Layers of the cornea of ​​the eye. Purpose of the cornea

The anterior epithelium of the cornea is directly connected to the conjunctiva and has an absolutely smooth surface. The epithelium is equipped with numerous nerve endings, which makes this layer sensitive to external influences. The surface layers of the epithelium are permeable to liquids and gases; this property is used to treat diseases using drops.

The posterior epithelium is an endothelium consisting of polygonal cells. The thickness of the cornea where the endothelium is located is in the range of 0.4-0.5 microns. The endothelium along the periphery of the cornea transitions to the trabecular meshwork.

The endothelium is examined using specular microscopy, this allows us to determine the structure and location epithelial cells. The corneal endothelium is able to recover through cell migration and expansion. After 60 years, the endothelium changes - the number of cells in this layer decreases, but they become larger in size. If we compare the number of cells in different ages, then at the age of 16 there will be 3700 of them in the posterior epithelium, and closer to 80 they will decrease to approximately 2330 cells. Damaged endothelium, diseases of this layer or nutritional disorders also lead to a decrease in the number of cells in the posterior epithelium. The injured endothelium leads to the penetration of fluid from the anterior chamber into all layers of the membrane, which, in turn, causes its cloudiness and leads to disruption of the cornea's nutrition.

However, these are not all layers of the cornea. It is worth mentioning the tear film; it also plays a certain role in the functioning of the entire eye apparatus.

Functions of the cornea

The function performed by the cornea for the entire eye can be compared to the work performed by a lens when taking photographs. An analogy can be drawn between the structure of the cornea and the design of a lens, which continuously collects all the scattered rays of a stream of light and focuses them in the desired direction.

That is why we can say that all layers of the cornea are the main refractive medium human eye. The shape of this shell is convex with a shiny and smooth surface. The cornea sits in the sclera like glass in a watch.

Cornea healthy eye has a refractive power that varies in the range from 40 to 44 diopters.

Corneal thickness

The thickness of the cornea along the periphery ranges from 1 to 1.2 mm, in the central part this size is smaller - 0.8–0.9 mm. The horizontal diameter of the cornea ranges from 11 to 12 mm on average, and this figure is smaller vertically (from 10.5 to 11 mm). The radius of curvature of the cornea reaches an average of 7.8 mm. The thickness of the cornea in the place where its stroma passes is 9/10 of its total size. The curvature of the cornea is important when selecting lenses; this value is determined using ophthalmometry.

The main properties of the cornea include transparency, high sensitivity, sphericity, absence blood vessels, specularity. All layers of the cornea protect the inner membranes of the eye from damage and the penetration of bacteria.

Corneal diseases

Almost all corneal diseases are inflammatory nature. Inflammation of the eyelids or other parts of the eye can quickly spread to the cornea. Corneal diseases are caused by external reasons – infectious agents, unfavorable environmental situation, influence of allergens, tobacco smoke, chemical substances. All these factors influence changes in the functions of the cornea, which leads to its clouding.

Sometimes corneal clouding is congenital. This occurs as a consequence of infectious diseases of a woman during pregnancy. Various infections lead to abnormal development cornea, as a result of which its structure is disrupted, and the child is already born with vision pathology.

Corneal diseases caused by fungi are especially dangerous. You can become infected with a fungus when the cornea is damaged by an object containing spores of this microorganism. fungal diseases difficult to treat.

Treatment of corneal diseases

When identifying corneal diseases, the most various types therapy. For diseases caused by infectious pathogens, it is necessary to use appropriate antibacterial local and systemic drugs. Thinning of the cornea, formation of scars on it, except conservative treatment, will require surgical intervention.

The cornea is a very important part of the human eye system and you should not self-medicate it. If there is the slightest deterioration in vision or other pathologies, you should immediately consult a doctor. Timely therapy in most cases it goes away quickly and helps avoid vision loss.

The cornea is anterior section capsule of the eye, which is the main component of the refractive system of the visual organs. The cornea looks like a convex-concave lens. Due to the fact that it has different thicknesses at the periphery and in the center, different curvatures of the internal and external planes of this component of the refractive system are achieved. The refractive power of the corneal layer of the eye is 40 diopters. The radius of curvature is approximately 7.8 mm. The cornea is completely transparent and has no blood vessels. Its diameter is 11 mm vertically and 12 mm horizontally. Normal thickness The corneal layer at the periphery is 700 µm, in the center 550 µm.

The cornea is an organic, biconvex lens that is attached to the sclera of the eye using thin fibrous fibers. The junction of the cornea and the sclera is called the limbus .

The cornea consists of 6 layers.

1. Stroma. This is the thickest and largest layer of the cornea, which occupies more than 90% of its area. Formed by collagen fibers, fibrocytes, keratsites, leukocytes. Responsible for the strength of the cornea. It is filled with the thinnest plates of collagen fibers. The plates are located parallel to each other, but the direction of the fibers in each plate is different, which ensures strength.
2. Epithelium. Performs a protective function. It tolerates mechanical damage very well. Multilayered squamous non-keratinizing epithelium can be regenerated within a day and no traces remain. The anterior and posterior epithelium retain moisture in the stroma. If their function is impaired, the cornea swells and loses transparency.
3. Bowman's membrane (membrane). Acellular surface layer stroma. Maintains the natural shape of the cornea.
4. Endothelium. The posterior and inner layer of the cornea, which plays an important role in its nutrition, maintenance, prevents its swelling as a result of increased intraocular pressure. The transparency of the cornea is due to this layer. The endothelium consists of hexagonal cells. Performs a pumping function, providing corneal cells nutrients from intraocular fluid. Various eye pathologies weaken this layer, as a result the number of its cells decreases. The fewer endothelial cells, the less transparency the cornea becomes and the more it swells. The endothelium consists of a single layer of cells and prevents the cornea from swelling. The older a person gets, the thinner the endothelium becomes. He is unable to regenerate.
5. Descemet's layer. Collagen shell, which is protective barrier, preventing infection from spreading to other ocular structures. Provides eye protection from internal and external adverse effects.
6. Layer of Dua (Dua). The thickness (normal) of this component of the corneal layer is approximately 15 microns. Dua layer is high strength, which can withstand pressure from 150 to 200 kPa. Located between Descemet's membrane and stroma.

Layers of the cornea.

The cornea is different from the rest ocular structures the absence of blood vessels that provide tissue cells with oxygen and nutrients. This structural feature leads to a slowdown metabolic processes in the corneal layers. Metabolism and nutrition of the cornea is carried out thanks to a thin network of capillaries, which are located around the cornea and penetrate 1 mm into it.

Innervation of the cornea is provided by trigeminal nerve.

Functions

The functions performed by the cornea are determined by its location and anatomy.

The main functions are:

1. Refraction of light rays. Cornea by anatomical structure represents optical lens, which brings into focus light rays entering the eye from different sides. Due to this function, it is one of the critical components refractive system of the eyeball.
2. Protection. The corneal layer performs a protective function against fine particles of dust and dirt that are constantly in the air. He also has high sensitivity to light and quickly responds to temperature influences. As a result, with any (even the slightest) injury, the eye reflexively closes, the cornea does not allow it to open for some time due to sharp increase photosensitivity, and at this time it is released a large number of tear fluid, which allows you to get rid of the foreign body.

Diseases

The cornea, performing its protective functions, is often exposed to strong impact, which results in various pathologies. Diseases of the cornea of ​​the eye are divided into groups.

Keratitis (inflammatory pathologies)

Most often, pathologies that affect the corneal layer of the eye are inflammatory. Pathologies are caused by infectious agents, exposure to damaging particles, and chemicals. Each of these factors has harmful influence on the cornea, reducing its light transmission and changing its properties.

Traumatic

They arise due to chemical and mechanical damage. Epithelial cells are damaged and their ability to regenerate is impaired.

With mechanical or thermal injury to the cornea, purulent inflammation often develops, which quickly destroys it. The one that lasts the longest with this disease is Descemet's membrane, which can withstand the action of destructive factors for quite a long time.

Dystrophic changes

Develops due to metabolic disorders in organism. Symptoms do not appear for a long time, but then the person is bothered by dry eyes and blurred vision.

Anomalies

Some people experience abnormal development of the cornea, which is expressed in changes in the degree of its transparency, changes in size and shape.

Among the anomalies are:

• giant cornea (megalocornea). It's mostly hereditary congenital disease, but sometimes in at a young age due to the development of uncompensated glaucoma, megalocornea appears as an acquired disease;
• small cornea (microcornea). The anomaly can be one- or two-sided. Due to the reduced size of the corneal layer, the eyeball also becomes smaller;
• . A change in the shape of the corneal layer, in which it becomes thinner and begins to stretch out in the form of a cone. The anomaly is genetic and develops, as a rule, in both eyes, but with some difference in time;
• keratoglobus. An anomaly in which the cornea has a spherical shape. The appearance of this anomaly is facilitated by the weakness of the elasticity of the corneal layer.

Research methods

To identify changes in the cornea in various diseases, a series of diagnostic procedures. Based on their results, the specialist will prescribe treatment.

The main methods of studying the cornea:

1. Biomicroscopy. Examination of the corneal layer using a microscope and illuminator.
2. Keratometry. Determination of corneal radius curvature.
3. Pachymetry. The thickness of the cornea is examined using a special ultrasound sensor.
4. Topography. Using topography, the entire surface of the cornea is examined, its shape (asphericity or eccentricity) and refractive power are accurately determined.
5. Microbiological examination . A scraping is taken from the superficial layers of the cornea.
6. Biopsy. Corneal tissue is taken for examination when culture and scraping are not sufficient for diagnosis.
7. Mirror microscopy. Analysis of cell shape and determination of their number in the endothelial layer. The norm is 3000 cells per square millimeter.

Treatment

The method of treatment is chosen depending on the disease, clinical picture, general condition person. Infectious lesions treated with antibacterial drops. If the cornea has changed its shape and refractive power, optical correction is carried out using glasses or lenses. To suppress inflammation, drugs with glucocorticoids are prescribed, with infectious process antiviral and antimycotic agents are used. If the injuries are superficial, agents are used that accelerate the restoration of epithelial tissue.

If conservative treatment is ineffective, extensive damage to the corneal layer, progressive deterioration of vision, congenital anomalies carry out surgery. This can be (donor cornea transplant) or keratoprosthesis (installation of an artificial cornea).

The cornea is part of the refractive system of the eye. If its structure is disrupted and dysfunction develops, then the entire optical system suffers.

Only timely attention to symptoms indicating problems with this important layer of the eyeball and diagnosis will allow timely treatment and preservation of vision.

Front transparent part fibrous membrane the eye is called the cornea. The functions of the cornea of ​​the eye are protection and refraction of light. It is a convex-concave lens and looks like convex glass wristwatch, being an important part optical system organs of vision. Occupies about 17% of the area, the remaining opaque part is called the sclera. The junction of the sclera and the cornea is called the limbus.

Anatomy and structure

The cornea of ​​the eye consists of 6 layers:

• The anterior epithelium is stratified squamous non-keratinized epithelium.
• Bowman's membrane is a derivative of the main substance.
• Stroma - makes up 90% of the volume. The structure is layered, each layer has a different arrangement of collagen fibers.
• Duha's layer is the thinnest transparent layer, located between the stroma and Descemet's membrane, different high strength, was opened in 2013.
• Descemet's membrane is a derivative of endothelium.
• Posterior epithelium (endothelium) - single layer epithelium lining the inner surface.

Sources of nutrition of the cornea. The structure of the cornea has a peculiarity - the absence of blood vessels, due to this it is transparent, but the metabolism in it is slow. The cornea is nourished by tear fluid, aqueous humor anterior chamber of the eye. They also matter ciliary nerves, which provide normal functional state cornea.

Innervation of the cornea. Sensitive innervation is provided by the first branch of the trigeminal nerve, from which the ciliary nerves approach the cornea. The protective corneal reflex is responsible for the close connection between the trigeminal and facial nerves, which carries out the reaction of closing the eyelids in response to the slightest irritation.

Main functions

The cornea has two main functions: it protects the eye and collects and refracts light rays.

• Protective. The thin cornea is a mechanical barrier between internal environment eyes and the surrounding area. The tear that washes the cornea contains lysozyme, which also has protective properties.
• Light refraction. Collects and refracts light rays hitting the surface of the eye, directing them through the pupil into the lens. The normal refractive power of the cornea is about 40 diopters. The thickness of this lens in the central part is 450-600 microns, in the peripheral part - 600-750 microns. The diameter of the cornea is 11.5-12 mm, the radius of curvature is on average 7.8 mm.

Normally, the human cornea looks completely transparent, moist, smooth, shiny and sensitive.

Diseases

• Anomalies - changes in shape and size.
• Keratitis is inflammation.
• Dystrophies are diseases caused by metabolic disorders.
• Tumors.

Common anomalies

One of the most common pathologies visual system is keratoconus, in which thinning of the stroma and its deformation occurs.

The most common abnormalities of corneal development are:

• Megalocornea - gigantic cornea, with a diameter of more than 12 mm.
• Microcornea is a small cornea, less than 10 mm in diameter.
• Embryotoxon - ring opacification.
• Conical shape - hereditary disease, thinning of the stroma and cone-shaped deformation.
• Acute keratoconus is a conical deformity due to cracks in Descemet's membrane.
• Weakness of the elastic framework, a condition preceding keratoconus, is characterized by progressive irregular astigmatism.
• Keratoglobus is a spherical change that is genetically determined.

Acquired diseases

Keratitis - inflammatory disease cornea. Keratitis can be traumatic and infectious. Depending on the pathogen, bacterial, viral, and fungal keratitis (keratomycosis) are distinguished. Endogenous keratitis is caused concomitant diseases humans, for example, tuberculosis, syphilis, vitamin deficiency, damage to the trigeminal nerve and others. Possible outcomes diseases: cloud-like opacification, spot (limited white opacification), cataract (dense opaque scar).

Dystrophy of the cornea is manifested by its clouding and is of two types: hereditary and acquired.

Corneal dystrophy is a non-inflammatory disease that leads to decreased transparency. The cause is metabolic disorders: amyloid, hyaline, lipids, uric acid and others. Dystrophies are:

• hereditarily determined (primary);
• acquired (secondary) dystrophies - occur against the background of the underlying disease: neurotrophic - occur with loss of sensitivity, recurrent erosions - after traumatic injury, Kaiser-Fleischner ring for Wilson's disease and copper metabolism disorders, age-related degenerations- senile arch, limbal girdle of Vogt.

Date: 12/28/2015

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• Anatomy of the cornea of ​​the eye
• Functions performed by the cornea of ​​the eye
• Abnormalities in corneal development
• Diseases of the cornea
• Diagnosis and treatment of diseases of the corneal layer

The cornea of ​​the eye is the anterior part of the capsule of the organ of vision, which has a certain degree of transparency. In addition, this section is a component of the main refractive system.

Anatomy of the cornea of ​​the eye

The cornea covers about 17% of the total area of ​​the outer capsule visual organ. It has a structure in the form convex-concave lens. The thickness of the cornea in the center is about 450-600 microns, and closer to the periphery - 650-750 microns. Due to the difference in the thickness of the cornea, different curvatures of the external and internal planes of this element of the optical system are achieved. The refractive index of light rays is 1.37, and the refractive power of the cornea is 40 diopters. The thickness of the corneal layer is 0.5 mm in the center, and 1-1.2 mm at the periphery.

The radius of curvature of the corneal layer of the eyeball is approximately 7.8 mm. The performance of the light-refracting function of the cornea of ​​the eye depends on the curvature of the cornea.

The main substance of the cornea is a transparent connective tissue stroma and corneal corpuscles. Adjacent to the stroma are two plates called border plates. The anterior lamina is a derivative formed from the main substance of the cornea. The posterior lamina is formed by changes in the endothelium that covers the posterior surface of the cornea. The anterior surface of the cornea is covered with a thick layer of stratified epithelium. The structure of the cornea of ​​the eyeball includes six layers:

• anterior epithelial layer;
• anterior boundary membrane;
• the main substance is the stroma;
• Dua's layer is a highly transparent layer;
• rear boundary membrane;
• layer of the corneal endothelium.

All layers of the cornea have a structure whose main function is to refract the light beam entering the eye. The mirror surface and characteristic shine of the surface are provided by tear fluid.

Tear fluid, mixing with the secretion of the glands, thin layer moistens the epithelium, protecting it from drying out, and at the same time evens out the optical surface. Characteristic difference The difference between the cornea and other tissues of the eyeball is the absence of blood vessels in it that nourish the tissues and supply the cells with oxygen. This structural feature leads to the fact that metabolic processes in the cells that make up the corneal layer are greatly slowed down. These processes occur due to the presence of moisture in the anterior chamber of the eye, tear fluid and vascular system located around the cornea. A thin network of capillaries extends into the corneal layers only 1 mm.

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Functions performed by the cornea of ​​the eye

The functions of the cornea are determined by its structure and anatomical location in the structure of the eyeball; the main functions are:

• protective;
• function of light refraction in the optical system of the organ of vision.

Anatomically, the cornea is an optical lens, that is, it collects and focuses a beam of light that comes from different sides onto the surface of the cornea.

Due to its main function, it is an integral part of the optical system of the eye, which ensures the refraction of rays in the eyeball. In geometric shape, the cornea is a convex sphere that performs a protective function.

The corneal layer protects the eye from external influence and is constantly exposed to environment. In the process of performing the functions assigned to the corneal layer, it is constantly exposed to the influence of dust and small suspended particles floating in the air. In addition, this part of the optical system of the eye has high photosensitivity and responds to temperature influences. In addition to those listed, the corneal layer also has whole line other properties on which largely depends normal operation visual apparatus person.

Protective function consists of a high degree of perception and sensitivity. The sensitivity of the corneal surface lies in the fact that when it comes into contact with foreign objects, dust particles and small debris, a person triggers a reflex response to irritation, which is expressed in a sharp closure of the eyelids.

When the surface of this part of the optical system of the eyeball is irritated, a sharp wrinkling of the eyes occurs; this reaction is a response to the influence of damaging and irritating factors that can provoke damage to the organ. In addition, when acting on the cornea irritating factor may occur in the form of defensive reaction photophobia, increased lacrimation. By increasing lacrimation, the eyeball cleans its surface of small irritating particles of dust and dirt.

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Abnormalities in corneal development

Abnormal development of the cornea is expressed, as a rule, by changes in its size, degree of translucency and shape.

The most common developmental anomalies are:

• megalocornea;
• microcornea;
• embryotoxon;
• conical cornea;
• weakness of the elastic framework of the cornea;
• acute keratoconus;
• keratoglobus.

Megalocornea, or giant cornea, is most often an inherited abnormality. There are cases of the development of a large cornea, not only congenital, but also acquired. Acquired megalocornea increases in size if there is an uncompensated form of glaucoma in the body at a young age.

Microcornea is a small cornea, the anomaly occurs in unilateral and bilateral forms. The eyeball in the case of the development of such an anomaly is also reduced in size. With the development of megalo- and microcornea in the body, there is a high probability of developing glaucoma. As an acquired pathology, a decrease in the size of the cornea contributes to the development of subatrophy of the eyeball. These diseases of the cornea cause it to lose its transparency.

Embryotoxon is an annular opacification of the cornea, which is located concentrically with the limbus and resembles a senile arch in appearance. This anomaly does not require treatment.

Keratoconus is a genetically determined abnormality in the development of the corneal layer, which is manifested by changes in shape. The cornea becomes thinner and stretches into a cone. One of the signs of the development of an anomaly is the loss of normal elasticity. Most often, this process develops in the form of a bilateral anomaly, but the development of the process does not occur simultaneously on both organs of vision.

Weakness of the elastic framework of the corneal layer is an anomaly, the progression of which provokes the occurrence and progression of irregular astigmatism. This type of anomaly is a precursor to the development of keratoconus in the organ of vision.

Acute keratoconus develops in humans when cracks occur in the thickness of Descemet's membrane.

The keratoglobus is a spherical cornea. The reason for the appearance and progression of this anomaly is the weakness of elastic properties caused by genetic disorders.

Cornea of ​​the eye- this is the anterior shell of the eye, which does not have blood vessels, so it is absolutely transparent, while it is well innervated.

The cornea of ​​the eye is the main part of the refractive apparatus of the eye with a refractive power of 40 diopters. The diameter of the cornea is 11 mm vertically and 12 mm horizontally, the thickness at the center is 550 µm, and at the periphery it is 700 µm. The radius of curvature of the cornea is equal to 7.8 mm. The diameter of the cornea of ​​the eye may increase slightly from the moment of birth, but from the moment of increase this figure becomes constant.

Layers of the cornea

Analyzing the structure of the cornea of ​​the eye, one cannot help but note that until 2013 it was believed thatcornea of ​​the eyehas only 5 layers. Now, after opening in 2013 There are 6 layers in the cornea.

The structure of the cornea of ​​the eye consists of 6 layers:

— The epithelial layer is a flat, multilayered, non-keratinizing epithelium. Performs a protective function. Resistant to mechanical damage and recovers quickly.

- Bowman's membrane is the surface layer of the stroma that does not have cells. After its damage, scars remain.

— The stroma of the cornea of ​​the eye is the most large area, which makes up 90% of the thickness of the cornea.

— The Dua layer is only about 15 microns thick, is highly durable, withstanding pressure of 150-200 kPa, and is located between the stroma and Descemet’s membrane.

- Descemet's membrane - the structure of this membrane is made up of collagen fibers. It serves as a protective barrier, preventing the spread of infection.

— The endothelium is the inner or posterior layer of the cornea that plays vital role in its nutrition and is responsible for the transparency of the cornea, and also participates in maintaining its condition, protects the cornea from swelling under the influence of intraocular pressure. Over time, the number of endothelial cells decreases, various diseases eyes speed up this process. The fewer endothelial cells, the greater the swelling of the cornea and the less transparency.

Functions of the cornea

The cornea of ​​the eye is the first obstacle on the way harmful effects environment - dust, wind, mechanical particles, chemical particles, etc. The protective function of the cornea is expressed by its high sensitivity. When the cornea is irritated by a foreign body, a person reflexively closes his eyelids, the eye rolls upward, and at that moment the copious discharge tears, washing away foreign body, at the same time, sensitivity to light increases, thus protecting the cornea from damage.

Cornea of ​​the eye and its research methods

- In order to determine all changes in the cornea during diseases, a microscope and a light source are used, this research method is called - Biomicroscopy of the cornea .

— Keratometry– allows you to measure the radius of curvature of the cornea.

- Using an ultrasound sensor, the thickness of the cornea is measured, this research method is called - Pachymetry.

— Examination of the entire surface of the cornea, precise definition its shape, as well as its refractive power allows you to make - Corneal topography.

— Microbiological examination- This is a scraping from the surface of the cornea.

— Corneal biopsy is a research method in which body tissue or cells are taken. It is used only when the results of scraping and culture were insufficient for diagnosis.

Diseases of the cornea of ​​the eye

— Keratitis;
— Keratoconus;
— Keratomalacia;
— Corneal dystrophy;
— Bullous keratopathy.