The cornea is the transparent membrane of the eye. Structure, functions, diseases, corneal transplantation

Date: 28.12.2015

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Anatomy of the cornea
Functions performed by the cornea of the eye
Anomalies in the development of the cornea
Diseases of the cornea of the eye
Diagnosis and treatment of diseases of the cornea

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

Anatomy of the cornea

The cornea covers about 17% of the entire area of the outer capsule visual organ. It has a structure in the form of a 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, a different curvature of the outer and inner planes of this element is achieved. optical system. The refractive index of light rays is 1.37, and the refractive power of the cornea is 40 diopters. The thickness of the stratum corneum is 0.5 mm in the center, and 1-1.2 mm on the periphery.

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

The main substance of the cornea is a transparent connective tissue stroma and corneal bodies. Adjacent to the stroma are two lamellae, called marginal lamellae. The anterior plate is a derivative formed from the main substance of the cornea. The posterior lamina is formed by alteration of the endothelium that covers the posterior surface of the cornea. The anterior surface of the cornea is covered with a layer of stratified epithelium. The structure of the cornea of the eyeball includes six layers:

anterior epithelial layer;
anterior border membrane;
the main substance is the stroma;
Dua layer - highly transparent layer;
posterior border membrane;
corneal endothelial layer.

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

Lacrimal fluid, mixing with the secret of the glands, thin layer wets the epithelium, protecting it from drying out, and at the same time levels the optical surface. A characteristic difference cornea of the eye from other tissues of the eyeball is the absence in it blood vessels that nourish tissues and supply cells with oxygen. This feature of the structure leads to the fact that the metabolic processes in the cells that make up the stratum corneum 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 enters the corneal layers by 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 optical lens, that is, it collects and focuses the beam of light that comes from different sides on the surface of the cornea.

In connection with the main function performed, it is an integral part of the optical system of the eye, which ensures the refraction of rays in the eyeball. Geometrically, the cornea is a convex sphere that performs a protective function.

The cornea 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, such a department of the optical system of the eye has a high photosensitivity and responds to temperature effects. In addition to those listed, the stratum corneum has a number of other properties, on which the normal work visual apparatus person.

The protective function consists in a high degree of perception and sensitivity. The sensitivity of the corneal surface lies in the fact that when foreign objects, dust particles and small debris get on it, a person turns on a reflex response to irritation, which is expressed in a sharp closing of the eyelids.

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

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Anomalies in the development of the cornea

Abnormal development of the cornea is expressed, as a rule, by a change 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 a hereditary anomaly. There are cases of the development of a large cornea, not only congenital, but also acquired. Acquired megalocornea increases in size in the presence of an uncompensated form of glaucoma in the body. young age.

Microcornea - a small cornea, an anomaly occurs in one-sided and two-sided form. 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, high degree likelihood 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 to the limbus and resembles a senile arc in appearance. Such an anomaly does not require treatment.

Keratoconus is a genetically determined anomaly in the development of the cornea, which is manifested by changes in shape. The cornea becomes thinner and it is stretched in the form of 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, however, the development of the process does not occur simultaneously on both organs of vision.

The weakness of the elastic skeleton of the cornea is an anomaly, the progression of which provokes the occurrence and progression of irregular astigmatism. This type of anomaly is a harbinger of the development of keratoconus in the organ of vision.

Acute keratoconus develops in a person in the event of cracks in the thickness of the Descemet's membrane.

Keratoglobus is a spherical cornea. The reason for the appearance and progression of such an anomaly is the weakness of elastic properties due to genetic disorders.

The eyeball has a spherical shape. Most of its surface is covered with sclera - a dense connective sheath. She performs the support and protective function. In the anterior part of the eye, the sclera passes into the transparent cornea, which occupies 1/6 of the surface of the eyeball and takes on the main function of refraction of light rays. It is she who is the optical medium, the properties of which determine visual acuity. optical power cornea is 44 diopters.

Normally, the cornea is represented by a transparent avascular tissue. It contains a strictly defined amount of water and has an ordered structure. A healthy cornea is not only transparent, but also smooth and shiny. It has a spherical shape and has high sensitivity.

The structure of the cornea

The average dimensions of the cornea are as follows: 11.5 mm vertically, 12 mm horizontally. The thickness of the stratum corneum varies from 500 microns in the center to 1 mm at the periphery. In the structure of the cornea, five layers are distinguished: anterior epithelium, Bowman's membrane, stroma, Descemet's membrane, endothelium.

Front epithelial layer is a shell that is fast recovery. It is not subject to keratinization, and scars do not form on it. The anterior epithelial layer performs a protective function and quickly regenerates.

bowman shell(membrane) is a cell-free layer that forms scars when damaged.

Stroma The cornea is made up of specifically oriented collagen fibers. This layer occupies 90% of the entire thickness of the cornea. Its intercellular space is filled with chondroitin sulfate and keratan sulfate.

Descemet's shell a consists of the thinnest collagen fibers and is the basement membrane of the endothelium. This layer prevents the infection from spreading into the eye.

Endothelium although it is a monolayer of hexagonal cells, it performs a number of essential functions. In particular, this layer is involved in the nutrition of the cornea and maintains the stability of its state during changes. intraocular pressure. Unfortunately, the endothelium is completely devoid of the ability to regenerate, therefore, with age, the number of cells in this layer decreases and it becomes thinner.

The innervation of the cornea occurs at the ends of the first branch of the trigeminal nerve.

The cornea is surrounded by a network of blood vessels. Its nutrition is provided by capillaries, moisture of the anterior chamber, nerve endings and tear film.

Corneal reflex and protective functions of the cornea

The function of optical refraction makes the cornea the first step in the operation of the entire visual system. However, in addition to this, like the sclera, this part of the shell of the eyeball protects it from external environment. In this case, it is the cornea that takes on all kinds of external influences (dust, wind, moisture, temperature changes).

Extreme sensitivity provides reliable protection not only to the deeper structures of the eye, but also to the cornea itself. The slightest irritation, fright or a particle that flashed before the eye causes an unconditioned reflex - blinking, combined with lacrimation. Thus, the cornea protects itself from damage, bright light and others unwanted impacts. When blinking, the eye rolls up under the eyelid and tearing occurs, washing away possible dust particles to the corner of the eye.

Corneal diseases and their symptoms

Changes in the shape and refractive power of the cornea

The deviation of the curvature of the cornea in the direction of greater steepness is characteristic of myopia.
With farsightedness, the cornea has a more flattened shape than normal.
Astigmatism is characterized by violations of the shape of the cornea in various planes.
Megalocornea and microcornea are congenital anomalies in the shape of the cornea.

Damage to the surface epithelium of the cornea

Point erosion. Violation of the integrity of the corneal epithelium often accompanies various eye diseases. The cornea can be eroded due to improper selection of contact lenses, with the "dry eye" syndrome, lagophthalmos, spring catarrh, keratitis, and also as a reaction to some eye drops.
Epithelial edema may result from jump intraocular pressure or indicate damage to the endothelial layer.
Pinpoint epithelial keratitis may accompany viral ophthalmic diseases. On examination, swollen granular epithelial cells are found.
Threads are mucous formations in the form of a comma. They can form against the background of keratoconjunctivitis, accompany recurrent erosion or dry eye syndrome. The threads are usually attached at one end to the surface of the cornea and are not washed away by tears.

Corneal stroma damage

formation of infiltrates. Infiltrates result from active inflammation and are areas of the cornea involved in this process. They can form from mechanical damage(for example, when wearing lenses) or have an infectious genesis.
Edema of the stroma. With the development of edema of the stroma, its thickening and loss of transparency are observed. The stroma can swell with keratitis, keratoconus, endothelial damage, Fuchs' dystrophy, and also after eye surgery.
Vascularization (ingrowth of blood vessels). Normally, the cornea is an avascular tissue. Vessels can grow into its layers due to inflammatory diseases.

Damage to the Descemet's membrane

Ruptures may result from corneal trauma or occur as a complication of keratoconus.
Folds are most often formed as a result of surgical trauma.

Methods for diagnosing the cornea

The cornea is examined in order to identify possible damage to its layers, as well as to assess its curvature as possible cause decrease in visual acuity. The following ophthalmological examinations are carried out:

Biomicroscopy of the cornea. Standard examination of the cornea under a microscope with illumination. Such diagnostics allows to identify most diseases, as well as trauma and changes in the curvature of the cornea.
Pachymetry measures the thickness of the cornea. This study is carried out using ultrasound.
Specular microscopy - a study of the endothelial layer by photographing. In this case, the shape of the cells is analyzed and their number per 1 sq. mm area. The normal density is considered to be 3000 cells per 1 sq. mm.
Keratometry measures the curvature of the anterior surface of the cornea.
Topography of the cornea - complete computer research the entire area of the cornea. Allows you to point analyze the cornea in terms of thickness, curvature and refractive power.
Microbiological research aimed at studying the microflora of the surface of the cornea. The material for this study is taken under local drip anesthesia.
A biopsy of the cornea is appropriate for indicative or uninformative results of scrapings and crops.

Basic principles of treatment of diseases of the cornea

Diseases caused by an altered curvature of the cornea require correction with lenses or glasses. In severe cases, to eliminate refractive disorders may be required surgical treatment through laser surgery(LASIK and its derivatives).

Belma and corneal opacities are treated by penetrating or layered keratoplasty.

Infectious diseases of the cornea require antibacterial and antiviral drugs in the form of drops, tablets, injections.

Glucocorticoids local action contribute to the suppression of inflammatory processes and prevent the formation of scars (Dexamethasone and its derivatives).

In case of superficial corneal injuries, agents that accelerate the regeneration of epithelial tissues (Korneregel, Taufon, Solcoseryl, Balarpan, etc.) are widely used.

In a number of diseases accompanied by dryness of the cornea, moisturizing the eye with tear-replacing drops (Sistein, Hilo-Komod and others) is indicated.

For keratoconus, rigid contact lenses, collagen crosslinking and implantation of intrastromal segments (rings). In more severe cases, they resort to through keratoplasty (corneal transplantation).

The cornea is the anterior part of the eye capsule, which is the main component of the refractive system of the organs of vision. The cornea looks like a convex-concave lens. Due to the fact that it has a different thickness at the periphery and in the center, different curvature of the inner and outer planes of this component of the refractive system is achieved. The refractive power of the cornea of the eye is 40 diopters. The radius of curvature is approximately 7.8 mm. The cornea is absolutely transparent, there are no blood vessels in it. Its diameter is 11 mm vertically and 12 mm horizontally. The normal thickness of the stratum corneum 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 with thin fibrous fibers. The place where the cornea meets the sclera is called the limbus. .

The cornea consists of 6 layers.

Stroma. It is the thickest and largest layer of the cornea, covering more than 90% of its area. Formed by collagen fibers, fibrocytes, keratites, leukocytes. Responsible for the strength of the cornea. It is filled with the thinnest plates of collagen fibers. The plates are parallel to each other, but the direction of the fibers in each plate is different, which ensures strength.
Epithelium. Performs a protective function. It tolerates mechanical damage very well. Stratified squamous non-keratinizing epithelium can be regenerated in 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 its transparency.
Bowman's membrane (membrane). acellular surface layer stroma. Supports natural form cornea.
Endothelium. rear and the inner layer cornea, which plays an important role in its nutrition, maintenance of the state, prevents its swelling as a result of increased intraocular pressure. The transparency of the cornea is due to this layer. The endothelium is made up of hexagonal cells. Performs a pumping function, providing corneal cells with nutrients from the intraocular fluid. Various eye pathologies weaken this layer, as a result, the number of its cells decreases. The fewer endothelial cells, the less becomes the transparency of the cornea and it swells more. The endothelium consists of a single layer of cells and does not allow the cornea to swell. How more years a person, the thinner the endothelium becomes. He is unable to regenerate.
Descemet's layer. Collagen sheath, which is a protective barrier, preventing the penetration of infection into the rest of the eye structures. Provides eye protection from internal and external adverse effects.
Dua (Dua) layer. The thickness (norm) of this component of the stratum corneum is approximately 15 microns. The Dua layer is high strength, which can withstand pressure from 150 to 200 kPa. Located between the Descemet's membrane and the stroma.

The layers of the cornea.

The cornea differs from other eye structures in the absence of blood vessels in it, which provide tissue cells with oxygen and nutrients. This feature of the structure 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 that are located around the cornea and penetrate into it by 1 mm.

The innervation of the cornea is provided by the trigeminal nerve.

Functions

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

The main functions are:

Refraction of light rays. Cornea by anatomical structure It is an optical lens that brings into focus the light rays entering the eye from different directions. Due to this function, it is one of the critical components refractive system of the eyeball.
Protection. The corneal layer performs a protective function, from fine particles of dust, dirt, which are constantly in the air. It is also highly sensitive to light and reacts quickly to temperature changes. As a result, with any (even the slightest) injury, the eye closes reflexively, the cornea does not allow it to open for some time due to a sharp increase in photosensitivity, and at this time a large number of lacrimal fluid, which allows you to get rid of a 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 diseases)

Most often, pathologies that affect the cornea of \u200b\u200bthe eye are inflammatory. Pathologies are caused by infectious agents, exposure to damaging particles, chemicals. Each of these factors has pernicious influence on the cornea, reducing its light transmission and changing properties.

traumatic

Occur due to chemical, mechanical damage. Epithelial cells are damaged, their ability to regenerate is impaired.

With mechanical, thermal injury to the cornea, purulent often develops, which quickly destroys it. The longest in such a disease is the Descemet's membrane, which for a long time withstands the action of destructive factors.

Dystrophic changes

Develops due to metabolic disorders in the body. Symptoms do not appear for a long time, but then the person is worried about dry eyes, blurred vision.

anomalies

Some people have an abnormal development of the cornea, which is expressed in a change in the degree of its transparency, a change in size and shape.

Anomalies include:

giant cornea (megalocornea). It's mostly hereditary. congenital disease, but sometimes at a young age, due to the development of uncompensated glaucoma, megalocornea appears as an acquired disease;
small cornea (microcornea). The anomaly can be unilateral or bilateral. Due to the reduced size of the cornea, the eyeball also decreases;
. A change in the shape of the stratum corneum, in which it becomes thinner and begins to stretch in the form of a cone. The anomaly refers to genetic, 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 contributes to the weakness of the elasticity of the cornea.

Research methods

To detect corneal changes in various diseases carry out a number diagnostic procedures. Based on their results, the specialist will prescribe treatment.

The main methods for examining the cornea:

Biomicroscopy. Examination of the stratum corneum using a microscope and an illuminator.
Keratometry. Determination of the curvature of the radius of the cornea.
pachymetry. The thickness of the cornea is examined using a special ultrasound probe.
Topography. With the help of topography, the entire surface of the cornea is examined, its shape (asphericity or eccentricity) and refractive power are accurately determined.
Microbiological research. Take a scraping from the surface layers of the cornea.
Biopsy. Corneal tissue is taken for examination when culture and scraping are insufficient for diagnosis.
Mirror microscopy. Analysis of the shape of cells 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 performed using glasses or lenses. To suppress inflammation, drugs with glucocorticoids are prescribed, with infectious process use antiviral, antimycotic agents. If the injuries are superficial, agents are used that accelerate the restoration of epithelial tissues.

With inefficiency conservative treatment, extensive damage to the cornea, progressive deterioration of vision, congenital anomalies carry out surgical intervention. This can be (donor cornea transplantation) or keratoprosthetics (installation of an artificial cornea).

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

Only timely appeal attention to symptoms that indicate problems with this important layer of the eyeball and diagnosis will allow timely treatment and save vision.

Vitality and development human body largely dependent on the functioning of the visual system. The cornea is considered one of the most important elements vision, as it is responsible for the quality of perceived objects. Violation of the functions of the cornea can lead to deterioration or complete loss of vision. The work of the outer shell of the eye can be compared to the lens of a camera, which focuses scattered rays of light.

The cornea of the eye. Structure

The cornea is an elastic shell of a transparent color, and is shaped like a convex-concave lens. The concave part of the lens is turned back. The cornea consists of five main layers: epithelium, Bowman's membrane, stroma, Descemet's membrane, endothelium. All layers of the cornea are important for vision.

The epithelium is the top layer of the cornea, consisting of the ectoderm. This layer performs the following functions:

1) mechanical protective function. This function is expressed in protection against hit foreign bodies and microorganisms in the eye;
2) optical function epithelium is to increase the resolution of the visual apparatus;
3) the biological protective function of the epithelium is directly related to the formation of a protective reaction of the body's immunity;
4) membrane function- the top layer of the cornea helps beneficial substances penetrate to the next layers of the eye. With this feature, some eye diseases can be cured with drops.

The epithelium, as a rule, is updated in one week. It has a smooth surface and is equipped with nerve endings. This layer is sensitive to external influences. The Bowman's membrane, located behind the epithelium, also plays a protective and nourishing function, which is not restored when the membrane is damaged. The widest layer of the cornea is the stroma, which is represented by collagen fibers and regenerated cells. Between the stroma and the upper layer of the cornea is Descemet's membrane, which has strong and elastic layers. Following the Descemet's membrane is the endothelium, which is not capable of regeneration, the functions of which are to excrete excess fluid and preventing swelling. Violation of the functions of this layer leads to serious problems with cornea.

Causes of corneal disease

According to statistics, about 30% of eye diseases are associated with the outer shell, since the cornea can be exposed to all harmful factors. The main diseases of the cornea are expressed in inflammatory processes that can move to the upper layer from other parts of the eye. External causes problems with the cornea can become chemical substances, bad ecological situation, tobacco smoke. Sometimes problems with this layer are congenital.

infectious diseases women in the period of fruiting lead to wrong development of the cornea of the eye, its structure is disturbed, and a pathology of vision occurs. fungal diseases most dangerous to the eyes, since it is very problematic to cure them.

Symptoms of eye disease

The most common symptoms of corneal disease are:
1) decrease in the transparency of the outer shell, the occurrence of turbidity;
2) reduced smoothness and lack of gloss on the surface of the eye;
3) changing the size and shape of the shell;
4) the appearance of red vessels on the eyeball;
5) causeless tearing;
6) fear of bright light;
7) spasm of the upper eyelid.

Very often it has a partial character, which is characterized by a yellowish tint and a violation of the integrity of the upper layer of the epithelium. The cornea may have fresh or old opacities. For fresh turbidity, photophobia and irritation are characteristic, and for the old - scarring. When identifying a disease, it is very important to pay attention to the localization of spots, size, depth, and also analyze the vessels that have appeared.

Cornea: research methods

Among the methods of studying the cornea, the following can be distinguished:
Biomicroscopy - in this type of examination, the cornea is examined using a microscope with illumination. This allows you to detect all changes in the cornea.
Pachymetry is a method that allows you to determine the thickness of the cornea using a special sensor.
Specular microscopy - the cornea is examined using special photographic equipment to determine cell density and shape analysis.
Keratometry - is to measure the curvature of the upper layer of the cornea.
Topography - the cornea is completely examined using a special computer, an accurate analysis of the shape and refractive power takes place.
Microbiological research is the removal of scrapings from the surface of the cornea under local anesthesia and further analysis.

What is keratitis and how is it treated?

Keratitis is a fairly common disease, accompanied by inflammatory process in the cornea of the eye. The cause of the disease can be various infections, damage, fungus, chronic diseases. Keratitis has many forms and varieties. Keratitis is associated with photophobia, severe pain, lacrimation, redness along the edge of the cornea. Keratitis can lead to deterioration or even loss of vision if it is not treated in time.

Superficial keratitis on initial stage can be treated at home. Various herbal infusions and lotions are used to treat the disease.
Optometrists may prescribe antibiotics to treat this inflammation. Among the ointments against this disease, solcoseryl and tetracycline ointment are the most common. Locally it is recommended to use solutions of chloramphenicol and sodium sulfacyl. In case of inflammation of the cornea, the mood of the cornflower and the decoction of whole-leaved mari are also used to wash the eyes. A decoction of plantain seeds is used inside a quarter cup.

If you have problems with the cornea, which are accompanied by the above symptoms, it is better not to self-medicate and consult a doctor who will prescribe the necessary treatment.

Our eyes are complex organ, consisting of many environments. One of them is the cornea, the most convex part of the eyeball (photo). Let's figure out what it is, what functions and structure it has.

The cornea is a transparent, light-refracting medium that does not have blood vessels (this explains its transparency). Metabolism occurs through nearby vessels and intraocular and tear fluid. The anterior food sources are the environment from which cells obtain oxygen.

The structure and layers of the cornea:

Anterior epithelium (photo). Upper shell consisting of several layers epithelial cells. It protects the eyes from the negative effects of the external environment, quickly recovers, smoothes the surface of the cornea, and regulates the flow of fluid into the eye. Oxygen flows through it. The layer thickness is about 50 µm.
Bowman's membrane. Sheath located under the epithelium. It consists of collagen fibrils and proteoglycans. The functions of the membrane are unclear: some scientists believe that it makes the epithelium as smooth as possible and ensures the accuracy of refraction. Others believe that it is the result of the interaction of the epithelium and stroma and does not perform any functions.
Stroma (ground substance). The thickest shell, consisting of collagen fibers. At negative impacts it reacts with edema, infiltration and vascular ingrowth.
Dua layer. High-strength interlayer, recently discovered. It is believed that some chronic vision problems are associated with it. It was also concluded that the accumulation of fluid between the cornea and other environments of the eyeball is caused by a rupture of this layer.
Descemet's shell. A layer of collagen-like fibrils resistant to infectious and thermal effects. Its thickness is 0.5-10 microns.
Endothelium (posterior epithelium). The inner shell of a layer of cells of a hexagonal shape, which is responsible for the transparency of the cornea. It is a kind of ferry that provides delivery nutrients from intraocular fluid and vice versa. Violation of this layer leads to edema of the stroma.

The human cornea occupies about 1/16 of the entire area of the outer shell of the eye. Its structure resembles a convex-concave lens, the concave part of which is turned back (photo). The diameter is 10±0.5 mm. In this case, the vertical is 0.5-1 mm less than the horizontal. The thickness in the center is 0.5-0.6 mm, on the periphery - 1-1.2 mm. The refractive index of the substance is 1.37, the refractive power is 40-43 D, - approximately 7.8 mm.

The diameter of the cornea increases slightly from birth to 4 years, then it becomes constant. That is, the eyeball grows slightly faster than the diameter of the cornea, so in young children the eyes look larger than in adults.

Purpose of the cornea

Normally, the characteristics of the cornea are as follows (photo):

Sphericity.
Mirroring.
Transparency.
High sensitivity.
Absence of blood vessels.

The structure of the cornea gives it a supporting and protective function. They are also provided due to the sensitivity and ability to fast regeneration. Conduction and refraction of light is provided by transparency and spherical shape.

Roughly speaking, the cornea performs the same functions for the eye as the lens for the camera. That is, its structure resembles a lens that collects and focuses differently directed rays of light in the right direction. That is why the cornea is assigned the function of the main refractive medium of the eye.

Since the cornea is the outer shell, it undergoes various influences environment. High sensitivity allows it to immediately respond to the slightest changes. The ingress of dust or a change in lighting causes unconditioned reflexes in us - closing of the eyelids, lacrimation or photophobia (photo). This is how the damage protection functions work.

Diseases and methods of examination of the cornea

The cornea can also "sick". For example, there is such an indicator as the curvature of the cornea. Its change leads to various violations:

Myopia. The cornea has a steeper shape than normal.
Farsightedness. Here, on the contrary, the shape is less steep.
Astigmatism. The shape is wrong in different planes.
Keratoconus. Congenital, often hereditary, anomaly.
Keratoglobus. Thinned cornea with a spherical protrusion.

Superficial damage can lead to pitting, epithelial edema, keratitis, and opaque spots (photo). Deeper ones - to infiltration, ingrowth of vessels and vascularization, tears and folds.

The structure and various indicators of the cornea of the eye are examined using methods such as biomicroscopy, pachymetry (thickness is measured), and mirror microscopy. And also keratometry (corneal curvature is measured), biopsy and topography.

A very interesting film (video) about corneal damage and latest methods treatment:

Have you had problems with your cornea? How did you deal with them? Tell other readers about it, perhaps your comment will be useful.