Fovea centralis
Schematic diagram of the human eye, with the fovea at the bottom. It shows a horizontal section through the right eye
Latin	fovea centralis

The fovea centralis, also generally known as the fovea (the term fovea comes from the Latin, meaning pit or pitfall), is a part of the eye, located in the center of the macula region of the retina. ^{[1] [2]} The fovea is responsible for sharp central vision (also called foveal vision), which is necessary in humans for reading, watching, driving, and any activity where visual detail is of primary importance. The fovea is surrounded by the parafovea belt, and the perifovea outer region.^[2] The parafovea is the intermediate belt, where the ganglion cell layer is composed of more than five rows of cells, as well as the highest density of cones; 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. The perifovea contains an even more diminished density of cones, having 12 per 100 micrometres versus 50 per 100 micrometres in the most central fovea. This, in turn, is surrounded by a larger peripheral area that delivers highly compressed information of low resolution. Approximately 50% of the nerve fibers in the optic nerve carry information from the fovea, while the other 50% carry information from the rest of the retina. The parafovea extends to a distance of 1¼ mm from the central fovea, and the perifovea is found 2¾ mm away from the fovea centralis.^[3]

Description[link]

In the human eye the term fovea (or fovea centralis) denotes the pit in the retina, which allows for maximum acuity of vision.

The diagram shows the relative acuity of the left human eye (horizontal section) in degrees from the fovea.^[4]

The human fovea has a diameter of about 1.0 mm with a high concentration of cone photoreceptors. The center of the fovea is the foveola – about 0.2 mm in diameter – where only cone photoreceptors are present and there are virtually no rods.^[1] The central fovea consists of very compact cones, thinner and more rod-like in appearance than cones elsewhere. Starting at the outskirts of the fovea, however, rods gradually appear, and the absolute density of cone receptors progressively decreases.

In the primate fovea (presumably including human) the ratio of ganglion cells to photoreceptors is about 2.5; almost every ganglion cell receives data from a single cone, and each cone feeds onto between 1 and 3 ganglion cells.^[5] Therefore, the acuity of foveal vision is limited only by the density of the cone mosaic, and the fovea is the area of the eye with the highest sensitivity to fine details.^[6]

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 hexagonal 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.

The fovea centralis is a central pit, near the optic axis. It eliminates the necessity to pass through the inner, non-sensitive neurons and allows direct passage to the receptors. It is employed for accurate vision in the direction where it is pointed. If an object is large and thus covering a large angle, the eyes must constantly shift their gaze to subsequently bring different portions of the image into the fovea (as in reading).

Since the macula 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 when under bright illumination.

Since cones contain the pigmented opsins 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 mammals.^{[citation needed]}

The fovea comprises less than 1% of retinal size but takes up over 50% of the visual cortex in the brain.^[7] 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.^[8]

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 averted vision, looking out of "the side of their eyes".

The fovea is covered in a yellow pigment called xanthophyll,^[1] with the carotenoids zeaxanthin and lutein (Balashov and Bernstein, 1998^{[citation needed]}), present in the cone axons of the Henle fibre layer.^[1] The pigment area absorbs blue light and is probably an evolutionary 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 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.

The only photo-receptors located in the fovea of most humans are three kinds of cone photo receptors. The red, blue, and green allow the eye to see the colours that humans need for survival; however, some organisms are known to possess four independent channels for conveying color information, or possessing four different types of cone cells in the eye, a characteristic called tetrachromacy. Organisms with tetrachromacy are called tetrachromats. The rods are located on the fovea's periphery. This assists the eye in seeing in the dark. Humans have an area in the centre of their fovea which lacks blue cones, possibly due to the effect of chromatic aberration on blue light.^[9]

See also[link]

• Eye movement
• Eye movement in language reading
• Eye movement in music reading
• Gaze-contingency paradigm
• Macular degeneration
• Foveated imaging

References[link]

v t e Sensory system – visual system – globe of eye (TA A15.2.1–6, TH 3.11.08.0-5, GA 10.1005) Fibrous tunic (outer) Sclera Episcleral layer • Schlemm's canal • Trabecular meshwork Cornea Limbus • layers (Epithelium, Bowman's, Stroma, Descemet's, Endothelium) Uvea/vascular tunic (middle) Choroid Capillary lamina of choroid • Bruch's membrane • Sattler's layer Ciliary body Ciliary processes • Ciliary muscle Iris Stroma • Pupil • Iris dilator muscle • Iris sphincter muscle Retina (inner) Layers Inner limiting membrane • Nerve fiber layer • Ganglion cell layer • Inner plexiform layer • Inner nuclear layer Outer plexiform layer • Outer nuclear layer External limiting membrane • Layer of rods and cones • Retinal pigment epithelium Cells Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Retina ganglion cell (Midget cell, Parasol cell, Bistratified cell, Giant retina ganglion cells, Photosensitive ganglion cell) → Diencephalon: P cell, M cell, K cell Muller glia Other Macula (Foveola, Fovea centralis) • Optic disc (Optic cup) Anterior segment Anterior chamber • Aqueous humour • Posterior chamber • Lens (Capsule of lens, Zonule of Zinn) Posterior segment Vitreous humour Other Ocular immune system • Tapetum lucidum • Keratocytes M: EYE anat(g/a/p)/phys/devp/prot noco/cong/tumr, epon proc, drug(S1A/1E/1F/1L)

Ron Haviv (1965)^[1] is a photojournalist, producing work covering a broad spectrum of international conflict. He is the author of several photographic collections and the recipient of a number of awards. Haviv is also a co-founder of VII Photo Agency, which is dedicated to documenting change, conflict, and development of individuals, cultures and societies worldwide. He also lectures at universities, conducts workshops worldwide, and has appeared on a number of television news shows.

Biography[link]

A graduate of New York University^[2], Ron Haviv has covered conflict and other humanitarian crises worldwide since the end of the Cold War. Haviv is known for his broad documentation of the Yugoslav Wars: the battle of Vukovar in Croatia, the Siege of Sarajevo, the atrocities committed at Serb concentration camps in Bosnia and Herzegovina, and the practice of ethnic cleansing as exhibited by Arkan's Tigers.^[3]

He has also photographed the city of Juárez,^[4] a battleground of the Mexican Drug War where civilian, law enforcement and cartel member casualties occur daily.^[5] Additionally, Haviv is noted for his coverage of the destruction of the 2010 Haiti Earthquake, as well as the subsequent Cholera epidemic, and celebrity support and involvement in its reconstruction. Haviv's photography also sheds light on malnutrition in Bangladesh, clashes between Los Angeles gangs and police forces, the 2009 Afghan presidential elections, the Sri Lankan Civil War, the struggle for children in Darfur, among many other situations of conflict.

Haviv’s images have been distributed widely by various publications including Business Week, Fortune, Le Monde, Newsweek, The New York Times Magazine, The New Yorker, Paris Match, Vanity Fair, Vogue, Time, and US News & World Report, among others worldwide. Additionally, numerous museums and galleries have featured his work, including the Louvre, the United Nations, and the Council on Foreign Relations. Haviv has spoken about his work on ABC World News, BBC, CNN, NPR, MSNBC, NBC Nightly News, Good Morning America and The Charlie Rose Show.^[6]

Haviv’s photography has been collected and published in the critically acclaimed books: Blood and Honey: A Balkan War Journal, Afghanistan: On the Road to Kabul, and Haiti: 12 January 2010. He is one of seven co-founders of VII Photo Agency, formed in 2001, along with Alexandra Boulat, Gary Knight, Antonin Kratochvil, Christopher Morris, James Nachtwey and John Stanmeyer. Haviv has channeled his focus on raising awareness for human rights violations by helping to create multi-platform projects for NGO’s, such as Doctors Without Borders’ DR Congo missions: The Forgotten War and Starved for Attention, UNICEF’s Child Alert for Darfur and Sri Lanka, and the International Committee of the Red Cross’ World at War.

Bibliography[link]

• Blood and Honey: A Balkan War Journal
• Afghanistan: On the Road to Kabul
• Haiti: 12 January 2010

Selected Solo Exhibitions[link]

Haiti: January 12, 2010

• VII Gallery, New York, NY (2010)
• Fovea Gallery, New York, NY (2010)

Children of Darfur

• San Francisco Mission Cultural Center, San Francisco, CA (2008)
• International Human Rights Film Festival, New Orleans, LA (2008)
• University of California, Los Angeles, CA (2006)
• The United Nations, New York, NY (2005)

Blood and Honey: A Balkan War Journal

• War Photo Museum, Dubrovnik, Croatia (2003-2010)
• Southeast Museum of Photography, Daytona Beach, FL (2005)
• Queen's Museum, Belfast, Northern Ireland (2005)
• Rex Cultural House, Belgrade, Serbia (2002)
• Freedom Forum, London, England (2001)
• Skopje Cultural Museum, Skopje, Macedonia (2001)
• National Gallery, Sarajevo, Bosnia and Herzegovina (2000)
• Saba Gallery, New York, NY (2000)

Afghanistan: The Road to Kabul

• Grazia Neri, Milan, Italy (2002)
• 92nd Street Y, New York, NY (2002)

Images of War

• Bayeux, France (2001)
• The Council on Foreign Relations, New York, NY (1999)
• International Festival of Photojournalism, Gijon, Spain (1999)
• The Newseum, New York, NY (1997)
• Fotofusion, Palm Beach, FL (1996)
• Perpignan, France (1995)

Selected Group Exhibitions[link]

• World at War, Newseum, Washington, D.C. (2009)
• Humankind, Hasted Hunt, New York, NY (2008)
• Act of Faith, The Noorderlicht Photofestival, Groningen, Netherlands (2007)
• DR Congo: The Forgotten War, Stephen Cohen Gallery, Los Angeles, CA (2006)
• VII, Hasted Hunt, New York, NY (2005)
• War Envoy, Verona, Italy (2005)
• WAR, International Center of Photography, New York, NY (2004)
• New York to Kabul, Louvre, Paris, France (2002)

References[link]

External links[link]

• Website
• VII Photo Agency
• Eyewitness: Ron Haviv photos of The Tigers massacring Bosniaks