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Optic FoveaThe fovea, a part of the eye, is a spot located in the center of the macula. The fovea is responsible for our sharp central vision, which is necessary in humans for reading, watching television or movies, driving, and any activity where visual detail is of primary importance. At the center of the fovea there is a pit with a diameter of about 0.2 mm. It has a high concentration of cone cells and virtually no rods. Compared to the rest of the retina, the cones in the foveal pit are smaller and more densely packed (in a hexagonal pattern), and they are not obscured by a layer of nerve cells and blood vessels; all of this together accounts for the sharp vision associated with them. The fovea is largely responsible for the color vision in humans which is superior to most other mammals. The foveal pit is located exactly on the optical axis: when we focus on an object, then the object, the center of the pupil and the fovea will form a straight line. Surrounding the foveal pit is the foveal rim, where the neurons displaced from the pit are located. This is the thickest part of the retina. Since the fovea does not have rods, it is not sensitive to dim lights. Astronomers know this: in order to observe a dim star, they use peripheral vision, looking out of "the side of their eyes". The fovea is covered in a yellow pigment called macula lutea. This absorbs blue light and is probably an evolutionary adaption to the problem of chromatic aberration. Schematic diagram of the human eye.
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