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The macula or macula lutea is an oval-shaped pigmented area near the center of the of the and some other animalian. The macula in humans has a diameter of around 5.5 mm (0.22 in) and is subdivided into the umbo, foveal avascular zone, and areas.
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The anatomical macula at 5.5 mm (0.22 in) is much larger than the clinical macula which, at 1.5 mm (0.059 in), corresponds to the anatomical fovea. The macula is responsible for the central, high-resolution, color vision that is possible in good light; and this kind of vision is impaired if the macula is damaged, for example in. The clinical macula is seen when viewed from the pupil, as in ophthalmoscopy or retinal photography. The term macula lutea comes from macula, 'spot', and lutea, 'yellow'. Schematic diagram of the macula lutea of the retina, showing perifovea, parafovea, fovea, and clinical macula The macula is an oval-shaped pigmented area near the center of the of the and some other animalian.
The macula in humans has a diameter of around 5.5 mm (0.22 in) and is subdivided into the umbo, foveal avascular zone, and areas. The anatomical macula at 5.5 mm (0.22 in) is much larger than the clinical macula which, at 1.5 mm (0.059 in), corresponds to the anatomical fovea. The clinical macula is seen when viewed from the pupil, as in ophthalmoscopy or retinal photography. The anatomical macula is defined in terms of having two or more layers of.
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 macula. It is a small pit that contains the largest concentration of. The retina contains two types of photosensitive cells, the and the cone cells. Color Because the macula 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 and, which are yellow, derived from the diet. Zeaxanthin predominates at the macula, while lutein predominates elsewhere in the retina.
There is some evidence that these carotenoids protect the pigmented region from some types of. A formulation of 10 lutein and 2 mg zeaxanthin has been shown to reduce the risk of age-related macular degeneration progressing to advanced stages, although these carotenoids have not been shown to prevent the disease. After death or (removal of the eye) the macula appears yellow, a color that is not visible in the living eye except when viewed with light from which red has been filtered. Regions.
1.55 mm (0.061 in). (FAZ) - 0.5 to 0.6 mm (0.020 to 0.024 in). 0.35 mm (0.014 in). 0.15 mm (0.0059 in) Function Structures in the macula are specialized for high- vision. Within the macula are the fovea and foveola that both contain a high density of, which are nerve cells that are with high acuity. In details, the normal human eye contains three different types of cones, with different ranges of spectral sensitivity. The brain combines the signals from neighboring cones to distinguish different colors.
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There is only one type of rod, but the rods are more sensitive than the cones, so in dim light they are the dominant photoreceeptors active, and without information provided by the separate spectral sensitivity of the cones it is impossible to discriminate colors. In the fovea centralis, cones predominate, and are present at high density. The macula is thus responsible for the central, high-resolution, color vision that is possible in good light; and this kind of vision is impaired if the macula is damaged, for example in. Clinical significance. Of the right eye (left image) and left eye (right image), seen from front so that left in each image is to the person's right.
The gaze is into the camera, so in each picture the macula is in the center of the image, and the is located towards the nose. The clinical macula is seen when viewed from the pupil, as in ophthalmoscopy or retinal photography. Whereas loss of may go unnoticed for some time, damage to the macula will result in loss of central vision, which is usually immediately obvious. The progressive destruction of the macula is a known as and can sometimes lead to the creation of a macular hole. Macular holes are rarely caused by trauma, but if a severe blow is delivered it can burst the blood vessels going to the macula, destroying it. Visual input from the macula occupies a substantial portion of the brain's visual capacity.
As a result, some forms of that occur without involving the macula are termed macular sparing. (For example, might demonstrate with macular sparing.) In the case of occipitoparietal ischemia owing to occlusion of elements of either, patients may display cortical (which, rarely, can involve blindness that the patient denies having, as seen in ), yet display sparing of the macula. This selective sparing is due to the collateral circulation offered to macular tracts by the.
Neurological examination that confirms macular sparing can go far in representing the type of damage mediated by an infarct, in this case, indicating that the caudal visual cortex (which is the principal recipient of macular projections of the optic nerve) has been spared. Further, it indicates that cortical damage rostral to, and including, is an unlikely outcome of the infarction, as too much of the lateral geniculate nucleus is, proportionally, devoted to macular-stream processing. Additional images. Project Orbis International. Archived from on 19 December 2014. Retrieved 11 October 2014.
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Hobbs RP, Bernstein PS (2014). Journal of Ophthalmic and Vision Research. 9 (4): 487–493.
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Essential Neuroscience (First Revised ed.). Baltimore, Maryland: Lippincott Williams & Wilkins. External links. Media related to at Wikimedia Commons.