The lens structure and functions. The lens is a professional lens of the "camera-eye

The lens is a transparent and flat body that is small in size but not of probable importance. This round formation has an elastic structure and plays important role in the visual system.

The lens consists of an accommodative optical mechanism, thanks to which we can see objects at different distances, adjust the incoming light and focus the image. In this article, we will consider in detail the structure of the lens of the human eye, its functionality and diseases.

Small size - a feature of the lens

The main feature of this optical body is its small size. In an adult, the lens does not exceed 10 mm in diameter. When examining the body, it can be noted that the lens resembles a biconvex lens, which differs in the radius of curvature depending on the surface. In histology, the transparent body consists of 3 parts: ground substance, capsule and capsular epithelium.

Base substance

Consists of epithelial cells that form filamentous fibers. Cells are the only component of the lens that are converted into a hexagonal prism. The main substance does not include the circulatory system, lymphatic tissue and nerve endings.

Epithelial cells, under the influence of the chemical protein crystallin, lose their true color and become transparent. In an adult, the nutrition of the lens and the ground substance occurs due to moisture transmitted from the vitreous body, and in intrauterine development saturation occurs due to the vitreous artery.

Capsular epithelium

A thin film that covers the main substance. It performs trophic (nutrition), cambial (cell regeneration and renewal) and barrier (protection from other tissues) functions. Depending on the location of the capsular epithelium, cell division and development occur. As a rule, the germ zone is located closer to the periphery of the main substance.

Capsule or bag

The upper part of the lens, which consists of an elastic shell. The capsule protects the body from the effects of harmful factors, helps to refract light. Attaches to the ciliary body with a belt. The walls of the capsule do not exceed 0.02 mm. Thicken depending on the location: the closer to the equator, the thicker.

Functions of the lens

Due to the unique structure of the transparent body, all visual and optical processes take place.

There are 5 functions of the lens, which together allow a person to see objects, distinguish colors and focus vision at various distances:

1. Light transmission. Rays of light pass through the cornea, enter the lens and freely penetrate the vitreous body and the retina. The sensitive shell of the eye (the retina) already performs its functions of perceiving color and light signals, processes them and sends impulses to the brain with the help of nervous excitation. Without light transmission, humanity would be completely devoid of vision.
2. Light refraction. The lens is a lens of biological origin. Light refraction occurs due to hexagonal prism lens. Depending on the state of accommodation, the refractive index varies (from 15 to 19 diopters).
3. Accommodation. This mechanism allows you to focus vision at any distance (near and far). When the accommodative mechanism fails, vision deteriorates. Such pathological processes as hyperopia and myopia develop.
4. Protection. Due to its structure and location, the lens protects vitreous body from the ingress of bacteria and microorganisms. The protective function is triggered by various inflammatory processes.
5. Separation. The lens is located strictly in the center in front of the vitreous body. A thin lens is placed behind the pupil, iris and cornea. Due to its location, the lens divides the eye into two parts: the posterior and anterior sections.

Due to this, the vitreous body is kept in the posterior chamber and is not able to move forward.

Diseases and pathologies of the lens of the eye

All pathological processes and diseases of the biconvex body appear against the background of the growth of epithelial cells and their accumulation. Because of this, the capsule and fibers lose their elasticity, the chemical properties change, the cells become cloudy, accommodative properties are lost, and presbyopia (eye anomaly, refraction) develops.

What diseases, pathologies and anomalies can the lens face?

• Cataract. A disease in which clouding of the lens occurs (either complete or partial). A cataract occurs when the lens chemistry changes and the epithelial cells of the lens become cloudy instead of clear. With a disease, the functionality of the lens decreases, the lens stops transmitting light. Cataract is a progressive disease. In the first stages, clarity and contrast of objects are lost, late stages there is a complete loss of vision.
• Ectopia. Displacement of the lens from its axis. Occurs against the background of eye injuries and with an increase in the eyeball, as well as with overripe cataracts.
• Deformation of the lens shape. There are 2 types of deformity - lenticonus and lentiglobus. In the first case, the change occurs in the anterior or posterior part, the shape of the lens takes on the shape of a cone. With a lentiglobus, the deformation occurs along its axis, in the region of the equator. As a rule, with deformation, a decrease in visual acuity occurs. Nearsightedness or farsightedness appears.
• Sclerosis of the lens, or phacosclerosis. Seal the walls of the capsule. Appears in people aged 60 years and above against the background of glaucoma, cataracts, myopia, corneal ulcers and diabetes mellitus.

Diagnosis and replacement of the lens

To identify pathological processes and anomalies of the biological lens of the eye, ophthalmologists resort to six research methods:

1. Ultrasound diagnostics, or ultrasound, is prescribed to diagnose the structure of the eye, as well as to determine the condition of the eye muscles, retina and lens.
2. Biomicroscopic examination using eye drops and a slit lamp is a non-contact diagnostic that allows you to study the structure of the anterior part of the eyeball and establish an accurate diagnosis.
3. Eye Conherence Tomography, or OCT. A non-invasive procedure that allows you to examine the eyeball and vitreous body using x-ray diagnostics. Conherence tomography is considered one of the most effective methods for detecting lens pathologies.
4. Visometric study, or assessment of visual acuity, is used without the use of ultrasound and x-ray machines. Visual acuity is checked according to a special visometric table, which the patient must read at a distance of 5 m.
5. Keratotopography - unique method which studies the refraction of the lens and cornea.
6. Pachymetry allows you to examine the thickness of the lens using a contact, laser or rotary apparatus.

The main feature of a transparent body is the possibility of its replacement.

Now, with the help of surgical intervention, the lens is implanted. As a rule, the lens requires replacement if it becomes cloudy and the refractive properties are impaired. Also, the replacement of the lens is prescribed for deterioration of vision (nearsightedness, farsightedness), with lens deformation and cataracts.

Contraindications for lens replacement

Contraindications for surgery:

• If the eyeball chamber is small.
• With dystrophy and detachment of the retina.
• When the size of the eyeball decreases.
• With a high degree of farsightedness and myopia.
• Features when replacing the lens

The patient is examined and prepared for several months. They carry out all the necessary diagnostics, identify anomalies and prepare for surgery. Passing all laboratory tests is a mandatory process, since any intervention, even in such a small body, can lead to complications.

5 days before surgery, it is necessary to drip an antibacterial and anti-inflammatory drug into the eyes in order to exclude infection during surgery. As a rule, the operation is performed by an ophthalmic surgeon with the help of local anesthesia. In just 5-15 minutes, the specialist will carefully remove the old lens and install a new implant.

After all the procedures, for several days, the patient will have to wear a protective bandage and apply a healing gel to the eyeball. Improvement occurs within 2-3 hours after surgery. Fully vision is restored after 3-5 days if the patient does not suffer diabetes or glaucoma.

The lens of the human eye performs such important functions as light transmission and light refraction. Any warning signs and symptoms are a definite reason to visit a specialist. The development of pathologies and anomalies of the natural lens can lead to complete loss of vision, so it is important to take care of your eyes, monitor your health and nutrition.

Learn more about the structure of the eye - in the video:

Great importance in the visual process has the lens of the human eye. With its help, accommodation occurs (the difference between objects at a distance), the process of refraction of light rays, protection from external negative factors and the transmission of an image from external environment. Over time or from injury, the lens begins to darken. A cataract appears, which cannot be cured with medication. Therefore, to stop the development of the disease, they use surgical intervention. This method allows you to completely recover from the disease.

Structure and anatomy

The lens is a convex lens that provides the visual process in the human eye apparatus. Its back part has a deflection, and in front the organ is almost flat. The refractive power of the lens is normally 20 diopters. But the optical power can vary. On the surface of the lens are small nodules that connect to muscle fibers. Depending on the tension or relaxation of the ligaments, the lens takes a certain shape. Such changes allow you to see objects at different distances.

The structure of the lens of the human eye includes the following parts:

• nucleus;
• shell or capsular bag;
• equatorial part;
• lens masses;
• capsule;
• fibers: central, transitional, main.

Located in the back chamber. Its thickness is approximately 5 millimeters and its size is 9 mm. The lens diameter is 5 mm. With age, the core loses its elasticity and becomes more rigid. The lens cells increase in number over the years and this is due to the growth of the epithelium. This makes the lens thicker and the quality of vision lower. The organ has no nerve endings, blood vessels or lymph nodes. Near the nucleus is the ciliary body. It produces fluid, which is then supplied to the front of the eyeball. And also the body is a continuation of the veins in the eye. The visual lens consists of such components, which are shown in the table:

Lens functions

The role of this body in the process of vision is one of the main ones. For normal operation, it must be transparent. The pupil and lens allow light to pass into the human eye. It refracts the rays, after which they fall on the retina. Its main task is to transmit an image from the outside to the macular area. After hitting this area, the light forms an image on the retina, it moves in the form of a nerve impulse to the brain, which interprets it. The images that fall on the lens are inverted. Already in the brain they turn over.

The functions of the lens are involved in the process of accommodation. This is the ability of a person to perceive objects at different distances. Depending on the location of the object, the anatomy of the lens changes, which allows you to see the image clearly. If the ligaments are stretched, the lens takes on a convex shape. The curvature of the lens makes it possible to see an object up close. During relaxation, the eye sees objects in the distance. Such changes are regulated eye muscle which is controlled by the nerves. That is, accommodation works reflexively without additional human effort. In this case, the radius of curvature at rest is 10 mm, and in tension - 6 mm.

This body performs protective functions. The lens is a kind of shell from microorganisms and bacteria from the external environment.

In addition, it separates the two sections of the eye and is responsible for the integrity of the eye mechanism: so the vitreous will not put too much pressure on the anterior segments of the visual apparatus. According to the study, if the lens ceases to function, then it simply disappears, and the body moves forward. Because of this, the functions of the pupil and the anterior chamber suffer. There is a risk of developing glaucoma.

Organ diseases

Due to cranial or ocular injuries, with age, the lens may become more cloudy, the nucleus changes its thickness. If the lens filaments break in the eye, and as a result, the lens is displaced. This leads to a deterioration in visual acuity. One of the most common diseases is cataract. This is lens fogging. The disease occurs after injury or appears at birth. There is age-related cataract, when the lens epithelium becomes thicker and cloudy. If the cortical layer of the lens becomes completely White color, then they talk about the mature stage of cataract. Depending on the place of occurrence of the pathology, the following types are distinguished:

• nuclear;
• layered;
• front;
• back.

Such violations lead to the fact that vision falls below normal. A person begins to distinguish objects at different distances worse. Older people complain of a decrease in contrast and a decrease in color perception. Clouding develops over several years, so people do not immediately notice changes. Against the background of the disease, inflammation occurs - iridocyclitis. According to the study, it has been proven that opacities develop faster if the patient has glaucoma.

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Description

Shape and size

(Lens) is a transparent, disc-shaped, biconvex, semi-solid formation located between the iris and the vitreous body (Fig. 3.4.1).

Rice. 3.4.1. The relationship of the lens with the surrounding structures and its shape: 1 - cornea; 2- iris; 3- lens; 4 - ciliary body

The lens is unique in that it is the only "organ" of the human body and most animals, consisting from the same cell type at all stages- from embryonic development and postnatal life up to death. Its essential difference is the absence of blood vessels and nerves in it. It is also unique in terms of the characteristics of metabolism (anaerobic oxidation predominates), chemical composition (the presence of specific proteins - crystallins), and the lack of tolerance of the body to its proteins. Most of these features of the lens are associated with the nature of its embryonic development, which will be discussed below.

Anterior and posterior surfaces of the lens unite in the so-called equatorial region. The equator of the lens opens into the posterior chamber of the eye and is attached to the ciliary epithelium with the help of the ligament of zon (ciliary girdle) (Fig. 3.4.2).

Rice. 3.4.2. Structural ratio anterior section eyes (diagram) (no Rohen; 1979): a - a section passing through the structures of the anterior part of the eye (1 - cornea: 2 - iris; 3 - ciliary body; 4 - ciliary girdle (zinn ligament); 5 - lens); b - scanning electron microscopy of the structures of the anterior part of the eye (1 - fibers of the zonular apparatus; 2 - ciliary processes; 3 - ciliary body; 4 - lens; 5 - iris; 6 - sclera; 7 - Schlemm's canal; 8 - anterior chamber angle)

Due to the relaxation of the ligament of zon, during the contraction of the ciliary muscle, the lens is deformed (an increase in the curvature of the anterior and, to a lesser extent, the posterior surfaces). In this case, its main function is performed - a change in refraction, which makes it possible to obtain a clear image on the retina, regardless of the distance to the object. At rest, without accommodation, the lens gives 19.11 of the 58.64 diopters of the refractive power of the schematic eye. To fulfill its primary role, the lens must be transparent and elastic, which it is.

The human lens grows continuously throughout life, thickening by about 29 microns per year. Starting from the 6-7th week of intrauterine life (18 mm embryo), it increases in the anterior-posterior size as a result of the growth of primary lens fibers. At the stage of development, when the embryo reaches a size of 18-24 mm, the lens has an approximately spherical shape. With the appearance of secondary fibers (embryo size 26 mm), the lens flattens and its diameter increases. Zonular apparatus, which appears when the length of the embryo is 65 mm, does not affect the increase in the diameter of the lens. Subsequently, the lens rapidly increases in mass and volume. At birth, it has an almost spherical shape.

In the first two decades of life, the increase in the thickness of the lens stops, but its diameter continues to increase. The factor contributing to the increase in diameter is core compaction. Tension of the ligament of Zinn contributes to a change in the shape of the lens.

The diameter of the lens (measured at the equator) of an adult is 9-10 mm. Its thickness at the time of birth in the center is approximately 3.5-4.0 mm, 4 mm at 40 years old, and then slowly increases to 4.75-5.0 mm by old age. The thickness also changes in connection with a change in the accommodative ability of the eye.

In contrast to the thickness, the equatorial diameter of the lens changes to a lesser extent with age. At birth, it is 6.5 mm, in the second decade of life - 9-10 mm. Subsequently, it practically does not change (Table 3.4.1).

Table 3.4.1. Lens dimensions (according to Rohen, 1977)

The anterior surface of the lens is less convex than the posterior (Fig. 3.4.1). It is a part of a sphere with a radius of curvature equal to an average of 10 mm (8.0-14.0 mm). The anterior surface is bordered by the anterior chamber of the eye through the pupil, and along the periphery by the posterior surface of the iris. The pupillary edge of the iris rests on the anterior surface of the lens. The lateral surface of the lens faces the posterior chamber of the eye and is attached to the processes of the ciliary body by means of the ligament of cinnamon.

The center of the anterior surface of the lens is called anterior pole. It is located approximately 3 mm behind the posterior surface of the cornea.

The posterior surface of the lens has a greater curvature (the radius of curvature is 6 mm (4.5-7.5 mm)). It is usually considered in combination with the vitreous membrane of the anterior surface of the vitreous body. However, between these structures there is slit-like space made by liquid. This space behind the lens was described by Berger in 1882. It can be observed using a slit lamp.

Lens equator lies within the ciliary processes at a distance of 0.5 mm from them. The equatorial surface is uneven. It has numerous folds, the formation of which is due to the fact that a zinn ligament is attached to this area. The folds disappear with accommodation, i.e., when the tension of the ligament stops.

Refractive index of the lens is equal to 1.39, i.e., somewhat larger than the refractive index of chamber moisture (1.33). It is for this reason that, despite the smaller radius of curvature, the optical power of the lens is less than that of the cornea. The contribution of the lens to the refractive system of the eye is approximately 15 out of 40 diopters.

At birth, the accommodative force, equal to 15-16 diopters, decreases by half by the age of 25, and at the age of 50 it is only 2 diopters.

Biomicroscopic examination of the lens with a dilated pupil reveals features of its structural organization (Fig. 3.4.3).

Rice. 3.4.3. The layered structure of the lens during its biomicroscopic examination in individuals of different ages (according to Bron et al., 1998): a - age 20 years; b - age 50 years; b - age 80 years (1 - capsule; 2 - first cortical light zone (C1 alpha); 3 - first zone of separation (C1 beta); 4 - second cortical light zone (C2): 5 - light scattering zone of the deep cortex (C3 ); 6 - light zone of the deep cortex; 7 - lens nucleus. There is an increase in the lens and increased light scattering

First, the multi-layered lens is revealed. The following layers are distinguished, counting from front to center:

• capsule;
• subcapsular light zone (cortical zone C 1a);
• light narrow zone of inhomogeneous scattering (C1);
• translucent zone of the cortex (C2).

lens nucleus considered as its prenatal part. It also has layering. In the center is a light zone, called the "embryonic" (embryonic) nucleus. When examining the lens with a slit lamp, the sutures of the lens can also be found. Specular microscopy at high magnification allows you to see epithelial cells and lens fibers.

The following structural elements of the lens are determined (Fig. 3.4.4-3.4.6):

Rice. 3.4.4. Scheme of the microscopic structure of the lens: 1 - lens capsule; 2 - epithelium of the lens of the central sections; 3- lens epithelium of the transition zone; 4- epithelium of the lens of the equatorial region; 5 - embryonic nucleus; 6-fetal nucleus; 7 - the core of an adult; 8 - bark

Rice. 3.4.5. Features of the structure of the equatorial region of the lens (according to Hogan et al., 1971): 1 - lens capsule; 2 - equatorial epithelial cells; 3- lens fibers. As the proliferation of epithelial cells located in the region of the lens equator, they shift to the center, turning into lens fibers

Rice. 3.4.6. Features of the ultrastructure of the lens capsule of the equatorial region, the ligament of zon and the vitreous body: 1 - vitreous body fibers; 2 - fibers of the zinn ligament; 3-precapsular fibers: 4-capsule lens

1. Capsule.
2. Epithelium.
3. fibers.

lens capsule(capsula lentis). The lens is covered on all sides by a capsule, which is nothing more than a basement membrane of epithelial cells. The lens capsule is the thickest basement membrane of the human body. The capsule is thicker in front (15.5 µm in front and 2.8 µm behind) (Fig. 3.4.7).

Rice. 3.4.7. The thickness of the lens capsule in different areas

The thickening along the periphery of the anterior capsule is more pronounced, since the main mass of the zonium ligament is attached in this place. With age, the thickness of the capsule increases, which is more pronounced in front. This is due to the fact that the epithelium, which is the source of the basement membrane, is located in front and participates in the remodulation of the capsule, which is noted as the lens grows.

The ability of epithelial cells to form capsules persists throughout life and manifests itself even under conditions of cultivation of epithelial cells.

The dynamics of changes in the thickness of the capsule is given in table. 3.4.2.

Table 3.4.2. Dynamics of changes in the thickness of the lens capsule with age, µm (according to Hogan, Alvarado, Wedell, 1971)

This information may be needed by surgeons performing cataract extraction and using a capsule for attaching posterior chamber intraocular lenses.

The capsule is pretty powerful barrier to bacteria and inflammatory cells, but freely passable for molecules whose size is commensurate with the size of hemoglobin. Although the capsule does not contain elastic fibers, it is extremely elastic and is almost constantly under the influence of external forces, i.e., in a stretched state. For this reason, the dissection or rupture of the capsule is accompanied by twisting. The property of elasticity is used when performing extracapsular cataract extraction. Due to the contraction of the capsule, the contents of the lens are removed. The same property is also used in laser capsulotomy.

In a light microscope, the capsule looks transparent, homogeneous (Fig. 3.4.8).

Rice. 3.4.8. Light-optical structure of the lens capsule, the epithelium of the lens capsule and the lens fibers of the outer layers: 1 - lens capsule; 2 - epithelial layer of the lens capsule; 3 - lens fibers

In polarized light, its lamellar fibrous structure is revealed. In this case, the fiber is located parallel to the surface of the lens. The capsule also stains positively during the PAS reaction, which indicates the presence of a large amount of proteoglycans in its composition.

The ultrastructural capsule has relatively amorphous structure(Fig. 3.4.6, 3.4.9).

Rice. 3.4.9. Ultrastructure of the ligament of zon, lens capsule, epithelium of the lens capsule and lens fibers of the outer layers: 1 - zinn ligament; 2 - lens capsule; 3- epithelial layer of the lens capsule; 4 - lens fibers

Insignificant lamellarity is outlined due to the scattering of electrons by filamentary elements that fold into plates.

Approximately 40 plates are identified, each of which is approximately 40 nm thick. At a higher magnification of the microscope, delicate collagen fibrils with a diameter of 2.5 nm are revealed.

In the postnatal period, there is some thickening of the posterior capsule, which indicates the possibility of secretion of basal material by the posterior cortical fibers.

Fisher found that 90% of the loss of elasticity of the lens occurs as a result of a change in the elasticity of the capsule.

In the equatorial zone of the anterior lens capsule with age, electron-dense inclusions, consisting of collagen fibers with a diameter of 15 nm and with a period of transverse striation equal to 50-60 nm. It is assumed that they are formed as a result of the synthetic activity of epithelial cells. With age, collagen fibers also appear, the striation frequency of which is 110 nm.

The sites of attachment of the ligament of zon to the capsule are named. Berger plates(Berger, 1882) (another name is the pericapsular membrane). This is a superficially located layer of the capsule, having a thickness of 0.6 to 0.9 microns. It is less dense and contains more glycosaminoglycans than the rest of the capsule. The fibers of this fibrogranular layer of the pericapsular membrane are only 1-3 nm thick, while the thickness of the fibrils of the zinn ligament is 10 nm.

found in the pericapsular membrane fibronectin, vitreonectin and other matrix proteins that play a role in the attachment of ligaments to the capsule. Recently, the presence of another microfibrillary material, namely fibrillin, has been established, the role of which is indicated above.

Like other basement membranes, the lens capsule is rich in type IV collagen. It also contains collagen types I, III and V. Many other extracellular matrix components are also found - laminin, fibronectin, heparan sulfate and entactin.

Permeability of the lens capsule human has been studied by many researchers. The capsule freely passes water, ions and other small molecules. It is a barrier to the path of protein molecules having the size of hemoglobin. Differences in the capacity of the capsule in the norm and in cataracts were not found by anyone.

lens epithelium(epithelium lentis) consists of a single layer of cells lying under the anterior lens capsule and extending to the equator (Fig. 3.4.4, 3.4.5, 3.4.8, 3.4.9). Cells are cuboidal in transverse sections, and polygonal in planar preparations. Their number ranges from 350,000 to 1,000,000. The density of epitheliocytes in the central zone is 5009 cells per mm2 in men and 5781 in women. Cell density slightly increases along the periphery of the lens.

It should be emphasized that in the tissues of the lens, in particular in the epithelium, anaerobic respiration. Aerobic oxidation (Krebs cycle) is observed only in epithelial cells and outer lens fibers, while this oxidation pathway provides up to 20% of the lens energy requirement. This energy is used to provide active transport and synthetic processes necessary for the growth of the lens, the synthesis of membranes, crystallins, cytoskeletal proteins and nucleoproteins. The pentose phosphate shunt also functions, providing the lens with pentoses necessary for the synthesis of nucleoproteins.

Lens epithelium and superficial fibers of the lens cortex involved in the removal of sodium from the lens, thanks to the activity of the Na -K + -pump. It uses the energy of ATP. In the posterior part of the lens, sodium ions are passively distributed into the moisture of the posterior chamber. The lens epithelium consists of several subpopulations of cells that differ primarily in their proliferative activity. Certain topographic features of the distribution of epitheliocytes of various subpopulations are revealed. Depending on the features of the structure, function and proliferative activity of cells, several zones of the epithelial lining are distinguished.

Central zone. The central zone consists of a relatively constant number of cells, the number of which slowly decreases with age. epitheliocytes polygonal shape(Fig. 3.4.9, 3.4.10, a),

Rice. 3.4.10. Ultrastructural organization of the epithelial cells of the lens capsule of the intermediate zone (a) and the equatorial region (b) (according to Hogan et al, 1971): 1 - lens capsule; 2 - apical surface of an adjacent epithelial cell; 3-finger in pressure into the cytoplasm of the epithelial cell of adjacent cells; 4 - epithelial cell oriented parallel to the capsule; 5 - nucleated epithelial cell located in the cortex of the lens

their width is 11-17 microns, and their height is 5-8 microns. With their apical surface, they are adjacent to the most superficially located lens fibers. The nuclei are displaced towards the apical surface of large cells and have numerous nuclear pores. In them. usually two nucleoli.

Cytoplasm of epitheliocytes contains a moderate amount of ribosomes, polysomes, smooth and rough endoplasmic reticulum, small mitochondria, lysosomes, and glycogen granules. The Golgi apparatus is expressed. Cylindrical microtubules with a diameter of 24 nm, microfilaments of an intermediate type (10 nm), alpha-actinin filaments are visible.

Using the methods of immunomorphology in the cytoplasm of epitheliocytes, the presence of the so-called matrix proteins- actin, vinmetin, spectrin and myosin, which provide rigidity to the cytoplasm of the cell.

Alpha-crystallin is also present in the epithelium. Beta and gamma crystallins are absent.

Epithelial cells are attached to the lens capsule by hemidesmosome. Desmosomes and gap junctions are visible between epithelial cells, having a typical structure. The system of intercellular contacts provides not only adhesion between the epithelial cells of the lens, but also determines the ionic and metabolic connection between cells.

Despite the presence of numerous intercellular contacts between epithelial cells, there are spaces filled with structureless material of low electron density. The width of these spaces ranges from 2 to 20 nm. It is thanks to these spaces that the exchange of metabolites between the lens and intraocular fluid is carried out.

Epithelial cells of the central zone differ exclusively low mitotic activity. The mitotic index is only 0.0004% and approaches the mitotic index of epithelial cells of the equatorial zone in age-related cataract. Significantly, mitotic activity increases under various pathological conditions and, first of all, after injury. The number of mitoses increases after exposure of epithelial cells to a number of hormones in experimental uveitis.

Intermediate zone. The intermediate zone is closer to the periphery of the lens. The cells of this zone are cylindrical with a centrally located nucleus. The basement membrane has a folded appearance.

germinal zone. The germinal zone is adjacent to the preequatorial zone. It is this zone that is characterized by high cell proliferative activity (66 mitoses per 100,000 cells), which gradually decreases with age. The duration of mitosis in different animals ranges from 30 minutes to 1 hour. At the same time, diurnal fluctuations in mitotic activity were revealed.

The cells of this zone after division are displaced posteriorly and subsequently turn into lens fibers. Some of them are also displaced anteriorly, into the intermediate zone.

The cytoplasm of epithelial cells contains small organelles. There are short profiles of the rough endoplasmic reticulum, ribosomes, small mitochondria and the Golgi apparatus (Fig. 3.4.10, b). The number of organelles increases in the equatorial region as the number of structural elements of the cytoskeleton of actin, vimentin, microtubule protein, spectrin, alpha-actinin, and myosin increases. It is possible to distinguish whole actin mesh-like structures, especially visible in the apical and basal parts of the cells. In addition to actin, vimentin and tubulin were found in the cytoplasm of epithelial cells. It is assumed that the contractile microfilaments of the cytoplasm of epithelial cells contribute by their contraction to the movement of the intercellular fluid.

In recent years, it has been shown that the proliferative activity of epithelial cells of the germinal zone is regulated by numerous biologically active substances - cytokines. The significance of interleukin-1, fibroblast growth factor, transforming growth factor beta, epidermal growth factor, insulin-like growth factor, hepatocyte growth factor, keratinocyte growth factor, postaglandin E2 was revealed. Some of these growth factors stimulate proliferative activity, while others inhibit it. It should be noted that the listed growth factors are synthesized either by the structures of the eyeball, or by other tissues of the body, entering the eye through the blood.

The process of formation of lens fibers. After the final division of the cell, one or both daughter cells are displaced into the adjacent transitional zone, in which the cells are organized in meridianally oriented rows (Fig. 3.4.4, 3.4.5, 3.4.11).

Rice. 3.4.11. Features of the location of the lens fibers: a - schematic representation; b - scanning electron microscopy (according to Kuszak, 1989)

Subsequently, these cells differentiate into secondary fibers of the lens, turning 180° and elongating. The new lens fibers maintain polarity in such a way that the posterior (basal) portion of the fiber maintains contact with the capsule (basal lamina), while the anterior (apical) portion is separated from this by the epithelium. As epitheliocytes turn into lens fibers, a nuclear arc is formed (under microscopic examination, a number of nuclei of epithelial cells arranged in the form of an arc).

The premitotic state of epithelial cells is preceded by DNA synthesis, while cell differentiation into lens fibers is accompanied by an increase in RNA synthesis, since this stage is marked by the synthesis of structural and membrane specific proteins. The nucleoli of differentiating cells increase sharply, and the cytoplasm becomes more basophilic due to an increase in the number of ribosomes, which is explained by increased synthesis of membrane components, cytoskeletal proteins, and lens crystallins. These structural changes reflect increased protein synthesis.

During the formation of the lens fiber, numerous microtubules 5 nm in diameter and intermediate fibrils appear in the cytoplasm of cells, oriented along the cell and playing an important role in the morphogenesis of lens fibers.

Cells of varying degrees of differentiation in the region of the nuclear arc are arranged as if in a checkerboard pattern. Due to this, channels are formed between them, providing a strict orientation in space of newly differentiating cells. It is into these channels that the cytoplasmic processes penetrate. In this case, meridional rows of lens fibers are formed.

It is important to emphasize that the violation of the meridional orientation of the fibers is one of the causes of cataract development both in experimental animals and in humans.

The transformation of epitheliocytes into lens fibers occurs quite quickly. This has been shown in an animal experiment using isotopically labeled thymidine. In rats, the epitheliocyte turns into a lens fiber after 5 weeks.

In the process of differentiation and displacement of cells to the center of the lens in the cytoplasm of the lens fibers the number of organelles and inclusions decreases. The cytoplasm becomes homogeneous. The nuclei undergo pycnosis and then completely disappear. Soon the organelles disappear. Basnett found that the loss of nuclei and mitochondria occurs suddenly and in one generation of cells.

The number of lens fibers throughout life is constantly increasing. "Old" fibers are shifted to the center. As a result, a dense core is formed.

With age, the intensity of the formation of lens fibers decreases. So, in young rats, approximately five new fibers are formed per day, while in old rats - one.

Features of epithelial cell membranes. Cytoplasmic membranes of neighboring epithelial cells form a kind of complex of intercellular connections. If a side surfaces cells are slightly wavy, then the apical zones of the membranes form "finger impressions" plunging into the proper lens fibers. The basal part of the cells is attached to the anterior capsule by hemidesmosomes, and the lateral surfaces of the cells are connected by desmosomes.

On the lateral surfaces of the membranes of adjacent cells, slot contacts through which small molecules can be exchanged between lens fibers. In the region of gap junctions, kennesins of various molecular weights are found. Some researchers suggest that gap junctions between lens fibers differ from those in other organs and tissues.

It is exceptionally rare to see tight contacts.

The structural organization of lens fiber membranes and the nature of intercellular contacts indicate the possible presence on the surface receptor cells that control the processes of endocytosis, which is of great importance in the movement of metabolites between these cells. The existence of receptors for insulin, growth hormone and beta-adrenergic antagonists is assumed. On the apical surface of epithelial cells, orthogonal particles embedded in the membrane and having a diameter of 6-7 nm were revealed. It is believed that these formations provide movement between cells. nutrients and metabolites.

lens fibers(fibrcie lentis) (Fig. 3.4.5, 3.4.10-3.4.12).

Rice. 3.4.12. The nature of the arrangement of the lens fibers. Scanning electron microscopy (according to Kuszak, 1989): a-densely packed lens fibers; b - "finger impressions"

The transition from the epithelial cells of the germinal zone to the lens fiber is accompanied by the disappearance of "finger impressions" between the cells, as well as the beginning of elongation of the basal and apical parts of the cell. The gradual accumulation of lens fibers and their displacement to the center of the lens is accompanied by the formation of the lens nucleus. This displacement of cells leads to the formation of an S- or C-like arc (nuclear puff), directed forward and consisting of a "chain" of cell nuclei. In the equatorial region, the zone of nuclear cells has a width of about 300-500 microns.

The deeper fibers of the lens have a thickness of 150 microns. When they lose nuclei, the nuclear arc disappears. The lens fibers are fusiform or belt-like, located along the arc in the form of concentric layers. On a transverse section in the equatorial region, they are hexagonal in shape. As they sink towards the center of the lens, their uniformity in size and shape is gradually broken. In the equatorial region in adults, the width of the lens fiber ranges from 10 to 12 microns, and the thickness is from 1.5 to 2.0 microns. In the posterior parts of the lens, the fibers are thinner, which is explained by the asymmetric shape of the lens and the greater thickness of the anterior cortex. The length of the lens fibers, depending on the depth of location, ranges from 7 to 12 mm. And this despite the fact that the initial height of the epithelial cell is only 10 microns.

The ends of the lens fibers meet at a specific location and form sutures.

Seams of the lens(Fig. 3.4.13).

Rice. 3.4.13. The formation of seams at the junction of the fibers, which occurs at different periods of life: 1 - Y-shaped seam, formed in the embryonic period; 2 - a more developed suture system that occurs in the childhood period; 3 is the most developed suture system found in adults

The fetal nucleus has an anterior vertical Y-shaped and a posterior inverted Y-shaped suture. After birth, as the lens grows and the number of layers of lens fibers that form their sutures increases, the sutures spatially coalesce to form the star-like structure found in adults.

The main significance of the sutures lies in the fact that, thanks to such a complex system of contact between cells the shape of the lens is preserved almost throughout life.

Features of lens fiber membranes. Button-loop contacts (Fig. 3.4.12). The membranes of adjacent lens fibers are connected by a variety of specialized formations that change their structure as the fiber moves from the surface into the depths of the lens. In the superficial 8-10 layers of the anterior cortex, the fibers are connected using formations of the "button-loop" type ("ball and socket" by American authors), distributed evenly along the entire length of the fiber. Contacts of this type exist only between cells of the same layer, i.e., cells of the same generation, and are absent between cells of different generations. This allows the fibers to move relative to each other during their growth.

Between the more deeply located fibers, the button-loop contact is found somewhat less frequently. They are distributed in the fibers unevenly and randomly. They also appear between cells of different generations.

In the deepest layers of the cortex and nucleus, in addition to the indicated contacts (“button-loop”), complex interdigitations appear in the form of ridges, depressions and furrows. Desmosomes have also been found, but only between differentiating rather than mature lens fibers.

It is assumed that contacts between lens fibers are necessary to maintain the rigidity of the structure throughout life, contributing to the preservation of the transparency of the lens. Another type of intercellular contacts has been found in the human lens. it gap contact. Gap junctions serve two roles. First, since they connect the lens fibers over a long distance, the architectonics of the tissue is preserved, thereby ensuring the transparency of the lens. Secondly, it is due to the presence of these contacts that the distribution of nutrients between the lens fibers occurs. This is especially important for the normal functioning of structures against the background of reduced metabolic activity of cells (insufficient number of organelles).

Revealed two types of gap contacts- crystalline (with high ohmic resistance) and non-crystalline (with low ohmic resistance). In some tissues (the liver), these types of gap junctions can be transformed into one another when the ionic composition of the environment changes. In the lens fiber, they are incapable of such a transformation. The first type of gap junctions was found in the places where the fibers adjoin epithelial cells, and the second - only between the fibers.

Low-resistance gap contacts contain intramembrane particles that do not allow neighboring membranes to approach each other by more than 2 nm. Due to this, in the deep layers of the lens, ions and molecules of small size propagate quite easily between the lens fibers, and their concentration levels out fairly quickly. There are also species differences in the number of gap junctions. So, in the human lens, they occupy the surface of the fiber by area of ​​5%, in a frog - 15%, in a rat - 30%, and in a chicken - 60%. There are no gap contacts in the seam area.

It is necessary to dwell briefly on the factors that ensure transparency and high refractive power of the lens. The high refractive power of the lens is achieved high concentration of protein filaments, and transparency - their strict spatial organization, the uniformity of the fiber structure within each generation and a small amount of intercellular space (less than 1% of the lens volume). Contributes to transparency and a small amount of intracytoplasmic organelles, as well as the absence of nuclei in the lens fibers. All of these factors minimize the scattering of light between the fibers.

There are other factors that affect refractive power. One of them is increase in protein concentration as it approaches the nucleus of the lens. It is due to the increase in protein concentration that there is no chromatic aberration.

No less important in the structural integrity and transparency of the lens is reflation of the ionic content and degree of hydration of the lens fibers. At birth, the lens is transparent. As the lens grows, the nucleus becomes yellow. The appearance of yellowness is probably associated with the influence of ultraviolet light on it (wavelength 315-400 nm). At the same time, fluorescent pigments appear in the cortex. It is believed that these pigments shield the retina from the damaging effects of short-wavelength light radiation. Pigments accumulate in the nucleus with age, and in some people are involved in the formation of pigment cataracts. In the nucleus of the lens in old age and especially in nuclear cataracts, the amount of insoluble proteins increases, which are crystallins, the molecules of which are “crosslinked”.

Metabolic activity in the central regions of the lens is negligible. Virtually no protein metabolism. That is why they belong to long-lived proteins and are easily damaged by oxidizing agents, leading to a change in the conformation of the protein molecule due to the formation of sulfhydryl groups between protein molecules. The development of cataracts is characterized by an increase in light scattering zones. This can be caused by a violation of the regularity of the arrangement of the lens fibers, a change in the structure of the membranes and an increase in the scattering of light, due to a change in the secondary and tertiary structure of protein molecules. Edema of lens fibers and their destruction leads to disruption of water-salt metabolism.

Article from the book: .

A huge beach of bare pebbles - Looking at everything without shrouds - And vigilant, like an eye lens, Unglazed sky.

B. Pasternak

12.1. The structure of the lens

The lens is part of the light-transmitting and refractive system of the eye. This is a transparent, biconvex biological lens that provides dynamic optics to the eye due to the mechanism of accommodation.

In the process of embryonic development, the lens is formed at the 3-4th week of the life of the embryo from the excrement.

toderma covering the wall of the eye cup. The ectoderm is drawn into the cavity of the eye cup, and from it the rudiment of the lens is formed in the form of a bubble. From the lengthening epithelial cells inside the vesicle, lens fibers are formed.

The lens is shaped biconvex lens. The anterior and posterior spherical surfaces of the lens have different radii of curvature (Fig. 12.1). Front top-

Rice. 12.1. The structure of the lens and the location of the ligament of zinus supporting it.

ness is flatter. The radius of its curvature (R = 10 mm) is greater than the radius of curvature of the rear surface (R = 6 mm). The centers of the anterior and posterior surfaces of the lens are called the anterior and posterior poles, respectively, and the line connecting them is called the axis of the lens, the length of which is 3.5-4.5 mm. The line of transition of the front surface to the back is the equator. The lens diameter is 9-10 mm.

The lens is covered with a thin structureless transparent capsule. The part of the capsule lining the anterior surface of the lens is called the "anterior capsule" ("anterior bag") of the lens. Its thickness is 11-18 microns. From the inside, the anterior capsule is covered with a single-layer epithelium, while the posterior one does not have it, it is almost 2 times thinner than the anterior one. The epithelium of the anterior capsule plays an important role in the metabolism of the lens and is characterized by a high activity of oxidative enzymes compared to the central part of the lens. Epithelial cells actively proliferate. At the equator, they elongate, forming the growth zone of the lens. Stretching cells turn into lens fibers. Young ribbon-like cells push old fibers to the center. This process continues throughout life. The centrally located fibers lose their nuclei, dehydrate and shrink. Layering tightly on top of each other, they form the nucleus of the lens (nucleus lentis). The size and density of the nucleus increase over the years. This does not affect the degree of transparency of the lens, however, due to a decrease in overall elasticity, the volume of accommodation gradually decreases (see section 5.5). By the age of 40-45, there is already a fairly dense core. This mechanism of lens growth ensures the stability of its outer dimensions. The closed capsule of the lens does not allow dead cells to

get out. Like all epithelial formations, the lens grows throughout life, but its size practically does not increase.

Young fibers, constantly formed on the periphery of the lens, form an elastic substance around the nucleus - the lens cortex (cortex lentis). The fibers of the cortex are surrounded by a specific substance that has the same refractive index of light as them. It provides their mobility during contraction and relaxation, when the lens changes shape and optical power in the process of accommodation.

The lens has a layered structure - it resembles an onion. All fibers extending from the growth zone along the circumference of the equator converge in the center and form a three-pointed star, which is visible during biomicroscopy, especially when turbidity appears.

From the description of the structure of the lens, it can be seen that it is an epithelial formation: it has neither nerves, nor blood and lymphatic vessels.

The artery of the vitreous body (a. hyaloidea), which in the early embryonic period is involved in the formation of the lens, is subsequently reduced. By the 7-8th month, the choroid plexus around the lens resolves.

The lens is surrounded on all sides by intraocular fluid. Nutrients enter through the capsule by diffusion and active transport. The energy requirements of avascular epithelial formation are 10-20 times lower than those of other organs and tissues. They are satisfied through anaerobic glycolysis.

Compared to other structures of the eye, the lens contains the largest amount of proteins (35-40%). These are soluble α- and β-crystallins and insoluble albuminoid. The lens proteins are organ-specific. When immunized

to this protein may occur anaphylactic reaction. The lens contains carbohydrates and their derivatives, reducing agents of glutathione, cysteine, ascorbic acid, etc. Unlike other tissues, there is little water in the lens (up to 60-65%), and its amount decreases with age. The content of protein, water, vitamins and electrolytes in the lens differs significantly from those proportions that are found in the intraocular fluid, vitreous body and blood plasma. The lens floats in water, but, despite this, it is a dehydrated formation, which is explained by the peculiarities of water-electrolyte transport. The lens has a high level of potassium ions and a low level of sodium ions: the concentration of potassium ions is 25 times higher than in the aqueous humor of the eye and the vitreous body, and the concentration of amino acids is 20 times higher.

The lens capsule has the property of selective permeability, therefore chemical composition transparent lens is maintained at a certain level. A change in the composition of the intraocular fluid is reflected in the state of transparency of the lens.

In an adult, the lens has a slight yellowish tint, the intensity of which may increase with age. This does not affect visual acuity, but may affect the perception of blue and purple colors.

The lens is located in the cavity of the eye in the frontal plane between the iris and the vitreous body, dividing the eyeball into anterior and posterior sections. In front, the lens serves as a support for the pupillary part of the iris. Its posterior surface is located in the deepening of the vitreous body, from which the lens is separated by a narrow capillary gap, expanding when exudate accumulates in it.

The lens maintains its position in the eye with the help of fibers of the circular supporting ligament of the ciliary body (ligament of cinnamon). Thin (20-22 microns thick) arachnoid filaments extend in radial bundles from the epithelium of the ciliary processes, partially cross and are woven into the lens capsule on the anterior and posterior surfaces, providing an impact on the lens capsule during the work of the muscular apparatus of the ciliary (ciliary) body.

12.2. Functions of the lens

The lens performs a number of very important functions in the eye. First of all, it is a medium through which light rays pass unhindered to the retina. it light transmission function. It is provided by the main property of the lens - its transparency.

The main function of the lens is light refraction. In terms of the degree of refraction of light rays, it ranks second after the cornea. The optical power of this living biological lens is within 19.0 diopters.

Interacting with the ciliary body, the lens provides the function of accommodation. He is able to smoothly change the optical power. The self-adjusting image focus mechanism (see Section 5.5) is made possible by the elasticity of the lens. This ensures dynamic refraction.

The lens divides the eyeball into two unequal sections - a smaller anterior and a larger posterior. Is it a barrier or separation barrier between them. The barrier protects the delicate structures of the anterior eye from the pressure of a large vitreous mass. In the event that the eye loses the lens, the vitreous body moves anteriorly. Anatomical relationships change, and after them, functions. Difficulty-

The conditions for the hydrodynamics of the eye are reduced due to the narrowing (compression) of the angle of the anterior chamber of the eye and the blockade of the pupil area. There are conditions for the development of secondary glaucoma. When the lens is removed along with the capsule, changes also occur in the posterior part of the eye due to the vacuum effect. The vitreous body, which has received some freedom of movement, moves away from the posterior pole and hits the walls of the eye during movements of the eyeball. This is the reason for the occurrence of severe pathology of the retina, such as edema, detachment, hemorrhages, ruptures.

The lens is an obstacle to the penetration of microbes from the anterior chamber into the vitreous cavity. - protective barrier.

12.3. Anomalies in the development of the lens

Malformations of the lens can have different manifestations. Any changes in the shape, size and localization of the lens cause pronounced violations of its function.

congenital aphakia - the absence of the lens - is rare and, as a rule, is combined with other malformations of the eye.

Microfakia - small crystal. This pathology is usually combined

It occurs with a change in the shape of the lens - spherophakia (spherical lens) or a violation of the hydrodynamics of the eye. Clinically, this is manifested by high myopia with incomplete vision correction. A small round lens, suspended on long weak threads of the circular ligament, has a much greater than normal mobility. It can insert into the pupillary lumen and cause pupillary block with a sharp increase intraocular pressure and pain syndrome. To release the lens, you need by medication expand the pupil.

Microphakia in combination with subluxation of the lens is one of the manifestations marfan syndrome, hereditary malformation of the entire connective tissue. Ectopia of the lens, a change in its shape, is caused by hypoplasia of the ligaments supporting it. With age, the detachment of the ligament of zon increases. In this place, the vitreous body protrudes in the form of a hernia. The equator of the lens becomes visible in the region of the pupil. Complete dislocation of the lens is also possible. In addition to ocular pathology, Marfan's syndrome is characterized by damage to the musculoskeletal system and internal organs (Fig. 12.2).

Rice. 12.2. Marfan syndrome.

a - the equator of the lens is visible in the pupil area; b - hands in Marfan's syndrome.

It is impossible not to pay attention to the features of the appearance of the patient: high growth, disproportionately long limbs, thin, long fingers (arachnodactyly), poorly developed muscles and subcutaneous fatty tissue, curvature of the spine. Long and thin ribs form an unusually shaped chest. In addition, developmental defects of cardio-vascular system, vegetative-vascular disorders, dysfunction of the adrenal cortex, violation of the daily rhythm of excretion of glucocorticoids in the urine.

Microspherophakia with subluxation or complete dislocation of the lens is also noted with marchesani syndrome- systemic hereditary lesion of mesenchymal tissue. Patients with this syndrome, in contrast to patients with Marfan's syndrome, have a completely different appearance: short stature, short arms, with which it is difficult for them to clasp their own head, short and thick fingers (brachydactyly), hypertrophied muscles, asymmetric compressed skull.

Coloboma of the lens- a defect in the lens tissue along the midline in lower section. This pathology is observed extremely rarely and is usually combined with coloboma of the iris, ciliary body and choroid. Such defects are formed due to incomplete closure of the germinal fissure during the formation of the secondary optic cup.

Lenticonus- cone-shaped protrusion of one of the surfaces of the lens. Another type of lens surface pathology is lentiglobus: the anterior or posterior surface of the lens has a spherical shape. Each of these developmental anomalies is usually noted in one eye, and may be combined with opacities in the lens. Clinically, lenticonus and lentiglobus are manifested by increased

refraction of the eye, i.e., the development of high myopia and difficult-to-correct astigmatism.

With anomalies in the development of the lens, not accompanied by glaucoma or cataracts, special treatment not required. In cases where, due to a congenital pathology of the lens, a refractive error that cannot be corrected by glasses occurs, the altered lens is removed and replaced with an artificial one (see section 12.4).

12.4. Lens pathology

Features of the structure and functions of the lens, the absence of nerves, blood and lymphatic vessels determine the originality of its pathology. There are no inflammatory and tumor processes in the lens. The main manifestations of the pathology of the lens are a violation of its transparency and the loss of the correct location in the eye.

12.4.1. Cataract

Any clouding of the lens is called a cataract.

Depending on the number and localization of opacities in the lens, polar (anterior and posterior), fusiform, zonular (layered), nuclear, cortical and complete cataracts are distinguished (Fig. 12.3). The characteristic pattern of the location of opacities in the lens may be evidence of congenital or acquired cataracts.

12.4.1.1. congenital cataract

Congenital lens opacities occur when exposed to toxic substances during its formation. Most often, these are viral diseases of the mother during pregnancy, such as

Rice. 12.3. Localization of opacities at various types cataract.

influenza, measles, rubella, and toxoplasmosis. Endocrine disorders in a woman during pregnancy and insufficiency of function are of great importance. parathyroid glands leading to hypocalcemia and impaired fetal development.

Congenital cataracts can be hereditary with a dominant type of transmission. In such cases, the disease is most often bilateral, often combined with malformations of the eye or other organs.

When examining the lens, certain signs can be identified that characterize congenital cataracts, most often polar or layered opacities that have either even rounded outlines or a symmetrical pattern, sometimes it can be like a snowflake or a picture of the starry sky.

Small congenital opacities in the peripheral parts of the lens and on the posterior capsule can be

found in healthy eyes. These are traces of attachment of vascular loops of the embryonic vitreous artery. Such opacities do not progress and do not interfere with vision.

Anterior polar cataract-

this is a clouding of the lens in the form of a round spot of white or gray color, which is located under the capsule at the anterior pole. It is formed as a result of a violation of the process of embryonic development of the epithelium (Fig. 12.4).

Posterior polar cataract in shape and color it is very similar to the anterior polar cataract, but is located at the posterior pole of the lens under the capsule. The area of ​​cloudiness can be fused with the capsule. The posterior polar cataract is the remnant of a reduced embryonic vitreous artery.

In one eye, opacities may be noted at both the anterior and posterior poles. In this case, one speaks of anteroposterior polar cataract. Congenital polar cataracts are characterized by regular rounded outlines. The sizes of such cataracts are small (1-2 mm). Ino-

Rice. 12.4. Congenital anterior polar cataract with remnants of the embryonic pupillary membrane.

where polar cataracts have a thin radiant halo. In transmitted light, a polar cataract is visible as a black spot on a pink background.

Fusiform cataract occupies the very center of the lens. Opacity is located strictly along the anteroposterior axis in the form of a thin gray ribbon, shaped like a spindle. It consists of three links, three thickenings. This is a chain of interconnected point opacities under the anterior and posterior capsules of the lens, as well as in the region of its nucleus.

Polar and fusiform cataracts usually do not progress. Patients from early childhood adapt to look through the transparent parts of the lens, often have complete or fairly high vision. With this pathology, treatment is not required.

layered(zonular) cataract is more common than other congenital cataracts. Opacities are located strictly in one or more layers around the lens nucleus. Transparent and cloudy layers alternate. Usually the first cloudy layer is located on the border of the embryonic and "adult" nuclei. This is clearly seen on the light cut with biomicroscopy. In transmitted light, such a cataract is visible as a dark disk with smooth edges against the background of a pink reflex. With a wide pupil, in some cases, local opacities are also determined in the form of short spokes, which are located in more superficial layers in relation to the cloudy disk and have a radial direction. They seem to be sitting astride the equator of a cloudy disk, which is why they are called "riders". Only in 5% of cases, layered cataracts are unilateral.

Bilateral lens lesion, clear boundaries of transparent and turbid layers around the nucleus, symmetrical arrangement of peripheral spoke-like opacities with

the relative orderliness of the pattern indicates congenital pathology. Layered cataracts can also develop in the postnatal period in children with congenital or acquired insufficiency of the parathyroid glands. Children with symptoms of tetany usually have stratified cataracts.

The degree of visual impairment is determined by the density of opacities in the center of the lens. The decision on surgical treatment depends mainly on visual acuity.

Total cataracts are rare and always bilateral. The entire substance of the lens turns into a cloudy soft mass due to a gross violation of the embryonic development of the lens. Such cataracts gradually resolve, leaving behind wrinkled cloudy capsules fused with each other. Complete resorption of the lens substance can occur even before the birth of the child. Total cataracts lead to a significant decrease in vision. With such cataracts, surgical treatment is required in the first months of life, since blindness in both eyes at an early age is a threat to the development of deep, irreversible amblyopia - atrophy of the visual analyzer due to its inactivity.

12.4.1.2. Acquired cataract

Cataract is the most common eye disease. This pathology occurs mainly in the elderly, although it can develop at any age due to various reasons. Opacification of the lens is a typical response of its avascular substance to the impact of any adverse factor, as well as to a change in the composition of the intraocular fluid surrounding the lens.

Microscopic examination of the cloudy lens reveals swelling and disintegration of the fibers, which lose their connection with the capsule and contract, vacuoles and gaps filled with a protein liquid are formed between them. Epithelial cells swell, lose their regular shape, and their ability to perceive dyes is impaired. The cell nuclei are compacted, intensely stained. The lens capsule changes slightly, which allows you to save the capsular bag during the operation and use it to fix the artificial lens.

Depending on the etiological factor, several types of cataracts are distinguished. For simplicity of presentation of the material, we divide them into two groups: age-related and complicated. Age-related cataracts can be considered as a manifestation of the processes of age-related involution. Complicated cataracts occur when exposed to adverse factors of the internal or external environment. Immune factors play a role in the development of cataracts (see Chapter 24).

Age-related cataract. Previously, she was called old. It is known that age-related changes in different organs and tissues do not proceed in the same way for everyone. Age-related (senile) cataracts can be found not only in the elderly, but also in the elderly and even active people. middle age. Usually it is bilateral, however, opacities do not always appear simultaneously in both eyes.

Depending on the localization of opacities, cortical and nuclear cataracts are distinguished. Cortical cataract occurs almost 10 times more often than nuclear. Consider first the development cortical form.

In the process of development, any cataract goes through four stages of maturation: initial, immature, mature and overripe.

Early signs initial cortical cataracts can serve as vacuoles located subcapsularly, and water gaps formed in the cortical layer of the lens. In the light section of the slit lamp, they are visible as optical voids. When areas of turbidity appear, these gaps are filled with fiber decay products and merge with the general background of opacities. Usually, the first foci of opacification occur in the peripheral areas of the lens cortex, and patients do not notice the developing cataract until opacities occur in the center, causing decreased vision.

Changes gradually increase both in the anterior and posterior cortical layers. The transparent and cloudy parts of the lens refract light differently; therefore, patients may complain of diplopia or polyopia: instead of one object, they see 2-3 or more. Other complaints are also possible. In the initial stage of cataract development, in the presence of limited small opacities in the center of the lens cortex, patients are worried about the appearance of flying flies that move in the direction the patient is looking. The duration of the course of the initial cataract can be different - from 1-2 to 10 years or more.

Stage immature cataract characterized by watering of the lens substance, the progression of opacities, a gradual decrease in visual acuity. The biomicroscopic picture is represented by lens opacities of varying intensity, interspersed with transparent areas. During normal external examination, the pupil may still be black or barely grayish due to the fact that the superficial subcapsular layers are still transparent. With side lighting, a crescentic “shadow” is formed from the iris on the side from which the light falls (Fig. 12.5, a).

Rice. 12.5.Cataract. a - immature; b - mature.

Swelling of the lens can lead to a serious complication - phacogenic glaucoma, which is also called phacomorphic. Due to the increase in the volume of the lens, the angle of the anterior chamber of the eye narrows, the outflow of intraocular fluid becomes more difficult, and intraocular pressure increases. In this case, it is necessary to remove the swollen lens during antihypertensive therapy. The operation ensures the normalization of intraocular pressure and restoration of visual acuity.

mature cataract is characterized by complete opacification and slight induration of the lens substance. With biomicroscopy, the nucleus and posterior cortical layers are not visible. On external examination, the pupil is bright gray or milky white. The lens appears to be inserted into the lumen of the pupil. There is no "shadow" from the iris (Fig. 12.5, b).

With complete clouding of the lens cortex, object vision is lost, but light perception and the ability to locate a light source (if the retina is preserved) are preserved. The patient can distinguish colors. These important indicators are the basis for favorable prognosis regarding the return of full vision after removal of cataracts

you. If the eye with a cataract does not distinguish between light and darkness, then this is evidence of complete blindness due to gross pathology in the visual-nerve apparatus. In this case, removing the cataract will not restore vision.

overripe cataract is extremely rare. It is also called lactic or morganian cataract after the scientist who first described this phase of cataract development (G. B. Morgagni). It is characterized by complete disintegration and liquefaction of the cloudy cortical substance of the lens. The core loses its support and sinks down. The lens capsule becomes like a bag with a cloudy liquid, at the bottom of which lies the nucleus. Further changes can be found in the literature clinical condition lens in the event that the operation was not performed. After resorption of the turbid liquid, vision improves for a certain period of time, and then the nucleus softens, dissolves, and only a wrinkled lens bag remains. In this case, the patient goes through many years of blindness.

With an overripe cataract, there is a risk of developing severe complications. With the resorption of a large amount of protein masses, a pronounced phagocytic

naya reaction. Macrophages and protein molecules clog the natural outflow pathways of fluid, resulting in the development of phacogenous (phacolytic) glaucoma.

An overripe milk cataract can be complicated by a rupture of the lens capsule and the release of protein detritus into the eye cavity. Following this, phacolytic iridocyclitis develops.

With the development of the noted complications of overmature cataract, it is urgent to remove the lens.

nuclear cataract is rare: it is no more than 8-10% of the total number of age-related cataracts. Opacity appears in the inner part of the embryonic nucleus and slowly spreads throughout the nucleus. At first, it is homogeneous and not intense, so it is regarded as age-related thickening or sclerosis of the lens. The core can acquire a yellowish, brown and even black color. The intensity of opacities and coloration of the nucleus increases slowly, vision gradually decreases. Immature nuclear cataract does not swell, thin cortical layers remain transparent (Fig. 12.6). A compacted large core refracts light rays more strongly, which

Rice. 12.6. Nuclear cataract. Light section of the lens in biomicroscopy.

It is clinically manifested by the development of myopia, which can reach 8.0-9.0 and even 12.0 diopters. When reading, patients stop using presbyopic glasses. In myopic eyes, cataracts usually develop in a nuclear type, and in these cases there is also an increase in refraction, i.e., an increase in the degree of myopia. Nuclear cataract remains immature for several years and even decades. In rare cases, when its full maturation occurs, we can talk about a mixed type cataract - nuclear-cortical.

Complicated cataract occurs when exposed to various adverse factors of the internal and external environment.

Unlike cortical and nuclear age-related cataracts, complicated ones are characterized by the development of opacities under the posterior lens capsule and in the peripheral parts of the posterior cortex. The predominant location of opacities in the posterior part of the lens can be explained by the worst conditions for nutrition and metabolism. In complicated cataracts, opacities first appear at the posterior pole in the form of a barely noticeable cloud, the intensity and size of which slowly increase until the opacification occupies the entire surface of the posterior capsule. Such cataracts are called posterior bowl cataracts. The nucleus and most of the cortex of the lens remain transparent, however, despite this, visual acuity is significantly reduced due to high density thin layer of haze.

Complicated cataract due to the influence of adverse internal factors. A negative impact on very vulnerable metabolic processes in the lens can be caused by changes occurring in other tissues of the eye, or by a general pathology of the body. Severe recurrent inflammation

All diseases of the eye, as well as dystrophic processes, are accompanied by a change in the composition of the intraocular fluid, which in turn leads to disruption of metabolic processes in the lens and the development of opacities. as a complication of the underlying eye disease cataract develops with recurrent iridocyclitis and chorioretinitis of various etiologies, dysfunction of the iris and ciliary body (Fuchs syndrome), advanced and terminal glaucoma, detachment and pigmentary degeneration of the retina.

An example of a combination of cataracts with a general pathology of the body is cachectic cataract, which occurs in connection with the general deep exhaustion of the body during starvation, after infectious diseases (typhus, malaria, smallpox, etc.), as a result of chronic anemia. Cataracts can occur on the basis of endocrine pathology (tetany, myotonic dystrophy, adiposogenital dystrophy), with Down's disease and some skin diseases (eczema, scleroderma, neurodermatitis, atrophic poikiloderma).

In modern clinical practice, diabetic cataracts are most often observed. It develops with a severe course of the disease at any age, is more often bilateral and is characterized by unusual initial manifestations. Opacities are formed subcapsularly in the anterior and posterior sections of the lens in the form of small, evenly spaced flakes, between which vacuoles and thin water slits are visible in places. The unusualness of the initial diabetic cataract lies not only in the localization of opacities, but also mainly in the ability to reverse development with adequate treatment diabetes. In elderly people with severe sclerosis of the lens nucleus, diabetic

Posterior capsular opacities may be associated with age-related nuclear cataract.

The initial manifestations of complicated cataracts that occur when metabolic processes in the body are disturbed due to endocrine, skin and other diseases are also characterized by the ability to resolve with rational treatment of a general disease.

Complicated cataract caused by external factors. The lens is very sensitive to all adverse environmental factors, be it mechanical, chemical, thermal or radiation exposure (Fig. 12.7, a). It can change even in cases where there is no direct damage. It is enough that parts of the eye adjacent to it are affected, since this always affects the quality of products and the rate of exchange of intraocular fluid.

Post-traumatic changes in the lens can be manifested not only by opacification, but also by displacement of the lens (dislocation or subluxation) as a result of complete or partial detachment of the ligament of Zinn (Fig. 12.7, b). After a blunt injury, a round pigmented imprint of the pupillary edge of the iris may remain on the lens - the so-called cataract, or Fossius ring. The pigment dissolves within a few weeks. Quite different consequences are noted if, after a concussion, a true clouding of the lens substance occurs, for example, a rosette, or radiant, cataract. Over time, opacities in the center of the socket increase and vision steadily decreases.

When the capsule breaks, aqueous humor containing proteolytic enzymes impregnates the substance of the lens, causing it to swell and become cloudy. Gradually disintegration and resorption occur

Rice. 12.7. Post-traumatic changes in the lens.

a - a foreign body under the capsule of the clouded lens; b - post-traumatic dislocation of the transparent lens.

lens fibers, after which a wrinkled lens bag remains.

The consequences of burns and penetrating wounds of the lens, as well as emergency measures, are described in chapter 23.

Radiation cataract. The lens is able to absorb rays with a very small wavelength in the invisible, infrared, part of the spectrum. It is under the influence of these rays that there is a danger of developing cataracts. X-rays and radium rays, as well as protons, neutrons and other elements of nuclear fission, leave traces in the lens. Exposure to the eye of ultrasound and microwave current can also lead to

development of cataracts. Rays of the visible spectrum (wavelength from 300 to 700 nm) pass through the lens without damaging it.

Occupational radiation cataracts can develop in workers in hot shops. Work experience, the duration of continuous contact with radiation and compliance with safety regulations are of great importance.

Care must be taken when performing radiotherapy to the head, especially when irradiating the orbit. Special devices are used to protect the eyes. After the explosion of the atomic bomb, residents of the Japanese cities of Hiroshima and Nagasaki were diagnosed with characteristic radiation cataracts. Of all the tissues of the eye, the lens turned out to be the most susceptible to hard ionizing radiation. It is more sensitive in children and young people than in the elderly and old age. Objective data indicate that the cataractogenic effect of neutron radiation is ten times stronger than other types of radiation.

The biomicroscopic picture in radiation cataract, as well as in other complicated cataracts, is characterized by opacities in the form of an irregular disk, located under the posterior lens capsule. The initial period of cataract development can be long, sometimes it is several months and even years, depending on the radiation dose and individual sensitivity. Reverse development of radiation cataracts does not occur.

Cataract in poisoning. Severe cases of ergot poisoning have been described in the literature, with mental distress, convulsions, and severe eye pathology- mydriasis, impaired oculomotor function and complicated cataract, which was detected several months later.

Naphthalene, thallium, dinitrophenol, trinitrotoluene and nitro dyes have a toxic effect on the lens. They can enter the body in different ways - through Airways, stomach and skin. Experimental cataracts in animals are obtained by adding naphthalene or thallium to feed.

Complicated cataracts can be caused not only by toxic substances, but also by an excess of certain drugs, such as sulfonamides, and common food ingredients. Thus, cataracts can develop when animals are fed galactose, lactose and xylose. Opacities of the lens found in patients with galactosemia and galactosuria are not an accident, but a consequence of the fact that galactose is not absorbed and accumulates in the body. There is no strong evidence for the role of vitamin deficiency in the occurrence of complicated cataracts.

Toxic cataracts in the initial period of development can resolve if the intake of the active substance into the body has stopped. Prolonged exposure to cataractogenic agents causes irreversible opacities. In these cases, surgical treatment is required.

12.4.1.3. Cataract treatment

In the initial stage of cataract development, conservative treatment to prevent rapid clouding of the entire substance of the lens. For this purpose, instillation of drugs that improve metabolic processes is prescribed. These preparations contain cysteine, ascorbic acid, glutamine and other ingredients (see section 25.4). The results of treatment are not always convincing. Rare forms of initial cataracts may resolve if treated in a timely manner. rational therapy that disease

vanishing, which was the cause of the formation of opacities in the lens.

Surgical removal of a cloudy lens is called a cataract extraction.

Cataract surgery was performed as early as 2500 BC, as evidenced by the monuments of Egypt and Assyria. Then they used the technique of “lowering”, or “reclining”, the lens into the vitreous cavity: the cornea was pierced with a needle, the lens was jerkily pressed, the zinn ligaments were torn off and it was overturned into the vitreous body. Operations were successful in only half of the patients, blindness occurred in the rest due to the development of inflammation and other complications.

The first operation to remove the lens for cataracts was performed by the French physician J. Daviel in 1745. Since then, the technique of the operation has been constantly changing and improving.

The indication for surgery is a decrease in visual acuity, leading to disability and discomfort in everyday life. The degree of maturity of the cataract does not matter when determining the indications for its removal. So, for example, with cup-shaped cataract, the nucleus and cortical masses can be completely transparent, but a thin layer of dense opacities localized under the posterior capsule in the central section sharply reduces visual acuity. With bilateral cataracts, the eye that has the worst vision is operated on first.

Before surgery, it is mandatory to examine both eyes and evaluate general condition organism. The prognosis of the results of the operation in terms of prevention is always important for the doctor and the patient possible complications, as well as regarding the function of the eye after surgery. For

in order to get an idea of ​​the safety of the visual-nerve analyzer of the eye, its ability to localize the direction of light (light projection) is determined, the field of view and bioelectric potentials are examined. The operation of cataract removal is also carried out in case of identified violations, hoping to restore at least residual vision. Surgical treatment is absolutely futile only with complete blindness, when the eye does not feel light. In the event that signs of inflammation are found in the anterior and posterior segments of the eye, as well as in its appendages, anti-inflammatory therapy must be carried out before surgery.

During the examination, previously undiagnosed glaucoma may be detected. This requires special attention from the doctor, since when a cataract is removed from a glaucoma eye, the risk of developing the most severe complication, expulsive hemorrhage, which can result in irreversible blindness, increases significantly. In case of glaucoma, the doctor decides whether to perform a preliminary anti-glaucoma operation or a combined intervention of cataract extraction and anti-glaucomatous surgery. Cataract extraction in operated, compensated glaucoma is safer, since sudden sharp drops in intraocular pressure are less likely during the operation.

When determining the tactics of surgical treatment, the doctor also takes into account any other features of the eye identified during the examination.

A general examination of the patient aims to identify possible foci of infection, primarily in organs and tissues located near the eye. Before the operation, foci of inflammation of any localization should be sanitized. Particular attention should be paid to the condition

teeth, nasopharynx and paranasal sinuses.

Blood and urine tests, ECG and X-ray examination lungs help to identify diseases that require emergency or planned treatment.

With a clinically calm state of the eye and its appendages, the study of the microflora of the contents of the conjunctival sac is not performed.

In modern conditions, direct preoperative preparation of the patient is greatly simplified, due to the fact that all microsurgical manipulations are less traumatic, they provide reliable sealing of the eye cavity, and patients do not need strict bed rest after surgery. The operation can be performed on an outpatient basis.

Cataract extraction is performed using microsurgical techniques. This means that the surgeon performs all manipulations under a microscope, uses the finest microsurgical instruments and suture material, and is provided with a comfortable chair. The mobility of the patient's head is limited by a special headboard of the operating table, which has the shape of a semicircular table on which the instruments lie, the surgeon's hands rest on it. The combination of these conditions allows the surgeon to perform precise manipulations without tremor of the fingers and random deviations patient's head.

In the 60-70s of the last century, the lens was removed entirely from the eye in a bag - intracapsular cataract extraction (IEC). The most popular was the cryoextraction method proposed in 1961 by the Polish scientist Krvavic (Fig. 12.8). Surgical access was performed from above through an arcuate corneoscleral incision along the limbus. The incision is large - a little

Rice. 12.8. Intracapsular cataract extraction.

a - the cornea is raised up, the edge of the iris is taken down by the iris retractor to expose the lens, the cryoextractor touches the surface of the lens, around the tip there is a white ring of freezing the lens; b - the cloudy lens is removed from the eye.

less than the semicircle of the cornea. It corresponded to the diameter of the removed lens (9-10 mm). With a special tool - an iris retractor, the upper edge of the pupil was captured and the lens was exposed. The cooled tip of the cryoextractor was applied to the anterior surface of the lens, frozen, and easily removed from the eye. To seal the wound, 8-10 interrupted sutures or one continuous suture were applied. Currently, this simple method is used extremely rarely due to the fact that in the postoperative period, even in the long term, severe complications can occur in the posterior part of the eye. This is due to the fact that after intracapsular cataract extraction, the entire mass of the vitreous body moves anteriorly and takes the place of the removed lens. The soft, pliable iris cannot hold back the movement of the vitreous body, resulting in hyperemia of the retinal vessels ex vacuo (vacuum effect).

This may be followed by hemorrhages in the retina, its edema central department, areas of retinal detachment.

Later, in the 80-90s of the last century, the main method for removing the cloudy lens was extracapsular cataract extraction (EEK). The essence of the operation is as follows: the anterior lens capsule is opened, the nucleus and cortical masses are removed, and the posterior capsule, together with the narrow rim of the anterior capsule, remains in place and performs its usual function - separating the anterior eye from the posterior. They serve as a barrier to moving the vitreous anteriorly. In this regard, after extracapsular cataract extraction, there are significantly fewer complications in the posterior part of the eye. The eye can more easily withstand various loads when running, pushing, lifting weights. In addition, the preserved lens bag is an ideal place for artificial optics.

There are different options for performing extracapsular cataract extraction. They can be divided into two groups - manual and energy cataract surgery.

With manual technique EEK surgical access almost twice as short as with intracapsular, since it is focused only on the removal of the lens nucleus, the diameter of which in an elderly person is 5-6 mm.

It is possible to reduce the operating incision to 3-4 mm to make the operation safer. In this case, it is necessary to cut the lens nucleus in half in the cavity of the eye with two hooks moving from opposite points of the equator towards each other. Both halves of the kernel are output alternately.

Currently, manual cataract surgery has already been superseded by modern methods using ultrasound, water or laser energy to destroy the lens in the eye cavity. This so-called energy surgery, or small incision surgery. It attracts surgeons with a significant reduction in the incidence of complications during surgery, as well as the absence of postoperative astigmatism. Wide surgical incisions have given way to punctures in the limbus, which do not require suturing.

Technique ultrasonic cataract phacoemulsification (FEC) was proposed in 1967 by the American scientist C. D. Kelman. The widespread use of this method began in the 1980s and 1990s.

Special devices have been created to perform ultrasonic FEC. Through a puncture at the limbus 1.8-2.2 mm long, a tip of the appropriate diameter is inserted into the eye, carrying ultrasonic energy. Using special techniques, they divide the core into four fragments and destroy them one by one. Through the same

Rice. 12.9. Energy methods of cataract extraction.

a - ultrasonic phacoemulsification of soft cataract; b - laser extraction of hard cataract, self-cleavage

kernels.

the tip enters the eye with BSS balanced salt solution. Washing out of the lens masses occurs through the aspiration channel (Fig. 12.9, a).

In the early 80s, N. E. Temirov proposed hydromonitor phacofragmentation of soft cataracts by transferring a heated isotonic sodium chloride solution through a special tip of high-speed pulsed streams.

The technology cataract destruction and evacuation any degree of hardness using laser energy and original vacuum installation. Known other laser systems can effectively destroy only soft cataracts. The operation is performed bimanually through two punctures at the limbus. At the first stage, the pupil is dilated and the anterior lens capsule is opened in the form of a circle with a diameter of 5-7 mm. Then, a laser (0.7 mm in diameter) and separately irrigation-aspiration (1.7 mm) tips are inserted into the eye (Fig. 12.9, b). They barely touch the surface of the lens in the center. The surgeon observes how the nucleus of the lens “melts” within a few seconds and a deep bowl is formed, the walls of which fall apart into fragments. When they are destroyed, the energy level is reduced. Soft cortical masses are aspirated without the use of a laser. The destruction of soft and medium hard cataracts occurs in a short period of time - from a few seconds to 2-3 minutes, to remove dense and very dense lenses, it takes from 4 to 6-7 minutes.

Laser cataract extraction (LEK) expands age indications, since during the operation there is no pressure on the lens, there is no need for mechanical fragmentation of the nucleus. The laser handpiece does not heat up during operation, so there is no need to inject large amounts of balanced salt solution. In patients under 40 years of age, laser energy often does not need to be switched on, since the powerful vacuum system of the device copes with the suction of the soft substance of the lens. Folding soft in-

traocular lenses are injected using an injector.

Cataract extraction is called the pearl of eye surgery. This is the most common eye surgery. It brings great satisfaction to the surgeon and the patient. Often patients come to the doctor by touch, and after the operation they immediately become sighted. The operation allows you to return the visual acuity that was in given eye before the development of cataracts.

12.4.2. Dislocation and subluxation of the lens

A dislocation is a complete detachment of the lens from the supporting ligament and its displacement into the anterior or posterior chamber of the eye. At the same time, it happens a sharp decline visual acuity, since a lens with a force of 19.0 diopters fell out of the optical system of the eye. The dislocated lens must be removed.

Lens subluxation is a partial detachment of the ligament of Zinn, which can have a different length around the circumference (see Fig. 12.7, b).

Congenital dislocations and subluxations of the lens are described above. Acquired displacement of the biological lens occurs as a result of blunt trauma or severe shaking. Clinical manifestations of lens subluxation depend on the size of the formed defect. Minimal damage may go unnoticed if the anterior vitreous limiting membrane is not damaged and the lens remains transparent.

The main symptom of lens subluxation is trembling of the iris (iridodonez). The delicate tissue of the iris rests on the lens at the anterior pole, so the trembling of the subluxated lens is transmitted

iris. Sometimes this symptom can be seen without applying special methods research. In other cases, one has to carefully observe the iris under side illumination or in the light of a slit lamp in order to catch a slight wave of movements with small displacements of the eyeball. With sharp abduction of the eye to the right and left, slight fluctuations of the iris cannot be detected. It should be noted that iridodonesis is not always present even with noticeable lens subluxations. This occurs when, along with a tear of the zinn ligament in the same sector, a defect appears in the anterior limiting membrane of the vitreous body. In this case, a strangulated hernia of the vitreous body occurs, which plugs the resulting hole, supports the lens and reduces its mobility. In such cases, lens subluxation can be recognized by two other symptoms detected by biomicroscopy: uneven depth of the anterior and posterior chambers of the eye due to more pronounced pressure or movement of the vitreous anteriorly in the zone of weakening of the lens support. With a hernia of the vitreous body that is restrained and fixed by adhesions, the posterior chamber in this sector increases and at the same time the depth of the anterior chamber of the eye changes, most often it becomes smaller. AT normal conditions the posterior chamber is not accessible for inspection, therefore, the depth of its peripheral sections is judged by an indirect sign - a different distance from the edge of the pupil to the lens on the right and left, or above and below.

The exact topographic position of the vitreous body, the lens and its supporting ligament behind the iris can only be seen with ultrasonic biomicroscopy(UBM).

With uncomplicated subluxation of the lens, visual acuity is essentially

venously does not decrease and treatment is not required, but complications may develop over time. A subluxated lens can become cloudy or cause secondary glaucoma. In such cases, the question arises of its removal. Timely diagnosis of lens subluxation allows you to choose the right surgical tactics, evaluate the possibility of strengthening the capsule and placing an artificial lens in it.

12.4.3. Aphakia and Artifakia

Afakia is the absence of the lens. An eye without a lens is called aphakic.

Congenital aphakia is rare. Usually the lens is removed surgically due to its clouding or dislocation. Cases of loss of the lens in penetrating wounds are known.

When examining an aphakic eye, a deep anterior chamber and trembling of the iris (iridodonesis) attract attention. If the posterior capsule of the lens is preserved in the eye, then it restrains the shocks of the vitreous body during eye movements and the trembling of the iris is less pronounced. With biomicroscopy, the light section reveals the location of the capsule, as well as the degree of its transparency. In the absence of a lens bag, the vitreous body, held only by the anterior limiting membrane, is pressed against the iris and slightly protrudes into the pupil area. This condition is called a vitreous hernia. When the membrane ruptures, vitreous fibers enter the anterior chamber. This is a complicated hernia.

aphakia correction. After removal of the lens, the refraction of the eye changes dramatically. There is a high degree of hypermetropia.

The refractive power of the lost lens must be compensated by optical means.- glasses, contact lens or an artificial lens.

Spectacle and contact correction of aphakia is now rarely used. When correcting aphakia of an emmetropic eye, a spectacle glass with a power of +10.0 diopters is required for the distance, which is significantly less than the refractive power of the removed lens, which on average

it is equal to 19.0 diopters. This difference is primarily due to the fact that the spectacle lens occupies a different place in the complex optical system of the eye. In addition, the glass lens is surrounded by air, while the lens is surrounded by liquid, with which it has almost the same refractive index of light. For a hypermetrop, the strength of the glass must be increased by the corresponding number of diopters, for a myop, on the contrary, it must be reduced. If before the opera-

Rice. 12.10. Designs of various models of IOLs and their place of fixation in the eye.

Since myopia was close to 19.0 diopters, then after the operation, too strong optics of myopic eyes is completely neutralized by removing the lens and the patient will do without distance glasses.

The aphakic eye is incapable of accommodation, therefore, for work at close range, glasses are prescribed 3.0 diopters stronger than for distance work. Spectacle correction cannot be used for monocular aphakia. The +10.0 diopter lens is a strong magnifying glass. If it is placed in front of one eye, then in this case the images in the two eyes will be too different in size, they will not merge into a single image. With monocular aphakia, contact (see section 5.9) or intraocular correction is possible.

Intraocular correction of aphakia - this is a surgical operation, the essence of which is that the clouded or dislocated natural lens is replaced with an artificial lens of the required strength (Fig. 12.11, a). The calculation of the diopter power of the new optics of the eye is performed by the doctor using special tables, nomograms or computer program. The following parameters are required for the calculation: the refractive power of the cornea, the depth of the anterior chamber of the eye, the thickness of the lens and the length of the eyeball. The general refraction of the eye is planned taking into account the wishes of the patients. For those of them who drive and drive active life most often plan emmetropia. Low myopic refraction can be planned if the other eye is nearsighted, and also for those patients who most spend the working day at a desk, want to write and read or do other precise work without glasses.

In recent years, bifocal, multifocal, accommodating, refractive-diffractive intraocular lenses have appeared.

PS (IOL), allowing you to see objects at different distances without additional spectacle correction.

The presence of an artificial lens in the eye is referred to as "artifakia". An eye with an artificial lens is called pseudophakic.

Intraocular correction of aphakia has a number of advantages over spectacle correction. It is more physiological, eliminates the dependence of patients on glasses, does not narrow the field of view, peripheral cattle, or distort objects. An image of normal size is formed on the retina.

Currently, there are many IOL designs (Fig. 12.10). According to the principle of attachment in the eye, there are three main types of artificial lenses:

Anterior chamber lenses are placed in the corner of the anterior chamber or attached to the iris (Fig. 12.11, b). They come into contact with very sensitive tissues of the eye - the iris and cornea, so they are rarely used at present;

Pupil lenses (pupillary) are also called iris clip lenses (ICL) (Fig. 12.11, c). They are inserted into the pupil according to the clip principle, these lenses are held by the anterior and posterior supporting (haptic) elements. The first lens of this type - the Fedorov-Zakharov lens - has 3 posterior arches and 3 anterior antennae. In the 60-70s of the XX century, when mainly intracapsular cataract extraction was performed, the Fedorov-Zakharov lens was widely used throughout the world. Its main disadvantage is the possibility of dislocation of the supporting elements or the entire lens;

Posterior chamber lenses (PCLs) are placed in the lens capsule after removal of the nucleus and

Rice. 12.11. Artificial and natural lens of the eye.

a - a cloudy lens removed from the eye entirely in a capsule, next to it an artificial lens; b - pseudophakia: the anterior chamber IOL is attached to the iris in two places; c- pseudophakia: iris-clip-lens is located in the pupil; d - pseudophakia: the posterior chamber IOL is located in the lens capsule, the light section of the anterior and posterior surfaces of the IOL is visible.

cortical masses during extracapsular cataract extraction (Fig. 12.11, d). They take the place of a natural lens in the overall complex optical system of the eye, and therefore provide the highest quality of vision. LCL better than others strengthen the dividing barrier between the anterior and posterior sections of the eye, prevent the development of many severe postoperative complications, such as secondary glaucoma, retinal detachment, etc. They contact only with the lens capsule, which does not have nerves and blood vessels, and is not capable of an inflammatory reaction. This type of lens is currently preferred.

IOLs are made from rigid (polymethyl methacrylate, leucosapphire, etc.) and soft (silicone, hydrogel, acrylate, collagen copolymer, etc.) materials. They can be monofocal or multifocal, spherical, aspherical or toric (for astigmatism correction).

Two artificial lenses can be inserted into one eye. If for some reason the optics of the pseudophakic eye turned out to be incompatible with the optics of the other eye, then it is supplemented with another artificial lens of the required optical power.

IOL manufacturing technology is constantly being improved, lens designs are being changed, as required by modern cataract surgery.

Correction of aphakia can also be performed by other surgical methods based on the enhancement of the refractive power of the cornea (see Chapter 5).

12.4.4. Secondary membranous cataract and fibrosis of the posterior lens capsule

Secondary cataract occurs in the aphakic eye after extracapsular cataract extraction. This is the growth of the subcapsular epithelium of the lens, remaining in the equatorial zone of the lens bag.

In the absence of the lens nucleus, the epithelial cells are not constrained, therefore they grow freely and do not stretch. They swell in the form of small transparent balls of various sizes and line the posterior capsule. With biomicroscopy, these cells look like soap bubbles or caviar grains in the lumen of the pupil (Fig. 12.12, a). They are called Adamyuk-Elschnig balls after the scientists who first described secondary cataract. In the initial stage of development of secondary cataract

You have no subjective symptoms. Visual acuity decreases when epithelial growths reach the central zone.

Secondary cataract is subject to surgical treatment: washing out of epithelial growths or discission (dissection) of the posterior lens capsule, on which Adamyuk-Elschnig balls are placed. Dissection is performed by a linear incision within the pupillary area. The operation can also be carried out using a laser beam. In this case, the secondary cataract is also destroyed within the pupil. A round hole is formed in the posterior lens capsule with a diameter of 2-2.5 mm. If this is not enough to ensure high visual acuity, then the hole can be enlarged (Fig. 12.12, b). In pseudophakic eyes, secondary cataract develops less frequently than in aphakic eyes.

A membranous cataract is formed as a result of spontaneous resorption of the lens after an injury, only the fused anterior and posterior lens capsules remain in the form of a thick cloudy film (Fig. 12.13).

Rice. 12.12. Secondary cataract and its dissection.

a - transparent corneal graft, aphakia, secondary cataract; b - the same eye after laser discission of a secondary cataract.

Rice. 12.13. membranous cataract. Large defect of the iris after a penetrating injury to the eye. A membranous cataract is visible through it. The pupil is displaced downward.

Filmy cataracts are dissected in the central zone with a laser beam or a special knife. In the resulting hole, if there is evidence, an artificial lens of a special design can be fixed.

Fibrosis of the posterior lens capsule is commonly referred to as thickening and clouding of the posterior capsule after extracapsular cataract extraction.

In rare cases, opacification of the posterior capsule can be found on the operating table after removal of the lens nucleus. Most often, opacification develops 1-2 months after the operation due to the fact that the posterior capsule was not sufficiently cleaned and the thinnest invisible areas of the transparent masses of the lens remained, which subsequently become cloudy. This fibrosis of the posterior capsule is considered a complication of cataract extraction. After the operation, there is always a contraction and compaction of the posterior capsule as a manifestation of physiological fibrosis, but at the same time it remains transparent.

Dissection of the clouded capsule is performed in cases where visual acuity is sharply reduced. Sometimes sufficiently high vision is maintained even in the presence of significant opacities on the posterior lens capsule. It all depends on the location of these opacities. If at least a small gap remains in the very center, this may be enough for the passage of light rays. In this regard, the surgeon decides on the dissection of the capsule only after assessing the function of the eye.

Questions for self-control

Having become acquainted with the structural features of a living biological lens, which has a self-regulating image focusing mechanism, you can establish a number of amazing and, to a certain extent, mysterious properties of the lens.

The riddle will not be difficult for you, When you have already read the answer.

1. The lens does not have vessels and nerves, but is constantly growing. Why?

2. The lens grows throughout life, and its size practically does not change. Why?

3. There are no tumors and inflammatory processes in the lens. Why?

4. The lens is surrounded on all sides by water, but the amount of water in the lens substance gradually decreases over the years. Why?

5. The lens does not have blood and lymphatic vessels, but it can become cloudy with galactosemia, diabetes, malaria, typhoid and others common diseases organism. Why?

6. You can pick up glasses for two aphakic eyes, but you can’t pick up glasses for one if the second eye is phakic. Why?

7. After the removal of cloudy lenses with an optical power of 19.0 diopters, a spectacle correction is prescribed for the distance not +19.0 diopters, but only +10.0 diopters. Why?

The lens - the structure, features of growth, its differences in adults and newborns; research methods, characteristics in normal and pathological conditions.

The lens of the eye(lens, lat.) - a transparent biological lens that has a biconvex shape and is part of the light-conducting and light-refracting system of the eye, and provides accommodation (the ability to focus on objects at different distances).

Structure:

lens similar in shape to a biconvex lens, with a flatter front surface (radius of curvature of the front surface lens about 10 mm, back - about 6 mm). The lens diameter is about 10 mm, the anteroposterior size (lens axis) is 3.5-5 mm. The main substance of the lens is enclosed in a thin capsule, under the anterior part of which there is an epithelium (there is no epithelium on the posterior capsule). Epithelial cells are constantly dividing (throughout life), but the constant volume of the lens is maintained due to the fact that the old cells located closer to the center (“nucleus”) of the lens are dehydrated and significantly reduced in volume. It is this mechanism that causes presbyopia ("age-related farsightedness") - after 40 years due to cell compaction lens loses its elasticity and ability to accommodate, which is usually manifested by a decrease in vision at close range.

lens located behind the pupil, behind the iris. It is fixed with the help of the thinnest threads (“zinn ligament”), which at one end are woven into the lens capsule, and at the other end are connected to the ciliary (ciliary body) and its processes. It is due to the change in the tension of these threads that the shape of the lens and its refractive power change, as a result of which the process of accommodation occurs. Occupying this position in the eyeball, the lens conditionally divides the eye into two sections: anterior and posterior.

Innervation and blood supply:

lens does not have blood and lymphatic vessels, nerves. metabolic processes carried out through the intraocular fluid, which the lens is surrounded on all sides.

The lens is located inside the eyeball between the iris and the vitreous body. It has the form of a biconvex lens with a refractive power of about 20 diopters. In an adult, the lens diameter is 9-10 mm, thickness - from 3.6 to 5 mm, depending on accommodation (the concept of accommodation will be discussed below). In the lens, the anterior and posterior surfaces are distinguished, the line of transition of the anterior surface to the posterior is called the lens equator.

The lens is held in its place by the fibers of the zinn ligament supporting it, which is attached circularly in the region of the lens equator on one side and to the processes of the ciliary body on the other. Partially crossing each other, the fibers are firmly woven into the lens capsule. Through the ligament of Viger, originating from the posterior pole of the lens, it is firmly connected to the vitreous body. From all sides, the lens is washed by aqueous humor produced by the processes of the ciliary body.

Examining the lens under a microscope, the following structures can be distinguished in it: the lens capsules, the lens epithelium and the lens substance itself.

lens capsule. On all sides, the lens is covered with a thin elastic shell - a capsule. The part of the capsule covering its anterior surface is called the anterior lens capsule; the portion of the capsule covering the posterior surface is the posterior lens capsule. The thickness of the anterior capsule is 11-15 microns, the posterior capsule is 4-5 microns.

Under the anterior lens capsule, there is one layer of cells, the lens epithelium, which extends to the equatorial region, where the cells become more elongated. The equatorial zone of the anterior capsule is a growth zone (germinal zone), since during the entire life of a person, lens fibers are formed from its epithelial cells.

The lens fibers, located in the same plane, are interconnected by an adhesive and form plates oriented in the radial direction. The soldered ends of the fibers of neighboring plates form lens sutures on the anterior and posterior surfaces of the lens, which, when connected to each other like orange slices, form the so-called lens star. Layers of fibers adjacent to the capsule form its cortex, deeper and denser ones form the lens nucleus.

A feature of the lens is the absence of blood and lymphatic vessels, as well as nerve fibers in it. The lens is nourished by diffusion or active transport through the capsule of nutrients and oxygen dissolved in the intraocular fluid. The lens consists of specific proteins and water (the latter accounts for about 65% of the mass of the lens).

The state of transparency of the lens is determined by the peculiarity of its structure and the peculiarity of metabolism. The preservation of the transparency of the lens is ensured by the balanced physicochemical state of its proteins and membrane lipids, the content of water and ions, the intake and release of metabolic products.

Functions of the lens:

Allocate 5 main functions lens:

Light transmission: The transparency of the lens allows the passage of light to the retina.

Light refraction: Being a biological lens, lens is the second (after the cornea) refractive medium of the eye (at rest, the refractive power is about 19 diopters).

Accommodation: The ability to change one's shape allows one to change lens its refractive power (from 19 to 33 diopters), which ensures focusing of vision on objects at various distances.

Dividing: Due to the location lens, it divides the eye into anterior and posterior sections, acting as an "anatomical barrier" of the eye, keeping structures from moving (preventing the vitreous from moving into the anterior chamber of the eye).

Protective function: presence lens hinders the penetration of microorganisms from the anterior chamber of the eye into the vitreous body during inflammatory processes.

Methods for examining the lens:

1) the method of lateral focal illumination (the front surface of the lens, which lies within the pupil, is examined; in the absence of opacities, the lens is not visible)

2) inspection in transmitted light

3) slit lamp examination (biomicroscopy)