Iris

Iris (iris) - front Department of vascular tract eyes, thin skin, peripheral part of which is on the border with ciliary body is fixed with him to the inner surface of sclera, and free mobile pupillary edge relies on the front surface of the lens, being able to slide it in the movements of the pupil. The pupil (pupilla) is a round hole in the center of the iris.
Iris has a specific figure and an uneven surface (Fig. 1), due to coming mainly in the radial direction by teicami (trabeculae), between which are formed deepening (crypt). As part of the vascular tract eyes, iris contains numerous blood vessels of different caliber; trabeculae correspond course the largest of them. Describes the structure of the iris is in the wider peripheral (ciliary zone; in a narrower, Central (pupillary) zone trabeculae acquire a circular direction due to the fact that here there are relatively large circular vessel - small arterial circle iris (circulus arteriosus iridis minor). On the border between the ciliary and pupillary belt fabric R. O. slightly elevated, and this area is called the fringe, or brygga (region Krause). In the peripheral part of the R. O. (root) on the border with ciliary body (see) in the thickness of the fabric laid second circular blood vessel (Fig. 2) - big arterial circle iris (circulus arteriosus iridis major). Large and small blood circles are connected by numerous going radially, respectively course of the trabeculae, vessels. The blood supply of the big arterial circle is mainly taken from the front of the ciliary arteries (aa. ciliares anticae), penetrating into the eye near the limb of the cornea, and partly from anastomosis with them within the big circle back long ciliary arteries (aa. ciliares posticae longae).


Fig. 1. The appearance of the iris:
1 - the pupil; 2 - pigment bezel; 3 - pupillary zone; 4 - a small range of the iris; 5 - contraction grooves; 6 - trabeculae; 7 - crypt; 8 - ciliary zone.


Fig. 2. Cross-section of the eye and the iris: 1 - limb; 2 - the ciliary body; 3 - schlemmov channel; 4 - high blood circle of the iris; 5 - pigment epithelium of the iris; 6 - contraction grooves; 7 - m. dilatator pupillae; 8 - the iris stroma; 9 - m. sphincter pupillae; 10 - the lens; 11 - pigment bezel pupillary edge of the iris.

On the front surface of the iris in the peripheral area visible ring (contraction) groove, formed as a result of continuous contractions and expansions of the pupil.
Iris painted in different people in different colors from light grey, blue, brown and dark brown. Iris color depends on the number located in its tissue pigment cells (chromatophores).
Histologically, in R. O. there are two layers: front, connective tissue (the so-called stroma), which in its origin and mesenchymal containing mainly vessels, and back, consisting of two layers of epithelial cells containing the retinal pigment, and which is in its embryonic Genesis of heavily modified the retina and, therefore, derived from the ectoderm. Ternopilvtormet bezel pupillary region was caused by a partial transition back pigment sheet iris on its front surface.
Changing the size of the pupil, his ability to sivetice and expand due to the presence in R. O. two involuntary muscle narrowing a pupil sphincter (m. sphincter pupillae), founded in stroma near pupillary territory and representing smooth muscle with a circular arrangement of fibers, and extending the pupil of dilatatore (m. dilatator pupillae), which is a thin layer of the contractile cells, lying between stromal and pigment sheets R. O. Sphincter pupil innerviruetsya oculomotor nerve (n. oculomotorius), dilatator - sympathetic (n. sympathicus). R. O. is very rich sensitive nerves (from the trigeminal nerve - n. trigemini).


Fig. 3. The root view of the iris and the angle of the anterior chamber of the eye when gonioskopia. 1 - optical cut the cornea; 2 - rear surface of the cornea; 3 - the place of attachment of trabeculae iris to the rear surface of the cornea (line svalbe); 4 - fiber comb bundles with translucent between them klimovym channel; 5 - ciliary crane iris; - the front surface of the iris; 7 - pupillary edge of the iris; 8 - the pupil.

The peripheral part of the iris (root) can not be seen as hidden behind an opaque limb. Method gonioskopia (see) this area corresponding to the so-called anterior chamber angle, it is possible to consider even microscopically using a binocular microscope (Fig. 3). In the corner of the front camera is comb ligament (lig. pectinatum); between its trabeculae have narrow (the so-called fontanova) of space through which the liquid and the anterior chamber (chamber moisture) penetrates into schlemmov channel - circular vessel laid down in the thickness of the sclera and serves to drain the main mass of the chamber of moisture.
The basic physiological role R. O. is to regulate the number of entrants into the eye light rays, which is achieved "game" (alternate contraction and expansion) of the pupil, functioning as a diaphragm. In normal width of the pupil scattered with natural daylight varies from 2 to 5 mm, but in some circumstances the pupil may expand to 8 mm and sivetice up to 1.5 mm or less. The width of the pupil is regulated automatically, because the muscles of the iris refer to the involuntary. The width of the pupils, in addition to the light intensity can be affected by other factors (for example, convergence; emotional moments - pain, fear and so on). The width of the pupil may be artificially modified by the application of certain drugs (such as atropine, scopolamine, cocaine, adrenaline extend the pupil, cause mydriasis; pilocarpine, ezerin its narrow, cause cramps). Under normal conditions the pupils are of the same diameter; the difference in width of the pupil - anisocoria (anisocoria, and various violations of their reactions to light, on convergence) are usually a symptom of pathological observed for a number of diseases or the eyes, or mainly the Central nervous system.
The width of the pupil is determined by the method of the graphics registration (see Pupilographical).
Congenital anomalies of the iris can be expressed in its absence (aniridia congenita)that is rare. Much more often there are cases of partial underdevelopment of the iris in one of its sectors - the so-called coloboma (coloboma iridis). Such congenital of coloboma (see) are usually located in the lower part P. O. the Sphincter in these cases, on the edge of coloboma is saved, unlike acquired by the kolob, formed as a result of trauma or surgery (see Iridectomy). Special painting "jitter" iris - iridophores (iridodonesis) - is created in dislocation of the lens or after surgery to remove it. From congenital (and sometimes acquired) changes R. O. it is necessary to indicate different coloring it in one and the other eye - heterochromia (heterochromia iridis); from geterohromia (see) it is necessary to distinguish between different coloring R. O. in different sectors her in the same eye (the so-called bicolor iris). Congenital flat limited or sometimes slightly rising plots thick pigmentation in stroma R. O. characteristic of birthmarks - nevi (naevus iridis). A peculiar picture of congenital anomalies in the area of the pupil gives the so-called membrana pupillaris perseverans - residues not otherwise reverse existing in the embryonic stage of the vascular system of the lens.
When eye injuries can occur tears pupillary edge of the iris, lead it to the root (iridodialysis) and even complete separation (aniridia traumatica).
Inflammation R. O. (irity, iritis) are observed in the clinic very often, mainly from various infectious diseases are local and mostly General (tuberculosis, syphilis, rheumatism and other), and some endocrine (diabetes), traumas, etc., Often inflammation R. O. occur with symptoms of participation in inflammation and ciliary body, i.e. in the form iridocyclitis (see). Irity can be accompanied by the appearance in the anterior chamber of pus (hypopion); sometimes with acute irate found in the anterior chamber blood (hyphaema).
In the iris there are cysts of malignant tumors, melanoblastoma (source latter are sometimes nevi). Cm. also the Eye.