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Radial muscle of the eye. Optical system of the eye. Construction of the image. Accommodation. Refraction and its violations. Outflow of aqueous humor from the eye

Ciliary muscle, or ciliary muscle (lat. musculus ciliaris) - internal paired muscle of the eye, which provides accommodation. Contains smooth muscle fibers. The ciliary muscle, like the muscles of the iris, is of neural origin.

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 quickly increases as it approaches the posterior edge of the muscle. Ultimately, they merge with each other and form loops, giving rise to the visible beginning of the ciliary muscle itself. This occurs at the level of the dentate line of the retina.

Structure

In the outer layers of the muscle, the fibers that form it have a strictly meridional direction (fibrae meridionales) and are called m. Brucci. Deeper-lying muscle fibers first acquire a radial direction (fibrae radiales, Ivanov's muscle, 1869), and then a circular direction (fabrae circulares, m. Mulleri, 1857). At the site of its attachment to the scleral spur, the ciliary muscle becomes noticeably thinner.

  • Meridian fibers (Brücke muscle) - the most powerful and longest (on average 7 mm), having an attachment in the area of ​​the corneo-scleral trabecula and scleral spur, freely extends to the dentate line, where it is woven into the choroid, reaching in separate fibers to the equator of the eye. Both in anatomy and function, it exactly corresponds to its ancient name - the choroidal tensor. When the Brücke muscle contracts, the ciliary muscle moves forward. The Brücke muscle is involved in focusing on distant objects; its activity is necessary for the process of disaccommodation. Disaccommodation ensures the projection of a clear image onto the retina when moving in space, driving, turning the head, etc. It is not as important as the Müller muscle. In addition, 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 canal. The generally accepted opinion is that this muscle has parasympathetic innervation.
  • Radial fibers (Ivanov muscle) makes up the main muscle mass of the crown of the ciliary body and, having an attachment to the uveal portion of the trabeculae in the basal zone of the iris, freely ends in the form of a radially diverging corolla on the back side of the crown facing the vitreous body. It is obvious that during their contraction, the radial muscle fibers, being pulled to the place of attachment, will change the configuration of the crown and shift the crown in the direction of the iris root. Despite the confusion of the issue of innervation of the radial muscle, most authors consider it sympathetic.
  • Circular fibers (Müller muscle) has no attachment, like the iris sphincter, and is located in the form of a ring at the very apex of the crown of the ciliary body. When it contracts, the apex of the crown “sharpens” and the processes of the ciliary body approach the equator of the lens.
    Changing the curvature of the lens leads to a change in its optical power and a shift in focus to nearby objects. In this way the process of accommodation is carried out. It is generally accepted that the innervation of the circular muscle is parasympathetic.

At the points 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 ganglion.

Parasympathetic fibers originate from the accessory nucleus of the oculomotor nerve (nucleus oculomotorius accessories) and as part of the root of the oculomotor nerve (radix oculomotoria, oculomotor nerve, III pair of cranial nerves) enter the ciliary ganglion.

Meridian fibers receive sympathetic innervation from the internal carotid plexus, located around the internal carotid artery.

Sensitive innervation is provided by the ciliary plexus, 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).

Functional significance of the ciliary muscle

When the ciliary muscle contracts, the tension of the ligament of zinn decreases and the lens becomes more convex (which increases its refractive power).

Damage to the ciliary muscle leads to paralysis of accommodation (cycloplegia). With prolonged stress of accommodation (for example, long reading or high uncorrected farsightedness), a convulsive contraction of the ciliary muscle occurs (spasm of accommodation).

The weakening of accommodative ability with age (presbyopia) is not associated with a loss of functional ability of the muscle, but with a decrease in the intrinsic elasticity of the lens.

Open- and closed-angle glaucoma can be treated with muscarinic receptor agonists (eg, pilocarpine), which causes miosis, contraction of the ciliary muscle and enlargement of the trabecular meshwork pores, facilitating the drainage of aqueous humor in the canal of Schlemm and reducing intraocular pressure.

Blood supply

The blood supply to the ciliary body is carried out by two long posterior ciliary arteries (branches of the ophthalmic artery), which, passing through the sclera at the posterior pole of the eye, then go in the suprachoroidal space along the 3 and 9 o'clock meridian. Anastomose with the branches of the anterior and posterior short ciliary arteries.

Venous drainage occurs through the anterior ciliary veins.

The eye, the eyeball, is almost spherical in shape, approximately 2.5 cm in diameter. It consists of several shells, of which three are the main ones:

  • sclera - outer layer
  • choroid - middle,
  • retina – internal.

Rice. 1. Schematic representation of the accommodation mechanism on the left - focusing into the distance; on the right - focusing on close objects.

The sclera is white with a milky tint, except for its anterior part, which is transparent and called the cornea. Light enters the eye through the cornea. The choroid, the middle layer, contains blood vessels that carry blood to nourish the eye. Just below the cornea, the choroid becomes the iris, which determines the color of the eyes. In its center is the pupil. The function of this shell is to limit the entry of light into the eye when it is very bright. This is achieved by constricting the pupil in high light conditions and dilating in low light conditions. Behind the iris is a lens, like a biconvex lens, that captures light as it passes through the pupil and focuses it on the retina. Around the lens, the choroid forms the ciliary body, which contains a muscle that regulates the curvature of the lens, which ensures 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 diameter of the pupil in daylight is 1.5–2 mm, and in the dark it increases to 7.5 mm. The primary physiological role of the pupil is to regulate the amount of light entering the retina.

Constriction of the pupil (miosis) occurs with increasing illumination (this limits the light flux entering the retina, and, therefore, serves as a protective mechanism), when viewing closely located objects, when accommodation and convergence of the visual axes (convergence) occur, as well as during.

Dilation of the pupil (mydriasis) occurs in low light (which increases the illumination of the retina and thereby increases the sensitivity of the eye), as well as with excitement of any afferent nerves, with emotional reactions of tension associated with an increase in sympathetic tone, with mental arousal, suffocation,.

The size of the pupil is regulated by the annular and radial muscles of the iris. The radial dilator muscle is innervated by the sympathetic nerve coming from the superior cervical ganglion. The annular muscle, which constricts the pupil, is innervated by parasympathetic fibers of the oculomotor nerve.

Fig 2. Diagram of the structure of the visual analyzer

1 - retina, 2 - uncrossed fibers of the optic nerve, 3 - crossed fibers of the optic nerve, 4 - optic tract, 5 - lateral geniculate body, 6 - lateral root, 7 - optic lobes.
The shortest 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 greatest distance is called the far point of clear vision. When the object is located at the near point, accommodation is maximum, at the far point there is no accommodation. The difference in the refractive powers of the eye at maximum accommodation and at rest is called the force of accommodation. The unit of optical power is the optical power of a lens with a focal length1 meter. This unit is called diopter. To determine the optical power of a lens in diopters, the unit should be divided by the focal length in meters. The amount of accommodation varies from person to person and varies depending on age from 0 to 14 diopters.

To see an object clearly, it is necessary that the rays of each point of it be focused on the retina. If you look into the distance, then close objects are seen unclearly, blurry, since the rays from nearby points are focused behind the retina. It is impossible to see objects at different distances from the eye with equal clarity 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 rays passing through the peripheral parts of the lens are refracted more strongly than 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 the 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), i.e. the ability of the eye to refract, is measured in conventional units - diopters. Diopter is the refractive power of a lens in which parallel rays, after refraction, converge at a focus at a distance of 1 m.

Rice. 3. The course of rays for 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 obviously must be in the back focus of the eye's optical system. Various disturbances in 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, farsightedness, 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 consider two separate points visible at an angle of 1 minute.

With refractive error, visual acuity is always below 1. There are three main types of refractive error - astigmatism, myopia (myopia) and farsightedness (hyperopia).

Refractive errors result in nearsightedness or farsightedness. The refraction of the eye changes with age: it is less than normal in newborns, and 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 its innate characteristics, the optical system of the eye (cornea and lens) refracts rays unequally 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). Thus, if the curvature of the corneal surface in the vertical section is greater than in the horizontal section, 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 section. Therefore, light rays passing through an astigmatic eye will be focused in different planes: if the horizontal lines of an object are focused on the retina, then the vertical lines will be in front of it. Wearing cylindrical lenses, selected taking into account the actual defect of the optical system, to a certain extent compensates for this refractive error.

Myopia and farsightedness caused by changes in the length of the eyeball. With normal refraction, the distance between the cornea and the fovea (macula) is 24.4 mm. With myopia (myopia), the longitudinal axis of the eye is greater than 24.4 mm, so 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 glasses in front of myopic eyes, which will push the focused image onto the retina. In the farsighted eye, the longitudinal axis of the eye is shortened, i.e. 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 accommodative effort, i.e. an increase in the convexity of the lens. Therefore, a farsighted person strains the accommodative muscle, examining not only close, but also distant objects. When viewing close objects, the accommodative efforts of farsighted people are insufficient. Therefore, to read, farsighted people must wear glasses with biconvex lenses that enhance the refraction of light.

Refractive errors, in particular myopia and farsightedness, are also common among animals, for example, horses; Myopia is very often observed in sheep, especially cultivated breeds.

The human eye adapts and sees objects equally clearly that are at different distances from a person. This process is ensured by the ciliary muscle, which is responsible for the focus of the organ of vision.

According to Hermann Helmholtz, the anatomical structure in question, at the moment of tension, increases the curvature of the eye lens - the organ of vision focuses the image of nearby objects on the retina. When the muscle relaxes, the eye is able to focus the image of distant objects.

What is the ciliary muscle?

- a paired organ of muscular structure, which is located inside the organ of vision. We are talking about the main component of the ciliary body, which is responsible for the accommodation of the eye. The anatomical location of the element is the area around the eye lens.

Structure

Muscles are made up of three types of fibers:

  • meridional (Brücke muscle). They fit tightly to, connected to the inner part of the limbus, woven into the trabecular meshwork. When the fibers contract, the structural element in question moves forward;
  • radial (Ivanov muscle). The origin is the scleral spur. From here the fibers are directed to the ciliary processes;
  • circular (Muller muscle). The fibers are located within the anatomical structure in question.

Functions

The functions of a structural unit are assigned to the fibers included in its composition. Thus, the Brücke muscle is responsible for disaccommodation. The same function is assigned to radial fibers. The Müller muscle carries out the reverse process - accommodation.

Symptoms

For ailments affecting the structural unit in question, the patient complains of the following phenomena:

  • decreased visual acuity;
  • increased fatigue of the visual organs;
  • periodic painful sensations in the eyes;
  • burning, stinging;
  • redness of the mucous membrane;
  • dry eye syndrome;
  • dizziness.

The ciliary muscle suffers as a result of regular eye strain (during prolonged exposure to the monitor, reading in the dark, etc.). Under such circumstances, accommodation syndrome (false myopia) most often develops.

Diagnostics

Diagnostic measures in the case of local ailments are reduced to external examination and hardware techniques.

In addition, the doctor determines the patient’s visual acuity at the current time. The procedure is performed using corrective glasses. As additional measures, the patient is advised to be examined by a therapist and a neurologist.

Upon completion of diagnostic measures, the ophthalmologist makes a diagnosis and plans a therapeutic course.

Treatment

When the muscles of the lens for some reason cease to perform their main functions, specialists begin complex treatment.

A conservative therapeutic course includes the use of medications, hardware methods and special therapeutic exercises for the eyes.

As part of drug therapy, ophthalmic drops are prescribed to relax muscles (for eye spasms). At the same time, it is recommended to take special vitamin complexes for the visual organs and use eye drops to moisturize the mucous membrane.

The patient can benefit from self-massage of the cervical spine. It will ensure blood flow to the brain and stimulate the circulatory system.

Within the framework of the hardware technique, the following is carried out:

  • electrical stimulation of the apple of the organ of vision;
  • laser treatment at the cellular-molecular level (stimulation of biochemical and biophysical phenomena in the body is carried out - the work of the muscle fibers of the eye returns to normal).

Gymnastic exercises for the visual organs are selected by an ophthalmologist and performed daily for 10-15 minutes. In addition to the therapeutic effect, regular exercise is one of the preventive measures for eye diseases.

Thus, the considered anatomical structure of the organ of vision acts as the basis of the ciliary body, is responsible for the accommodation of the eye and has a fairly simple structure.

Its functional ability is jeopardized by regular visual loads - in this case, the patient is indicated for a comprehensive therapeutic course.

The iris is a round diaphragm with a hole (pupil) in the center, which regulates the flow of light into the eye depending on the conditions. Thanks to this, the pupil narrows in strong light, and dilates in weak light.

The iris is the anterior part of the vascular tract. Constituting a direct continuation of the ciliary body, adjacent almost closely to the fibrous capsule of the eye, the iris at the level of the limbus departs from the outer capsule of the eye and is located in the frontal plane in such a way that there remains free space between it and the cornea - the anterior chamber, filled with liquid contents - chamber moisture .

Through the transparent cornea, it is easily accessible to inspection with the naked eye, except for its extreme periphery, the so-called root of the iris, covered by a translucent ring of the limbus.

Iris dimensions: when examining the front surface of the iris (an face), it appears as a thin, almost rounded plate, only slightly elliptical in shape: its horizontal diameter is 12.5 mm, its vertical diameter is 12 mm, the thickness of the iris is 0.2-0.4 mm. It is especially thin in the root zone, i.e. at the border with the ciliary body. It is here that, with severe contusions of the eyeball, its separation can occur.

Its free edge forms a rounded hole - the pupil, located not strictly in the center, but slightly shifted towards the nose and downwards. It serves to regulate the amount of light rays entering the eye. At the edge of the pupil, along its entire length, there is a black jagged edge, bordering it along its entire length and representing the inversion of the posterior pigment layer of the iris.

The iris with its pupillary zone is adjacent to the lens, rests on it and slides freely over its surface when the pupil moves. The pupillary zone of the iris is pushed somewhat anteriorly by the convex anterior surface of the lens adjacent to it from behind, as a result of which the iris as a whole has the shape of a truncated cone. In the absence of a lens, for example after cataract extraction, the iris appears flatter and visibly shakes when the eyeball moves.

Optimal conditions for high visual acuity are provided with a pupil width of 3 mm (the maximum width can reach 8 mm, the minimum - 1 mm). Children and nearsighted people have wider pupils, while older people and farsighted people have narrower pupils. The width of the pupil is constantly changing. Thus, the pupils regulate the flow of light into the eyes: in low light, the pupil dilates, which facilitates greater passage of light rays into the eye, and in strong light, the pupil constricts. Fear, strong and unexpected experiences, some physical influences (squeezing an arm, leg, strong embrace of the body) are accompanied by dilation of the pupils. Joy, pain (pricks, pinches, blows) also lead to dilation of the pupils. When you inhale, the pupils dilate, when you exhale, they constrict.

Medicines such as atropine, homatropine, scopolamine (they paralyze the parasympathetic endings in the sphincter), cocaine (stimulates sympathetic fibers in the pupillary dilator) lead to pupil dilation. Pupil dilation also occurs under the influence of adrenaline drugs. Many drugs, particularly marijuana, also have a pupillary dilating effect.

The main properties of the iris, determined by the anatomical features of its structure, are

  • drawing,
  • relief,
  • color,
  • location relative to neighboring eye structures
  • condition of the pupillary opening.

A certain number of melanocytes (pigment cells) in the stroma is responsible for the color of the iris, which is an inherited trait. The brown iris is dominant in inheritance, the blue iris is recessive.

Most newborn babies have a light blue iris due to weak pigmentation. However, by 3-6 months the number of melanocytes increases and the iris darkens. The complete absence of melanosomes makes the iris pink (albinism). Sometimes the irises of the eyes differ in color (heterochromia). Often, melanocytes of the iris become the source of melanoma development.

Parallel to the pupillary edge, concentrically to it at a distance of 1.5 mm, there is a low serrated ridge - the circle of Krause or the mesentery, where the iris has the greatest thickness of 0.4 mm (with an average pupil width of 3.5 mm). Towards the pupil, the iris becomes thinner, but its thinnest section corresponds to the root of the iris, its thickness here is only 0.2 mm. Here, during a contusion, the membrane is often torn (iridodialysis) or completely torn off, resulting in traumatic aniridia.

The Krause circle is used to identify two topographic zones of this membrane: the inner, narrower, pupillary and the outer, wider, ciliary. On the anterior surface of the iris, radial striations are noted, well expressed in its ciliary zone. It is caused by the radial arrangement of the vessels, along which the stroma of the iris is oriented.

On both sides of the Krause circle on the surface of the iris, slit-like depressions are visible, penetrating deeply into it - crypts or lacunae. The same crypts, but smaller in size, are located along the root of the iris. Under conditions of miosis, the crypts narrow somewhat.

In the outer part of the ciliary zone, folds of the iris are noticeable, running concentrically to its root - contraction grooves, or contraction grooves. They usually represent only a segment of the arc, but do not cover the entire circumference of the iris. When the pupil contracts, they are smoothed out, and when the pupil dilates, they are most pronounced. All of the listed formations on the surface of the iris determine both its pattern and relief.

Functions

  1. takes part in ultrafiltration and outflow of intraocular fluid;
  2. ensures a constant temperature of the moisture of the anterior chamber and the tissue itself by changing the width of the vessels.
  3. diaphragmatic

Structure

The iris is a pigmented round plate that can have different colors. In a newborn, pigment is almost absent and the posterior pigment plate is visible through the stroma, causing the bluish color of the eyes. The iris acquires permanent color by the age of 10-12 years.

Surfaces of the iris:

  • Anterior - facing the anterior chamber of the eyeball. It has different colors in people, providing eye color due to different amounts of pigment. If there is a lot of pigment, then the eyes have a brown, even black, color; if there is little or almost no pigment, then the result is greenish-gray, blue tones.
  • Posterior - facing the posterior chamber of the eyeball.

    The posterior surface of the iris microscopically has a dark brown color and an uneven surface due to the large number of circular and radial folds running along it. A meridional section of the iris shows that only a small part of the posterior pigment layer, adjacent to the stroma of the iris and looking like a narrow homogeneous strip (the so-called posterior border plate), is devoid of pigment; throughout the rest of the length, the cells of the posterior pigment layer are densely pigmented.

The stroma of the iris provides a peculiar pattern (lacunae and trabeculae) due to the content of radially located, rather densely intertwined blood vessels and collagen fibers. It contains pigment cells and fibroblasts.

Edges of the iris:

  • The inner or pupillary edge surrounds the pupil, it is free, its edges are covered with a pigmented fringe.
  • The outer or ciliary edge is connected by the iris to the ciliary body and sclera.

There are two layers in the iris:

  • anterior, mesodermal, uveal, constituting a continuation of the vascular tract;
  • posterior, ectodermal, retinal, constituting a continuation of the embryonic retina, in the stage of the secondary optic vesicle, or optic cup.

The anterior boundary layer of the mesodermal layer consists of a dense accumulation of cells located closely to each other, parallel to the surface of the iris. Its stromal cells contain oval nuclei. Along with them, cells with numerous thin, branching processes anastomosing with each other are visible - melanoblasts (according to the old terminology - chromatophores) with an abundant content of dark pigment grains in the protoplasm of their body and processes. The anterior boundary layer at the edge of the crypts is interrupted.

Due to the fact that the posterior pigment layer of the iris is a derivative of the undifferentiated part of the retina, developing from the anterior wall of the optic cup, it is called pars iridica retinae or pars retinalis iridis. From the outer layer of the posterior pigment layer during embryonic development, two muscles of the iris are formed: the sphincter, which constricts the pupil, and the dilator, which causes its expansion. During development, the sphincter moves from the thickness of the posterior pigment layer into the stroma of the iris, into its deep layers, and is located at the pupillary edge, surrounding the pupil in the form of a ring. Its fibers run parallel to the pupillary edge, adjacent directly to its pigment border. In eyes with a blue iris with its characteristic delicate structure, the sphincter can sometimes be distinguished in a slit lamp in the form of a whitish strip about 1 mm wide, visible in the depths of the stroma and passing concentrically to the pupil. The ciliary edge of the muscle is somewhat washed away; muscle fibers extend from it posteriorly in an oblique direction to the dilator. In the vicinity of the sphincter, in the stroma of the iris, large, round, densely pigmented cells, devoid of processes, are scattered in large numbers - “blocky cells”, which also arose as a result of the displacement of pigmented cells from the outer pigment layer into the stroma. In eyes with blue irises or partial albinism, they can be distinguished by slit lamp examination.

Due to the outer layer of the posterior pigment layer, the dilator develops - a muscle that dilates the pupil. Unlike the sphincter, which has shifted into the stroma of the iris, the dilator remains at the site of its formation, as part of the posterior pigment layer, in its outer layer. In addition, in contrast to the sphincter, dilator cells do not undergo complete differentiation: on the one hand, they retain the ability to form pigment, on the other, they contain myofibrils characteristic of muscle tissue. In this regard, dilator cells are classified as myoepithelial formations.

Adjacent to the anterior section of the posterior pigment layer from the inside is its second section, consisting of one row of epithelial cells of various sizes, which creates unevenness of its posterior surface. The cytoplasm of epithelial cells is so densely filled with pigment that the entire epithelial layer is visible only in depigmented sections. Starting from the ciliary edge of the sphincter, where the dilator simultaneously ends, to the pupillary edge, the posterior pigment layer is represented by a two-layer epithelium. At the edge of the pupil, one layer of epithelium passes directly into another.

Blood supply to the iris

Blood vessels, abundantly branching in the stroma of the iris, originate from the large arterial circle (circulus arteriosus iridis major).

At the border of the pupillary and ciliary zones, by the age of 3-5 years, a collar (mesentery) is formed, in which, according to the Krause circle in the stroma of the iris, concentrically to the pupil, there is a plexus of vessels anastomosing with each other (circulus iridis minor) - the lesser circle, blood circulation iris.

The small arterial circle is formed by the anastomosing branches of the greater circle and providing blood supply to the pupillary 9th zone. The large arterial circle of the iris is formed at the border with the ciliary body due to the branches of the posterior long and anterior ciliary arteries, anastomosing among themselves and giving return branches to the choroid proper.

Muscles that regulate changes in pupil size:

  • sphincter of the pupil - a circular muscle that constricts the pupil, consists of smooth fibers located concentrically with respect to the pupillary edge (pupillary girdle), innervated by parasympathetic fibers of the oculomotor nerve;
  • dilator pupil - a muscle that dilates the pupil, consists of pigmented smooth fibers lying radially in the posterior layers of the iris, has sympathetic innervation.

The dilator has the form of a thin plate located between the ciliary part of the sphincter and the root of the iris, where it is connected to the trabecular apparatus and the ciliary muscle. The dilator cells are located in one layer, radially relative to the pupil. The bases of the dilator cells, containing myofibrils (identified by special processing methods), face the stroma of the iris, are devoid of pigment and together constitute the posterior limiting plate described above. The rest of the cytoplasm of the dilator cells is pigmented and is visible only in depigmented sections, where the rod-shaped nuclei of muscle cells located parallel to the surface of the iris are clearly visible. The boundaries of individual cells are unclear. The dilator contracts due to myofibrils, and both the size and shape of its cells change.

As a result of the interaction of two antagonists - the sphnikter and the dilator - the iris is able, through reflex constriction and dilation of the pupil, to regulate the flow of light rays penetrating into the eye, and the diameter of the pupil can vary from 2 to 8 mm. The sphincter receives innervation from the oculomotor nerve (n. oculomotorius) with branches of the short ciliary nerves; along the same path, the sympathetic fibers innervating it approach the dilator. However, the widespread opinion that the sphincter of the iris and the ciliary muscle are provided exclusively by the parasympathetic, and the dilator of the pupil only by the sympathetic nerve, is unacceptable today. There is evidence, at least for the sphincter and ciliary muscles, for their dual innervation.

Innervation of the iris

Using special staining methods, a richly branched nerve network can be identified in the stroma of the iris. Sensitive fibers are branches of the ciliary nerves (n. trigemini). In addition to them, there are vasomotor branches from the sympathetic root of the ciliary ganglion and motor branches, ultimately emanating from the oculomotor nerve (n. oculomotorii). Motor fibers also come with the ciliary nerves. In places in the stroma of the iris there are nerve cells that are detected during serpal viewing of sections.

  • sensitive - from the trigeminal nerve,
  • parasympathetic - from the oculomotor nerve
  • sympathetic - from the cervical sympathetic trunk.

Methods for studying the iris and pupil

The main diagnostic methods for examining the iris and pupil are:

  • Inspection with side lighting
  • Examination under a microscope (biomicroscopy)
  • Determination of pupil diameter (pupillometry)

Such studies may reveal congenital anomalies:

  • Residual fragments of the embryonic pupillary membrane
  • Absence of the iris or aniridia
  • Coloboma of the iris
  • Pupil dislocation
  • Multiple pupils
  • Heterochromia
  • Albinism

The list of acquired disorders is also very diverse:

  • Fusion of the pupil
  • Posterior synechiae
  • Circular posterior synechia
  • Trembling of the iris - iridodonesis
  • Rubeose
  • Mesodermal dystrophy
  • Iris dissection
  • Traumatic changes (iridodialysis)

Specific changes in the pupil:

  • Miosis - constriction of the pupil
  • Mydriasis – dilation of the pupil
  • Anisocoria – unevenly dilated pupils
  • Disorders of pupil movement for accommodation, convergence, light

№ 28 Peripheral vision: definition of the concept, criteria for normality. Methods for studying the boundaries of the visual field for white and colored objects. Scotomas: classification, significance in the diagnosis of diseases of the organ of vision.

Peripheral vision is a function of the rod and cone apparatus of the entire optically active retina and is determined by the field of view. Line of sight- this is the space visible to the eye (eyes) with a fixed gaze. Peripheral vision helps to navigate in space.

The visual field is examined using perimetry.

The easiest way - control (indicative) study according to Donders. The subject and the doctor are positioned facing each other at a distance of 50-60 cm, after which the doctor closes his right eye, and the subject closes his left. In this case, the examinee looks with his open right eye into the doctor’s open left eye and vice versa. The field of view of the doctor's left eye serves as a control when determining the field of vision of the subject. At the median distance between them, the doctor shows his fingers, moving them in the direction from the periphery to the center. If the detection limits of the demonstrated fingers coincide with the doctor and the examinee, the field of view of the latter is considered unchanged. If there is a discrepancy, there is a narrowing of the field of vision of the right eye of the subject in the directions of movement of the fingers (up, down, from the nasal or temporal side, as well as in the radii between them). After checking the zero vision of the right eye, the field of vision of the subject’s left eye is determined with the right eye closed, while the doctor’s left eye is closed.

The simplest device for studying the visual field is the Förster perimeter, which is a black arc (on a stand) that can be shifted in different meridians.

Perimetry on the universal projection perimeter (UPP), which is widely used in practice, is also carried out monocularly. The correct alignment of the eye is monitored using an eyepiece. First, perimetry is performed for white color.

Modern perimeters are more complex , including on a computer basis. On a hemispherical or some other screen, white or colored marks move or flash in various meridians. The corresponding sensor records the test subject's indicators, indicating the boundaries of the visual field and areas of loss in it on a special form or in the form of a computer printout.

Normal boundaries of the visual field For white color, consider upward 45-55°, upward outward 65°, outward 90°, downward 60-70°, downward inward 45°, inward 55°, upward inward 50°. Changes in the boundaries of the visual field can occur with various lesions of the retina, choroid and visual pathways, and with pathology of the brain.

In recent years, visual contrast perimetry has come into practice., which is a method of assessing spatial vision using black-and-white or color stripes of different spatial frequencies, presented in the form of tables or on a computer display.

Local loss of internal parts of the visual field that are not related to its boundaries are called scotomas.

There are scotomas absolute (complete loss of visual function) and relative (decreased perception of an object in the studied area of ​​the visual field). The presence of scotomas indicates focal lesions of the retina and visual pathways. Scotoma can be positive or negative.

Positive scotoma The patient himself sees it as a dark or gray spot in front of the eye. This loss of vision occurs when there is damage to the retina and optic nerve.

Negative scotoma The patient himself does not detect it; it is revealed during examination. Typically, the presence of such a scotoma indicates damage to the pathways.

Atrial scotomas- These are suddenly appearing short-term moving deposits in the field of view. Even when the patient closes his eyes, he sees bright, flickering zigzag lines extending to the periphery. This symptom is a sign of cerebral vascular spasm.

According to the location of the cattle Peripheral, central and paracentral scotomas are visible in the field of view.

At a distance of 12-18° from the center in the temporal half there is a blind spot. This is a physiological absolute scotoma. It corresponds to the projection of the optic nerve head. An enlarged blind spot has important diagnostic value.

Central and paracentral scotomas are detected by stone testing.

Central and paracentral scotomas appear when the papillomacular bundle of the optic nerve, retina and choroid are damaged. Central scotoma may be the first manifestation of multiple sclerosis.