Photograph of the retina of the human eye, with overlay diagrams showing the positions and sizes of the<unk> , fovea, and optic disc Schematic diagram of the<unk>  lutea of the retina, showing perifovea, parafovea, fovea, and clinical<unk>  The<unk>  is an oval-shaped pigmented area in the center of the retina of the human eye and other animal eyes. Its center is shifted slightly away from the optical axis (laterally, by 5°=1.5 mm). The<unk>  in humans has a diameter of around and is subdivided into the umbo, foveola, foveal avascular zone, fovea, parafovea, and perifovea areas. An even smaller central region of highest receptor density (40–80 μm) is sometimes referred to as the foveal bouquet. The anatomical<unk>  at is much larger than the clinical<unk>  which, at , corresponds to the anatomical fovea. The clinical<unk>  is seen when viewed from the pupil, as in ophthalmoscopy or retinal photography. The anatomical<unk>  is defined histologically in terms of having two or more layers of ganglion cells. The umbo is the center of the foveola which in turn is located at the center of the fovea. The fovea is located near the center of the<unk> . It is a small pit that contains the largest concentration of cone cells. The retina contains two types of photosensitive cells, the rod cells and the cone cells. Color Because the<unk>  is yellow in colour it absorbs excess blue and ultraviolet light that enter the eye and acts as a natural sunblock (analogous to sunglasses) for this area of the retina. The yellow color comes from its content of lutein and zeaxanthin, which are yellow xanthophyll carotenoids, derived from the diet. Zeaxanthin predominates at the<unk> , while lutein predominates elsewhere in the retina. There is some evidence that these carotenoids protect the pigmented region from some types of<unk> r degeneration. A formulation of 10 mg lutein and 2 mg zeaxanthin has been shown to reduce the risk of age-related<unk> r degeneration progressing to advanced stages, although these carotenoids have not been shown to prevent the disease. After death or enucleation (removal of the eye), the<unk>  appears yellow, a color that is not visible in the living eye except when viewed with light from which red has been filtered. Regions * Fovea – * Foveal avascular zone (FAZ) – * Foveola – * Umbo –
Macula of retina
Retinal nerve fiber layer
Scleral lens
Optic pit
Iris pigment epithelium
Optic cup 
Optic vesicle
Foveal avascular zone