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Encyclopedia > Iris (anatomy)
Iris
The iris is the green/grey/brown area. The other structures visible are the pupil in the centre and the white sclera surrounding the iris. The overlying cornea is pictured, but not visible, as it is transparent.
Schematic diagram of the human eye. (Iris labeled at upper left.)
Gray's subject #225 1012
Artery long posterior ciliary arteries
Nerve long ciliary nerves, short ciliary nerves
MeSH Iris

In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. The following describes the iris of vertebrates, not the independently evolved iris found in some cephalopods. The word comes from Greek mythology, in which Iris is the anthropomorphized form of the rainbow. ImageMetadata File history File links Humaniris. ... The human eye The pupil is the central transparent area (showing as black). ... Schematic diagram of the human eye. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Image File history File links Schematic_diagram_of_the_human_eye_en. ... Section of an artery For other uses, see Artery (disambiguation). ... The long posterior ciliary arteries, two in number, pierce the posterior part of the sclera at some little distance from the optic nerve, and run forward, along either side of the eyeball, between the sclera and choroid, to the ciliary muscle, where they divide into two branches. ... Nerves (yellow) Nerves redirects here. ... The long ciliary nerves, two or three in number, are given off from the nasociliary, as it crosses the optic nerve. ... The branches of the ciliary ganglion are the short ciliary nerves. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Human heart and lungs, from an older edition of Grays Anatomy. ... For other uses, see Eye (disambiguation). ... This article does not cite any references or sources. ... This article is about modern humans. ... In evolutionary biology, convergent evolution is the process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. ... Orders Subclass Nautiloidea †Plectronocerida †Ellesmerocerida †Actinocerida †Pseudorthocerida †Endocerida †Tarphycerida †Oncocerida †Discosorida Nautilida †Orthocerida †Ascocerida †Bactritida Subclass †Ammonoidea †Goniatitida †Ceratitida †Ammonitida Subclass Coleoidea †Belemnoidea †Aulacocerida †Belemnitida †Hematitida †Phragmoteuthida Neocoleoidea (most living cephalopods) ?†Boletzkyida Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida The cephalopods (Greek plural (kephalópoda); head-foot) are the mollusk class... The bust of Zeus found at Otricoli (Sala Rotonda, Museo Pio-Clementino, Vatican) Greek mythology is the body of stories belonging to the Ancient Greeks concerning their gods and heroes, the nature of the world and the origins and significance of their own cult and ritual practices. ... Iris, by Luca Giordano In Greek mythology, Iris is the personification of the rainbow and messenger of the gods. ...


The iris consists of pigmented fibrovascular tissue known as a stroma. The stroma connects a sphincter muscle (sphincter pupillae), which contracts the pupil, and a set of dilator muscles (dilator pupillae) which open it. The back surface is covered by an epithelial layer two cells thick (the iris pigment epithelium), but the front surface has no epithelium. The outer edge of the iris, known as the root, is attached to the sclera and the anterior ciliary body. The iris and ciliary body together are known as the anterior uvea. Just in front of the root of the iris is the region through which the aqueous humour constantly drains out of the eye, with the result that diseases of the iris often have important effects on intraocular pressure, and indirectly on vision. Natural Ultramarine pigment in powdered form. ... The stroma of the iris consists of fibers and cells. ... Look up Sphincter in Wiktionary, the free dictionary. ... The iris sphincter muscle (pupillary sphincter, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. ... The human eye The pupil is the central transparent area (showing as black). ... The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a muscle of the eye. ... This article is about the epithelium as it relates to animal anatomy. ... Schematic diagram of the human eye. ... Schematic diagram of the human eye The ciliary body is the part of the eye containing the ciliary muscle and ciliary processes. ... Schematic diagram of the human eye. ... Intraocular pressure (IOP) is the fluid pressure inside the eye. ...

Contents

General structure

The iris is divided into two major regions:

  1. The pupillary zone is the inner region whose edge forms the boundary of the pupil.
  2. The ciliary zone is the rest of the iris that extends to its origin at the ciliary body.

The collarette is the region of the iris separating the pupillary portion from the ciliary portion. It is typically defined as the region where the sphincter muscle and dilator muscle overlap.


Histological features

From anterior (front) to posterior (back), the layers of the iris are:

The stroma of the iris consists of fibers and cells. ... The Iris sphincter muscle is a muscle of the human body. ... The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a muscle of the eye. ...

Anterior surface features

  • The Crypts of Fuchs are a series of openings located on either side of the collarette that allow the stroma and deeper iris tissues to be bathed in aqueous humor. Collagen trabeculae that surround the border of the crypts can be seen in blue irises.
  • The pupillary ruff is a series of small ridges at the pupillary margin formed by the continuation of the pigmented epithelium from the posterior surface.
  • The Circular contraction folds, also known as contraction furrows, are a series of circular bands or folds about midway between the collarette and the origin of the iris. These folds result from changes in the surface of the iris as it dilates.
  • Crypts at the base of the iris are additional openings that can be observed close to the outermost part of the ciliary portion of the iris.

Posterior surface features

  • The Radial contraction folds of Schwalbe are a series of very fine radial folds in the pupillary portion of the iris extending from the pupillary margin to the collarette. They are associated with the scalloped appearance of the pupillary ruff.
  • The Structural folds of Schwalbe are radial folds extending the length of the iris that are much broader and more widely-spaced.
  • The Circular contraction folds are a fine series of ridges that run in a circular pattern over the entire posterior surface.

Embryology

The various structures of the iris ultimately originate from two of the three primary germ layers of the developing embryo. The stroma derives from mesoderm; the sphincter pupillae and dilator pupillae muscles, as well as the anterior and posterior pigmented epithelium, derive from neural ectoderm. Organs derived from each germ layer. ... Stroma can refer to: The connective supportive framework of a biological cell, tissue, or organ. ... The mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... The iris sphincter muscle (pupillary sphincter, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. ... The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a muscle of the eye. ... The ectoderm is outermost of the three germ layers of the developing embryo, the other two being the mesoderm and the endoderm. ...


Color

Main article: Eye color
Among human phenotypes, Blue-Green-Grey eyes are a relatively rare eye color and the exact color is often perceived to vary according to its surroundings

The iris is usually strongly pigmented, with colors ranging from brown to green, blue, grey, and hazel. Occasionally its color is due to lack of pigmentation, as in the pinkish-white of oculo-cutaneous albinism, or to obscuration of its pigment by blood vessels, as in the red of an abnormally vascularised iris. Despite the wide range of colors, there is only one pigment that contributes substantially to normal human iris color, the dark pigment called melanin. Structurally, this huge molecule is only slightly different from its equivalent found in skin and hair. Brown eyes redirects here. ... Image File history File links Green-grey-eyes. ... Image File history File links Green-grey-eyes. ... Natural Ultramarine pigment in powdered form. ... Color is an important part of the visual arts. ... Albino redirects here. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ... Beyond overall skin structure, refer below to: See-also. ... For the 1968 stage production, see Hair (musical), for the 1979 film, see Hair (film). ...


Genetic and physical factors determining iris colour

Iris colour is a highly complex phenomenon consisting of the combined effects of texture, pigmentation, fibrous tissue and blood vessels within the iris stroma, which together make up an individual's epigenetic constitution in this context. A person's "eye colour" is actually the colour of one's iris, the cornea being transparent and the white sclera entirely outside the area of interest. It is a common misconception that the iris color is entirely due to its melanin pigment; this varies only from brown to black. Stroma can refer to: The connective supportive framework of a biological cell, tissue, or organ. ... Epigenetic inheritance is the transmission of information from a cell or multicellular organism to its descendants without that information being encoded in the nucleotide sequence of the gene. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Schematic diagram of the human eye. ...

An example of a Blue-Gray Iris

Melanin is yellowish-brown to dark brown in the stromal pigment cells, and black in the iris pigment epithelium, which lies in a thin but very opaque layer across the back of the iris. Most human irises also show a condensation of the brownish stromal melanin in the thin anterior border layer, which by its position has an overt influence on the overall color. The degree of dispersion of the melanin, which is in subcellular bundles called melanosomes, has some influence on the observed color, but melanosomes in the iris of humans and other vertebrates are not mobile, and the degree of pigment dispersion cannot be reversed. Abnormal clumping of melanosomes does occur in disease and may lead to irreversible changes in iris color (see heterochromia, below). Colors other than brown or black are due to selective reflection and absorption from the other stromal components. Sometimes lipofuscin, a yellow "wear and tear" pigment also enters into the visible eye color, especially in aged or diseased green eyes (but not in healthy green human eyes). Image File history File links Bluishgrayeye. ... Image File history File links Bluishgrayeye. ... Anatomy The iris pigment epithelium (IPE) is a two-cell thick layer of cuboidal cells lying behind the iris. ... Anterior border can refer to: Anterior margin of pancreas Anterior border of lung Category: ... In a biological cell, a melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom. ... For the tightly packed form of DNA, see Heterochromatin. ... Lipofuscin is the name given to brown pigment granules composed of lipid-containing residues of lysosomal digestion. ...


The optical mechanisms by which the non-pigmented stromal components influence eye color are complex, and many erroneous statements exist in the literature. Simple selective absorption and reflection by biological molecules (hemoglobin in the blood vessels, collagen in the vessel walls and stroma) is the most important element. Rayleigh scattering and Tyndall scattering, (which also happen in the sky) and diffraction also occur. Raman scattering, and constructive interference, as in the feathers of birds, do not contribute to the color of the human eye, but interference phenomena are important in the brilliantly colored iris pigment cells (iridophores) in many animals. Interference effects can occur at both molecular and light microscopic scales, and are often associated (in melanin-bearing cells) with quasi-crystalline formations which enhance the optical effects. Interference is recognised by characteristic dependence of color on the angle of view, as seen in eyespots of some butterfly wings, although the chemical components remain the same. Structure of hemoglobin. ... Tropocollagen triple helix. ... Rayleigh scattering causing the blue hue of the sky and the reddening at sunset Rayleigh scattering (named after Lord Rayleigh) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ... Shot of sunbeams breaking through nebula bank The term Tyndall effect is usually applied to the effect of light scattering on particles in colloid systems, such as suspensions or emulsions. ... The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ... Raman scattering or the Raman effect is the inelastic scattering of a photon. ... For other uses, see Interference (disambiguation). ... Iridophores are a type of chromatophore cell found in the skin of many cephalopods, fish and reptiles. ... Eyespot can refer to: Eyespot (insect photoreceptor): The area of an arthropod body (especially an insect) where the ocelli (photoreceptors) are located; Eyespot (mimicry): A form of automimicry in which a spot on the body of an animal resembles an eye of a different animal to deceive potential predator or... Superfamilies and families Superfamily Hedyloidea: Hedylidae Superfamily Hesperioidea: Hesperiidae Superfamily Papilionoidea: Papilionidae Pieridae Nymphalidae Lycaenidae Riodinidae A butterfly is an insect of the order Lepidoptera. ... For other uses, see Wing (disambiguation). ...


Blue is one of the possible eye colors in humans. The "blue" allele, existing in the Bey2 and Gey genes of chromosome 15, is recessive. This means that both genes must have both blue alleles i.e. "blue-blue", in a person with blue eyes. If one of the alleles were not "blue" ("green" for Gey or "brown" for Bey2) then the person would have those colored eyes respectively. As either allele (though not both) can be passed on to offspring it is perfectly possible for someone who does not have blue eyes to have blue-eyed children. In general, blue eyed parents have blue eyed children; rare exceptions occur due to genes which control the patway to determining eye color. Though this explanation gives an idea of eye color delineation, it is incomplete, and all the contributing factors towards eye color and its variation are not fully understood. For the hard rock band, see Allele (band). ... Chromosome 15 is one of the 23 pairs of chromosomes in humans. ... In genetics, the term recessive gene refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in a homozygous genotype (an organism that has two copies of the same allele). ...


Different colors in the two eyes

Main article: Heterochromia
An example of heterochromia. The subject has a brown and hazel eye.

Heterochromia (also known as a heterochromia iridis or heterochromia iridium) is an ocular condition in which one iris is a different color from the other iris (complete heterochromia), or where the part of one iris is a different color from the remainder (partial heterochromia or sectoral heterochromia). Uncommon in humans, it is often an indicator of ocular disease, such as chronic iritis or diffuse iris melanoma, but may also occur as a normal variant. Sectors or patches of strikingly different colors in the same iris are less common. Alexander the Great and Anastasios the First were dubbed dikoro*s (dikoros, "with two pupils") for their patent heterochromias. In their case, this was not a true dicoria (two pupils in the same iris). Real polycoria can be due to disease but is most often due to previous trauma or surgery. For the tightly packed form of DNA, see Heterochromatin. ... Image File history File links Download high resolution version (1071x250, 355 KB) Summary Photograph of a Hispanic woman with heterochromia. ... Image File history File links Download high resolution version (1071x250, 355 KB) Summary Photograph of a Hispanic woman with heterochromia. ... For the tightly packed form of DNA, see Heterochromatin. ... For the film of the same name, see Alexander the Great (1956 film). ... Flavius Anastasius or Anastasius I (c. ... Polycoria is a pathological condition of the eye characterized by more than one pupillary opening in the iris. ...


In contrast, heterochromia and variegated iris patterns are common in veterinary practice. Siberian Huskies show heterochromia, possibly analogous to the genetically-determined Waardenburg syndrome of humans. Some white cat fancies (e.g., white Persians) may show striking heterochromia, with the commonest pattern being one uniformly blue, the other green. Striking variegation within the same iris is also common in some animals, and is the norm in some species. Several herding breeds, particularly those with a blue merle coat color (such as Australian Shepherds and Border Collies) may show well-defined blue areas within a brown iris as well as separate blue and darker eyes. Some horses (usually within the white, spotted, palomino or cremello groups of breeds) may show amber, brown, white, and blue all within the same eye, without any sign of eye disease. The Siberian Husky is a medium-size, dense-coat working dog breed that originated in eastern Siberia, belonging to the Spitz genetic family. ... Waardenburg syndrome is a rare genetic disorder most often characterized by varying degrees of deafness, minor defects in structures arising from the neural crest, and pigmentation anomalies. ... Blue merle Border Collie puppy Merle is a colour combination in dogs’ coats. ... The Australian Shepherd is a breed of working dog that was developed in the Western United States in the 19th century from several different breeds. ... The Border Collie is a breed of herding dog that originated in the border country of England and Scotland. ...


One eye with a white or bluish-white iris is also known as a walleye.


Diseases

Diseases which involve the iris include: ocular albinism, aniridia, iris coloboma, iritis, iris melanoma, iris metastases and Waardenburg syndrome. Albino redirects here. ... Aniridia is a rare congenital condition characterized by the underdevelopment of the eyes iris. ... A coloboma (also part of the rare Cat Eye syndrome) is the term used to describe a hole in one of the structures of the eye, such as the lens, eyelid, iris, retina, choroid or optic disc. ... Iritis is a form of anterior uveitis and refers to the inflammation of the iris of the eye. ... Melanoma is a malignant tumor of melanocytes which are found predominantly in skin but also in the bowel and the eye (see uveal melanoma). ... Metastasis (Greek: change of the state) is the spread of cancer from its primary site to other places in the body. ... Waardenburg syndrome is a rare genetic disorder most often characterized by varying degrees of deafness, minor defects in structures arising from the neural crest, and pigmentation anomalies. ...


"Red eye"

When photographed with a flash, the iris constricts but not fast enough to avoid the red-eye effect. This represents reflection of light from the back of the eye, and is closely related to the term red reflex, used by ophthalmologists and optometrists in describing appearances on fundal examination. The red-eye effect The red-eye effect is seen in animals as well. ...


When used as a descriptive term in medicine, the meaning of "red eye" is quite different, and indicates that the bulbar conjunctiva is reddened due to dilatation of superficial blood vessels. Leaving aside rarities, it indicates surface infection (conjunctivitis), intraocular inflammation (e.g., iridocyclitis) or high intraocular pressure (acute glaucoma or occasionally severe, untreated chronic glaucoma). This use of "red eye" implies disease. The term is therefore not used in medicine for ocular albinism, in which the eye is otherwise healthy despite an obviously red pupil and a translucent pinkish iris due to reflected light from the fundus. "Red eye" is used more loosely in veterinary practice, where investigation of eye diseases can be difficult, but even so albinotic breeds are easily recognised and are usually described as having "pink eye" rather than "red eye". Iridocyclitis, also known as anterior uveitis, is a condition in which the uvea of the eye suffers inflammation. ... Human eye cross-sectional view. ...


See also

Albino redirects here. ... Brushfield spots are small white spots on the periphery of the iris and are a feature of Down syndrome. ... Brown eyes redirects here. ... It has been suggested that this article or section be merged with Gaze aversion. ... Iridocyclitis, also known as anterior uveitis, is a condition in which the uvea of the eye suffers inflammation. ... Iridodialysis, sometimes known as a coredialysis, is a localized separation or tearing away of the iris from its attachment to the ciliary body. ... Iridology, also known as iridodiagnosis[1], is an alternative medicine practice in which patterns, colors, and other characteristics of the iris are examined for information about a patients systemic health. ... An iris scan is one of the most currently used methods of biometric authentication. ... For the actress who plays Tracy Quartermaine on General Hospital, please see Jane Elliot. ... In medicine, synechia refers to an adhesion, usually involving the iris (see article below) but also within the uterus as in Ashermans syndrome. ... The visual system is the part of the nervous system which allows organisms to see. ...

Additional images

External links


  Results from FactBites:
 
Iris (anatomy) - Wikipedia, the free encyclopedia (1999 words)
The iris is an annulus (or flattened ring) consisting of pigmented fibrovascular tissue known as a stroma.
Just in front of the root of the iris is the region through which the aqueous humour constantly drains out of the eye, with the result that diseases of the iris often have important effects on intraocular pressure, and indirectly on vision.
Iris color is a highly complex phenomenon consisting of the combined effects of texture, pigmentation, fibrous tissue and blood vessels within the iris stroma, which together make up an individual's epigenetic constitution.
Encyclopedia: Iris (anatomy) (4261 words)
In Greek mythology, Iris was the daughter of Thaumas and the ocean nymph Electra and one of the Oceanids (according to Hesiod), the personification of the rainbow and messenger of the gods.
Definitions The iris in vertebrates (and even chordates at large) is an apposition of two classes of biological tissue material, of distinct embryological origins: the epithelia, posteriorly (towards the posterior pole of the eyeball) the stroma, anteriorly (towards the anterior pole of the eyeball) Origins The epithelia are two in...
Anatomy The iris pigment epithelium (IPE) is a two-cell thick layer of cuboidal cells lying behind the iris.
  More results at FactBites »

 
 

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