Fovea 749853 225785658 2008-07-15T11:42:53Z ToePeu.bot 4082686 robot Adding: [[he:רשתית#.D7.9E.D7.91.D7.A0.D7.94_.D7.A8.D7.A9.D7.AA.D7.99.D7.AA_.D7.94.D7.90.D7.93.D7.9D]] [[Image:Schematic diagram of the human eye en.svg|thumb|350px|Schematic diagram of the human eye, with the fovea at the bottom. It shows a horizontal section through the right eye]] The '''fovea''', also known as the '''fovea centralis''', is a part of the [[eye]], located in the center of the [[macula]] region of the [[retina]]. <ref name=WebvisionRetina> "Webvision: Simple Anatomy of the Retina" (definition of terms), University of Utah, Webvision: The Organization of the Retina and Visual System, September 2005, Webvision.med.utah.edu webpage: [http://webvision.med.utah.edu/sretina.html Med-UtahEdu-retina]. </ref> <ref name=IOVSnomen> "Relation Between Superficial Capillaries and Foveal Structures in the Human Retina" (with nomenclature of fovea terms), Masayuki Iwasaki and Hajime Inomara, ''Investigative Ophthalmology & Visual Science'' (journal), volume 27, pages 1698-1705, 1986, IOVS.org, webpage: [http://www.iovs.org/cgi/reprint/27/12/1698.pdf IOVS-fovea-capillaries]. </ref> The fovea is responsible for sharp central [[Visual perception|vision]] (also called [[foveal]] vision), which is necessary in humans for [[reading (activity)|reading]], watching [[television]] or movies, driving, and any activity where visual detail is of primary importance. The fovea is surrounded by the ''parafovea'' belt, and the ''perifovea'' outer region:<ref name=IOVSnomen/> the parafovea is the intermediate belt where the [[ganglion]] cell layer is composed of more than five rows of cells; 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. This, in turn, is surrounded by a larger [[peripheral vision|peripheral]] area that delivers highly compressed information of low resolution. The [[optic nerve]] carries approximately 50% of nerve fibers for transmitting information from the fovea, while the other 50% carry information from the rest of the retina. ==Description== The term ''fovea'' comes from the Latin, meaning ''pitty'' or ''pitfall''. As an anatomical term, there are several foveae around the body, including in the head of the [[femur]]. In the human eye the term ''fovea'' (or ''fovea centralis'') denotes the pit in the [[retina]] which allows for 100% acuity of vision. [[Image:AcuityHumanEye.jpg |270px |thumb |left| The diagram shows the relative acuity of the right human eye (horizontal section) in degrees from the fovea.<ref>Hans-Werner Hunziker, (2006) Im Auge des Lesers: foveale und periphere Wahrnehmung - vom Buchstabieren zur Lesefreude [ The function of the fovea is to catch detailed visual information 3 to 4 times per second at different parts of the [[visual field]]. The brain integrates these informations within the framework of the condensed [[peripheral vision]] (extra-foveal information). the eye of the reader: foveal and peripheral perception - from letter recognition to the joy of reading] Transmedia Stäubli Verlag Zürich 2006 ISBN 978-3-7266-0068-6</ref> ]] In the human fovea the ratio of [[ganglion cell]]s to [[photoreceptor]]s is close to one; almost every photoreceptor has one ganglion cell receiving data from it. That is why it has little loss of sensory data, thus it is the area of the eye where most details can be seen.<ref>''Smithsonian/The National Academies''. <u>Light:Student guide and Source Book.</u> Published by Carolina Biological Supply Company, 2002. ISBN 0-89278-892-5.</ref> The human fovea has a diameter of about 1.0 mm with a high concentration of [[Cone cell|cone photoreceptor]]s. The centre of the fovea is the foveola - about 0.2&nbsp;mm in diameter - where only cone photoreceptors are present and there are virtually no [[rod cell|rods]].<ref name=WebvisionRetina/> Compared to the rest of the [[retina]], the cones in the foveal pit have a smaller diameter and can therefore be more densely packed (in a [[hexagon]]al pattern). The high spatial density of cones accounts for the high visual acuity capability at the fovea. This is enhanced by the local absence of retinal blood vessels from the fovea, which, if present, would interfere with the passage of [[light]] striking the foveal cone mosaic. The absence of inner retinal cells from the foveae of primates is assumed to contribute further to the high acuity function of the fovea. Since the retina does not have a [[blood supply]], the fovea must receive [[oxygen]] from the vessels in the [[choroid]], which is across the [[retinal pigment epithelium]] and [[Bruch's membrane]]. This blood supply alone does not satisfy the metabolic needs of the fovea under conditions of bright light, and the fovea thus exists in a state of [[Hypoxia (medical)|hypoxia]] when under bright illumination. Since cones contain the pigmented [[opsin]]s that allow humans to discriminate color, the fovea is largely responsible for the [[color vision]] in [[humans]] which is superior to that of most other [[mammal]]s. The fovea comprises less than 1% of retinal size but takes up over 50% of the [[visual cortex]] in the brain. <ref> "The Stimulus and Anatomy of the Visual System" (with fovea description), Hanover College, Psychology Department, [http://72.14.209.104/search?q=cache:lKxaO6dAKrsJ:psych.hanover.edu/classes/sensation/chapters/Chapter%25203.doc HanoverCollege-Fovea-PDF-as-HTML]. </ref> The foveal pit is not located exactly on the [[optical axis]], but is displaced about 4 to 8 degrees temporal to it. The fovea sees only the central two degrees of the visual field, which is roughly equivalent to twice the width of your thumbnail at arm's length.<ref> Fairchild, Mark. (1998), <u>''Color Appearance Models''</u>. Reading, Mass.: Addison, Wesley, & Longman, p.7. </ref> 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. [[Astronomer]]s know this: in order to observe a dim star, they use [[averted vision]], looking out of "the side of their eyes". The fovea is covered in a yellow pigment called [[xanthophyll]],<ref name=WebvisionRetina/> with the [[carotenoid]]s [[zeaxanthin]] and [[lutein]] (Balashov and Bernstein, 1998), present in the cone [[axon]]s of the Henle fibre layer.<ref name=WebvisionRetina/> The pigment area absorbs blue light and is probably an [[evolution]]ary adaptation to the problem of [[chromatic aberration]]. 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 which elsewhere in the retina form more superficial layers having been displaced away from the foveal region during late [[fetus|fetal]] and early [[postnatal]] life. Other foveae may show only a reduced thickness in the inner cell layers, rather than an almost complete absence. ==See also== *[[Eye movement]] *[[Eye movement in language reading]] *[[Eye movement in music reading]] *[[Gaze-contingency paradigm]] *[[Macular degeneration]] *[[foveal]] system ==References== {{reflist}} {{Eye}} {{Visual_system}} [[Category:Eye]] [[bn:ফোভিয়া]] [[ca:Fòvea òptica]] [[de:Fovea centralis]] [[es:Fóvea]] [[fr:Fovéa]] [[ko:중심와]] [[it:Fovea]] [[he:רשתית#.D7.9E.D7.91.D7.A0.D7.94_.D7.A8.D7.A9.D7.AA.D7.99.D7.AA_.D7.94.D7.90.D7.93.D7.9D]] [[nl:Fovea centralis]] [[pl:Dołek środkowy siatkówki oka]] [[pt:Fóvea]] [[sk:Fovea]] [[sv:Fovea]]