The human iris
The iris is the green/grey/brown area. The other structures visible are the pupil in irs the centre and the white sclera surrounding the iris. The overlying cornea iis is pictured, but not visible, as it is transparent.
Schematic diagram of the oris human eye.
In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, ris including humans. The following describes the iris of vertebrates, not the independently evolved iris found in iria some cephalopods. The word comes from Greek mythology, iri in which Iris is the personification of the rainbow.
The iris iras consists of pigmented fibrovascular tissue known as a stroma. The stroma connects a sphincter muscle itis (sphincter pupillae), which contracts the pupil, and a set of dialator muscles (dilator pupillae) which irls open it. The back surface is covered by an epithelial layer irus two cells thick (the iris pigment epithelium), but the front surface has no uris epithelium. The outer edge of the iris, known as the root, is attached irix to the sclera and the anterior ciliary body. The iris and ciliary body together riis are known as the anterior uvea. Just in front irid of the root of the iris is the region through which the aqueous humour constantly irsi drains out of the eye, with the result that ifis diseases of the iris often have important effects on intraocular pressure, and indirectly irris on vision.
- 1 General structure
- 1.1 Histological features
- 1.2 Anterior iirs surface features
- 1.3 Posterior surface features
- 2 Iris lris Embryology
- 3 Color
- 3.1 Genetic and physical factors determining iros iris color
- 3.2 Altering the iris color
- 3.3 Iris color as paternity test
- 3.4 Different iris goo goo dolls iris colors in the two eyes
- 3.5 Iris diseases
- 4 "Red eye"
- 5 See iris goo goo dolls also
The iris is divided into two major regions:
- The pupillary zone is the iris mp3 inner region whose edge forms the boundary of the pupil.
- The ciliary zone is iris chacon the rest of the iris that extends to iris bahr its origin at the ciliary body.
The collarette is the region of the iris separating the pupillary portion from the ciliary iris folding portion. It is typically donnie iris defined as the region where the sphincter muscle and dilator muscle overlap.
From anterior (front) to posterior (back), the layers of the iris are:
- Anterior border layer
- Sphincter muscle
- Dilator muscle
- Anterior pigment epithelium
- Posterior pigment iris kyle epithelium
Anterior surface features
- The Crypts of Fuch are a series of openings located on either goo goo dolls- iris side of the collarette that allow the stroma and deeper iris tissues to be bathed in aqueous humor. Collagen trabeculae that surround the border durgin iris of the crypts can be seen in blue irises.
- The pupillary ruff is iris dement a series of small ridges at the pupillary margin formed by the continuation of iris ministries the pigmented epithelium from the iris lyrics posterior surface.
- The Circular contraction folds, also known as contraction furrows, are a series of circular bands or folds about bearded iris midway between the collarette and the through the iris origin of the iris. These folds result from changes in the surface of the iris as it dilates.
- Crypts at the base of iris berben the iris are blue iris additional openings that can be observed close to the outermost part of the ciliary portion of the iris.
Posterior surface iris giclee features
- The Radial contraction folds of Schwalbe are iris googoo dolls a series of very fine radial folds in the pupillary portion of the iris extending from the pupillary giclee iris prints margin to the collarette. They are associated with the scalloped appearance of the pupillary ruff.
- The Structural folds iris recognition of Schwalbe are radial folds extending the length of iris angel baby the iris that are much broader and more widely-spaced.
- The Circular contraction folds are iris johansen a fine series of ridges that run in a circular pattern over the entire posterior surface.
The various iris by goo goo dolls structures of the iris ultimately originate from two of the three primary germ layers. The stroma derives from mesoderm (mesenchyme); the free patterns for iris folding sphincter and dilator muscles, as well as googoo dolls iris the anterior and posterior pigmented epithelium, derive from ectoderm the goo goo dolls iris (neural ectoderm).
Among human phenotypes, Blue-Green-Grey eyes are a relatively rare eye iris folding patterns color and the exact color is often perceived to vary according to its free iris folding patterns surroundings
The iris is usually iris bulbs strongly pigmented, with colors ranging from brown to green, blue, grey, and hazel. Occasionally its color is due to iris goo goo lack of pigmentation, as in the pinkish-white of oculo-cutaneous albinism, or to gardening iris obscuration of its pigment by blood vessels, as in the red of an abnormally vascularised iris flowers iris (although human albinos generally have very light blue eyes, as the planting iris unpigmented color of the human iris is a pale blue). Despite the wide range of colors, iris ronan keating there is iris santos only one pigment that contributes substantially to normal human iris color, the dark pigment called melanin. Structurally, this iris estrada huge molecule is only slightly different from its equivalent found in skin and hair.
Genetic and physical factors goo goo dolls, iris determining iris color
Iris color siberian iris is a highly complex phenomenon consisting of the combined effects of texture, pigmentation, fibrous tissue iris by the goo goo dolls and blood vessels within the iris stroma, which together make up an individual's epigenetic glen iris realestate constitution. A person's "eye color" is actually iris goo the color of one's iris, the cornea being transparent and the white sclera entirely outside the area of interest. It is a iris catalog common misconception that the iris color is goo goo dolls + iris entirely due to its melanin pigment; this varies only from brown to black.
Melanin is buy iris online yellowish-brown to dark brown in the stromal pigment cells, and black in the iris pigment epithelium, which donny iris lies in a thin but very opaque layer across the back japanese iris of the iris. Most human irises also show a condensation of the brownish stromal melanin in the thin anterior border african iris layer, which by its position has an overt influence on the overall goo goo dolls iris lyrics color. The iris goddess 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 by durgin iris of man and other vertebrates are not mobile, iris care and the degree of pigment dispersion cannot be reversed. Abnormal clumping of melanosomes does occur in iris goddess of the rainbow disease and may lead to irreversible changes in iris color (see heterochromia, below). iris goo goo dolls mp3 Colors other than brown or black are due to selective reflection and absorption goo goo dolls: iris from the other stromal components. Sometimes lipofuscin, a yellow "wear and iris chacon gallery iris chacon tear" pigment also enters into the iris murdoch visible eye color, especially in aged or diseased green eyes (but not in healthy green human eyes).
The optical mechanisms by which the non-pigmented 10 years through the iris stromal components influence eye color are complex, and glen iris inn many erroneous statements exist in the iris acoustic literature. Simple selective absorption and reflection by biological molecules (hæmoglobin in the blood vessels, collagen iris carving in the vessel walls and stroma) is the most important element. Rayleigh scattering (which iris mokshefski also happens in the sky), Tyndall scattering, and diffraction also occur. Raman scattering, and constructive interference, as in the iris the goo goo dolls feathers of birds, do not contribute to the color of the human eye, but interference phenomena are iris the goo-goo dolls important in the brilliantly colored iris pigment cells (iridophores) in many animals. Interference ronan keating - iris effects can occur at both molecular and iris janitorial supply light microscopic scales, and are often dutch iris associated (in melanin-bearing cells) with quasi-crystalline formations which enhance the optical effects. Interference is recognised by characteristic dependence of louisiana iris color on the angle of view, as seen in eye spots of water iris some butterfly wings, although the chemical components remain the same.
Blue is blue iris flowers one of the possible eye colors in humans. The "blue" allele, existing in the Bey2 and Gey genes of chromosome 15, iris garden is recessive. This means that both genes must have both blue alleles i.e. "blue-blue", iris paper folding in a person with iris wilson blue eyes. If one of the alleles were not "blue" ("green" for Gey or "brown" for iris chang Bey2) then the person would have those colored eyes iris dolls respectively. As either allele (though not both) can be passed on to offspring it is perfectly possible for iris folding templates someone who does not have blue eyes goo goo dolls iris mp3 to have blue-eyed children. Because of its recessive nature, this is a certainty if both parents have blue eyes. Though purple iris this explanation gives an idea of eye color delineation, it is incomplete, wild iris and all the contributing factors towards buy iris bulbs online eye color and its variation are not fully understood.
Altering the iris color
Certain eye colors are sometimes seen as being especially attractive through the iris 10 years and motif-expressing contact lenses can be worn to goo goo iris mask one's natural eye color with another. They are rarely needed and almost never recommended by iris macdonald serious medical doctors, unless the patient's retina needs extra protection, as in aniridia. red iris flower guild war Since the introduction of machines which can dividing iris automatically analyze iris patterns, and their use at some airports as a security measure, it is goo goo dools iris reported that some people have used colored contact lenses, or deliberate googoo dolls- iris iris injury with lasers, to prevent personal identification.
Iris color as paternity test
As stated iris hotel venice italy above, although there has been much fuss about finding the genes for eye color, there is no simple genetic determinism for stargate iris such a complex trait, as there is more iris chacon videos to iris color than pigmentation. Overall, there is no simple Mendelian inheritance in iris goo goo dolls acoustic iris color. Consequently no serious test of paternity iris valves can be based on observations or even measurements of iris color, except to live iris note that blue eyes are normally phenotypically recessive, so that a brown-eyed child of two blue-eyed parents 10 years - through the iris may create some doubt about paternity. However, due goo-goo dolls iris to incomplete evidence on the way eye colour is inherited, this cannot be seen as conclusive proof.
Different colors in iris dement mp3 the two eyes
An example of heterochromia. The subject has a brown and green eye.
Heterochromia (also ronan keating- iris known as a heterochromia iridis or american iris society heterochromia iridium) is an ocular condition in which one iris is a different color from the other iris (complete heterochromia), or iris applique where the part of one iris is a different iris borers color from the remainder (partial heterochromia or sectoral heterochromia). Uncommon in humans, it is often an indicator of ocular disease, such as iris recognition systems chronic iritis or diffuse iris melanoma, but may also occur as a iris versicolor normal variant. Sectors or patches of strikingly different colors in the same lyrics to iris iris are less common. ronan keating iris mp3 Alexander the Great and Anastasios the First were dubbed δικορος (dikoros, "with two pupils") for their blue iris sanctuary patent heterochromias. In their case, this was not a true dicoria (two pupils in the same iris). Real polycoria can divide iris be due to disease but is most often due to previous durrance, iris hybridizer trauma or surgery.
In contrast, heterochromia and variegated iris patterns are common in veterinary practice. Siberian Huskies free templates for iris folding show heterochromia due to interbreeding, possibly analogous to the genetically-determined Waardenburg syndrome hotel iris of humans. Some white cat fancies (e.g., white how to divide iris Persians) may show striking heterochromia, with the commonest pattern being one iris eye uniformly blue, the other green. Striking variegation within the same iris is also common iris ronan in some animals, and is the norm in iris storage some species. Several herding breeds, particularly those with a blue merle coat color (such as Australian Shepherds and Border iris valve Collies) may show well-defined blue areas within a brown iris as well as separate blue and darker eyes. irredesent iris and herringbone antique dishes Some horses (usually within the meyda tiffany mosaic iris accent lamp white, spotted, palomino or cremello groups of breeds) may show amber, brown, white, and blue all within the same eye, without any german iris sign of husqvarna viking iris embroidery / sewing machine eye disease.
One eye with a white or bluish-white iris is also known iris goo-goo dolls as a walleye.
Diseases which involve the iris include: ocular albinism, aniridia, iris coloboma, iritis, iris kao iris melanoma, iris metastases and Waardenburg syndrome.
When photographed with a flash, the iris iris tattoo constricts but not fast enough to avoid red iris flower the red-eye effect. This represents reflection of light from the back of the eye, and is closely transplanting iris related to the term red reflex, used avril lavigne iris by ophthalmologists in describing appearances on fundal examination.
When used as a descriptive term in medicine, the free print piano sheet music iris goo goo dolls meaning of "red eye" is quite different, and indicates that iris foetida the bulbar conjunctiva is reddened due to dilatation of superficial blood vessels. Leaving aside rarities, it indicates surface infection iris goo goo dolls lyrics (conjunctivitis), intraocular inflammation (e.g., iridocyclitis) or high intraocular pressure (acute glaucoma or occasionally severe, untreated chronic glaucoma). iris kristjansdottir This use of "red iris magic kingdom eye" implies disease. The term is therefore not used in medicine for ocular iris paintings albinism, in which the eye is otherwise healthy despite an obviously red iris proofer pupil and a translucent pinkish iris due to reflected light from the fundus. iris silk "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 large iris are usually described as having "pink eye" rather than "red eye".
- Brushfield spots
- Eye contact
- Iris nevus
- Iris scan
- Jane Elliott's silver iris "brown eyes, blue eyes exercise"
- Visual system
|Sensory system - Visual system - Eye
|Fibrous tunic: Conjunctiva | Sclera | Cornea | blue flag iris Schlemm's canal | Trabecular meshwork
Uvea: Choroid | Iris | Pupil | Ciliary body
Retina : Macula | Fovea | Optic disc
Anterior segment (Anterior chamber, Aqueous humour, Posterior chamber, Lens) donnie iris videos | Posterior segment (Vitreous humour)
|Sensory system - Visual system
|Eye | Optic nerve | Optic chiasm | fragrant iris Optic tract | Lateral geniculate nucleus | Optic radiation | Visual cortex
| iris bulb iris catalogs iris chacon 20 grandes exitos iris flower picture iris germanica iris pumila iris song iris tab
Categories: Articles with unsourced statements | Eye