the from Latin foves, meaning 'pit'. Fovea is the depression in the inner retinal surface, about 1.5 mm wide, the photoreceptor layer of which is entirely cones and which is specialized for maximum visual acuity. Within the Fovea is a region of 0.5mm diameter called the foveal avascular zone (an area without any blood vessels). This allows the light to be sensed without any dispersion or loss. This anatomy is responsible for the depression in the center of the fovea. The foveal pit is surrounded by the foveal rim that contains the neurons displaced from the pit. This is the thickest part of the retina. The fovea is located in a small avascular zone and receives most of its oxygen from the vessels in the choroid, which is across the retinal pigment epithelium and Bruch's membrane. The high spatial density of cones along with the absence of blood vessels at the fovea accounts for the high visual acuity capability at the fovea. The center of the fovea is the foveola – about 0.35 mm in diameter – or central pit where only cone photoreceptors are present and there are virtually no rods. The central fovea consists of very compact cones, thinner and more rod-like in appearance than cones elsewhere. These cones are very densely packed (in a hexagonal pattern). Starting at the outskirts of the fovea, however, rods gradually appear, and the absolute density of cone receptors progressively decreases. The anatomy of the foveola was recently reinvestigated, and it was discovered that outer segments from the central foveolar cones of monkeys are not straight and twice as long as those from the parafovea. The size of the fovea is relatively small with regard to the rest of the retina. However, it is the only area in the retina where 20/20 vision is attainable, and is the area where fine detail and colour can be distinguished.