5 layers of the cornea. B. Keratitis of unknown etiology

Cornea is located in the outermost layer and acts as a kind of frame. Normally it is transparent and is part of the conduction system eyeball.

Structure of the cornea of the eye

The shape of the cornea resembles, it is convex-concave. The structure of the cornea consists of five layers, which are located from the outside to the inside:

1. Stratified squamous epithelium that covers the cornea. It protects it from damaging effects and ensures the exchange of air and heat. Also it supports spherical shape cornea.
2. Bowman's membrane is very durable and helps maintain a certain shape.
3. The stromal layer consists of huge amount collagen, the fibers of which are closely intertwined. In addition, it contains leukocytes that provide immune protection from pathogenic microbes. Fibrocytes located in the stroma produce collagen, maintaining its balance.
4. Descemet's membrane is resistant to attack high temperatures and infections.
5. Single-layer endothelium is semi-permeable and allows nutrients coming from aqueous humor. If the function of this layer is disrupted, swelling occurs, which prevents normal nutrition cornea. In this case, there are no other pathways for metabolism, since there are no blood vessels in the cornea. This valuable property helps to transplant donor flaps without fear of possible rejection.

Physiological role of the cornea

The cornea performs several functions:

Support;
Protective;
Refractive;
Conductive.

All this becomes possible thanks to such characteristics of the cornea as:

Strength;
High sensitivity to various stimuli;
Fast regeneration;
Transparency for light flows;
Spherical shape;
Lack of blood vessels;
Specularity.

Video about the structure of the cornea

Symptoms of corneal damage

Corneal pathology can be suspected based on the following symptoms:

Changes in the shape of the cornea;
Decreased visual acuity;
His ;
Pain in the eyeball;
Narrowing of visual fields;

Diagnostic methods for corneal lesions

In case of suspected corneal pathology, it is necessary to conduct an examination:

Side beam imaging;
eyes;
Bacteriological research;
Keratotopography.

In case of corneal pathology, it is usually possible to identify the following diagnostically significant signs:

Change in the shape or size of the cornea;
Lack of mirror shine;
The presence of opacities of the cornea;
Formation of abnormal vessels;
Spasm.

In conclusion, I would like to remind you that the cornea is an important structure of the eyeball. If its structure is disturbed, dysfunction of both the cornea and the entire optical system. To diagnose in time pathological process, it is necessary to carry out additional methods examinations. This will allow you to prescribe timely and effective treatment.

Cornea - a transparent, avascular membrane of the eyeball, which is a continuation of the sclera. Thanks to it, light can enter the deeper layers of the eye.

The cornea looks like concave-convex lens about 10 millimeters in diameter. It is characterized by low temperature, but high tactile and pain sensitivity.

Corneal diseases account for one fourth of all eye diseases. The danger of diseases of the cornea of the eye is that without appropriate treatment a person can quickly lose vision!

The cornea of the eye consists of 5 layers:

surface layer consists of cells squamous epithelium, which is a continuation of the conjunctiva (highly vulnerable);
border anterior plate weakly attached to the epithelium, therefore, at the slightest deviation it is quickly rejected. When cells are damaged, it does not recover, but quickly becomes cloudy;
stroma - the thickest shell of the cornea, contains about 200 layers of collagen fibrils, between which there is a connecting component mucoprotein;
Descemet's membrane - posterior border plate (acellular layer), from which all corneal cells are formed;
endothelium - inner part membrane that protects the stroma from moisture in the eye.

Functions of the cornea:

eye protection (the cornea is quite strong and can recover quickly);
refraction of light (the cornea is part of the optical system of the eye; due to its sphericity and transparency, it conducts and refracts light rays);
maintaining eye shape.

When damaged, the cornea begins to become cloudy, which leads to decreased vision. In the cornea they begin quickly and last a long time inflammatory processes.

Diseases of the cornea of the eye

Diseases of the cornea of the eye can be either acquired or congenital.

Types of corneal diseases:

injuries;
violations of the size and shape of the cornea;
degenerative and dystrophic lesions and etc.

Injuries

Damage to the cornea may occur during exposure.

These could be grains of sand, metal shavings, wood chips. Depending on the degree of penetration, deep and superficial injuries are distinguished.

For superficial trauma foreign objects are located in the outer layers of the eye and cornea, and in case of deep injuries - in the depths of the eyeball. In some cases, when the eye is injured, corneal erosion develops.

On our website you can find more full information about the diagnosis of eye injury and removal methods.

Keratitis

Violation of the size and shape of the shell

You can select the following diseases cornea of the eye associated with changes in its shape and size.

Megacornea - genetic disease, in which the cornea becomes larger than usual, its size reaches 10 mm.

Microcornea - the cornea, on the contrary, is too small, about 5 mm, in size. This leads to a reduction in the size of the eyeball. In this condition, clouding of the cornea and...

Keratoglobus - congenital spherical protrusion of the cornea due to impaired development of mesodermal tissue. Inflammation begins to appear already in childhood, combined with and . The cornea becomes convex throughout its entire length, and an increase in its diameter is observed.

Keratoconus - hereditary disease, in which the shape of the cornea changes, it becomes conical. This occurs as a result of thinning of the center of the cornea and loss of elasticity of the anterior chamber of the eye.

The pathology occurs at 11-12 years of age and is accompanied by astigmatism, which cannot be treated. With this disease, the degree and axes constantly change, so it is necessary to re-select lenses each time. At strong development keratoconus, the lens can no longer stay on the cornea.

When strong degree keratoconus and keratoglobus shown surgical treatment to remove part of the cornea - penetrating subtotal keratoplasty .

Corneal dystrophy

Corneal dystrophy - congenital disease, accompanied by rapid development and clouding of the cornea. Doctors identify several forms: spotted, nodular, lattice, mixed dystrophies, etc.

Corneal dystrophy can be primary or secondary. At primary dystrophy the disease usually affects both eyes and develops quite slowly, so it is difficult to detect.

Secondary dystrophy usually unilateral and develops against the background of trauma, disease or ophthalmic surgery.

With this pathology, the sensitivity of the cornea of the eye worsens.

At microscopic diagnostics The cornea of the eye in the middle of the cornea may experience slight opacities in the form of stripes and small spots. The deep layers of the epithelium are unaffected.

If the pathology manifests itself in adolescence, then by the age of 40, blepharospasm and photophobia arise.

Diagnosis of corneal pathology

Diagnosis of diseases of the cornea of the eye includes the following methods:

biomicroscopy of the eye;
keratopography;
confocal microscopy.

Surgical treatment of diseases of the cornea of the eye

Surgical treatment of the cornea can occur using several methods, which we will discuss in more detail.

Corneal crosslinking - an operation intended to treat keratonus. During this manipulation, it is cut off upper layer corneas, then the eyes are irradiated with ultraviolet light, processed antibacterial drops. For 3 days after surgery, you must constantly wear special lenses.

Keratectomy - removal of small superficial opacities of the central part of the cornea. Surgery is underway, possibly laser treatment corneal erosion. The resulting defect heals on its own after surgery.

Keratoplasty (cornea transplant) is used in the following cases:

when the transparency of the cornea is impaired;
at ;
for acute keratoconus, etc.;
to strengthen corneal tissue and improve conditions for subsequent optical keratoplasty.

There are 2 keratoplasty techniques: layer-by-layer And end-to-end

Layer keratoplasty carried out for superficial opacities of the cornea. The superficial part of the cornea is cut off and replaced with a graft similar shapes, size and thickness.

Penetrating keratoplasty consists of excision and replacement of all layers of the cornea. Depending on the excision, partial excision (an area less than 2-4 mm), subtotal keratoplasty (more than 5 mm) and total surgery (the entire cornea) are divided.

Keratoprosthetics - replacement of a cloudy cornea with a biologically inert plastic material.

The outer shell of the eyeball is spherical in shape. Five-sixths of it is the sclera, a dense tendon tissue that performs a skeletal function.

Cornea or cornea, occupies the anterior 1/6 part fibrous membrane eyeball and performs the function of the main optical refractive medium, its optical power on average 44 dioptres. This is possible due to the peculiarities of its structure - transparent and avascular tissue with an ordered structure and a strictly defined water content.

Normally, the cornea is a transparent, shiny, smooth, spherical tissue with high sensitivity.

Structure of the cornea

The diameter of the cornea averages 11.5 mm vertically and 12 mm horizontally, thicknesses range from 500 microns in the center to 1 mm at the periphery.

The cornea consists of 5 layers: anterior epithelium, Bowman's membrane, stroma, Descemet's membrane, endothelium.

The anterior epithelial layer is a multilayered squamous non-keratinizing epithelium that performs protective function. It is resistant to mechanical stress and, if damaged, is quickly restored within a few days. Due to the extremely high ability epithelium to regenerate, scars do not form in it.
Bowman's membrane is an acellular layer of the stroma surface. When it is damaged, scars form.
Corneal stroma – Occupies up to 90% of its thickness. Consists of correctly oriented collagen fibers. The intercellular space is filled with the main substance - chondroitin sulfate and keratan sulfate.
Descemet's membrane – basement membrane The endothelium of the cornea consists of a network of thin collagen fibers. It is a reliable barrier to the spread of infection.
Endothelium is a monolayer of hexagonal-shaped cells. Performs vital role in nutrition and maintenance of the condition of the cornea, prevents its swelling under the influence of IOP. Does not have the ability to regenerate. With age, the number of endothelial cells gradually decreases.

The cornea is innervated by the endings of the first branch of the trigeminal nerve.

The cornea is nourished by its surrounding vascular network, corneal nerves, anterior chamber moisture and tear film.

Protective function of the cornea and corneal reflex

While remaining the outer protective shell of the eye, the cornea is exposed to harmful effects environment– mechanical particles suspended in the air, chemical substances, air movement, temperature influence, etc.

The high sensitivity of the cornea determines its protective function. The slightest irritation of the surface of the cornea, for example by a speck of dust, causes an unconditioned reflex in a person - closing the eyelids, increased lacrimation and photophobia. In this way, the cornea protects itself from possible damage. When the eyelids close, the eye simultaneously rolls upward and copious discharge tears, which wash away small mechanical particles or chemical agents from the surface of the eye.

Symptoms of corneal diseases

Changes in the shape and refractive power of the cornea

With myopia, the cornea may have a steeper shape than normal, which causes greater refractive power.
With farsightedness, the opposite situation is observed when the cornea is flattened and its optical power is reduced.
Astigmatism occurs when irregular shape corneas in different planes.
There are congenital changes in the shape of the cornea - megalocornea and microcornea.

Superficial damage to the corneal epithelium:

Point erosions are small epithelial defects stained with fluorescein. This nonspecific symptom diseases of the cornea, which, depending on the location, can occur with spring catarrh, poor selection contact lenses, dry eye syndrome, lagophthalmos, keratitis, with toxic effect eye drops.
Swelling of the corneal epithelium indicates damage to the endothelial layer or a rapid and significant increase in IOP.
Punctate epithelial keratitis is common in viral infections eyeball. Granular, swollen epithelial cells are found.
Threads are thin mucous threads in the shape of a comma, connected on one side to the surface of the cornea. Occurs with keratoconjunctivitis, dry eye syndrome, and recurrent corneal erosion.

Damage to the corneal stroma:

Infiltrates are areas of active inflammatory process in the cornea, which have both non-infectious - wearing contact lenses, and infectious nature– viral, bacterial, fungal keratitis.
Stromal edema – an increase in the thickness of the cornea and a decrease in its transparency. Occurs in keratitis, keratoconus, Fuchs' dystrophy, endothelial damage after surgical operations before our eyes.
Ingrowth of blood vessels or vascularization - manifests itself as the outcome of previous inflammatory diseases cornea.

Damage to Descemet's membrane

Ruptures – due to corneal trauma, also occur with keratoconus.
Folds – caused by surgical trauma.

Methods for examining the cornea

Corneal biomicroscopy - examination of the cornea using a microscope with an illuminator, allows you to identify almost the entire range of changes in the cornea during its diseases.
Pachymetry is the measurement of corneal thickness using an ultrasound sensor.
Mirror microscopy is a photographic examination of the endothelial layer of the cornea by counting the number of cells per 1 mm2 and analyzing the shape. The normal cell density is 3000 per 1 mm2.
Keratometry is the measurement of the curvature of the anterior surface of the cornea.
Corneal topography – computer research the entire surface of the cornea with accurate analysis shape and refractive power.
At microbiological research using scraping from the surface of the cornea under local drip anesthesia. A corneal biopsy is performed if the results of scrapings and cultures are inconclusive.

Principles of treatment of corneal diseases

Changes in the shape and refractive power of the cornea, such as nearsightedness, farsightedness, and astigmatism, are corrected with glasses, contact lenses, or refractive surgery.

For persistent opacities and corneal cataracts, keratoplasty and corneal endothelial transplantation are possible.

Antibacterial, antiviral and antifungal drugs are used for corneal infections depending on the etiology of the process. Local glucocorticoids suppress inflammatory reaction and limit scarring processes. Drugs that accelerate regeneration are widely used for superficial damage to the cornea. Moisturizers and tear replacement medications are used for tear film disorders.

Our eyes - 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 its functions and structure are.

The cornea is a transparent, light-refracting medium that has no blood vessels(this explains its transparency). Metabolism occurs through nearby vessels and intraocular and tear fluid. The food sources of the anterior part are the environment from which the cells receive oxygen.

Structure and layers of the cornea:

Anterior epithelium (photo). Upper shell, consisting of several layers epithelial cells. It protects the eyes from negative influences external environment, quickly recovers, smoothes the surface of the cornea, regulates the flow of fluid into the eye. Oxygen flows through it. The layer thickness is approximately 50 microns.
Bowman's membrane. The membrane 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 swelling, infiltration and vascular ingrowth.
Dua layer. High-strength layer, recently discovered. It is believed that some chronic problems with vision are connected precisely 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 membrane. A layer of collagen-like fibrils that is resistant to infectious and thermal influences. Its thickness is 0.5-10 microns.
Endothelium (posterior epithelium). The inner shell is made of a layer of hexagonal-shaped cells, which is responsible for the transparency of the cornea. It is a kind of ferry that provides delivery nutrients from intraocular fluid and back. Violation of this layer leads to stromal edema.

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 faces backward (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, at the periphery - 1-1.2 mm. The refractive value 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 the eyes of young children look larger than those of adults.

Purpose of the cornea

Normal characteristics of the cornea are as follows (photo):

Sphericity.
Specularity.
Transparency.
High sensitivity.
Lack of blood vessels.

The structure of the cornea gives it supporting and protective functions. They are also provided due to sensitivity and the ability to quickly regenerate. The conduction and refraction of light is ensured by transparency and a spherical shape.

Roughly speaking, the cornea performs the same functions for the eye as a lens for a camera. That is, its structure resembles a lens that collects and focuses differently directed rays of light in the desired 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 is subject to various influences environment. High sensitivity allows her to immediately respond to the slightest changes. Ingress of dust or changes in lighting causes us unconditioned reflexes– closing of the eyelids, lacrimation or photophobia (photo). This is how the damage protection functions work.

Diseases and methods of studying the cornea

The cornea can also “sore”. 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 irregular in different planes.
Keratoconus. Congenital, often hereditary, anomaly.
Keratoglobus. Thinning cornea with spherical shape protrusions.

Superficial damage can lead to pinpoint erosions, swelling of the epithelium, keratitis and the appearance of opaque spots (photo). Deeper ones lead to infiltration, vascular ingrowth and vascularization, ruptures and folds.

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

Very interesting film(video) about corneal injuries and the latest methods treatment:

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

One of the enough important elements visual system The eye is the cornea, because it is on its health and ability to perform its main task that the correctness of the obtained images depends, and therefore the reliability of the information, and in case of diseases of this element eyes, there is a high probability of complete loss of vision.

What is the cornea of the eye?

Cornea– a convex transparent 5-layer shell of the eyeball, the main medium (lens) in the optics of the eye. From her normal functioning the reality of the perception of objects depends. Corneal disease leads to partial or complete loss of vision.

Structure

The top layer of the cornea is called the epithelium and performs a protective function for the organ itself, delivering oxygen and regulating the amount of fluid inside the eye. Directly under the epithelial layer is Bowman's membrane, which provides nutrition and also performs a protective function. Moreover, it is worth noting that with the slightest damage it is impossible to restore the functions of this membrane.

The largest, main part of the cornea, the stroma, consists of collagen fibers, which are arranged in layers and oriented horizontally, and also contain cells designed to repair damage.

Between the stroma and the endothelium, there is Descemet's membrane, which is very resistant to mechanical damage and quite elastic. And a special layer, the endothelium, is responsible for ensuring that the cornea of the eye remains transparent and does not swell. It plays the role of a kind of pump that removes excess fluid and participates in the nutrition of the cornea.

One more layer of this body is the tear film, which is also very important for the normal functioning of the ocular apparatus.

Functions

Basically the cornea performs the same function for human eye, like a camera lens. At its core, the cornea is a lens that brings together and focuses in the desired direction scattered directed different sides rays of light flux.

Therefore, it is the cornea that is assigned the function of the main refractive medium of the human eyeball. In shape, this shell resembles a convex sphere, and also has a smooth and shiny surface. A similar part of the eye apparatus is located in the eye, like glass in a watch.

Refractive power of the cornea healthy eye can range from forty to forty-four diopters.

Diseases

Basically, almost all diseases of the cornea are inflammatory nature. Any inflammatory processes that originate on the eyelids or other eye membranes can affect this part of the eye. Moreover, quite often similar diseases may be caused external reasons, type various infections, unfavorable environmental conditions and even tobacco smoke. As a result of any of the listed diseases, the cornea of the eye becomes cloudy and cannot perform its functions normally.

In some cases, corneal opacity may be congenital, due to the mother's history of infectious diseases During pregnancy, this part of the child’s vision system may not form correctly, as a result of which the baby is born with an already cloudy cornea.

Also quite dangerous fungal infections corneas, which can occur when the membrane of the eye is damaged by an object on the surface of which there is a fungus. Such lesions are quite difficult to treat and are not always cured completely.

Treatment

Treatment methods can be used in a variety of ways, and will mainly depend not only on the causes of the disease, but also on the patient’s age and general clinical picture. For example, diseases infectious nature suggest the use of eye drops containing antibiotics. If the problem is caused by more serious reasons, such as thinning of the cornea, the formation of scars and blisters on it, then the patient long time Observe and, if absolutely necessary, operate.

The main thing to remember is that, regardless of the reasons, in case of any deterioration in vision, you must immediately consult an ophthalmologist who can diagnose correct diagnosis and prescribe effective treatment.