IRIS

From Big Medical Encyclopedia

IRIS [iris (PNA, JNA, BNA); synonym: iris of the eye, raduzhina] — the front department of a choroid of an eyeglobe seen through a transparent cornea.

The histogenesis

the Iris is put on the 6th week of the pre-natal period of development from a neuroepithelial part of an eye bubble, a mesenchyma of a crested origin and mesodermal elements. R.'s muscles — a sphincter and the dilator of a pupil — have a neuroectodermal origin, they develop from an outside leaf of a neuroepithelium. In the post-natal period the sphincter of a pupil is similar to smooth muscle fabric and keeps close connection with the dilator which is a specialized muscular part of cells of a front pigmental epithelium. At children of the first 2 — 4 months of life of a muscle of R. are poorly expressed, the dilator almost does not function, action of a sphincter and a pupil during this period of life considerably already, than at more advanced age prevails.

Anatomy

Fig. 1 — 3. Microdrugs of an iris are normal. Fig. 1. Iris, cornea, ciliary body: 1 — a front (uveal) layer of an iris; 2 — a cornea; 3 — a ciliary body; 4 — a back (retinal) layer of an iris; coloring hematoxylin-eosine; x 70. Fig. 2. Pupillary and partially ciliary edges of an iris: 1 — an outside boundary layer; 2 - fibroblasts; 3 — the dilator of a pupil; 4 — a sphincter of a pupil; 5 — macrophages; 6 — melanocytes; coloring gematoksilin-eozinom-x 200. Fig. 3. Ciliary edge and root of an iris: 1 — structures of an angle of iris; 2 — a stroma of an iris; 3 - blood vessels; coloring hematoxylin-eosine; X 200. Fig. 4 — 6. Microdrugs of an iris at separate types of pathology. Fig. 4. Healing of the adapted wound of an iris with formation of a hem (the hem is painted more intensively, shooters specified a suture material); coloring across Mallori; x 100. Fig. 5. Iris at an acute iritis: 1 — focal inflammatory infiltration; 2 — exudate in front and back cameras of an eyeglobe; coloring hematoxylin-eosine; x 70. Fig. 6. Iris after the postponed iritis: 1 — a cornea; 2 — structures of an angle of iris; 3 — an iris; 4 — front synechias; coloring hematoxylin-eosine; x 70. Fig. 7 — 9. The biomicroscopic picture of an iris is normal also at separate types of pathology. Fig. 7. The front surface of an iris is normal: 1 — the gear line (Krause's circle); 2 — a pupillary border. Fig. 8. Inborn ectropion of a back pigmental epithelium (it is specified by an arrow). Fig. 9. Serous cyst (it is specified by an arrow) In the center a white spot — a light patch of light.

The iris represents the round mobile diaphragm diameter apprx. 12 mm separating an anterior chamber of an eyeglobe from back. Almost in the center P. the round opening — a pupil (pupilla) is located. On a front surface of R. allocate pupillary edge (margo pupillaris) 1 mm wide and ciliary edge (margo ciliaris) 3 — 4 mm wide. In the field of pupillary edge the sphincter of a pupil is located (t. sphincter pupillae) — the muscle narrowing a pupil; in the field of ciliary edge there is a dilator of a pupil (m. dilatator pupillae) — the muscle expanding a pupil. The conjunction of R. with a ciliary (tsiliarny) body (see. Ciliary body ) is called a root of an iris, other part P. is in free suspension in liquid of front and back cameras of an eyeglobe. In the conjunction of a root P. and back layers of a cornea structures of a corner of an anterior chamber are located (an angle of iris, T.; angulus iridocomealis), providing the main outflow of intraocular liquid (see. Eye ). At biomicroscopy the drawing of an iris clearly is visible (tsvetn. fig. 7): it has an appearance of the spongy fabric consisting of a set of radial thin crossing points (trabeculas) formed by a thick adventitia of vessels and the connecting fabric surrounding them. Between trabeculas deepenings are located (lacunas and crypts). On border of pupillary and ciliary edge of R. the gear line, or Krause's circle (internal ring of an iris) — area of an attachment of an embryonal pupillary vascular membrane is defined. The pupil is framed with a dark brown pupillary border. On a front surface of R. R.'s folds are visible, at a narrow pupil radial folds are more boldly allocated, at a wide pupil — concentric. In the pupillary region of R. of blue color the sphincter of a pupil having an appearance of the pink tape which is located around a pupillary border is visible.

The river has genetically caused drawing and color. Brown color P. is inherited on dominant type, blue — on recessive. The drawing and color P. change during life. Color P. is relatively stabilized by 10 — 12 years. At advanced age of R. becomes slightly lighter owing to dystrophic changes. Emergence of spots on R.'s surface in connection with diseases of various bodies is possible.

Blood supply The river is carried out by the long back and front ciliary arteries anastomosing among themselves in the field of a root P. forming big and small arterial circles of an iris (circuli arteriosi iridis major et minor). A venous blood flows in the vortikozny veins falling into an upper orbital vein.

Sensitive innervation The river is carried out by branches of an optic nerve (item ophthalmicus); an innervation of a sphincter of a pupil — postganglionic parasympathetic fibers of a ciliary node. The dilator of a pupil postganglionic sympathetic fibers of an upper cervical node innervate.

Histology

On a radial cut of R. distinguish front (uveal, or vascular) the layer consisting of an outside boundary layer, a stroma and a sphincter of a pupil and the back (retinal) layer presented by a front pigmental epithelium with a plate of the dilator of a pupil and a back pigmental epithelium — an inner boundary layer (tsvetn. fig. 1, 2, 3). The front surface of R. at the expense of crypts has a spongy relief. By means of electronic microscopic examinations lack of an endothelial layer on a front surface of River is established. The outside boundary layer of R. is created by unevenly distributed melanocytes and fibroblasts which in the field of crypts lie in 1 — 2 layer, and in the field of thickenings form multilayer accumulations. Cells are oriented parallel to R.'s surface. their numerous shoots contact among themselves. R.'s stroma is formed by blood vessels, rykhlo the located collagenic fibers and freely lying fibroblasts and melanocytes (see. Pigment cells ), in it also labrocytes — mast cells (see), macrophages (see) and lymphocytes meet (see). Intercellular substance is presented by acid glikozaminoglikana. R.'s vessels have the radial direction. Their structural feature are collagenic couplings with concentrically the located fibers which interfere with reduction of a gleam of vessels at a mydriasis. In vascular network arterioles, venules and capillaries, an endothelium of the last of nefenestrirovanny type prevail, we do not pass for plasma proteins. The sphincter of a pupil located in the pupillary region of R. consists of bunches of smooth muscle cells. The forefront of a back (retinal) layer of R. is presented by a front pigmental epithelium, each cell to-rogo has basal and apical speak rapidly. Basal parts of cells of a pigmental epithelium are turned to R.'s stroma and in the field of ciliary edge form a plate of the dilator of a pupil at the expense of radially located spindle-shaped shoots, densely connected with each other and covered with a basal membrane. According to ultrastructural characteristics basal parts of cells of a front pigmental epithelium approach smooth muscle cells. Apical parts of cells of a front pigmental epithelium connect to a back pigmental epithelium, contain a kernel, mitochondrions (see), sigarovidny granules of melanin, a ribosome (see), Golgi's complex (see. Golgi complex ), large number melanosy and separate myofilaments. Epithelial and muscular elements of a front pigmental epithelium are connected among themselves with the help of desmosomes (see) and dense unions. The front pigmental epithelium in the field of a pupil passes into the back pigmental epithelium covering a back surface of River. Cells of a back pigmental epithelium — purely epithelial, cytoplasm supports them sigarovidny granules of melanin of a .glikogen and Golgi's complex. The back surface of these cells is covered with a basal membrane.

The physiology

Thanks to change of size of a pupil is provided regulation of amount of light falling on a retina and localization of a light flow along an optical axis of an eye in the direction of macular area of a retina.

The ruble participates in outflow of intraocular liquid. Mobility of pupillary edge of R. improves the movement of intraocular liquid from the back camera of an eyeglobe in a lobby. The spongy structure of a front layer of R., structure of a corner of an anterior chamber provide R.'s participation in outflow of intraocular liquid on drainage system (see. Hydrodynamics of an eye ). The river is a part of a blood-ocular barrier thanks to the nefenestrirovanny endothelium of its vessels and a back pigmental epithelium which are not passing a squirrel of a blood plasma in intraocular liquid. Thus, R. plays an important role in maintenance of constancy of internal environment of an eye.

Methods of a research. For a research P. use focal illumination, biomicroscopy of an eye (see), a gonioskopiya (see), a diafanoskopiya (see), an angiography of vessels of an iris (see. Fluorescent angiography ). The basic and the most informative method of a research P. is the biomicroscopy of an eye.

Pathology

Distinguish malformations of R., damage, inflammatory and vascular diseases, tumors, dystrophies. Distinguish R.'s absence from malformations (see. Aniridiya ), various coloring of R. of both eyes or unequal coloring of parts P. of one eye (see. Heterochromia ), R.'s defects (see. Coloboma ), multiple pupillary openings (polycoria), an excentric arrangement of a pupil — a korektopiya, an ectropion of a back pigmental epithelium — ectropion (tsvetn. fig. 8), and also a hypoplasia of a stroma of R. and a persistent pupillary membrane (membrane) which is the rest of an embryonal vascular bag of a crystalline lens (see).

Owing to a stupid injury of an eye (see an Eye, pathology) carry a separation of a root P. to R.'s damages — an iridodialysis, ruptures of a sphincter of a pupil, R.'s trembling owing to an incomplete dislocation of a crystalline lens — an iridodonesis. At getting R.'s wounds hit of foreign bodys (see), formation of colobomas, R.'s unions with a back surface of a cornea, R.'s cysts is possible (tsvetn. fig. 9). Fabric P. is capable to healing in the conditions of good adaptation (comparison) of edges of a wound opening (tsvetn. fig. 4).

The river is rather steady against impact of ionizing radiation. Beam irites and iridocyclites (see) arise at R.'s radiation in a dose of 1000 is glad (10 Gr), and at R.'s radiation in a dose 17 000 is glad (170 Gr) its atrophy and a rubeosis (network of neogenic vessels) develops.

Carry irites, iridocyclites to inflammatory diseases of R. In fig. 5 and 6 (tsvetn. fig.) are represented microdrugs P. at an acute iritis and after the postponed iritis.

Ischemic necroses of R. can arise at glaucoma owing to an obliteration and vasoconstriction. R.'s rubeosis is observed at fibrinferment of the central vein of a retina and a diabetes mellitus. Treatment of a basic disease is carried out.

The progressing essential atrophy of R. (iridoshizis) is connected with dystrophy of a stroma and growth on R.'s surface of a corneal endothelium. At a complication carry out by secondary glaucoma treatment of glaucoma.

From R.'s tumors most often meet myoma, the melanoma (see) and an epithelioma is more rare. Treatment of tumors of R. operational. The forecast at R.'s tumors is more favorable, than at tumors of an idiovascular cover of an eyeglobe (chorioidea).

Pathology of a pupil — see. Pupillary reflexes , Mydriasis , Miosis .

Operations on R. make treatment in the medical and cosmetic purposes. Treat them creation of artificial colobomas of R. (e.g., at glaucoma), plastics of colobomas (e.g., traumatic), correction and creation of a new pupil, R.'s release from commissures with a cornea and a crystalline lens, corectomy (see), etc. At an iridodialysis carry out a transcorneal podshivaniye of a root P. to a limb (Shotter's operation). Some operations (corectomy, operations in the field of an angle of iris) carry out by means of the laser (see).

See also Eye .


Bibliography: Krasnov M. L. Elements of anatomy in clinical practice of the ophthalmologist, M., 1952; The Multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 2, book 2, page 491, M., 1960; Romashov F. N. and Velkho-v e r E. S. Opportunities and errors of iridology, Eksperim. hir. and anesteziol., No. 2, page 49, 1973; Fine B. a. Y and-noff M. of Ocular histology, N. Y., 1972; Gray’s anatomy, ed. by T. B. Johnston a. o., p. 1240, L. a. o., 1958; HoganM. J., Alvarado J. A. a. Weddell J. E. Histology of the human eye, an atlas and textbook, Philadelphia, 1971.

G. G. Ziangirova.

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