Radial muscle of the eye. Ciliary muscle: structure, functions, symptoms and treatment. Diseases, anomalies, their causes and symptoms
12-12-2012, 19:22
Description
The eyeball contains several hydrodynamic systems associated with the circulation of aqueous humor, vitreous humor, uveal tissue fluid and blood. The circulation of intraocular fluids provides a normal level of intraocular pressure and nutrition of all tissue structures of the eye.At the same time, the eye is a complex hydrostatic system consisting of cavities and slits separated by elastic diaphragms. The spherical shape of the eyeball, the correct position of all intraocular structures, and the normal functioning of the optical apparatus of the eye depend on hydrostatic factors. Hydrostatic buffer effect determines the resistance of eye tissues to the damaging action of mechanical factors. Violations of hydrostatic balance in the cavities of the eye lead to significant changes in the circulation of intraocular fluids and the development of glaucoma. In this case, disturbances in the circulation of aqueous humor are of the greatest importance, the main features of which are discussed below.
aqueous humor
aqueous humor fills the anterior and posterior chambers of the eye and flows through a special drainage system into the epi- and intrascleral veins. Thus, aqueous humor circulates predominantly in the anterior segment of the eyeball. It is involved in the metabolism of the lens, cornea and trabecular apparatus, plays an important role in maintaining a certain level of intraocular pressure. The human eye contains about 250-300 mm3, which is approximately 3-4% of the total volume of the eyeball.
Aqueous moisture composition significantly different from the composition of blood plasma. Its molecular weight is only 1.005 (blood plasma - 1.024), 100 ml of aqueous humor contains 1.08 g of dry matter (100 ml of blood plasma - more than 7 g). The intraocular fluid is more acidic than blood plasma, it has an increased content of chlorides, ascorbic and lactic acids. The excess of the latter seems to be associated with the metabolism of the lens. The concentration of ascorbic acid in moisture is 25 times higher than in blood plasma. The main cations are potassium and sodium.
Non-electrolytes, especially glucose and urea, are less in moisture than in blood plasma. The lack of glucose can be explained by its utilization by the lens. Aqueous moisture contains only a small amount of proteins - no more than 0.02%, the proportion of albumins and globulins is the same as in blood plasma. Small amounts of hyaluronic acid, hexosamine, nicotinic acid, riboflavin, histamine, and creatine were also found in the chamber moisture. According to A. Ya. Bunin and A. A. Yakovlev (1973), aqueous humor contains a buffer system that ensures pH constancy by neutralizing the metabolic products of intraocular tissues.
Aqueous moisture is formed mainly processes of the ciliary (ciliary) body. Each process consists of a stroma, wide thin-walled capillaries, and two layers of epithelium (pigmented and non-pigmented). Epithelial cells are separated from the stroma and the posterior chamber by the outer and inner boundary membranes. The surfaces of non-pigmented cells have well-developed membranes with numerous folds and depressions, as is usually the case with secretory cells.
The main factor that ensures the difference between primary chamber moisture and blood plasma is active transport of substances. Each substance passes from the blood into the posterior chamber of the eye at a rate characteristic of that substance. Thus, moisture as a whole is an integral value, composed of individual metabolic processes.
The ciliary epithelium carries out not only secretion, but also the reabsorption of certain substances from aqueous humor. Reabsorption is carried out through special folded structures of cell membranes that face the posterior chamber. It has been proven that iodine and some organic ions actively pass from the moisture in the blood.
The mechanisms of active transport of ions through the epithelium of the ciliary body are not well understood. It is believed that the sodium pump plays a leading role in this, with the help of which about 2/3 of sodium ions enter the posterior chamber. To a lesser extent, chloride, potassium, bicarbonate, and amino acids enter the eye chambers due to active transport. The mechanism of the transition of ascorbic acid to aqueous humor is unclear.. When the concentration of ascorbate in the blood is above 0.2 mmol/kg, the secretion mechanism is saturated, therefore, an increase in the concentration of ascorbate in the blood plasma above this level is not accompanied by its further accumulation in the chamber moisture. Active transport of some ions (especially Na) leads to hypertonic primary moisture. This causes water to enter the posterior chamber of the eye by osmosis. Primary moisture is continuously diluted, so the concentration of most non-electrolytes in it is lower than in plasma.
Thus, aqueous humor is actively produced. Energy costs for its formation are covered by metabolic processes in the cells of the epithelium of the ciliary body and the activity of the heart, due to which the level of pressure in the capillaries of the ciliary processes sufficient for ultrafiltration is maintained.
Diffusion processes have a great influence on the composition. Lipid-soluble substances pass through the hematoophthalmic barrier the easier, the higher their solubility in fats. As for fat-insoluble substances, they leave the capillaries through the cracks in their walls at a rate inversely proportional to the size of the molecules. For substances having a molecular weight greater than 600, the blood-ophthalmic barrier is practically impermeable. Studies using radioactive isotopes have shown that some substances (chlorine, thiocyanate) enter the eye by diffusion, others (ascorbic acid, bicarbonate, sodium, bromine) - through active transport.
In conclusion, we note that ultrafiltration of the liquid takes part (although very little) in the formation of aqueous humor. The average rate of production of aqueous humor is about 2 mm/min, therefore, about 3 ml of fluid flows through the anterior part of the eye within 1 day.
Eye cameras
Aqueous moisture first enters posterior chamber of the eye, which is a slit-like space of complex configuration, located posterior to the iris. The lens equator divides the chamber into anterior and posterior parts (Fig. 3).
Rice. 3. Chambers of the eye (diagram). 1 - Schlemm's channel; 2 - anterior chamber; 3 - anterior and 4 - posterior sections of the posterior chamber; 5 - vitreous body.
In a normal eye, the equator is separated from the ciliary corona by a gap of about 0.5 mm, and this is quite enough for the free circulation of fluid inside the posterior chamber. This distance depends on the refraction of the eye, the thickness of the ciliary crown and the size of the lens. It is greater in the myopic eye and less in the hypermetropic eye. Under certain conditions, the lens seems to be infringed in the ring of the ciliary crown (ciliocrystal block).
The posterior chamber is connected to the anterior through the pupil. With a tight fit of the iris to the lens, the transition of fluid from the posterior chamber to the anterior is difficult, which leads to an increase in pressure in the posterior chamber (relative pupillary block). The anterior chamber serves as the main reservoir for aqueous humor (0.15-0.25 mm). Changes in its volume smooth out random fluctuations in ophthalmotonus.
A particularly important role in the circulation of aqueous humor is played by peripheral part of the anterior chamber, or its angle (UPC). Anatomically, the following structures of the APC are distinguished: the entrance (aperture), the bay, the anterior and posterior walls, the apex of the angle, and the niche (Fig. 4).
Rice. four. Anterior chamber angle. 1 - trabecula; 2 - Schlemm's channel; 3 - ciliary muscle; 4 - scleral spur. SW. 140.
The entrance to the corner is located where the Descemet's shell ends. The back border of the entrance is iris, which forms here the last stroma fold to the periphery, called the "Fuchs fold". To the periphery of the entrance is the bay of the UPK. The anterior wall of the bay is the trabecular diaphragm and scleral spur, the posterior wall is the root of the iris. The root is the thinnest part of the iris, as it contains only one layer of stroma. The top of the APC is occupied by the base of the ciliary body, which has a small notch - the APC niche (angle recess). In the niche and next to it, remnants of embryonic uveal tissue are often located in the form of thin or wide cords running from the root of the iris to the scleral spur or further to the trabecula (combing ligament).
Drainage system of the eye
The drainage system of the eye is located in the outer wall of the APC. It consists of the trabecular diaphragm, scleral sinus, and collecting ducts. The drainage zone of the eye also includes the scleral spur, ciliary (ciliary) muscle and recipient veins.
Trabecular apparatus
Trabecular apparatus has several names: "trabecula (or trabeculae)", "trabecular diaphragm", "trabecular network", "trellised ligament". It is an annular crossbar thrown between the anterior and posterior edges of the internal scleral groove. This groove is formed due to the thinning of the sclera near its end at the cornea. In section (see Fig. 4), the trabecula has a triangular shape. Its apex is attached to the anterior edge of the scleral groove, the base is connected with the scleral spur and partially with the longitudinal fibers of the ciliary muscle. The anterior edge of the groove, formed by a dense bundle of circular collagen fibers, is called " front boundary ring Schwalbe". trailing edge - scleral. spur- represents a protrusion of the sclera (resembling a spur in the cut), which covers part of the scleral groove from the inside. The trabecular diaphragm separates a slit-like space from the anterior chamber, which is called the venous sinus of the sclera, Schlemm's canal, or scleral sinus. The sinus is connected by thin vessels (graduates, or collector tubules) with epi- and intrascleral veins (recipient veins).
Trabecular diaphragm consists of three main parts:
- uveal trabeculae,
- corneoscleral trabeculae
- and juxtacanalicular tissue.
The outer layer of the trabecular apparatus, adjacent to the Schlemm's canal, differs significantly from other trabecular layers. Its thickness varies from 5 to 20 µm, increasing with age. When describing this layer, various terms are used: "the inner wall of the Schlemm's canal", "porous tissue", "endothelial tissue (or network)", "juxtacanalicular connective tissue" (Fig. 5).
Rice. 5. Electron diffraction pattern of juxtacanalicular tissue. Under the epithelium of the inner wall of the Schlemm's canal, there is a loose fibrous tissue containing histiocytes, collagen and elastic fibers, and an extracellular matrix. SW. 26,000.
Juxtacanalicular tissue consists of 2-5 layers of fibrocytes, freely and in no particular order lying in loose fibrous tissue. The cells are similar to the endothelium of trabecular plates. They have a stellate shape, their long, thin processes, in contact with each other and with the endothelium of the Schlemm's canal, form a kind of network. The extracellular matrix is a product of endothelial cells, it consists of elastic and collagen fibrils and a homogeneous ground substance. It has been established that this substance contains acid mucopolysaccharides sensitive to hyaluronidase. In the juxtacanalicular tissue there are many nerve fibers of the same nature as in the trabecular plates.
Schlemm's channel
Schlemm's canal or scleral sinus, is a circular fissure located in the posterior outer part of the internal scleral groove (see Fig. 4). It is separated from the anterior chamber of the eye by a trabecular apparatus, outside the canal there is a thick layer of sclera and episclera, containing superficially and deeply located venous plexuses and arterial branches involved in the formation of the marginal looped network around the cornea. On histological sections, the average width of the sinus lumen is 300-500 microns, the height is about 25 microns. The inner wall of the sinus is uneven and in some places forms rather deep pockets. The lumen of the canal is often single, but can be double and even multiple. In some eyes, it is divided by partitions into separate compartments (Fig. 6).
Rice. 6. Drainage system of the eye. A massive septum is visible in the lumen of the Schlemm's canal. SW. 220.
Endothelium of the inner wall of Schlemm's canal represented by very thin, but long (40-70 microns) and rather wide (10-15 microns) cells. The thickness of the cell in the peripheral parts is about 1 µm, in the center it is much thicker due to the large rounded nucleus. The cells form a continuous layer, but their ends do not overlap (Fig. 7),
Rice. 7. Endothelium of the inner wall of Schlemm's canal. Two adjacent endothelial cells are separated by a narrow slit-like space (arrows). SW. 42,000.
therefore, the possibility of fluid filtration between cells is not excluded. Using electron microscopy, giant vacuoles were found in the cells, located mainly in the perinuclear zone (Fig. 8).
Rice. eight. Giant vacuole (1) located in the endothelial cell of the inner wall of Schlemm's canal (2). SW. 30,000.
One cell may contain several oval-shaped vacuoles, the maximum diameter of which varies from 5 to 20 microns. According to N. Inomata et al. (1972), there are 1600 endothelial nuclei and 3200 vacuoles per 1 mm of Schlemm's canal. All vacuoles are open towards the trabecular tissue, but only some of them have pores leading to Schlemm's canal. The size of the openings connecting the vacuoles with the juxtacanalicular tissue is 1-3.5 microns, with the Schlemm's canal - 0.2-1.8 microns.
Endothelial cells of the inner wall of the sinus do not have a pronounced basement membrane. They lie on a very thin uneven layer of fibers (mostly elastic) associated with the underlying substance. Short endoplasmic processes of cells penetrate deep into this layer, as a result of which the strength of their connection with the juxtacanalicular tissue increases.
Endothelium of the outer wall of the sinus differs in that it does not have large vacuoles, the cell nuclei are flat and the endothelial layer lies on a well-formed basement membrane.
Collector tubules, venous plexuses
Outside of the Schlemm's canal, in the sclera, there is a dense network of blood vessels - intrascleral venous plexus, another plexus is located in the superficial layers of the sclera. Schlemm's canal is connected to both plexuses by the so-called collector tubules, or graduates. According to Yu. E. Batmanov (1968), the number of tubules varies from 37 to 49, the diameter is from 20 to 45 microns. Most graduates begin in the posterior sinus. Four types of collector tubules can be distinguished: 
Collector tubules of the 2nd type are clearly visible with biomicroscopy. They were first described by K. Ascher (1942) and were called "water veins". These veins contain pure or mixed with blood fluid. They appear in the limbus and go back, falling at an acute angle into the recipient veins that carry blood. Aqueous moisture and blood in these veins do not mix immediately: for some distance you can see a layer of colorless liquid and a layer (sometimes two layers along the edges) of blood in them. Such veins are called laminar. The mouths of the large collecting tubules are covered from the side of the sinus by a non-continuous septum, which, apparently, to some extent protects them from blockade by the inner wall of the Schlemm's canal with an increase in intraocular pressure. The outlet of large collectors has an oval shape and a diameter of 40-80 microns.
Episcleral and intrascleral venous plexuses are connected by anastomoses. The number of such anastomoses is 25-30, the diameter is 30-47 microns.
ciliary muscle
ciliary muscle closely related to the drainage system of the eye. There are four types of muscle fibers in a muscle:
- meridional (brücke muscle),
- radial, or oblique (Ivanov's muscle),
- circular (Muller muscle)
- and iridal fibers (Calazans muscle).
Rice. ten. Muscles of the ciliary body. 1 - meridional; 2 - radial; 3 - iridal; 4 - circular. SW. 35.
radial muscle has a less regular and more loose structure. Its fibers lie freely in the stroma of the ciliary body, fanning out from the angle of the anterior chamber to the ciliary processes. Part of the radial fibers starts from the uveal trabecula.
Circular muscle consists of individual bundles of fibers located in the anterior internal section of the ciliary body. The existence of this muscle is currently questioned. It can be considered as part of a radial muscle, the fibers of which are located not only radially, but also partially circular.
Iridal muscle located at the junction of the iris and ciliary body. It is represented by a thin bundle of muscle fibers going to the root of the iris. All parts of the ciliary muscle have a double - parasympathetic and sympathetic - innervation.
Contraction of the longitudinal fibers of the ciliary muscle leads to stretching of the trabecular membrane and expansion of the Schlemm's canal. Radial fibers have a similar but apparently weaker effect on the drainage system of the eye.
Variants of the structure of the drainage system of the eye
The iridocorneal angle in an adult has pronounced individual structural features [Nesterov A.P., Batmanov Yu.E., 1971]. We classify the angle not only as generally accepted, according to the width of the entrance to it, but also according to the shape of its top and the configuration of the bay. The apex of the angle can be acute, medium and obtuse. sharp top observed with the anterior location of the root of the iris (Fig. 11).
Rice. eleven. APC with a sharp apex and a posterior position of the Schlemm's canal. SW. 90.
In such eyes, the band of the ciliary body separating the iris and the corneoscleral side of the angle is very narrow. blunt top the angle is noted at the posterior connection of the iris root with the ciliary body (Fig. 12).
Rice. 12. The blunt apex of the APC and the middle position of the Schlemm's canal. SW. 200.
In this case, the front surface of the latter has the form of a wide strip. Middle corner point occupies an intermediate position between acute and obtuse.
The configuration of the corner bay in the section can be even and flask-shaped. With an even configuration, the anterior surface of the iris gradually passes into the ciliary body (see Fig. 12). The cone-shaped configuration is observed when the root of the iris forms a rather long thin isthmus.
With a sharp apex of the angle, the iris root is displaced anteriorly. This facilitates the formation of all types of angle-closure glaucoma, especially the so-called flat iris glaucoma. With a flask-shaped configuration of the angle bay, that part of the iris root, which is adjacent to the ciliary body, is especially thin. In the event of an increase in pressure in the posterior chamber, this part protrudes sharply anteriorly. In some eyes, the posterior wall of the angle bay is partly formed by the ciliary body. At the same time, its front part departs from the sclera, turns inside the eye and is located in the same plane with the iris (Fig. 13).
Rice. 13. CPC, the back wall of which is formed by the crown of the ciliary body. SW. 35.
In such cases, when performing antiglaucoma operations with iridectomy, the ciliary body can be damaged, causing severe bleeding.
There are three options for the location of the posterior edge of the Schlemm's canal relative to the apex of the angle of the anterior chamber: anterior, middle, and posterior. At the front(41% of observations) part of the angle bay is behind the sinus (Fig. 14).
Rice. fourteen. Anterior position of Schlemm's canal (1). The meridional muscle (2) originates in the sclera at a considerable distance from the canal. SW. 86.
Middle location(40% of observations) is characterized by the fact that the rear edge of the sine coincides with the top of the angle (see Fig. 12). It is essentially a variant of the anterior arrangement, since the entire Schlemm canal borders the anterior chamber. At the rear channel (19% of observations), part of it (sometimes up to 1/2 of the width) extends beyond the corner bay into the region bordering the ciliary body (see Fig. 11).
The angle of inclination of the lumen of the Schlemm's canal to the anterior chamber, more precisely to the inner surface of the trabeculae, varies from 0 to 35°, most often it is 10-15°.
The degree of development of the scleral spur varies widely among individuals. It can cover almost half of the lumen of the Schlemm's canal (see Fig. 4), but in some eyes the spur is short or completely absent (see Fig. 14).
Gonioscopic anatomy of the iridocorneal angle
Individual features of the structure of the APC can be studied in a clinical setting using gonioscopy. The main structures of the CPC are shown in fig. fifteen.
Rice. fifteen. Structures of the Criminal Procedure Code. 1 - front boundary ring Schwalbe; 2 - trabecula; 3 - Schlemm's channel; 4 - scleral spur; 5 - ciliary body.
In typical cases, the Schwalbe ring is seen as a slightly protruding grayish opaque line on the border between the cornea and sclera. When viewed with a slit, two beams of a light fork from the anterior and posterior surfaces of the cornea converge on this line. Behind the Schwalbe ring there is a slight depression - incisura, in which pigment granules settled there are often visible, especially noticeable in the lower segment. In some people, the Schwalbe ring prominates posteriorly very significantly and is displaced anteriorly (posterior embryotoxon). In such cases, it can be seen with biomicroscopy without a gonioscope.
Trabecular membrane stretched between the ring of Schwalbe in front and the scleral spur in the back. On gonioscopy, it appears as a rough grayish stripe. In children, the trabecula is translucent; with age, its transparency decreases and the trabecular tissue appears denser. Age-related changes also include the deposition of pigment granules in the trabecular binding, and sometimes exfoliative scales. In most cases, only the posterior half of the trabecular ring is pigmented. Much less often, the pigment is deposited in the inactive part of the trabeculae and even in the scleral spur. The width of the part of the trabecular strip visible during gonioscopy depends on the angle of view: the narrower the APC, the sharper the angle of its structures and the narrower they seem to the observer.
Scleral sinus separated from the anterior chamber by the posterior half of the trabecular band. The posteriormost part of the sinus often extends beyond the scleral spur. With gonioscopy, the sinus is visible only in cases where it is filled with blood, and only in those eyes in which trabecular pigmentation is absent or weakly expressed. In healthy eyes, the sinus fills with blood much easier than in glaucomatous eyes.
The scleral spur located posterior to the trabecula looks like a narrow whitish strip. It is difficult to identify in eyes with abundant pigmentation or a developed uveal structure at the ACA apex.
At the top of the APC, in the form of a strip of different widths, there is a ciliary body, more precisely, its front surface. The color of this stripe varies from light gray to dark brown depending on eye color. The width of the band of the ciliary body is determined by the place of attachment of the iris to it: the farther posteriorly the iris connects to the ciliary body, the wider the band visible during gonioscopy. With the posterior attachment of the iris, the apex of the angle is obtuse (see Fig. 12), with the anterior attachment it is sharp (see Fig. 11). With an excessively anterior attachment of the iris, the ciliary body is not visible on gonioscopy and the root of the iris begins at the level of the scleral spur or even the trabeculae.
The stroma of the iris forms folds, of which the most peripheral, often called the Fuchs fold, is located opposite the Schwalbe ring. The distance between these structures determines the width of the entrance (aperture) to the UPK bay. Between the fold of Fuchs and the ciliary body is located iris root. This is its thinnest part, which can move anteriorly, causing narrowing of the ACA, or posteriorly, leading to its expansion, depending on the ratio of pressures in the anterior and posterior chambers of the eye. Often, processes in the form of thin filaments, strands or narrow leaves depart from the stroma of the iris root. In some cases, they, bending around the top of the APC, pass to the scleral spur and form a uveal trabecula, in others they cross the bay of the angle, attaching to its anterior wall: to the scleral spur, trabecula, or even to the Schwalbe ring (processes of the iris, or pectinate ligament). It should be noted that in newborns, the uveal tissue in the APC is significantly expressed, but it atrophies with age, and in adults it is rarely detected during gonioscopy. The processes of the iris should not be confused with the goniosynechia, which are coarser and more irregularly arranged.
In the root of the iris and uveal tissue at the top of the APC, thin vessels are sometimes seen, located radially or circularly. In such cases, hypoplasia or atrophy of the iris stroma is usually found.
In clinical practice, it is important configuration, width and pigmentation of the CPC. The position of the iris root between the anterior and posterior chambers of the eye has a significant effect on the configuration of the APC bay. The root may be flat, protruding anteriorly, or sunken backwards. In the first case, the pressure in the anterior and posterior sections of the eye is the same or almost the same, in the second, the pressure is higher in the posterior section, and in the third, in the anterior chamber of the eye. Anterior protrusion of the entire iris indicates the state of a relative pupillary block with an increase in pressure in the posterior chamber of the eye. The protrusion of only the root of the iris indicates its atrophy or hypoplasia. Against the background of the general bombardment of the root of the iris, one can see focal tissue protrusions resembling bumps. These protrusions are associated with small focal atrophy of the stroma of the iris. The cause of the retraction of the root of the iris, which is observed in some eyes, is not entirely clear. One can think of either a higher pressure in the anterior than the posterior region of the eye, or some anatomical features that give the impression of a retraction of the iris root.
Width of the CPC depends on the distance between the Schwalbe ring and the iris, its configuration and the place of attachment of the iris to the ciliary body. The classification of the width U of the PC below is made taking into account the zones of the angle visible during gonioscopy and its approximate estimate in degrees (Table 1).
Table 1. Gonioscopic classification of the width of the CPC
With a wide APC, you can see all its structures, with a closed one - only the Schwalbe ring and sometimes the anterior part of the trabecula. Correctly assessing the width of the APC during gonioscopy is possible only if the patient is looking straight ahead. By changing the position of the eye or the inclination of the gonioscope, all structures can be seen even with a narrow APC.
The width of the CPC can be tentatively estimated even without a gonioscope. A narrow beam of light from a slit lamp is directed to the iris through the peripheral part of the cornea as close to the limbus as possible. The thickness of the cut of the cornea and the width of the entrance to the CPC are compared, i.e., the distance between the posterior surface of the cornea and the iris is determined. With a wide APC, this distance is approximately equal to the thickness of the cut of the cornea, medium-wide - 1/2 of the thickness of the cut, narrow - 1/4 of the thickness of the cornea and slit-like - less than 1/4 of the thickness of the corneal cut. This method makes it possible to estimate the width of the CCA only in the nasal and temporal segments. It should be borne in mind that the APC is somewhat narrower at the top, and wider at the bottom than in the lateral parts of the eye.
The simplest test for estimating the width of the CCA was proposed by M. V. Vurgaft et al. (1973). He based on the phenomenon of total internal reflection of light by the cornea. The light source (table lamp, flashlight, etc.) is placed on the outside of the eye under study: first at the level of the cornea, and then slowly shifted backwards. At a certain moment, when the rays of light hit the inner surface of the cornea at a critical angle, a bright light spot appears on the nasal side of the eye in the area of the scleral limbus. A wide spot - with a diameter of 1.5-2 mm - corresponds to a wide, and a diameter of 0.5-1 mm - to a narrow CPC. The blurred glow of the limbus, which appears only when the eye is turned inward, is characteristic of a slit-like APC. When the iridocorneal angle is closed, the luminescence of the limbus cannot be caused.
The narrow and especially slit-like APC is prone to blockade by its iris root in the event of pupillary block or pupil dilation. A closed corner indicates a pre-existing blockade. In order to differentiate the functional block of the angle from the organic one, the cornea is pressed with a gonioscope without a haptic part. In this case, the fluid from the central part of the anterior chamber is displaced to the periphery, and with a functional blockade, the angle opens. The detection of narrow or wide adhesions in the APC indicates its partial organic blockade.
The trabecula and adjacent structures often acquire a dark color due to the deposition of pigment granules in them, which enter the aqueous humor during the breakdown of the pigment epithelium of the iris and ciliary body. The degree of pigmentation is usually assessed in points from 0 to 4. The absence of pigment in the trabecula is indicated by the number 0, weak pigmentation of its posterior part - 1, intense pigmentation of the same part - 2, intense pigmentation of the entire trabecular zone - 3 and all structures of the anterior wall of the APC - 4 In healthy eyes, pigmentation of trabeculae appears only in middle or old age, and its severity according to the above scale is estimated at 1-2 points. A more intense pigmentation of the structures of the APC indicates a pathology.
Outflow of aqueous humor from the eye
Distinguish between the main and additional (uveoscleral) outflow tracts. According to some calculations, approximately 85-95% of aqueous humor flows out along the main route, and 5-15% along the uveoscleral route. The main outflow passes through the trabecular system, Schlemm's canal and its graduates.
The trabecular apparatus is a multi-layer, self-cleaning filter that provides one-way movement of fluid and small particles from the anterior chamber to the scleral sinus. Resistance to the movement of fluid in the trabecular system in healthy eyes mainly determines the individual level of IOP and its relative constancy.
There are four anatomical layers in the trabecular apparatus. The first one, uveal trabecula, can be compared with a sieve that does not impede the movement of liquid. Corneoscleral trabecula has a more complex structure. It consists of several "floors" - narrow slits, divided by layers of fibrous tissue and processes of endothelial cells into numerous compartments. The holes in the trabecular plates do not line up with each other. The movement of fluid is carried out in two directions: in the transverse direction, through the holes in the plates, and longitudinally, along the intertrabecular fissures. Taking into account the peculiarities of the architectonics of the trabecular meshwork and the complex nature of the movement of fluid in it, it can be assumed that part of the resistance to the outflow of aqueous humor is localized in the corneoscleral trabeculae.
in the juxtacanalicular tissue no clear, formalized outflow paths. Nevertheless, according to J. Rohen (1986), moisture moves through this layer along certain routes, delimited by less permeable tissue areas containing glycosaminoglycans. It is believed that the main part of the outflow resistance in normal eyes is localized in the juxtacanalicular layer of the trabecular diaphragm.
The fourth functional layer of the trabecular diaphragm is represented by a continuous layer of endothelium. The outflow through this layer occurs mainly through dynamic pores or giant vacuoles. Due to their significant number and size, the resistance to outflow here is small; according to A. Bill (1978), no more than 10% of its total value.
The trabecular plates are connected to the longitudinal fibers by the ciliary muscle and through the uveal trabecula to the root of the iris. Under normal conditions, the tone of the ciliary muscle changes continuously. This is accompanied by fluctuations in the tension of the trabecular plates. As a result trabecular fissures alternately widen and contract, which contributes to the movement of fluid within the trabecular system, its constant mixing and renewal. A similar, but weaker effect on the trabecular structures is exerted by fluctuations in the tone of the pupillary muscles. The oscillatory movements of the pupil prevent the stagnation of moisture in the crypts of the iris and facilitate the outflow of venous blood from it.
Continuous fluctuations in the tone of the trabecular plates play an important role in maintaining their elasticity and resilience. It can be assumed that the cessation of oscillatory movements of the trabecular apparatus leads to coarsening of fibrous structures, degeneration of elastic fibers and, ultimately, to a deterioration in the outflow of aqueous humor from the eye.
The movement of fluid through the trabeculae performs another important function: washing, cleaning the trabecular filter. The trabecular meshwork receives cell decay products and pigment particles, which are removed with a current of aqueous humor. The trabecular apparatus is separated from the scleral sinus by a thin layer of tissue (juxtacanalicular tissue) containing fibrous structures and fibrocytes. The latter continuously produce, on the one hand, mucopolysaccharides, and on the other hand, enzymes that depolymerize them. After depolymerization, mucopolysaccharide residues are washed out with aqueous humor into the lumen of the scleral sinus.
Washing function of aqueous humor well studied in experiments. Its effectiveness is proportional to the minute volume of fluid filtering through the trabeculae, and, therefore, depends on the intensity of the secretory function of the ciliary body.
It has been established that small particles, up to 2-3 microns in size, are partially retained in the trabecular meshwork, while larger particles are completely retained. Interestingly, normal erythrocytes, which are 7–8 µm in diameter, pass quite freely through the trabecular filter. This is due to the elasticity of erythrocytes and their ability to pass through pores with a diameter of 2-2.5 microns. At the same time, erythrocytes that have changed and lost their elasticity are retained by the trabecular filter.
Cleaning the trabecular filter from large particles occurs by phagocytosis. Phagocytic activity is characteristic of trabecular endothelial cells. The state of hypoxia, which occurs when the outflow of aqueous humor through the trabecula is disturbed under conditions of a decrease in its production, leads to a decrease in the activity of the phagocytic mechanism for cleaning the trabecular filter.
The ability of the trabecular filter to self-cleaning decreases in old age due to a decrease in the rate of production of aqueous humor and dystrophic changes in the trabecular tissue. It should be borne in mind that trabeculae do not have blood vessels and receive nutrition from aqueous humor, so even a partial violation of its circulation affects the state of the trabecular diaphragm.
Valvular function of the trabecular system, passing liquid and particles only in the direction from the eye to the scleral sinus, is associated primarily with the dynamic nature of the pores in the sinus endothelium. If the pressure in the sinus is higher than in the anterior chamber, then giant vacuoles do not form and the intracellular pores close. At the same time, the outer layers of the trabeculae are displaced inwards. This compresses the juxtacanalicular tissue and intertrabecular fissures. The sinus often fills with blood, but neither plasma nor red blood cells pass into the eye unless the endothelium of the inner wall of the sinus is damaged.
The scleral sinus in the living eye is a very narrow gap, the movement of fluid through which is associated with a significant expenditure of energy. As a result, aqueous humor entering the sinus through the trabecula flows through its lumen only to the nearest collector canal. With an increase in IOP, the sinus lumen narrows and the outflow resistance through it increases. Due to the large number of collector tubules, the outflow resistance in them is small and more stable than in the trabecular apparatus and sinus.
Outflow of aqueous humor and Poiseuille's law
The drainage apparatus of the eye can be considered as a system consisting of tubules and pores. The laminar motion of a fluid in such a system obeys Poiseuille's law. In accordance with this law, the volumetric velocity of the fluid is directly proportional to the pressure difference at the initial and final points of movement. Poiseuille's law is the basis of many studies on the hydrodynamics of the eye. In particular, all tonographic calculations are based on this law. Meanwhile, a lot of data has now accumulated, indicating that with an increase in intraocular pressure, the minute volume of aqueous humor increases to a much lesser extent than follows from Poiseuille's law. This phenomenon can be explained by the deformation of the lumen of the Schlemm canal and trabecular fissures with an increase in ophthalmotonus. The results of studies on isolated human eyes with perfusion of the Schlemm's canal with ink showed that the width of its lumen progressively decreases with an increase in intraocular pressure [Nesterov A.P., Batmanov Yu.E., 1978]. In this case, the sinus is compressed at first only in the anterior section, and then focal, patchy compression of the canal lumen occurs in other parts of the canal. With an increase in ophthalmotonus up to 70 mm Hg. Art. a narrow strip of the sinus remains open in its most posterior section, protected from compression by a scleral spur.
With a short-term increase in intraocular pressure, the trabecular apparatus, moving outward into the lumen of the sinus, stretches and its permeability increases. However, the results of our studies have shown that if a high level of ophthalmotonus is maintained for several hours, then progressive compression of the trabecular fissures occurs: first in the area adjacent to the Schlemm's canal, and then in the rest of the corneoscleral trabeculae.
Uveoscleral outflow
In addition to fluid filtration through the drainage system of the eye, in monkeys and humans, the more ancient outflow route was partially preserved - through the anterior vascular tract (Fig. 16).
Rice. 16. CPC and ciliary body. The arrows show the uveoscleral outflow tract of aqueous humor. SW. 36.
Uveal (or uveoscleral) outflow is carried out from the angle of the anterior chamber through the anterior section of the ciliary body along the fibers of the Brücke muscle into the suprachoroidal space. From the latter, the fluid flows through the emissaries and directly through the sclera or is absorbed into the venous sections of the capillaries of the choroid.
The studies carried out in our laboratory [Cherkasova IN, Nesterov AP, 1976] showed the following. The uveal outflow functions under the condition that the pressure in the anterior chamber exceeds the pressure in the suprachoroidal space by at least 2 mm Hg. st. In the suprachoroidal space, there is significant resistance to fluid movement, especially in the meridional direction. The sclera is permeable to fluid. The outflow through it obeys the Poiseuille law, that is, it is proportional to the value of the filtering pressure. At a pressure of 20 mm Hg. through 1 cm2 of the sclera, an average of 0.07 mm3 of liquid is filtered per minute. With thinning of the sclera, the outflow through it proportionally increases. Thus, each section of the uveoscleral outflow tract (uveal, suprachoroidal, and scleral) resists the outflow of aqueous humor. An increase in ophthalmotonus is not accompanied by an increase in uveal outflow, since the pressure in the suprachoroidal space also increases by the same amount, which also narrows. Miotics reduce uveoscleral outflow, while cycloplegics increase it. According to A. Bill and C. Phillips (1971), in humans, from 4 to 27% of aqueous humor flows through the uveoscleral pathway.
Individual differences in the intensity of uveoscleral outflow appear to be quite significant. They are depend on individual anatomical features and age. Van der Zippen (1970) found open spaces around the ciliary muscle bundles in children. With age, these spaces are filled with connective tissue. When the ciliary muscle contracts, the free spaces are compressed, and when it relaxes, they expand.
According to our observations, uveoscleral outflow does not function in acute glaucoma and malignant glaucoma. This is due to the blockade of the APC by the root of the iris and a sharp increase in pressure in the posterior part of the eye.
Uveoscleral outflow seems to play some role in the development of ciliochoroidal detachment. As is known, uveal tissue fluid contains a significant amount of protein due to the high permeability of the capillaries of the ciliary body and choroid. The colloid osmotic pressure of blood plasma is approximately 25 mm Hg, uveal fluid - 16 mm Hg, and the value of this indicator for aqueous humor is close to zero. At the same time, the difference in hydrostatic pressure in the anterior chamber and suprachoroid does not exceed 2 mm Hg. Therefore, the main driving force for the outflow of aqueous humor from the anterior chamber to the suprachoroid is the difference is not hydrostatic, but colloidal osmotic pressure. The colloid osmotic pressure of the blood plasma is also the reason for the absorption of uveal fluid into the venous sections of the vascular network of the ciliary body and choroid. Hypotension of the eye, whatever it is caused, leads to the expansion of uveal capillaries and increase their permeability. The protein concentration, and consequently, the colloid osmotic pressure of the blood plasma and uveal fluid become approximately equal. As a result, the absorption of aqueous humor from the anterior chamber into the suprachoroid increases, and the ultrafiltration of the uveal fluid into the vasculature stops. Retention of the uveal tissue fluid leads to detachment of the ciliary body of the choroid, cessation of the secretion of aqueous humor.
Regulation of production and outflow of aqueous humor
Aqueous moisture formation rate regulated by both passive and active mechanisms. With an increase in IOP, uveal vessels narrow, blood flow and filtration pressure in the capillaries of the ciliary body decrease. A decrease in IOP leads to the opposite effects. Changes in uveal blood flow during fluctuations in IOP are to some extent useful, as they contribute to maintaining a stable IOP.
There is reason to believe that the active regulation of aqueous humor production is influenced by the hypothalamus. Both functional and organic hypothalamic disorders are often associated with increased amplitude of daily fluctuations in IOP and hypersecretion of intraocular fluid [Bunin A. Ya., 1971].
Passive and active regulation of the outflow of fluid from the eye is partly discussed above. Of major importance in the mechanisms of outflow regulation is ciliary muscle. In our opinion, the iris also plays a role. The root of the iris is associated with the anterior surface of the ciliary body and the uveal trabecula. When the pupil is constricted, the iris root, and with it the trabecula, is stretched, the trabecular diaphragm moves inward, and the trabecular fissures and Schlemm's canal expand. A similar effect is produced by contraction of the pupil dilator. The fibers of this muscle not only dilate the pupil, but also stretch the root of the iris. The effect of tension on the root of the iris and trabeculae is especially pronounced in cases where the pupil is rigid or fixed with miotics. This allows us to explain the positive effect on the outflow of aqueous humor?-Adrenoagonists and especially their combination (for example, adrenaline) with miotics.
Changing the depth of the anterior chamber also has a regulatory effect on the outflow of aqueous humor. As shown by perfusion experiments, deepening the chamber leads to an immediate increase in outflow, and its shallowing leads to its delay. We came to the same conclusion, studying outflow changes in normal and glaucomatous eyes under the influence of anterior, lateral and posterior compression of the eyeball [Nesterov A.P. et al., 1974]. With anterior compression through the cornea, the iris and lens were pressed backwards and the outflow of moisture increased on average 1.5 times compared with its value with lateral compression of the same force. Posterior compression led to an anterior displacement of the iridolenticular diaphragm, and the outflow rate decreased by 1.2–1.5 times. The effect of changes in the position of the iridolenticular diaphragm on the outflow can only be explained by the mechanical action of the tension of the iris root and zonn ligaments on the trabecular apparatus of the eye. Since the anterior chamber deepens with increased moisture production, this phenomenon contributes to maintaining a stable IOP.
Article from the book: .
The eye, the eyeball has an almost spherical shape, approximately 2.5 cm in diameter. It consists of several shells, of which three are the main ones:
- sclera is the outer layer
- choroid - middle,
- the retina is internal.
Rice. 1. Schematic representation of the mechanism of accommodation on the left - focusing into the distance; on the right - focusing on close objects.
The sclera is white with a milky sheen, except for its anterior part, which is transparent and is called the cornea. Light enters the eye through the cornea. The choroid, the middle layer, contains the blood vessels that carry blood to feed the eye. Just below the cornea, the choroid passes into the iris, which determines the color of the eyes. In the center of it is the pupil. The function of this shell is to limit the entry of light into the eye at high brightness. This is achieved by constricting the pupil in high light and dilating in low light. Behind the iris is a biconvex lens-like lens that captures light as it passes through the pupil and focuses it on the retina. Around the lens, the choroid forms a ciliary body, which contains a muscle that regulates the curvature of the lens, which provides a clear and distinct vision of objects at different distances. This is achieved as follows (Fig. 1).
Pupil is a hole in the center of the iris through which light rays pass into the eye. In an adult at rest, the pupil diameter in daylight is 1.5–2 mm, and in the dark it increases to 7.5 mm. The main physiological role of the pupil is to regulate the amount of light entering the retina.
Pupil constriction (miosis) occurs with an increase in illumination (this limits the light flux entering the retina, and, therefore, serves as a protective mechanism), when viewing closely spaced objects, when accommodation and convergence of visual axes occur (convergence), as well as during.
Pupil dilation (mydriasis) occurs in low light (which increases the illumination of the retina and thereby increases the sensitivity of the eye), as well as when excited, any afferent nerves, with emotional stress reactions associated with an increase in sympathetic tone, with mental excitations, suffocation,.
Pupil size is regulated by the annular and radial muscles of the iris. The radial muscle, which dilates the pupil, is innervated by a sympathetic nerve coming from the superior cervical ganglion. The annular muscle, which narrows the pupil, is innervated by parasympathetic fibers of the oculomotor nerve.
Fig 2. Scheme of the structure of the visual analyzer
1 - retina, 2 - uncrossed optic nerve fibers, 3 - crossed optic nerve fibers, 4 - optic tract, 5 - lateral geniculate body, 6 - lateral root, 7 - visual lobes.
The smallest distance from an object to the eye, at which this object is still clearly visible, is called the near point of clear vision, and the largest distance is called the far point of clear vision. When an object is located at a near point, accommodation is maximum, at a far point, there is no accommodation. The difference between the refractive powers of the eye at maximum accommodation and at rest is called the accommodation power. The unit of optical power is the optical power of a lens with a focal length1 meter. This unit is called the diopter. To determine the optical power of the lens in diopters, one should be divided by the focal length in meters. The amount of accommodation is not the same for different people and varies depending on age from 0 to 14 diopters.
For a clear vision of an object, it is necessary that the rays of each of its points be focused on the retina. If you look into the distance, then close objects are not clearly visible, blurry, since the rays from near points are focused behind the retina. It is impossible to see objects equally clearly at different distances from the eye at the same time.
Refraction(ray refraction) reflects the ability of the optical system of the eye to focus the image of an object on the retina. The peculiarities of the refractive properties of any eye include the phenomenon spherical aberration . It lies in the fact that the rays passing through the peripheral parts of the lens are refracted more strongly than the rays passing through its central parts (Fig. 65). Therefore, the central and peripheral rays do not converge at one point. However, this feature of refraction does not interfere with a clear vision of the object, since the iris does not transmit rays and thereby eliminates those that pass through the periphery of the lens. The unequal refraction of rays of different wavelengths is called chromatic aberration .
The refractive power of the optical system (refraction), that is, the ability of the eye to refract, is measured in conventional units - diopters. The diopter is the refractive power of a lens, in which parallel rays, after refraction, are collected at a focus at a distance of 1 m.
Rice. 3. The course of rays in various types of clinical refraction of the eye a - emetropia (normal); b - myopia (myopia); c - hypermetropia (farsightedness); d - astigmatism.
We see the world around us clearly when all departments “work” harmoniously and without interference. In order for the image to be sharp, the retina must obviously be in the back focus of the optical system of the eye. Various violations of the refraction of light rays in the optical system of the eye, leading to defocusing of the image on the retina, are called refractive errors (ametropia). These include myopia, hyperopia, age-related farsightedness and astigmatism (Fig. 3).
With normal vision, which is called emmetropic, visual acuity, i.e. the maximum ability of the eye to distinguish individual details of objects usually reaches one conventional unit. This means that a person is able to see two separate points, visible at an angle of 1 minute.
With an anomaly of refraction, visual acuity is always below 1. There are three main types of refractive error - astigmatism, myopia (myopia) and farsightedness (hypermetropia).
Refractive errors cause nearsightedness or farsightedness. The refraction of the eye changes with age: it is less than normal in newborns, in old age it can decrease again (the so-called senile farsightedness or presbyopia).
Myopia correction scheme
Astigmatism due to the fact that, due to congenital features, the optical system of the eye (cornea and lens) refracts rays differently in different directions (along the horizontal or vertical meridian). In other words, the phenomenon of spherical aberration in these people is much more pronounced than usual (and it is not compensated by pupil constriction). So, if the curvature of the surface of the cornea in a vertical section is greater than in a horizontal one, the image on the retina will not be clear, regardless of the distance to the object.
The cornea will have, as it were, two main focuses: one for the vertical section, the other for the horizontal. Therefore, the rays of light passing through the astigmatic eye will be focused in different planes: if the horizontal lines of the object are focused on the retina, then the vertical lines are in front of it. Wearing cylindrical lenses, matched to the real defect in the optical system, to a certain extent compensates for this refractive error.
Nearsightedness and farsightedness due to changes in the length of the eyeball. With normal refraction, the distance between the cornea and the central fovea (yellow spot) is 24.4 mm. With myopia (nearsightedness), the longitudinal axis of the eye is larger than 24.4 mm, so the rays from a distant object are focused not on the retina, but in front of it, in the vitreous body. To see clearly into the distance, it is necessary to place concave lenses in front of myopic eyes, which will push the focused image onto the retina. In a far-sighted eye, the longitudinal axis of the eye is shortened; less than 24.4 mm. Therefore, rays from a distant object are focused not on the retina, but behind it. This lack of refraction can be compensated by an accommodative effort, i.e. an increase in the convexity of the lens. Therefore, a far-sighted person strains the accommodative muscle, considering not only close, but also distant objects. When viewing close objects, the accommodative efforts of far-sighted people are insufficient. Therefore, for reading, farsighted people should wear glasses with biconvex lenses that enhance the refraction of light.
Refractive errors, in particular myopia and hyperopia, are also common among animals, for example, in horses; myopia is very often observed in sheep, especially cultivated breeds.
The ciliary muscle is annular in shape and makes up the main part of the ciliary body. located around the lens. In the thickness of the muscle, the following types of smooth muscle fibers are distinguished:
- meridional fibers(Brücke muscle) are adjacent directly to the sclera and are attached to the inside of the limbus, partially woven into the trabecular meshwork. When the Brücke muscle contracts, the ciliary muscle moves forward. The Brücke muscle is involved in focusing on nearby objects, its activity is necessary for the process of accommodation. Doesn't matter as much as the Mueller muscle. In addition, the contraction and relaxation of the meridional fibers causes an increase and decrease in the size of the pores of the trabecular meshwork, and, accordingly, changes the rate of outflow of aqueous humor into the Schlemm's canal.
- Radial fibers(Ivanov's muscle) depart from the scleral spur towards the ciliary processes. Like the Brücke muscle, it provides decompression.
- Circular fibers(Muller muscle) are located in the inner part of the ciliary muscle. With their contraction, the internal space narrows, the tension of the fibers of the zinn ligament is weakened, and the elastic lens becomes more spherical. A change in the curvature of the lens leads to a change in its optical power and a shift in focus to close objects. Thus, the process of accommodation is carried out.
The process of accommodation is a complex process, which is provided by the reduction of all three of the above types of fibers.
In places of attachment to the sclera, the ciliary muscle becomes very thin.
innervation
Radial and circular fibers receive parasympathetic innervation as part of short ciliary branches (nn.ciliaris breves) from the ciliary node. Parasympathetic fibers originate from the additional nucleus of the oculomotor nerve (nucleus oculomotorius accessorius) and, as part of the root of the oculomotor nerve (radix oculomotoria, oculomotor nerve, III pair of cranial nerves), enter the ciliary node.
The meridional fibers receive sympathetic innervation from the internal carotid plexus located around the internal carotid artery.
Sensitive innervation is provided by the ciliary plexus, which is formed from the long and short branches of the ciliary nerve, which are sent to the central nervous system as part of the trigeminal nerve (V pair of cranial nerves).
medical significance
Damage to the ciliary muscle leads to paralysis of accommodation (cycloplegia). With prolonged tension of accommodation (for example, prolonged reading or high uncorrected farsightedness), a convulsive contraction of the ciliary muscle occurs (accommodation spasm).
The weakening of the accommodative ability with age (presbyopia) is not associated with the loss of the functional ability of the muscle, but with a decrease in its own elasticity.
The iris is the anterior part of the choroid of the eye. It is located, unlike its other two departments (the ciliary body and the choroid itself), not parietal, but in the frontal plane with respect to the limbus. It has the shape of a disk with a hole in the center and consists of three sheets (layers) - anterior border, stromal (mesodermal) and posterior, pigment-muscular (ectodermal).
The anterior boundary layer of the anterior leaf of the iris is formed by fibroblasts, connected by their processes. Below them is a thin layer of pigment-containing melanocytes. Even deeper in the stroma is a dense network of capillaries and collagen fibers. The latter extend to the muscles of the iris and in the region of its root are connected to the ciliary body. Spongy tissue is richly supplied with sensitive nerve endings from the ciliary plexus. The surface of the iris does not have a continuous endothelial cover, and therefore chamber moisture easily penetrates into its tissue through numerous gaps (crypts).
The posterior leaf of the iris includes two muscles - the annular sphincter of the pupil (innervated by the fibers of the oculomotor nerve) and the radially oriented dilator (innervated by sympathetic nerve fibers from the internal carotid plexus), as well as the pigment epithelium (epithelium pigmentorum) from two layers of cells (is a continuation of the undifferentiated retina - pars iridica retinae).
The thickness of the iris ranges from 0.2 to 0.4 mm. It is especially thin in the root part, i.e., on the border with the ciliary body. It is in this zone that, with severe contusions of the eyeball, its detachments (iridodialys) can occur.
In the center of the iris, as already mentioned, there is a pupil (pupilla), the width of which is regulated by the work of the antagonist muscles. Due to this, it varies depending on the level of illumination of the external environment and the level of illumination of the retina. The higher it is, the narrower the pupil, and vice versa.
The anterior surface of the iris is usually divided into two zones: pupillary (about 1 mm wide) and ciliary (3-4 mm). The border is a slightly raised jagged circular roller - mesentery. In the pupillary zone, near the pigment border, there is a pupillary sphincter, in the ciliary zone - a dilator.
Abundant blood supply to the iris is carried out by two long posterior and several anterior ciliary arteries (branches of the muscular arteries), which eventually form a large arterial circle (circulus arteriosus iridis major). New branches then depart from it in a radial direction, forming, in turn, already at the border of the pupillary and ciliary zones of the iris, a small arterial circle (circulis arteriosus iridis minor).
The iris receives its sensitive innervation from nn. ciliares longi (branches n. nasociliaris),
The condition of the iris should be assessed according to a number of criteria:
color (normal for a particular patient or changed); drawing (clear, blurred); the state of the vessels (not visible, dilated, there are newly formed trunks); location relative to other structures of the eye (fusions with
cornea, lens); tissue density (normal, / there are thinning). Criteria for evaluating pupils: it is necessary to take into account their size, shape, as well as reaction to light, convergence and accommodation.
Vessels are based on:
Participate in the production and outflow of intraocular fluid (3 - 5%).
When injured, the moisture of the anterior chamber flows out - the iris is adjacent to the wound - a barrier against infection.
Diaphragm that regulates the flow of light through the muscles (sphincter and dilator) and pigment on the posterior surface of the cornea.
Opacity of the iris due to the presence of the pigment epithelium, which is the pigment layer of the retina.
The iris enters the anterior segment of the eye, which is most often injured - abundant innervation - pain syndrome is pronounced.
In inflammation, the exudative component predominates.
2. Ciliary body
On a vertical section of the eye, the ciliary (ciliary) body has the shape of a ring with an average width of 5-6 mm (in the nasal half and at the top 4.6-5.2 mm, in the temporal and below - 5.6-6.3 mm) , on the meridional - a triangle protruding into its cavity. Macroscopically, in this belt of the choroid itself, two parts can be distinguished - a flat one (orbiculus ciliaris), 4 mm wide, which borders on the ora serrata of the retina, and a ciliary (corona ciliaris) with 70-80 whitish ciliary processes (processus ciliares) with a width of 2 mm . Each ciliary process has the form of a roller or plate about 0.8 mm high and 2 mm long (in the meridional direction). The surface of the interprocessal cavities is also uneven and covered with small protrusions. The ciliary body is projected onto the surface of the sclera in the form of a belt of the width indicated above (6 mm), starting, and actually ending, at the scleral spur, i.e., 2 mm from the limbus.
Histologically, several layers are distinguished in the ciliary body, which, in the direction from the outside to the inside, are arranged in the following order: muscular, vascular, basal plate, pigmented and non-pigmented epithelium (pars ciliaris retinae) and, finally, membrana limitans interna, to which the fibers of the ciliary girdle are attached.
The smooth ciliary muscle begins at the equator of the eye from the delicate pigmented tissue of the suprachoroid in the form of muscle stars, the number of which rapidly increases as it approaches the posterior edge of the muscle. Ultimately, they merge with each other and form loops, giving a visible beginning to the ciliary muscle itself. This happens at the level of the dentate line of the retina. In the outer layers of the muscle, the fibers that form it have a strictly meridional direction (fibrae meridionales) and are called m. Brucci. More deeply lying muscle fibers acquire first a radial (Ivanov's muscle), and then a circular (m. Mulleri) direction. At the place of its attachment to the scleral spur, the ciliary muscle becomes noticeably thinner. Two portions of it (radial and circular) are innervated by the oculomotor nerve, and the longitudinal fibers are sympathetic. Sensitive innervation is provided from the plexus ciliaris, formed by the long and short branches of the ciliary nerves.
The vascular layer of the ciliary body is a direct continuation of the same layer of the choroid and consists mainly of veins of various calibers, since the main arterial vessels of this anatomical region pass in the perichoroidal space and through the ciliary muscle. The individual small arteries present here go in the opposite direction, i.e., into the choroid. As for the ciliary processes, they include a conglomerate of wide capillaries and small veins.
Lam. basalis of the ciliary body also serves as a continuation of a similar structure of the choroid and is covered from the inside by two layers of epithelial cells - pigmented (in the outer layer) and pigmentless. Both are extensions of the reduced retina.
The inner surface of the ciliary body is connected with the lens through the so-called ciliary girdle (zonula ciliaris), consisting of many very thin vitreous fibers (fibrae zonulares). This girdle acts as a suspension ligament of the lens and, together with it, as well as with the ciliary muscle, forms a single accommodative apparatus of the eye.
The blood supply to the ciliary body is carried out mainly by two long posterior ciliary arteries (branches of the ophthalmic artery).
Functions of the ciliary body: produces intraocular fluid (ciliary processes and epithelium) and participates in accommodation (muscular part with ciliary girdle and lens).
Peculiarities: participates in accommodation by changing the optical power of the lens.
It has a coronal (triangular, has processes - a zone of moisture production by ultrafiltration of blood) and a flat part.
Functions:
Ø production of intraorbital fluid:
intraorbital fluid washes the vitreous body, the lens, enters the posterior chamber (iris, ciliary body, lens), then through the pupil area into the anterior chamber and through the angle into the venous network. The production rate exceeds the outflow rate, therefore, intraocular pressure is created, which ensures the efficiency of feeding avascular environments. With a decrease in intraorbital pressure, the retina will not be adjacent to the choroid, therefore, detachment and wrinkling of the eye will occur.
Ø participation in the act of accommodation:
Accommodation- the ability of the eye to see objects at different distances due to a change in the refractive power of the lens.
Three groups of muscle fibers:
Muller - circular pulp - flattening of the lens, an increase in the anteroposterior size;
Ivanova - stretching of the lens;
Brucke - from the choroid to the angle of the anterior chamber, the outflow of fluid.
The ciliary body itself is attached to the lens by a ligament.
Ø changes the quantity and quality of intraorbital fluid produced, exudation
Ø has its own innervation == with inflammation, strong, nocturnal pains (in the coronal part more than in the flat)
The ciliary (ciliary) muscle is a paired organ of the eyeball, which is involved in the process of accommodation.
Structure
The muscle consists of different types of fibers (meridional, radial, circular), which, in turn, perform different functions.
meridional
The part that is attached to the limbus is adjacent to the sclera and partially goes into the trabecular meshwork. This part is also called the Brücke muscle. In a tense state, it moves forward and participates in the processes of focusing and disaccommodation (distant vision). This function helps to maintain the ability to project light on the retina during sudden movements of the head. The contraction of the meridional fibers also promotes the circulation of intraocular fluid through the Schlemm canal.
Radial
Location - from the scleral spur to the ciliary processes. Also called Ivanov's muscle. Like the meridional ones, it participates in disaccommodation.
Circular
Or Müller's muscles, located radially in the area of \u200b\u200bthe inner part of the ciliary muscle. In tension, a narrowing of the internal space occurs and the tension of the zinn ligament is weakened. The result of the contraction is the acquisition of a spherical lens. This change in focus is more favorable for near vision.
Gradually, with age, the process of accommodation is weakened due to the loss of elasticity of the lens. Muscular activity does not lose its ability in old age.
The blood supply to the ciliary muscle is carried out with the help of three arteries, says obaglaza.ru. The outflow of blood occurs through the anteriorly located ciliary veins.
Diseases
With intense loads (reading in transport, a long stay in front of a computer monitor) and overvoltage, a convulsive contraction develops. In this case, a spasm of accommodation occurs (false myopia). When such a process is delayed, it leads to true myopia.
With some injuries of the eyeball, the ciliary muscle can also be damaged. This can cause absolute accommodation paralysis (loss of ability to see clearly up close).
Disease prevention
With prolonged loads, in order to prevent disruption of the ciliary muscle, the site recommends the following:
- perform strengthening exercises for the eyes and cervical spine;
- take breaks of 10 - 15 minutes every hour;
- to refuse from bad habits;
- take vitamins for the eyes.
