In humans and most mammals and birds, iris (plural: irides or iris ) is a thin and round structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina. Eye color is defined by iris. In optical terms, the pupil is the aperture of the eye, while the iris is the diaphragm.
Video Iris (anatomy)
Structure
The iris consists of two layers: a front-sided fibroascular fibrovascular known as stroma and, under stroma, pigmented epithelium cells.
Stroma connects to the sphincter muscle (sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles (dilator pupillae) that pulls the iris radially to enlarge the pupil, pulling it in the crease. The back surface is covered by a highly pigmented epithelial layer that is two thick cells (iris pigment epithelium), but the front surface has no epithelium. Project this anterior surface as a dilator muscle. High pigment content blocks the light through the iris into the retina, restricting it to the pupil. The outer edge of the iris, known as the root, is attached to the sclera and anterior siliary body. The iris and ciliary bodies together are known as the anterior uvea. Right in front of the iris root is an area called trabecular meshwork, where aqueous humor continually flows out of the eye, with the result that iris disease often has an important effect on intraocular pressure and indirectly on vision.. The iris along with the anterior cephalic body provides a secondary pathway for the aqueous humor to flow from the eye.
Iris is divided into two main areas:
- The pupillary zone is the inside with the edges forming the pupil boundaries.
- ciliary zone is the remaining iris extending to its origin in the ciliary body.
The kerahette is the thickest region of the iris, separating the pupillary part of the ciliary part. The collar is a cladding of the embryonic pupillary layer. This is usually defined as the region in which the sphincter muscles and dilator muscles overlap. The radial back extends from the periphery to the pupil zone, to supply the iris with the blood vessels. The root of the iris is the thinner and the most peripheral.
Muscle cells from the iris are smooth muscle in mammals and amphibians, but striated muscles in reptiles (including birds). Many fish do not have, and, as a result, their irides can not be dilated and contracted, so the pupils always remain fixed-sized.
Home
- The crypts of Fuchs is a series of openings located on either side of the collar allowing deeper stroma and deeper iris tissue to be bathed in aqueous humor. The trabecular collagen that surrounds the border of the crypts can be seen with the blue iris.
- The center between the collar and the origin of the iris. These creases result from changes in the iris surface as they widen.
- Crypt at the base of the iris is an additional opening which can be observed near the outer portion of the sili part of the iris.
Back
- Schwalbe radial contraction fold is a series of very fine radial creases in the iris part that extends from the edge of the pupil to the collar. They relate to the appearance of a muscular pupil.
- Schwalbe's structural folds are the radial creases extending from the far wider and broader borders of the ciliary zone and pupils, continuing with the "valley" between the ciliary processes.
- Some folds of circular contractions are a series of smooth ridges that run near the pupil's edge and vary in the thickness of the iris pigment epithelium; the other is in the sili part of the iris.
Microanatomy
From anterior (front) to posterior (back), the iris layers are:
- The anterior border layer
- Iris Stroma
- Iris Sphincter muscle
- Slice dilator muscle (myopeithelium)
- Anterior pigment epithelium
- Posterior pigment epithelium
Development
The stroma and anterior border of the iris are derived from neural crystals, and behind the iris stroma, the sphincter pupillae muscle and the dilator pupillae and the iris epith developed from neuroectodic optical cups.
Maps Iris (anatomy)
Eye color
Iris is usually very pigmented, with colors usually ranging from brown, brown, green, gray, or blue. Occasionally, the iris color is due to a lack of pigmentation, as in the pink-white algaisme oculo-skin, or the blurring of the pigment by blood vessels, as in the red color of the irregular abnormal vascularization. Despite the variety of colors, the only pigment that contributes greatly to the normal human iris color is melanin dark pigment. The quantity of melanin pigment in the iris is one of the factors in determining the color of a person's phenotypic eye. Structurally, these large molecules are only slightly different from those found in skin and hair. The iris color is due to the variable amount of eumelanin (brown melanin/black) and pheomelanin (red/yellow melanin) produced by melanocytes. More than the first found on brown eyed people and the last on blue people and green eyed.
Genetic and physical factors that define iris colors
Iris color is a very complex phenomenon consisting of a combined effect of texture, pigmentation, fibrous tissue and blood vessels in the iris stroma, which together form an individual epigenetic constitution in this context. The "eye color" of a person is actually the color of a person's iris, the cornea becomes transparent and the white sclera is completely outside the desired area.
Melanin is yellowish brown to dark brown in stromal pigment cells, and black on the iris pigment epithelium, located in a thin but very opaque layer on the back of the iris. Most iris in humans also shows the condensation of chocolate brown melanin in a thin anterior layer, which because of its position has a real effect on the overall color. Melanin dispersion levels, which are in subcellular bundles called melanosomes, have an effect on the observed color, but melanosomes in human irises and other vertebrates are immobile, and the pigment dispersion rate is irreversible. Abnormal melanosomal clots occur in the disease and may cause irreversible iris changes (see heterochromia, below). Colors other than brown or black are due to the reflection and selective absorption of other stroma components. Sometimes lipofuscin, yellow "wear and tear" yellow pigments also enter into visible eye colors, especially in aged green or diseased eyes.
Optical mechanisms in which the non-pigmented stroma component affects the eye color is complex, and many wrong statements are present in the literature. Simple selective absorption and reflection by biological molecules (hemoglobin in blood vessels, collagen in vessels and stroma) are the most important elements. Rayleigh scattering and Tyndall scattering, (which also occur in the sky) and diffraction also occur. Raman scattering, and constructive distractions, such as in bird feathers, do not contribute to the color of the human eye, but important interference phenomena in the pigment of brightly colored pigment cells (iridophores) in many animals. Interference effects can occur on molecular and light microscopic scales, and are often associated (in melanin cushion cells) with quasi-crystal formations that enhance optical effects. Interference is recognized by the dependence of color characteristics on the point of view, as seen on the eyespots of some butterfly wings, although the chemical components remain the same. White babies are usually born with blue eyes because there is no pigment in the stroma, and their eyes appear blue due to scattering and selective absorption of the posterior epithelium. If melanin is deposited substantially, there will be a brown or black color, otherwise they will remain blue or gray.
All factors that contribute to eye color and its variation are not fully understood. Autosomal recessive/dominant traits on iris colors are attached to other species but colors can follow different patterns.
Yellow Eyes
Yellow eyes are very rare in humans. They consist of a solid orange/gold color that may contain lighter shades of the same pigment inside the iris. This is an unusual occurrence that occurs when a yellow pigment called pheomelanin (also known as lipochrome), is dominant in the iris. Pheomelanin is also found in individuals with green eyes in a much smaller amount. This is because green eyes have a strong presence of melanin and pheomelanin. Often in poor lighting, people may misinterpret the yellow eye for chocolate. This also happens when viewed from afar or in pictures with poor lighting as well. However, in a natural or bright area, it is easy to distinguish between two colors. Another common mistake people make is to think of the yellow eye as hazel. Although similar, brown eyes have a stronger melanin presence with two very different colors within the iris (usually green/brown) and often contain many freckles or mixed-color blotches.
Different colors in two eyes
Heterochromia (also known as heterochromia iridis or heterochromia iridum ) is an ocular condition in which one iris is a different color than the other iris (complete heterochromia), or where part of one iris is a different color from the rest (partial heterochromia or sectoral heterochromia). Rarely in humans, often an indicator of eye disease, such as chronic iritis or diffuse iris melanoma, but can also occur as a normal variant. Sectors or patches with very different colors on the same iris are less common. Alexander the Great and the First Anastasios dubbed dikoro * s ( dikoros , "with two disciples") for their patents heterochromias . In their case, this is not true dicoria (two students in the same iris). Polycoria can actually be caused by illness but most often due to previous trauma or surgery.
In contrast, heterochromia and iris patterns are common in veterinary practice. Siberian Huskies show heterochromia, probably analogous to the genetically determined Waardenburg syndrome in humans. Some white cats (eg, Turkish Angora or white Turkish van cats) may show striking heterochromia, with the most common patterns being uniform blue, other copper, orange, yellow, or green. Striking variations in the same iris are also common in some animals, and are the norm in some species. Some shepherd breeds, especially those with blue merle coat (such as Australian Shepherds and Border Collies) can show well-defined blue areas in brown irises and separate dark and blue eyes. Some horses (usually in groups of white, spotted, palomino or cremello breeds) may show amber, brown, white and blue all in the same eye, without any sign of eye disease.
One eye with a white or bluish white slice is also known as walleye .
Clinical interests
When photographed with flash, the irises constrict but not fast enough to avoid the red-eye effect. This is a reflection of light from the back of the eye, and is closely related to the term red reflex, used by ophthalmologists and ophthalmologists in describing appearance on fundus examination.
Conjunctivitis
When used as a descriptive term in medicine, the meaning of red eye is very different, and shows that bulbar conjunctiva is flushed due to superficial veins dilatation. Ruling out scarcity, it suggests surface infections (conjunctivitis), intraocular inflammation (eg, iridocyclitis) or high intraocular pressure (acute or sometimes severe glaucoma, untreated chronic glaucoma). The use of this "red eye" implies illness. Hence this term is not used in medicine for ocular albinism, in which the eye is otherwise healthy although the pupil is clearly red and pink irises due to the reflected light of the fundus. "Red eye" is used more loosely in veterinary practice, where eye disease investigations can be difficult, but even so the albinotic offspring are easily recognizable and are usually described as having "red eyes" rather than "red eyes".
Society and culture
Iridology
Iridology (also known as iridodiagnosis ) is an alternative treatment technique whose supporters believe that patterns, colors and other characteristics of the iris can be examined to determine information about the patient's systemic health. Practitioners match their observations with the iris chart which divides the iris into a zone corresponding to a particular part of the human body. Iridologists see the eye as a "window" into a state of health.
Iridology is not supported by quality research research and is considered pseudoscience by the majority of medical practitioners and eye care professionals.
Etymology
The word iris comes from the Greek goddess of the rainbow, because of the many colors of the iris.
Graph
See also
- Iridoplegia - paralysis of the sphincter muscle in the iris
- Iris (disambiguation)
- The human eye
- Retina
- The blood-ocular border
- Iris Introduction
- Aniridia
- Coloboma
References
External links
- Details of human iridora photos
- Histology: 08010loa - Histology Learning System at Boston University
- Atlas Image: eye_1 on Michigan University Healthcare System - "Sagittal Section Through the Eyeballs"
Source of the article : Wikipedia
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