http://upload.wikimedia.org/wikipedia/commons/1/1e/Schematic_diagram_of_the_human_eye_en.svg

A small pit in the center of the macula lutea, the area of clearest vision, where the retinal layers are spread aside, and light falls directly on the cones. [TFD][VHOG]

high acuity vision

fovea

uberon

centre of fovea

foveal

Definition of fovea centralis should be considered here as 'an area centralis at the visual axis' (reference 1). There is an uncertaincy of the relation, because: 1.-The fovea first appeared in evolution in the temporal retina of fishes. Then, in birds, the nasal fovea and bifoveal system with nasal and temporal foveas developed. The fovea disappeared in primitive mammals, and reappeared in primates. A residue of the fovea is conserved in the visual streak, and the disappearance and reappearance of the fovea, in primitive mammals and primates respectively, correlates with degeneration and restoration of cone pigment genes in photoreceptors (reference 2). 2.-Many retinal features (foveas, trichromacy, midget pathways and associated cell types) appear specific to primates. This has led to investigations in parallel with other mammalian models such as cat or rabbit. Correlation of the results often proves to be difficult, since an evolutionary scenario with transitions between the mammalian models is largely lacking (reference 3).[uncertain][VHOG]

UBERON:0001786

The fovea is also a pit in the surface of the retinas of many types of fish, reptiles, and birds. Among mammals, it is found only in simian primates. The retinal fovea takes slightly different forms in different types of animals. For example, in primates, cone photoreceptors line the base of the foveal pit, the cells that elsewhere in the retina form more superficial layers having been displaced away from the foveal region during late fetal and early postnatal life. Other foveae may show only a reduced thickness in the inner cell layers, rather than an almost complete absence