fovea
Information about fovea
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Schematic diagram of the human eye, with the fovea at the bottom.
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. [1] [2] The fovea is responsible for 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. 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; 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 area that delivers information of low resolution.
Description
The term 'fovea' comes from the Latin, meaning 'pit'or 'arm pit'. As an anatomical term there are several foveae around the body, including in the head of the femur.The fovea centralis is a pit in the surface of the retinas of many types of fish, reptiles and birds and amongst mammals 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 fetal and early postnatal life. Other foveae may show only a reduced thickness in the inner cell layers, rather than an almost complete absence.
At the center of the macula, approximately on the visual axis, there is a pit (termed the "foveal pit") with a diameter of about 1.0 mm, that is associated with a high concentration of cone photoreceptors. The centre of the fovea is the foveola - about 0.2mm in diameter - where only cone photoreceptors are present and there are virtually no rods.[1] 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 interfer with the passage of light striking the foveal cone mosaic. The absence of inner retinal cells from the foveae of primates is assumed also to contribute to the high acuity function of the fovea although there is no convincing evidence to this effect, since the refractive index of the retina is not significantly different from that of the vitreous filling the pit.
Due to the lack of a retinal 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 most other mammals'.
The foveal pit is not located exactly on the optical axis, but is displaced about 4 to 8 degrees temporal to it.
The fovea is less than 1% of the retina but takes up over 50% of the visual cortex in the brain. [3] 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. [4]
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), 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.
See also
Sensory system - Visual system - Eye | |
|---|---|
| Fibrous tunic (outer) | Conjunctiva • Sclera • Schlemm's canal • Trabecular meshwork • Limbus Cornea (Epithelium, Bowman's, Stroma, Descemet's, Endothelium) |
| Uvea (middle) | Choroid (Ciliary processes, Choriocapillaris, Bruch's membrane) • Iris (Stroma) • Pupil • Ciliary body |
| Retina (inner) | Macula • Fovea • Optic disc |
| Anterior segment | Anterior chamber • Aqueous humour • Posterior chamber • Lens |
| Posterior segment | Vitreous humour • Zonular fibers • Zonule of Zinn |
Sensory system - Visual system |
|---|
| Eye • Optic nerve • Optic chiasm • Optic tract • Lateral geniculate nucleus • Optic radiation • Visual cortex • Blobs |
- Eye movement
- Eye movement in language reading
- Eye movement in music reading
- Gaze-contingency paradigm
- Macular degeneration
Additional images
) Horizontal section of the eyeball. |
References
1. ^ "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: Med-UtahEdu-retina.
2. ^ "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: IOVS-fovea-capillaries.
3. ^ "The Stimulus and Anatomy of the Visual System" (with fovea description), Hanover College, Psychology Department, HanoverCollege-Fovea-PDF-as-HTML.
4. ^ Fairchild, Mark. (1998), Color Appearance Models. Reading, Mass.: Addison, Wesley, & Longman, p.7.
2. ^ "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: IOVS-fovea-capillaries.
3. ^ "The Stimulus and Anatomy of the Visual System" (with fovea description), Hanover College, Psychology Department, HanoverCollege-Fovea-PDF-as-HTML.
4. ^ Fairchild, Mark. (1998), Color Appearance Models. Reading, Mass.: Addison, Wesley, & Longman, p.7.
Eyes are organs of vision that detect light. Different kinds of light-sensitive organs are found in a variety of organisms. The simplest eyes do nothing but detect whether the surroundings are light or dark, while more complex eyes can distinguish shapes and colors.
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macula or macula lutea (from Latin macula, "spot" + lutea, "yellow") is an oval yellow spot near the center of the retina of the human eye. It has a diameter of about 1.5 mm and is often histologically defined as having two or more layers of ganglion cells.
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- For the moth genus, see Retina (moth).
The retina is a thin layer of neural cells that lines the back of the eyeball of vertebrates and some cephalopods. It is comparable to the film in a camera.
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In psychology, visual perception is the ability to interpret visible light information reaching the eyes which is then made available for planning and action. The resulting perception is also known as eyesight, sight or vision.
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Reading is an active skill-based process of constructing meaning and/or gaining knowledge from oral, visual, and written text (including Braille).
It is a means of language acquisition, of communication, and of sharing information and ideas.
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It is a means of language acquisition, of communication, and of sharing information and ideas.
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Television (often abbreviated to TV, T.V., or more recently, tv; sometimes called telly, the tube, boob tube, or idiot box in British English) is a widely used telecommunication system for broadcasting and receiving moving pictures
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ganglion (pl. ganglia) is a tissue mass, which is composed mainly of somata and dendritic structures, which often interconnect with each other to form a complex system of ganglia known as a plexus.
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Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision.
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1 millimetre =
SI units
010−3 m 0 cm
US customary / Imperial units
010−3 ft 010−3 in
The millimetre (American spelling: millimeter, symbol mmSI units
010−3 m 0 cm
US customary / Imperial units
010−3 ft 010−3 in
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Cone cells, or cones, are photoreceptor cells in the retina of the eye which function best in relatively bright light. The cone cells gradually become more sparse towards the periphery of the retina.
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Location Retina
Function Low light photoreceptor
Morphology rod shaped
Presynaptic connections None
Postsynaptic connections Bipolar Cells and Horizontal cells
Rod cells, or rods
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Function Low light photoreceptor
Morphology rod shaped
Presynaptic connections None
Postsynaptic connections Bipolar Cells and Horizontal cells
Rod cells, or rods
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- For the moth genus, see Retina (moth).
The retina is a thin layer of neural cells that lines the back of the eyeball of vertebrates and some cephalopods. It is comparable to the film in a camera.
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In geometry, a hexagon is a polygon with six edges and six vertices. A regular hexagon has Schläfli symbol .
The internal angles of a regular hexagon (one where all sides and all angles are equal) are all 120° and the hexagon has 720 degrees.
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Regular hexagon
The internal angles of a regular hexagon (one where all sides and all angles are equal) are all 120° and the hexagon has 720 degrees.
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The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye lying between the retina and the sclera, with a thickness about 0.5 mm. The choroid provides oxygen and nourishment to the outer layers of the retina [1] .
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The retinal pigment epithelium (RPE) is the pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells, and is firmly attached to the underlying choroid and overlying retinal visual cells.
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Bruch's membrane is the innermost layer of the choroid. It is also called the vitreous lamina, because of its glassy microscopic appearance. It is 2–4 μm thick.
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- For other uses of the term "hypoxia", see hypoxia.
Hypoxia is a pathological condition in which the body as a whole (generalised hypoxia) or region of the body (tissue hypoxia) is deprived of adequate oxygen supply.
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Opsins are a group of light-sensitive 35-55 kDa membrane-bound G protein-coupled receptors of the retinylidene protein family found in photoreceptor cells of the retina. They are involved in vision, mediating the conversion of a photon of light into an electrochemical signal, the
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Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. The nervous system derives color by comparing the responses to light from the several types of cone photoreceptors in the eye.
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Mammalia
Linnaeus, 1758
Subclasses & Infraclasses
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Linnaeus, 1758
Subclasses & Infraclasses
- Subclass †Allotheria*
- Subclass Prototheria
- Subclass Theria
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In optics, the term optical axis is used to define a direction along which there is some degree of rotational symmetry. It can be used in several contexts:
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- In an optical system, the optical axis is an imaginary line that defines the path along which light propagates through
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The term visual cortex refers to the primary visual cortex (also known as striate cortex or V1) and extrastriate visual cortical areas such as V2, V3, V4, and V5.
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An astronomer or astrophysicist is a person whose area of interest is astronomy or astrophysics.
Astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences
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Astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences
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Averted vision is a technique for viewing faint objects which involves not looking directly at the object, but looking a little off to the side, while continuing to concentrate on the object.
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Xanthophylls (originally phylloxanthins) are yellow pigments from the carotenoid group. Their molecular structure is based on carotenes; contrary to the carotenes, some hydrogen atoms are substituted by hydroxyl groups and/or some pairs of hydrogen atoms are substituted by
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Carotenoids are organic pigments that are naturally occurring in plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria. There are over 600 known carotenoids; they are split into two classes, xanthophylls and carotenes.
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Zeaxanthin is one of the two carotenoids contained within the retina of the eye.
Within the central macula, zeaxanthin is the dominant component, whereas in the peripheral retina, lutein predominates.
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Within the central macula, zeaxanthin is the dominant component, whereas in the peripheral retina, lutein predominates.
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Lutein (LOO-teen) (from Latin lutea meaning "yellow") is one of over 600 known naturally occurring carotenoids. Found in green leafy vegetables such as spinach and kale, lutein is employed by organisms as an antioxidant and for blue light absorption.
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axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma.
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Anatomy
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