Lens - structure and functions, symptoms and diseases. All about the natural lens: the structure of the lens of the human eye, its functionality, pathologies and diagnostics

The lens is one of the most important elements of the optical system of the eye, located in the posterior eye chamber. Its average dimensions are 4-5 mm in thickness and up to 9 mm in height, with a refractive power of 20-22D. The shape of the lens resembles a biconvex lens, the front surface of which has a flatter configuration, and the back one is more convex. The thickness of the lens increases quite slowly but steadily with age.

Normally, the lens is transparent, thanks to the special proteins crystallins included in its composition. It has a thin, transparent capsule - the lens sac. Along the circumference, fibers of the ligaments of zinn from the ciliary body are attached to this sac. The ligaments fix the position of the lens and, if necessary, change the curvature of the surface. The ligamentous lens apparatus ensures the immobility of the organ’s position on the visual axis, thereby ensuring clear vision.

The lens consists of a nucleus and cortical layers around this nucleus - the cortex. In young people, the lens has a fairly soft, gelatinous consistency, which facilitates the tension of the ciliary body ligaments during accommodation.

Some congenital diseases lens make its position in the eye incorrect due to weakness or imperfection of the ligamentous apparatus, in addition, they can cause local congenital opacities nuclei or cortex, which can reduce visual acuity.

Symptoms of lens damage

Age-related changes make the structure of the nucleus and cortex of the lens more dense, which causes its weaker response to ligament tension and changes in surface curvature. Therefore, upon reaching the age of 40, it becomes increasingly difficult to read at close range, even if a person has had excellent vision all his life.

An age-related slowdown in metabolism, which also affects intraocular structures, leads to changes in the optical properties of the lens. It begins to thicken and lose its transparency. The images visible in this case may lose their former contrast and even color. There is a feeling of looking at objects “through cellophane film”, which does not go away even with glasses. With the development of more pronounced cloudings, vision decreases significantly.

Inherent opacities can be localized in the nucleus and cortex of the lens, as well as directly under the capsule. Depending on the location of the opacities, vision decreases to a greater or lesser extent, faster or slower.

Age-related lens opacities develop quite slowly, over months and even years. Therefore, people sometimes do not notice the deterioration of vision in one eye for a long time. There is a simple test to identify cataracts at home: look at the white and Blank sheet paper first with one eye, then with the other, if at some point it seems yellowish and dull to you, then there is a possibility of developing cataracts. In addition, with cataracts, halos appear around the light source when looking at it. People notice that they see well only in bright light.

Often, clouding of the lens is caused not by age-related changes in metabolism, but by a long-term inflammatory process in the media of the eye (chronically ongoing), as well as prolonged use of tablets or the use of drops with steroid hormones. In addition, many studies have confirmed that the presence of the lens makes lens clouding faster and occurs much more often.

The cause of clouding of the lens can be blunt force and/or damage to the ligamentous apparatus.

Video about the structure and functions of the lens

Diagnostics

Diagnostic measures for the condition and functioning of the lens, as well as its ligamentous apparatus, include checking visual acuity and the anterior segment. At the same time, the doctor evaluates the size and structure of the lens, determines the degree of its transparency, and checks for the presence and location of opacities that can reduce visual acuity. Often, dilation of the pupil is required for detailed studies. Since, when specific localization opacities, pupil dilation, leads to improved vision, because the diaphragm begins to transmit light through the transparent areas of the lens.

Occasionally, a thicker diameter or longer lens fits so closely to the iris or ciliary body that it narrows the angle of the anterior chamber through which the main outflow of existing fluid occurs into the eye. This condition is the main cause of glaucoma (narrow-angle or closed-angle). To assess the relative position of the lens and ciliary body, as well as, ultrasound biomicroscopy or coherence tomography of the anterior segment of the eye should be performed.

Thus, if there is a suspicion of lens damage diagnostic examinations include:

• Visual examination in transmitted light.
• Biomicroscopy – examination with a slit lamp.
• – visual examination of the anterior chamber angle with a slit lamp using a gonioscope.
• Ultrasound diagnostics, including ultrasound biomicroscopy.
• Optical coherence tomography anterior segment of the eye.
• Pachymetry of the anterior chamber with assessment of chamber depth.
• , for detailed identification of the amount of production and outflow of aqueous humor.

Lens diseases

• Cataract.
• Anomalies of lens development (lens coloboma, lenticonus, lentiglobus, aphakia).
• Traumatic ectopia of the lens (subluxation, luxation).

Treatment of lens diseases

Surgical methods are usually chosen to treat lens diseases.

Lots of drops offered pharmacy chain, designed to stop the clouding of the lens cannot return its original transparency or guarantee the cessation of further clouding. Cataract surgery only ( cloudy lens) with its replacement with an intraocular lens, is considered a procedure with complete recovery.

Cataract removal can be performed in several ways: from extracapsular extraction, which involves sutures, to which involves making minimal self-sealing incisions. The choice of removal method largely depends on the degree of maturity of the cataract (density of opacities), the condition of the ligamentous apparatus and, most importantly, on the qualifications of the ophthalmic surgeon.

The lens is an element that is responsible for the refraction of light rays before their further projection onto the retina. Thanks to this, a person can see surrounding objects. This part visual system is formed in the first weeks of embryo development. The eye lens gives vision the ability to focus on distant and nearby objects when located at one point in space.

Physically, the structure of the eye lens can be compared to a strong lens, convex on both sides. Its back and front surfaces have different radii of curvature. That is, it is flatter in front than in the back.

Location of the lens in the eye

The size of the lens in an adult is about 10mm. The central points behind and in front of the eye lens are called poles. A conventional line that runs from one pole to another is called an axis. Its length ranges from 3.6 to 5 mm. Simply put, the axis is the thickness of the lens. In a newborn, the optical lens of the eye is close in shape to a ball; with age, it stretches out. As you get older, the power of light refraction by the lens decreases. This explains the unfocused gaze in infants.Behind the lens is the vitreous body. In front it is adjacent to the iris and chambers of the eye.

Adaptability of vision to focusing on distant and near objects is made possible due to the elasticity of the lens. It has this property due to its structural features. Lens surface human eye covers a transparent capsule, which is also called the “lens sac”. Its anterior part is lined from the inside with epithelium, which, when dividing and multiplying, allows the lens to grow. The fibers of the ligaments of the ciliary body of the eye are attached to it. This allows you to reliably fix the lens motionless on the visual axis, and also change the radius of curvature. This ensures clear, clear vision.

Transparency of the lens is given by special proteins - crystallins. The consistency of the internal substance is soft, gelatinous. Inside there is a core, which is covered on top with cortex - cortical layers. The whole structure is similar in structure to an onion.

The lens has no blood vessels and nerve endings and consists of the following parts:

• Capsule

This is an elastic transparent shell of a homogeneous structure. It refracts light rays and also performs a mechanical function - it protects the lens substance from exposure external factors. Capsule bag attached to the ciliary girdle.

The thickness of the lens shell is not the same around the entire circumference. In front it is thicker due to the location of a layer of epithelial cells underneath it. In concentric circles, the so-called “belts,” the greatest thickness of the capsule is in the places where the ciliary belt is attached. The thinnest layer is in the area of ​​the posterior pole.

The capsule is semi-permeable, so it does not interfere with exchange in the lens.

The structure of the eye lens

• Epithelial layer

The epithelium is localized on the inner anterior part of the capsule and is located in one layer. Its cells are flat and do not have a stratum corneum.

It acts as a barrier and also ensures the absorption of nutrients. Lens fibers grow from epithelial cells. Then radial plates are formed from fibers of one row. This process occurs throughout life, so the thickness of the lens increases in old age. In the area of ​​the pupils, cells divide with little activity, so there active growth No.

• transparent substance

In addition to water, the substance contains proteins. In a healthy person, the contents of the lens are completely transparent, but in some diseases its chemical composition changes and it becomes cloudy. At the same time, vision deteriorates.In the center the substance is denser than at the periphery near the capsule.

Symptoms of lens damage

As a person ages, the nucleus and cortex become denser, and the eye lens is less and less able to change the radius of its curvature. The ligamentous apparatus also malfunctions, it does not stretch well, and the ligament attached to the lens becomes less elastic. Having overcome the age limit of 40-50 years, a person who previously had perfect vision, begins to notice that his vision has become worse and it is more difficult for him to read. Letters blur before your eyes, and the image on the screen or monitor looks blurry.

To determine the condition of the lens, the doctor performs diagnostics using a biomicroscope.

The cause of deterioration in the condition of the lens may be blunt trauma eyes or the presence of a concomitant disease, such as glaucoma. In the latter case, the lens becomes cloudy faster than it would happen in the same person with age-related changes.

Diagnosis of pathologies of the eye lens

The basis of diagnosis, which allows us to determine the pathology of the lens or its ligamentous apparatus, is biomicroscopy of the anterior segment and testing of visual acuity. Using the device, the ophthalmologist checks the following parameters in the patient:

• Lens size;
• Presence and localization of opacities;
• Degree of transparency;
• Integrity and disturbances in the structure of the lens.

To examine the eyes in more detail, pupil dilation may be necessary. In some cases, this measure may temporarily improve vision. This happens because the diaphragm begins to transmit light through the opened transparent areas.

In case of deviations from the norm, parameters such as thickness or length can cause an excessively tight fit of the lens to the ciliary body or iris of the eye. In this case, the angle of the anterior chamber narrows. Because of this, the outflow of fluid contained inside the eye worsens. This can result in a narrow angle. In order to assess the location of the lens, ultrasound microscopy or optical tomography is used.

Types of lens diseases and their treatment

Lens pathologies can be congenital. Due to certain diseases, the optical lens of the eye may have Not correct position, including due to weak ligamentous apparatus. Cloudy areas may be localized in the nucleus or cortex (periphery). This reduces vision.

The most common diseases affecting the lens are cataracts and glaucoma.

Age-related clouding can be stopped or slowed down with the help of special drops, but changes that have already occurred cannot be corrected by such a measure. Usually the lens is restored surgically. If the condition of this part of the eye significantly deteriorates, a complete replacement is made with an artificial analogue - an intraocular lens. Surgery on your own lens does not guarantee complete elimination of opacification and the surgeon cannot guarantee that this process will be stopped in the future.

Lens cataract

Cataracts are removed using various techniques. The option is selected individually for each patient depending on the state of health, the presence of contraindications, the degree of disease, the density and turbidity of the eye lens, the patient’s financial capabilities, and the qualifications of the ophthalmologist.

This could be, for example, intra- or extracapsular extraction, in which surgeons remove the lens with or without a capsule, then replace it with an implant, and subsequently suture the cornea. Or you can resort to less traumatic, but more expensive phacoemulsification, in which minimal tunnel incisions are made, which are then sealed independently.

Also among the pathologies of the eye lens there is ectopia. It is expressed in the displacement of the lens, both within the pupil zone and beyond its borders. Its causes may be tumors, myopia high degree, injuries, overripe cataract. Also, this disease may be associated with congenital underdevelopment of the ligamentous apparatus of the eye, when the ligament is weak or partially lacks fibers. The consequences of this pathology include complications such as astigmatism, uveitis, and refraction. Due to the fault of the latter, a person may experience optical defects.

There is also such a pathology as. This condition is also called “lazy eye syndrome”. In this case, the brain, if there are any problems with the eye, “turns off” it from the visual process in order to avoid double vision. As a result of constant suppression of vision function, there is a risk of its complete loss.

Anomalies of the lens of the eye

The lens may have an abnormal shape. In this case, the patient may be diagnosed with one of the following pathologies: lenticonus, coloboma, microphakia, biphakia (double lens) or aphakia (complete absence), spherophakia. In case of such structural disorders, the patient is prevented from complications such as amblyopia.

With microphakia, the crystal lens may become pinched or even fall out. In this case, it increases intraocular pressure and severe pain occurs. In this situation, the lens is immediately removed.

Abnormal condition of the lens and iris

With an anomaly such as spherophakia, the lens remains in the shape of a ball, without stretching out in shape. This pathology is usually hereditary and is combined with dislocations, secondary or microphakia. The anterior chamber of the eye is deep. The patient is often diagnosed at the same time. With this pathology, only the consequences and complications are treated. The underlying cause cannot be treated.

In a pathology called “biphakia” in medicine, the patient has two lenses of different sizes in the eye. They can be located in different planes. This phenomenon is extremely rare. Its cause is a delay in the regression of certain vessels, which during the prenatal period put pressure on the lens of the embryo.

Coloboma in patients is rare and is caused by hereditary factor. This pathology is encoded in a person’s genetic code and his relatives also have this phenomenon in their anamnesis. With this anomalous phenomenon, in the area of ​​the equatorial edge of the lens, there is the absence of one piece, a small part that should normally be present. The missing segment has the shape of an ellipse, a triangle, or may be crescent-shaped. There is usually one coloboma in the eye, less often - two. If it is small, it usually does not affect visual acuity. Otherwise, myopia or lenticular lens may appear. With this pathology, the lens itself retains its transparency. A patient with coloboma is most often prescribed optical correction refractive errors, amblyopia is prevented.

Lenticonus is an anomaly that occurs after an eye injury or is congenital. It is characterized by a change in the surface shape of the lens. This pathology is localized in one eye, inside, behind or in front. With this anomalous phenomenon, one can observe a protrusion of a cone-shaped or spherical shape towards the anterior chamber, its own thickness or the vitreous body of the eye.

Lens removal is indicated only when large sizes lenticonus. In other cases, treatment courses are carried out with the help and dilation of the pupil with the help of medications. Pathology can cause a decrease in visual acuity or cause amblyopia.

The lens is a biological formation that is part of the optical system in the organ of vision, which is involved in the process of accommodation. It looks like a biconvex lens, the refractive power of which averages approximately 20D; in a state of accommodation, the optical power increases significantly, often reaching 30-33D. The lens is placed inside eyeball in the frontal plane between the iris and the vitreous body. Together with the iris, they make up the iridolenticular diaphragm, which divides the eyeball into anterior and posterior sections.

The lens has anterior and posterior surfaces. In this case, the line limiting the transition of the front surface to the back is usually called the equator. The center of the anterior lens surface is called the anterior pole, the center of the posterior surface is called the posterior pole. The line that connects both poles is called the lens axis.

Dimensions and curvature of the lens

The radius of curvature of the anterior lens surface at rest of accommodation is 10 mm, the posterior one is 6 mm. The length of the lens axis is usually 3.6 mm. A narrow fissure separating the posterior lens surface from the vitreous body forms the retrolenticular or postlenticular space. In the eye, the lens is held in place by the ligament of zinn, which is formed by thin fibers. They are attached to it in the equatorial region. The other ends of the ligament of Zinn are attached to the processes of the ciliary body.

The lens capsule is the membrane covering it, which is a transparent and elastic ocular tissue. The part of the capsule that covers the anterior surface of the lens is usually called the anterior capsule, the second part is called the posterior capsule. The thickness of the anterior capsule tissue can range from 11 µm to 15 µm, and the posterior one - from 4 µm to 5 µm. Under the surface of the anterior capsule there is a single-layer cubic epithelium, reaching the equator of the lens and in this place, its cells become more elongated.

Layers of the lens

The germinal zone or growth zone of the lens is the equatorial zone of its anterior capsule; it is here that during a person’s life young lens fibers are formed from its epithelial cells.

The lens fibers are placed in the same plane and are connected to each other by a certain adhesive substance, forming radial plates. The glued ends of the fibers of adjacent plates form seams on the anterior and posterior surfaces of the lens. When connected to each other, these seams create a lens star. The outer layers of its substance adjacent to the lens capsule (subcapsular layers) form the cortex of the lens, and the deep layers form its nuclear zone.

Lens proteins

Anatomical feature of the lens - complete absence it contains lymphatic and blood vessels, as well as nerve fibers. The lens consists of a protein substrate and water. Moreover, the share of water is approximately 65%, and proteins - almost 35%.

Normally, the lens substance includes nucleoprotein, mucoprotein, compounds of calcium, potassium, sodium, phosphorus, sulfur, magnesium, chlorine, traces of copper, manganese, iron, boron and zinc. Participants in its redox processes are the tripeptide glutathione and ascorbic acid. The lens also contains lipids, vitamins (A, B1, B2, PP) and other substances necessary for proper metabolism.

Metabolism occurs slowly in the lens through diffusion and osmosis. In this case, the lens capsule is assigned the function of a semi-permeable biological membrane. Required for normal function The substance is brought into the lens by the intraocular fluid that washes the lens.

Age-related changes in the lens

The size, shape, transparency, and consistency of the lens undergo changes throughout human life. So, in newborns, the lens has almost spherical shape, soft consistency and almost absolute transparency without color. In an adult, the shape of the lens transforms into a biconvex lens with a flat front surface. Its color becomes yellowish, but transparency remains. The intensity of yellow in the shade of the lens increases with age.

By the age of 40-45, the core of the human lens becomes dense and it loses its former elasticity. By this age, accommodation weakens and presbyopia develops.

By about the age of 60, the ability to accommodate is almost completely lost. This is due to severe sclerosis of the lens nucleus - phacosclerosis. At this age, due to natural aging - deterioration and slowdown of metabolism, tissue respiration and energy metabolism, in different layers of the lens, opacities of varying severity and magnitude may appear, which are called senile cataracts. This disease is detected by examination using a slit lamp while dilating the pupil with mydriatic drugs.

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Description

Particular attention was paid to the structure of the lens at the most early stages microscopy. It was the lens that was first examined microscopically by Leeuwenhoek, who pointed out its fibrous structure.

Shape and size

(Lens) is a transparent, biconvex, disc-shaped, 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 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 that consists from the same cell type at all stages- from embryonic development and postnatal life until death. Its significant difference is the absence of blood vessels and nerves. It is also unique in terms of metabolic characteristics (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 connect in the so-called equatorial region. The equator of the lens opens into rear camera eyes and with the help of the ligament of cinnamon (ciliary girdle) is attached to the ciliary epithelium (Fig. 3.4.2).

Rice. 3.4.2. The relationship between the structures of the anterior part of the eye (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 band (ligament of Zinn); 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 zinc during contraction of the ciliary muscle, deformation of the lens occurs (increased curvature of the anterior and, to a lesser extent, posterior surfaces). In this case, its main function is performed - a change in refraction, which allows you to obtain a clear image on the retina, regardless of the distance to the object. At rest without accommodation, the lens provides 19.11 of the 58.64 diopters of refractive power of the schematic eye. To fulfill its main role, the lens must be transparent and elastic, which it is.

The human lens grows continuously throughout life, thickening by approximately 29 microns per year. Starting from the 6-7th week of intrauterine life (18 mm embryo), it increases in anteroposterior 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 embryo is 65 mm long, does not affect the increase in lens diameter. Subsequently, the lens quickly 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. A factor contributing to an increase in diameter is core compaction. Tension of the ligament of Zinn contributes to changes in the shape of the lens.

The diameter of the lens (measured along 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 of age, and then slowly increases to 4.75-5.0 mm in old age. The thickness also changes due to changes in the accommodative ability of the eye.

In contrast to thickness, the equatorial diameter of the lens changes less 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 one (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 borders the anterior chamber of the eye through the pupil, and along the periphery with 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, through the ligament of Zinn, is attached to the processes of the ciliary body.

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 greater curvature (radius of curvature is 6 mm (4.5-7.5 mm)). It is usually considered in conjunction with the vitreous membrane of the anterior surface of the vitreous body. However, between these structures there is slit-like space made with 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 the ligament of cinnamon is attached to this area. The folds disappear upon accommodation, i.e., when the tension of the ligament ceases.

Lens refractive index is equal to 1.39, i.e., slightly greater 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 equal to only 2 diopters.

When bio microscopic examination lens with a dilated pupil, one can detect the 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 - nucleus of the lens. There is an increase in the lens and increased light scattering

Firstly, the multilayered nature of the 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).

The listed zones make up the superficial cortex of the lens. There are two more deeper zones of the cortex. They are also called pernuclear. These zones fluoresce when the lens is illuminated with blue light (C3 and C4).

Lens nucleus considered as its prenatal part. It also has layering. In the center there is a light zone called the “germinal” (embryonic) nucleus. Examination of the lens with a slit lamp can also reveal lens sutures. Mirror 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 microscopic structure lens: 1 - lens capsule; 2 - epithelium of the lens of the central areas; 3- epithelium of the lens of the transition zone; 4- epithelium of the lens of the equatorial region; 5 - embryonic nucleus; 6-fetal nucleus; 7 - adult core; 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 epithelial cells located in the equator region of the lens proliferate, they move toward 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 Zinn and the vitreous body: 1 - vitreous fibers; 2 - fibers of the ligament of zinn; 3-precapsular fibers: 4-lens capsule

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 the 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 the front and 2.8 µm in the back) (Fig. 3.4.7).

Rice. 3.4.7. Thickness of the lens capsule in different zones

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

The ability of epithelial cells to form capsules persists throughout life and is manifested even in conditions of cultivation of epithelial cells.

The dynamics of changes in capsule thickness are 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 cataract surgeons who use the capsule to attach posterior chamber intraocular lenses.

The capsule is quite powerful barrier against bacteria and inflammatory cells, but is freely passable for molecules whose size is comparable to 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, that is, in a stretched state. For this reason, 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. This same property is also used in laser capsulotomy.

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

Rice. 3.4.8. Light-optical structure of the lens capsule, epithelium of the lens capsule and 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 fibers are located parallel to the surface of the lens. The capsule also stains positively during the PHIK reaction, which indicates the presence of large quantities proteoglycans.

Ultrastructurally the capsule has relatively amorphous structure(Fig. 3.4.6, 3.4.9).

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

A slight lamellarity is observed due to the scattering of electrons by thread-like elements folded into plates.

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

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

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

In the equatorial zone of the anterior capsule of the lens, 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 frequency of striations of which is 110 nm.

The places of attachment of the ligament of cinnamon to the capsule are named Berger plates(Berger, 1882) (other name is pericapsular membrane). This is a superficial 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 fibrils of the zonule of zinn are 10 nm thick.

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 microfibrillar material has been established, namely fibrillin, 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 detected - laminin, fibronectin, heparan sulfate and entactin.

Lens capsule permeability man has been studied by many researchers. The capsule freely allows water, ions and other molecules to pass through big size. It is a barrier to protein molecules the size of hemoglobin. No one found any differences in the capacity of the capsule under normal conditions and with cataracts.

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

It must be emphasized that in the tissues of the lens, in particular in the epithelium, anaerobic type of respiration. Aerobic oxidation (Krebs cycle) is observed only in epithelial cells and outer lens fibers, and this oxidation pathway provides up to 20% of the energy requirement of the lens. This energy is used to provide active transport and synthetic processes necessary for lens growth, 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 participate in the removal of sodium from the lens, thanks to the activity of the Na -K + pump. This uses the energy of ATP. In the posterior part of the lens, sodium ions diffuse passively into the posterior chamber aqueous. The lens epithelium consists of several subpopulations of cells that differ primarily in their proliferative activity. Certain topographical features of the distribution of epithelial cells of various subpopulations are revealed. Depending on the structural features, 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. Polygonal epithelial cells (Fig. 3.4.9, 3.4.10, a),

Rice. 3.4.10. Ultrastructural organization of epithelial cells of the lens capsule in the intermediate zone (a) and equatorial region (b) (according to Hogan et al, 1971): 1 - lens capsule; 2 - apical surface of an adjacent epithelial cell; 3-finger pressure into the cytoplasm of the epithelial cell of neighboring 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 to the apical surface of large cells and have numerous nuclear pores. In them. usually two nucleoli.

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

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

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

Epithelial cells are attached to the lens capsule using hemidesmosome. Desmosomes and gap junctions, which have a typical structure, are visible between the epithelial cells. The system of intercellular contacts provides not only adhesion between the epithelial cells of the lens, but determines the ionic and metabolic communication between the 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 occurs between the lens and the intraocular fluid.

The 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 with age-related cataracts. Significantly mitotic activity increases at different 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 located 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 distinguished by high proliferative activity of cells (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, daily fluctuations in mitotic activity were revealed.

The cells of this zone, after dividing, move posteriorly and subsequently turn into lens fibers. Some of them also shift anteriorly, into the intermediate zone.

The cytoplasm of epithelial cells contains few organelles. There are short profiles of 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 actin, vimentin, microtubule protein, spectrin, alpha-actinin and myosin increases. It is possible to distinguish entire actin network-like structures, especially visible in the apical and basal parts of cells. In addition to actin, vimentin and tubulin were detected in the cytoplasm of epithelial cells. It is assumed that contractile microfilaments in the cytoplasm of epithelial cells promote, through their contraction, the movement of intercellular fluid.

IN last 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 importance 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, and some 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 cell division, one or both daughter cells move into an adjacent transition zone, in which the cells are organized into 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. New lens fibers maintain polarity such that the posterior (basal) portion of the fiber maintains contact with the capsule (basal lamina) while the anterior (apical) portion is separated from it by the epithelium. As epithelial cells transform 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 the differentiation of cells into lens fibers is accompanied by increased RNA synthesis, since at this stage the synthesis of structural and membrane specific proteins is noted. 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 with a diameter of 5 nm and intermediate fibrils appear in the cytoplasm of the cells, oriented along the cell and playing 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, ensuring strict orientation in space of newly differentiated cells. It is into these channels that the cytoplasmic processes penetrate. In this case, meridian rows of lens fibers are formed.

It is important to emphasize that disruption of the meridian orientation of fibers is one of the reasons for the development of cataracts in both experimental animals and humans.

The transformation of epithelial cells into lens fibers occurs quite quickly. This was demonstrated in an animal experiment using isotope-labeled thymidine. In rats, the epithelial cell turns into a lens fiber after 5 weeks.

During the process of differentiation and displacement of cells towards the center of the lens in the cytoplasm of the lens fibers the number of organelles and inclusions decreases. The cytoplasm takes on a homogeneous appearance. The nuclei undergo pyknosis and then completely disappear. Soon the organelles disappear. Basnett discovered that the loss of nuclei and mitochondria occurs suddenly and in one cell generation.

The number of lens fibers constantly increases throughout life. "Old" fibers move towards the center. As a result, a dense core is formed.

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

Features of epithelial cell membranes. The cytoplasmic membranes of neighboring epithelial cells form a unique complex of intercellular connections. If the lateral surfaces of the cells are slightly wavy, then the apical zones of the membranes form “finger impressions”, plunging into the corresponding lens fibers. The basal part of the cells is attached to the anterior capsule using hemidesmosomes, and the lateral surfaces of the cells are connected by desmosomes.

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

It is extremely rare to see tight junctions.

The structural organization of lens fiber membranes and the nature of intercellular contacts indicate the possible presence of receptor cells that control endocytosis processes, 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 identified. It is believed that these formations ensure the movement of nutrients and metabolites between cells.

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

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

The transition from 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 towards 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 bow), directed forward and consisting of a “chain” of cell nuclei. In the equator region, the zone of nuclear cells has a width of about 300-500 microns.

The deeper fibers of the lens are 150 microns thick. When they lose their cores, the nuclear arc disappears. Lens fibers have a spindle or belt-like shape, located along an arc in the form of concentric layers. In a cross section at the equator they are hexagonal in shape. As they move toward the center of the lens, their uniformity in size and shape is gradually disrupted. In the equator region in adults, the width of the lens fiber ranges from 10 to 12 µm, and the thickness - from 1.5 to 2.0 µm. In the posterior parts of the lens, the fibers are thinner, which is explained by the asymmetrical 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.

Lens sutures(Fig. 3.4.13).

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

The fetal nucleus has an anterior vertical Y-shaped suture 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, spatial union of the sutures occurs to form the star-like structure found in adults.

The main significance of sutures is that due to such a complex system of contact between cells The shape of the lens is maintained almost throughout life.

Features of lens fiber membranes. Contacts of the “button-loop” type (Fig. 3.4.12). The membranes of adjacent lens fibers are connected using a variety of specialized formations that change their structure as the fiber moves from the surface to the depths of the lens. In the superficial 8-10 layers of the anterior cortex, the fibers are connected using “button-loop” type formations (“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 different generations. This allows fibers to move relative to each other as they grow.

Between deeper fibers, button-loop contact is found somewhat less frequently. They are distributed unevenly and randomly in the fibers. 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 were also found, but only between differentiating and not mature lens fibers.

It is assumed that contacts between lens fibers are necessary to maintain the rigidity of the structure throughout life, which helps maintain the transparency of the lens. Another type of intercellular contacts has been found in the human lens. This gap contact. Gap contacts serve two roles. Firstly, since they connect the lens fibers over a long distance, the architecture 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 slot contacts- crystalline (with high ohmic resistance) and non-crystalline (with low ohmic resistance). In some tissues (liver), these types of gap junctions can be converted from one to another when the ionic composition changes environment. In the lens fiber they are incapable of such a transformation. The first type of gap junctions is found in places where the fibers adhere to 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 small molecules spread quite easily between the lens fibers, and their concentration levels out quite quickly. There are also species differences in the number of gap junctions. Thus, in the human lens they occupy 5% of the fiber surface area, 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 briefly dwell on the factors that ensure the transparency and high refractive power of the lens. High refractive power of the lens is achieved high concentration of protein filaments, and transparency - by their strict spatial organization, uniformity of fiber structure within each generation and small volume of intercellular space (less than 1% of the lens volume). Transparency is also facilitated by a small number of intracytoplasmic organelles, as well as the absence of nuclei in the lens fibers. All of these factors minimize light scattering between fibers.

There are other factors that affect refractive power. One of them is protein concentration increases as it approaches the lens nucleus. It is thanks to the increase in protein concentration that chromatic aberration is eliminated.

No less important in the structural integrity and transparency of the lens is reflation of ionic content and degree of hydration of lens fibers. At birth, the lens is transparent. As the lens grows, a yellowish core appears. The appearance of yellowness is probably due to the influence of ultraviolet light (wavelength 315-400 nm) on it. At the same time, fluorescent pigments appear in the cortex. It is believed that these pigments shield the retina from destructive action shortwave light radiation. Pigments accumulate in the nucleus with age, and in some people they are involved in the formation of pigmentary cataracts. In the nucleus of the lens old age and especially with nuclear cataracts, the amount of insoluble proteins increases, which are crystallins, the molecules of which are “cross-linked”.

Metabolic activity in the central areas of the lens is insignificant. Virtually no protein turnover. That is why they are 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 may be caused by a violation of the regularity of the arrangement of lens fibers, changes in the structure of membranes and an increase in light scattering, due to changes in the secondary and tertiary structure of protein molecules. Swelling of the lens fibers and their destruction leads to disruption of water-salt metabolism.

Article from the book: .

The function of the lens of the eye is always discussed in anatomy classes at a specialized university. Often the features of the human visual system are analyzed in detail and school curriculum. Indeed, the functions of the lens of the human eye are curious: the system is very complex, subtle, natural - it is truly admirable how skillfully and naturally the optical organs that allow us to see are constructed according to the laws of the living world. The lens is one of the most important parts of such an organ. The refractive power of the element is about 20-22 diopters (average values).

Peculiarities

It should be noted when considering the structure of the eye and its functions: the lens is located in the posterior chamber. The thickness of this element is up to five millimeters, the height reaches nine millimeters. With age, the thickness gradually increases. The process is happening slowly but inevitably.

The functions of the lens are ensured by its characteristic biconvex lens shape. The back has a more pronounced curve, while the front is relatively flat.

Key functionality

Without a lens, a person would not be able to see anything. This element of the optical system plays a very, very significant role for humans. In fact, it is the medium that makes it possible for light to reach the retina. Considering what functions the lens performs, the first one can safely be called light transmission. Nature made this possible by creating the lens from a transparent substance.

The second is conditioned, no less important function lens, structure: this is light refraction. If the cornea is in first place in terms of the refractive index of light flux, then the lens occupies second place, representing a perfect lens natural origin. This function of the lens (light refraction) is quantitatively described in diopters; normally in humans the figure reaches 19.

And what else?

Briefly describing the functions of the eye lens, it is necessary to pay attention to accommodation, realized through interaction with the ciliary body. The term usually refers to the ability of focusing, that is, a smooth change in optical power. This function of the eye lens is independent - the organ focuses without additional conscious tension of the person. The feature that makes it possible is the elasticity of the substance from which the organ is created. Self-regulation makes dynamic refraction possible.

Biologists can also talk about what function of the lens allows the eye to be a system of cameras - separation. It is thanks to the presence of the lens that the apple is divided into two parts, one of which is slightly larger than the second. The partition not only separates elements from each other. The function of the lens is protective, since biological tissue allows you to protect against negative factors the anterior section, formed by very delicate, sensitive tissues. Vitreous body quite large and would compress the anterior section. As studies have shown, if the functions of the lens are lost, the organ itself disappears for some reason, the vitreous body gradually moves forward.

And that will be?

Studies have shown that without a lens, the eye cannot maintain its anatomical correct form. The ratios of parts change, which negatively affects all functions. Hydrodynamics are inhibited, as the anterior chamber is compressed, and the pupil is completely blocked. In such a situation, the likelihood of secondary glaucoma is high.

If there is a need to remove the lens, capsule, posterior section under the influence of such an operation undergoes strong changes, caused by the vacuum effect. The vitreous body can move quite freely within the optical system, so it moves away from the posterior pole. This provokes a collision with the eye walls with any movement of the apple. This situation soon leads to retinal pathologies, and extremely severe ones, such as:

• violation of tissue integrity;
• detachment;
• swelling;
• hemorrhages.

Structure

Understanding how this organ works, it is easier to understand its functionality. Biologists have found that there is a body enclosed in a protective capsule that prevents tissue damage. The capsule at the front is supplemented with epithelium, which changes and grows over time.

The shape of the lens changes, adapting to the particular position of the object being viewed by a person. The corner of the corner provides the opportunity to clearly see the surrounding space. At the same time, the lens prevents microscopic life forms from entering the posterior chamber of the eye. At inflammatory processes Normally, thanks to the lens, bacteria cannot infect the biological optical system.

Main problems

The lens is very thin, a complex system, which means it can be easily damaged. The organ is characterized various pathologies, and most of the diseases affecting it are considered serious. A certain percentage of humanity suffers from birth defects, developmental problems, but in certain cases negative processes are provoked by injury, illness and similar acquired factors.

An eye injury is considered a rather serious situation. Its treatment is quite complicated and not always successful. Often the only option is urgent surgical intervention, lens implantation.

Eye diseases: cataracts

This term is usually used to denote a problem that has a strong negative impact on the quality of the lens. The most effective way to solve it at present is replacement. Cataracts have many causes: trauma, radiation, age. The latter occurs most often in practice; it is due to natural processes in the human body.

Not a day without change

With age, the lens changes quite a lot, and we are talking not only about the functionality of the organ, but also about the shape, color, and dimensions. When a person is just born, the lens is almost transparent, but over time it can acquire a yellowish tint.

Such variability over time is a natural mechanism for adjusting external conditions, protection from aggressive environmental factors. It is thanks to the lens that the retina is protected from the negative effects of ultraviolet radiation - and this protection is due to color. To some extent, the lens is nature's sunglasses.

About age and pathologies

The specific structure of the lens is the absence of blood vessels, lymph, and fibers of the nervous system. The metabolic processes necessary for the normal functioning of living tissues are determined by the presence of intraocular fluid surrounding the organ. With age, the body of the lens becomes denser, and the connecting threads become thinner and weaken. The refractive power of the lens decreases, which causes farsightedness. Relentless medical statistics states that this disease threatens all people who have crossed the threshold of forty years of age.

The thickening of the lens caused by age-related changes causes lens failure. metabolic processes, since the tissues cannot receive the necessary components from the intraocular fluid due to structural adjustments. This leads to suppression of functions, transparency is lost. With age, the situation becomes more complicated, negative processes are activated, clouding increases, and vision weakens, since the lens simply cannot transmit light rays. It is recommended to treat such a problem when degradation has just begun and the processes have not started. Delaying the start effective therapy, a person may be completely unable to see.

What to do?

The most effective method at present is replacing the degraded lens with an artificial lens (IOL). In recent years, this operation has been performed more and more often. Many people think that this intervention is very difficult and scary, but the experience accumulated by doctors shows that there are practically no complications, and if the rules are followed, rehabilitation period people get the opportunity to maintain sharp vision for a long time.

The operation lasts no more than a third of an hour, pain relief is local. When the intervention is completed, you can immediately go home and continue living as usual. There is no ban on using technology or reading, but you will have to refrain from strong physical activity and lifting objects weighing more than two kilograms.

Features of the operation

Anesthesia during lens replacement is hypoallergenic drops. After using them, a specialized device is used to widen the eye, then the surgeon makes an incision in the cornea, removes the lens that has lost its transparency without harming the capsule, and installs an artificial lens.

Officially, the operation is one of the most complex, as it needs to be done with extreme precision. At the same time, practice shows that the procedure is safe, since the lens does not come into contact with surfaces, does not cause irritation, does not provoke negative reactions - rejection is simply impossible. If the surgical intervention is performed correctly and sterility is observed, and subsequently the rules of rehabilitation, complications are excluded.

Intraocular lenses

This method of vision correction is currently considered one of the most effective. The latest developments by doctors have made it possible to gain access to lenses whose parameters are extremely close to the natural lens formed by nature. A high-quality copy will last a lifetime and will not have to be replaced. An artificial implant helps eliminate the effects of cataracts and correct insufficiently sharp vision.

In general, it is recommended to replace the lens after the fortieth anniversary, if age-related changes are quite pronounced. The indication for intervention is poor vision. Multifocal modern lenses effectively implement the functions and tasks assigned by nature to the eye lens.

Why is he like this?

One of the interesting questions considered in biology is the reason for the transparency of the lens. Researchers have found that this feature is ensured by the presence of a protein structure - crystallins. The effectiveness of the lens is guaranteed by its stable position due to the ligamentous apparatus. The human vision system presupposes the presence of a unique axis in each eye, and the correct position of the lens relative to it is the key to good, clear vision.

The lens contains a core surrounded by layers of cortex. In young people, the consistency of the lens is soft and gelatinous.