Structure and functions of the cornea of ​​the eye. Corneal thickness as a risk factor for the development of primary open-angle glaucoma Corneal refractive index

The eyeball has a spherical shape. Most of its surface is covered with sclera - a dense connective membrane. It performs supporting and protective functions. In the front 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 refracting light rays. It is precisely this optical medium whose properties determine visual acuity. The optical power of the cornea is 44 diopters.

Normally, the cornea is 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 is highly sensitive.

Structure of the cornea

The average dimensions of the cornea are: 11.5 mm vertically, 12 mm horizontally. The thickness of the corneal layer varies from 500 microns in the center to 1 mm at the periphery. The structure of the cornea is divided into five layers: anterior epithelium, Bowman's membrane, stroma, Descemet's membrane, endothelium.

Front epithelial layer is a shell that is characterized by rapid 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's shell(membrane) is an acellular layer that, when damaged, forms scars.

Stroma The cornea consists of collagen fibers oriented in a certain way. This layer occupies 90% of the entire thickness of the cornea. Its intercellular space is filled with chondroitin sulfate and keratan sulfate.

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

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

Innervation of the cornea occurs at the endings of the first branch of the trigeminal nerve.

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

Corneal reflex and protective functions of the cornea

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

Extreme sensitivity provides reliable protection not only for the deeper structures of the eye, but also for the cornea itself. The slightest irritation, fear, or a particle flashing before the eye causes an unconditioned reflex - blinking, combined with lacrimation. Thus, the cornea protects itself from damage, bright light and other unwanted influences. When you blink, the eye rolls up under the eyelid and tears are released, 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

• Deviation of the bend of the cornea towards greater steepness is characteristic of myopia.
• With farsightedness, the cornea has a more flattened shape than it normally does.
• Astigmatism is characterized by irregularities in the shape of the cornea in various planes.
• Megalocornea and microcornea are congenital abnormalities of 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 erode due to improper selection of contact lenses, with dry eye syndrome, lagophthalmos, vernal catarrh, keratitis, and also as a reaction to certain eye drops.
• Edema of the epithelium may be a consequence of a sharp jump in intraocular pressure or indicate damage to the endothelial layer.
• Punctate epithelial keratitis may accompany viral ophthalmic diseases. Upon examination, swollen granular epithelial cells are detected.
• Threads are mucous formations in the shape 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.

Damage to the corneal stroma

• Formation of infiltrates. Infiltrates result from active inflammation and are the areas of the cornea involved in this process. They can form from mechanical damage (for example, when wearing lenses) or have an infectious origin.
• Stromal edema. With the development of stromal edema, 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 past inflammatory diseases.

Damage to Descemet's membrane

• Tears may result from corneal trauma or occur as a complication of keratoconus.
• Folds most often form as a result of surgical trauma.

Cornea diagnostic methods

The cornea is studied to identify possible damage to its layers, as well as to evaluate its curvature as a possible cause of decreased visual acuity. The following ophthalmological examinations are carried out:

• Biomicroscopy of the cornea. Standard examination of the cornea under a microscope with illumination. This diagnosis makes it possible to identify most diseases, as well as injuries and changes in the curvature of the cornea.
• Pachymetry allows you to measure the thickness of the cornea. This test is performed using ultrasound.
• Mirror microscopy is the study of the endothelial layer using photography. In this case, the shape of the cells is analyzed and their number per 1 square meter is calculated. mm area. The normal density is considered to be 3000 cells per 1 square meter. mm.
• Keratometry measures the curvature of the anterior surface of the cornea.
• Corneal topography is a complete computer examination of the entire area of ​​the cornea. Allows point-by-point analysis of the cornea by thickness, curvature and refractive power.
• Microbiological studies are aimed at studying the microflora of the corneal surface. The material for this study is taken under local drip anesthesia.
• A corneal biopsy is advisable if the results of scrapings and cultures are inconclusive or uninformative.

Basic principles of treatment of corneal diseases

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

Corneal cataracts and opacities are treated using penetrating or layered keratoplasty.

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

Local glucocorticoids help suppress inflammatory processes and prevent scar formation (Dexamethasone and its derivatives).

For superficial injuries of the cornea, agents are widely used that accelerate the regeneration of epithelial tissue (Korneregel, Taufon, Solcoseryl, Balarpan, etc.).

For a number of diseases accompanied by dry cornea, eye hydration with tear-replacement drops (Systane, Hilo-Komod and others) is indicated.

For keratoconus, hard contact lenses, collagen cross-linking and implantation of infrastromal segments (rings) can be used. In more severe cases, penetrating keratoplasty (cornea transplant) is used.

One of the most important human organs is the eyes. Thanks to them, we receive information about the outside world. The structure of the eyeball is quite complex. This organ has its own characteristics. We'll talk about which ones next. We will also dwell in more detail on the structure of the eye as a whole and one of its components - the cornea - in particular. Let's discuss the role of the cornea in the functioning of the organ of vision and whether there is a relationship between its structure and the functions performed by this element of the eye.

Human organ of vision

A person with the help of his eyes has the ability to receive a large amount of information. It is very difficult for those who for some reason have lost their sight. Life loses its colors, a person can no longer contemplate beauty.

In addition, performing daily activities also becomes difficult. A person becomes limited, he cannot live fully. Therefore, people who have lost their sight are classified as a disability group.

Functions of the eye

The eye performs the following functions:

Distinguishing the brightness and color of objects, their shape and size. Observing the movement of objects. Determining the distance to objects.

Thus, the eyes, along with other human organs, help him live fully, without experiencing the need for outside help. If vision is lost, a person becomes helpless.

The eye apparatus is an optical system that helps a person perceive the world around him, process information with high accuracy, and also transmit it. A similar goal is fulfilled by all components of the eye, the work of which is coordinated and harmonious.

Light rays are reflected from objects and then touch the cornea of ​​the eye, which is an optical lens. As a result of this, the rays are collected at one point. After all, the main functions of the cornea are refractive and protective.

The light then passes through the iris to the pupil of the eye and then to the retina. The result is a finished image in an upside-down position.

Structure of the eye

The human eye consists of four parts:

The peripheral, or perceptive part, which includes the eyeball, eye apparatus. Conducting pathways. Subcortical centers. Higher visual centers.

The oculomotor muscles are divided into oblique and rectus muscles of the eye, in addition, there is also the circular muscle and the one that raises the eyelid. The functions of the extraocular muscles are obvious:

Rotating the eyes. Raising and lowering the upper eyelid. Squeezing the eyelids.

If all eye devices are working correctly, then the eye functions normally - it is protected from damage and harmful environmental influences. This helps a person to visually perceive reality and live a full life.

Eyeball

The eyeball is a spherical body located in the eye socket. The eye sockets are located on the facial surface of the skeleton; their main function is to protect the eyeball from external influences.

The eyeball has three membranes: outer, middle and inner.

The first is also called fibrous. It consists of two departments:

The cornea is the transparent anterior section. The functions of the cornea of ​​the eye are extremely important. The sclera is the opaque posterior part.

The sclera and cornea are elastic, giving the eye its specific shape.

The sclera is about 1.1 mm thick and is covered by a thin transparent mucous membrane - the conjunctiva.

Cornea of ​​the eye

The cornea is the transparent part of the outer shell. The limbus is where the iris meets the sclera. The thickness of the cornea corresponds to 0.9 mm. The cornea is transparent, its structure is unique. This is explained by the arrangement of cells in a strict optical order, and there are no blood vessels in the cornea.

The shape of the cornea resembles a convex-concave lens. It is often compared to glass for watches that have an opaque frame. The sensitivity of the cornea is due to a large number of nerve endings. It has the ability to transmit and refract light rays. Its refractive power is enormous.

When a child turns ten years old, the parameters of the cornea are equal to those of an adult. These include shape, size and optical power. But when a person becomes elderly, an opaque arch forms on the cornea, which is called senile. The reason for this is salts and lipids.

What function does the cornea perform? More on this later.

The structure of the cornea and its functions

The cornea has five layers, each with its own functionality. The layers are as follows:

stroma; epithelium, which is divided into anterior and posterior; Bowman's membrane; Descemet's membrane; endothelium.

The stroma has the thickest layer. It is filled with the thinnest plates, the fibers of which are collagen. The arrangement of the plates is parallel to the cornea and to each other, but the direction of the fibers in each plate is different. Thanks to this, the strong cornea of ​​the eye performs the function of protecting the eye from damage. If you try to pierce the cornea with a scalpel that is poorly sharpened, it will be quite difficult to do so.

The epithelial layer has the ability to self-heal. Its cells regenerate, and not even a scar remains at the site of damage. Moreover, recovery occurs very quickly - in one day. The anterior and posterior epithelium are responsible for the fluid content in the stroma. If the integrity of the anterior and posterior epithelium is compromised, the cornea may lose its transparency due to hydration.

The stroma has a special layer - Bowman's membrane, which has no cells, and if it is damaged, scars will certainly remain.

Descemet's membrane is located next to the endothelium. It also consists of collagen fibers and prevents the spread of pathogenic microorganisms.

The endothelium is a single cell layer that nourishes and supports the cornea, preventing it from swelling. It is not a regenerating layer. The older the person, the thinner the endothelial layer.

The trigeminal nerve supplies the cornea with innervation. The vascular network, nerves, moisture of the anterior chamber, tear film - all this provides its nutrition.

Functions of the human cornea

The cornea is strong and highly sensitive, so it performs a protective function - it protects the eyes from damage. The cornea is transparent and has a convex-concave shape, so it conducts and refracts light. The epithelium is a protective layer, thanks to which the cornea performs a function similar to the protective one - it prevents infection getting inside. Such a nuisance can only occur due to mechanical damage. But even after this, the anterior epithelium will quickly recover (within 24 hours).

Harmful factors affecting the cornea

The eyes are regularly exposed to the following harmful effects:

contact with mechanical particles suspended in the air; chemicals; air movement; temperature changes.

When foreign particles enter the eye, a person’s eyelids close according to an unconditional reflex, tears flow intensely and a reaction to light is observed. Tears help flush foreign agents from the surface of the eye. As a result, the protective functions of the cornea are fully demonstrated. No serious damage to the shell occurs.

The same protective reaction is observed during chemical exposure, strong wind, bright sun, cold and heat.

Eye diseases

There are a large number of eye diseases. Let's list some of them:

Presbyopia is an age-related form of farsightedness in which the elasticity of the lens is lost and the zonules that hold it in place weaken. A person can only see objects at a far distance clearly. This deviation from the norm manifests itself with age. Astigmatism is a disease in which light rays are refracted unequally in different directions. Myopia (myopia) - rays intersect in front of the retina. Farsightedness (hypermetropia) - rays intersect behind the retina. Protanopia, or color blindness - when With this disease, a person has almost no ability to see all shades of red. Deuteranopia - green color and all its shades are not perceived. The anomaly is congenital. Tritanopia - with this refractive error of the eye, a person is unable to see all shades of blue.

If any disturbances in the functioning of the visual organs occur, you must contact a specialist - an ophthalmologist. The doctor will conduct all the necessary tests and make a diagnosis based on the results obtained. After which you can begin treatment. As a rule, most diseases associated with disruption of the eyeball can be corrected. The only exceptions are congenital anomalies.

Science does not stand still, so now the functions of the human cornea can be restored surgically. The operation is quick and painless, but thanks to this you can get rid of the forced need to wear glasses.

The transparent, avascular layer of the eyeball is called the cornea. It is a continuation of the sclera and looks like a convex-concave lens.

Structural features

It is noteworthy that in all people the cornea of ​​the eye has approximately the same diameter. It is 10 mm, permissible deviations do not exceed 0.56 mm. Moreover, it is not round, but slightly elongated in width - the horizontal size for everyone is 0.5-1 mm less than the vertical one.

The cornea of ​​the eye is characterized by high pain and tactile, but low temperature sensitivity. Consists of five layers:

The superficial part is represented by squamous epithelium, which is a continuation of the conjunctiva. If this layer is damaged, it is easily restored. Border anterior plate. This membrane is loosely attached to the epithelium, so it can easily be torn off at the slightest pathology. It does not regenerate, and when damaged it becomes cloudy. The substance of the cornea is stroma. The thickest part of the shell, consisting of 200 layers of plates containing collagen fibrils. Between them there is a connecting component - mucoprotein. The posterior border plate is called Descemet's membrane. This acellular layer is the basement membrane for the corneal endothelium. It is from this part that all cells are formed. The inner part of the cornea is called the endothelium. It is responsible for metabolic processes and protects the stroma from the action of moisture in the eye.

Functions of the cornea

To understand how dangerous diseases of this membrane of the eye are, you need to know why it is needed and what it is responsible for. First of all, the cornea of ​​the eye performs a protective and supporting function. This is possible due to the high strength and ability to quickly restore its outer layer. It also has high sensitivity. This is ensured by the rapid reaction of the fibers of the parasympathetic and sympathetic nerves to any irritation.

In addition to its protective function, it also provides light transmission and refraction in the eye. This is facilitated by its characteristic convex-concave shape and absolute transparency.

Corneal diseases

Knowing how necessary the protective shell of the eye is, people begin to more closely monitor the condition of their visual apparatus. But it is immediately worth noting that there are both acquired diseases and anomalies of its development. If we are talking about any congenital characteristics, then in most cases they do not require treatment.

Acquired diseases of the cornea, in turn, are divided into inflammatory and dystrophic. Treatment of the cornea of ​​the eye begins no earlier than an accurate diagnosis is established.

Developmental anomalies that do not require treatment

Some people have a genetic predisposition to changes in the shape and size of the cornea. The increase in the diameter of this membrane is called megalocornea. Moreover, its size exceeds 11 mm. But such an anomaly can not only be congenital - sometimes it appears as a result of uncompensated glaucoma, which developed at a fairly young age.

Microcornea is a condition in which the size of a person's cornea does not exceed 9 mm. Moreover, in most cases it is accompanied by a decrease in the size of the eyeball. This pathology can become acquired as a result of subatrophy of the eyeball, while the cornea of ​​the eye becomes opaque.

Also this outer shell may be flat. At the same time, its refraction is significantly reduced. People with such problems are predisposed to increased intraocular pressure.

Some people have a condition similar to a condition called senile arcus. Doctors call this ring-shaped clouding of the cornea of ​​the eye embryotoxon.

Developmental anomalies subject to correction

One of the structural features of the cornea is its conical shape. This pathology is considered genetic and is called keratoconus. In this condition, the center of the cornea is pulled forward. The reason is the underdevelopment of the mesenchymal tissue that forms this shell. This damage to the cornea of ​​the eye does not appear from birth - it develops by 10-18 years. The only way to get rid of the problem is through surgery.

In childhood, another pathology of eye development also appears - keratoglobus. This is the name given to the spherical cornea of ​​the eye. In this case, it is not the central part of the shell that is stretched, but its peripheral parts. Acute corneal edema is also called dropsy of the eye. In this case, surgery is often recommended.

Inflammatory diseases

With many corneal problems, people complain of photophobia, blepharospasm, characterized by involuntary blinking, and a foreign body sensation under the eyelids. For example, erosion of the cornea of ​​the eye is accompanied by pain that can spread to the half of the head in which the damaged eye is located. After all, any damage to the integrity of the epithelium will be felt as a foreign body. All inflammatory diseases are called keratitis. The main symptoms of their appearance include redness of the eye, changes in the properties of the cornea, and even the ingrowth of newly formed vessels.

Classification of keratitis

Depending on the causes of the problems, there are several types of inflammatory processes that cause damage to the cornea of ​​the eye. Treatment will depend solely on what exactly caused the inflammation.

Exogenous factors include fungal infections such as actinomycosis and aspergillosis, bacterial diseases of the eye appendages, and a number of viral problems.

Endogenous causes of the development of keratitis include neurogenic, vitamin deficiency and hypovitaminosis problems. They are also caused by specific infections: syphilis, brucellosis, tuberculosis, malaria and others. But there are also atypical causes: filamentous keratitis, recurrent erosion, rosacea keratitis.

Stages of keratitis

The first sign of the onset of the inflammatory process is the appearance of infiltrates. The normally transparent and smooth shell becomes rough and cloudy. At the same time, its sensitivity decreases. Within a few days, vessels grow into the resulting infiltrate.

At the second stage, erosion of the cornea of ​​the eye begins, and tissue necrosis begins in the central part of the infiltrate. The emerging ulcer may be located only in the area of ​​the primary lesion, but there are situations when it can damage the entire protective shell in a few hours.

Having passed into the third stage, inflammation of the cornea of ​​the eye begins to regress. During the process, the ulcer is cleaned, its edges are smoothed, and the bottom is lined with white scar tissue.

Consequences of inflammatory processes

If the infiltrates and erosions formed during keratitis do not reach the so-called Bowman's membrane, then there will be no traces of damage. Deeper lesions leave marks. The result may be a cloud, a spot or a cataract. They are distinguished depending on the degree of damage.

The cloud is not visible to the naked eye - it is a grayish translucent cloudiness. It affects visual acuity only when it is located in the center of the cornea. The spots are visible during normal examination; they appear as white dense areas. When they form, vision noticeably deteriorates. A thorn, depending on its size, can cause partial blindness. This is a white, opaque scar.

Diagnosis of problems

In most cases, identifying keratitis is quite simple. In addition to the presence of obvious symptoms that indicate that inflammation of the cornea has begun, the doctor can see the lesion during a routine examination. But to determine the cause and prescribe adequate treatment, it is necessary to use special laboratory methods. The ophthalmologist must not only conduct an examination, but also check the sensitivity of the cornea.

The doctor must also determine whether the inflammation is caused by exogenous or endogenous factors. Further actions will depend on this.

Treatment of inflammatory processes

If the eye has been affected by superficial (exogenous) keratitis, then the patient needs emergency help. He is prescribed local antimicrobial agents: Levomycetin, Okatsin, Tsipromed, Kanamycin, Neomycin. During the period of resorption of the infiltrate, steroid drugs are prescribed. Immunocorrectors and vitamins are also prescribed. Drugs are recommended that are intended to stimulate the process of epithelization of the cornea. For these purposes, Etaden, Solcoseryl and other drugs are used. If keratitis was caused by bacterial causes, then even with timely and adequate treatment, clouding of the cornea may occur.

Reconstructive surgical treatment can be carried out no earlier than one year after the ulcers have healed.

Corneal damage

But often problems with the outer shell of the eyes arise not only due to infection, bacteria or fungi. The cause of the lesion is injury to the cornea of ​​the eye. It occurs due to foreign bodies getting under the eyelid, wounds and burns. It is worth noting that any traumatic injury can lead to the development of keratitis. This scenario cannot be excluded even if any speck or eyelash gets into the eye. It is better to immediately begin preventive antibacterial treatment to protect yourself from possible infection.

The most severe consequences are caused by a burn of the cornea of ​​the eye. Indeed, in almost 40% of cases it causes vision loss. Burns are divided into four degrees:

superficial damage; clouding of the cornea of ​​the eye; deep damage - the outer shell of the eye becomes like frosted glass; the cornea is severely damaged, it resembles porcelain.

Burns can be caused by exposure to chemicals, high temperatures, bright flashes of light, or a combination of these causes. In any case, it is necessary to see a specialist as soon as possible who can assess the damage to the cornea of ​​the eye. Treatment should only be prescribed by an ophthalmologist. In such cases, the eye must be washed and a bandage with an antiseptic applied to it. Actions should be aimed at restoring visual function and preventing the development of all kinds of complications, including keratitis.

Anatomy of the cornea of ​​the eye 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 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 entire area of ​​the outer capsule of the visual organ. It has a structure in the shape 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, 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.

The tear fluid, mixing with the secretion of the glands, moistens the epithelium in a thin layer, protecting it from drying out, and at the same time levels the optical surface. A characteristic 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 the vascular system located around the cornea. A thin network of capillaries extends into the corneal layers only 1 mm.

Pachymetry is a diagnostic procedure in which the thickness of the cornea is determined. This is an instrumental diagnostic method that allows you to determine the condition of the cornea, obtain basic data, which is important information for making certain diagnoses and planning certain eye treatments.

Why is pachymetry needed to measure corneal thickness in adults?

Pachymetry is necessary to make a diagnosis and also to determine the feasibility of certain surgical procedures in the cornea. This type of diagnostics is used mainly for:

• Assessing the stage of development of corneal edema if endothelial function is impaired;
• Assessing the degree of reduction in the thickness of the cornea with a diagnosis such as keratoconus;
• Obtaining data when planning keratotomy or Lasik;
• Monitoring the condition of the cornea after transplantation.

This procedure is most often performed in conjunction with biomicroscopy in order to obtain the maximum amount of information about the condition of the cornea. These data are of great importance not only for making a diagnosis, but also when planning surgical intervention.

Indications for this hardware study are:

• Keratoglobus;
• Keratoconus;
• Corneal edema. But why it appears, and what can be done about such a problem, is indicated in the article at the link;
• Fuchs' dystrophy.

Also, a diagnostic procedure must be carried out after a corneal transplant or before laser correction for refractive error.

Like any procedure, pachymetry has its own contraindications. They cannot be ignored and such data should be reported to the doctor before all manipulations are carried out.

But how corneal clouding of the eye is treated and how effective this or that remedy is, this will help you understand

This test is not performed if the patient has toxic effects from alcohol or drugs. Also, the procedure cannot be performed for mental illnesses that are accompanied by agitation and psychosis. The contact type of study is not carried out in case of impaired integrity of the cornea, as well as in case of infectious, purulent, inflammatory processes in the eye.

The video describes the procedure:

There are two types of this procedure – contact and non-contact. Non-contact is also called optical and is carried out through a slit lamp. But contact is done with the appropriate equipment, in particular ultrasound. Contact is done under local anesthesia.

How to do it

First of all, it is important for the patient to prepare for the procedure, whether it is a contact or non-contact examination. It is necessary to fulfill a number of conditions under which the diagnosis will be as correct and complete as possible, identifying all the correct data:

1. Stop using lenses two days before the test.
2. Women should stop using cosmetics two days before the procedure.
3. You should come to the hospital without makeup to avoid particles of makeup getting on the conjunctiva.
4. If you are allergic to anesthetics or specific substances, you must inform your doctor before the procedure.
5. You should also report if you have previously developed an allergy to antiseptic substances.

Optical pachymetry is a non-contact method for measuring corneal thickness. The process uses a slit lamp, which in this case serves as an analogue of a microscope. A special attachment is put on it, with the help of which the thickness of various parts of the area under study is measured. Sometimes a coherence tomograph is used instead of a slit lamp. The procedure is then called OCT or coherence pachymetry.

But what to do if there is a chemical burn to the cornea of ​​the eye, this will help you understand

The video shows how the procedure is carried out:

The doctor places the patient on one side of the lamp so that the chin is on a special stand. The doctor stands on the other side and examines the eye. The measurement is carried out by rotating the pachymeter handle, during which one of the lenses in the attachment rotates along the vertical axis. I direct a beam of light to the desired area, and the doctor takes measurements on a special scale.

Optical pachymetry is considered not as accurate as ultrasound, and therefore, if possible, it is better to decide on a contact diagnostic method.

It will also be useful to learn about what treatments exist and what are the most effective.

If we talk about ultrasonic pachymetry, the measurements obtained by this method are considered to be as accurate as possible. The readings are correct down to 10 microns. Unlike the optical type of examination, this does not produce large errors and allows you to determine the necessary information as accurately as possible, which is very important especially in relation to preparation for surgery.

The patient lies down on a couch near the device. A local anesthetic is necessarily injected into the eye being examined - eye drops (Inocaine) are mainly used.

The nozzle of the device touches the cornea. The monitor automatically performs calculations and displays the finished result of the diagnostic procedure. upon completion of the examination, the patient is also instilled with antibiotics (Albucid, etc.). This approach helps prevent infection of the eye after contact with the nozzle of the ultrasound machine. But what inflammation of the cornea of ​​the eye looks like in the photo and what can be done about such a problem is indicated

It is very important that the ultrasound is performed by an experienced specialist. During the examination, do not squeeze the eyeball and the corneal layer. In addition to traumatization, this also leads to distorted research results. Correct decoding of the received data is also necessary. But what is corneal keratotopography and why is it performed?

How conclusions are drawn about what is normal in ophthalmology

The normal thickness of the cornea in ophthalmology in adults is considered to be a range of 0.49-0.56 mm for the central part. In the periphery, that is, near the limbus, the indicators accordingly increase to 0.7-0.9 mm.

Thickening is most often observed with corneal edema and glaucoma. Thinning of the cornea is observed in Fuchs' dystrophy and keratoconus.

Thickening is not a 100% guarantee of the onset of glaucoma. A more detailed examination is necessary to make an accurate diagnosis.

This study is especially relevant when planning laser correction for astigmatism. Using the data obtained, it is possible to determine the degree and volume of intervention in specific areas of the cornea. If a cornea transplant was performed, then this method allows you to determine how well the transplanted material has taken root.

In the process of determining indicators, it is worth taking into account the gender of the patient, since women have higher indicators than men - the thickness of the female cornea is 0.551 mm, and the male cornea is 0.542 mm. It is also worth knowing that the thickness of this section can change during the day, and significantly. Pathological processes are suspected only when the average norm is exceeded.

The patient can hardly draw conclusions on his own by studying these numbers. Only a specialist familiar with the standards and all the nuances can say for sure about the presence or absence of deviations in the data obtained. The methodology by which the figures were obtained is also taken into account. Therefore, you should not try to independently determine the pathology and type of treatment, but entrust this matter to specially prepared and trained specialists.

According to ophthalmologists, the thickness of the cornea plays an important role in determining the pathologies of the visual organs and choosing the optimal treatment tactics. If negative symptoms occur, it is recommended to examine the outer transparent membrane. Timely diagnosed abnormalities will help stop degenerative processes in the eyes and prevent complications.

What is the cornea?

When choosing a method for examining the cornea, it is recommended to give preference to the ultrasound contact technique, as it gives more accurate results. The risk of bias is minimal, but it is important to review additional contraindications.

The outer part of the eyeball, responsible for the refraction of artificial and natural light, is similar in shape to a lens. Ophthalmologists evaluate the condition of the cornea by thickness, diameter, radius of curvature and refractive power. To identify deviations, you need to contact an ophthalmologist. Intraocular pressure indicators depend on the thickness of the cornea. Disturbances in the cornea provoke serious pathologies that lead to the following negative symptoms:

If the thickness of the cornea is incorrect, double vision appears.

• blurred vision;
• complete or partial loss of visual abilities;
• doubling of objects;
• attacks accompanied by nausea and vomiting;
• loss of the eyeball;
• frequent headaches.

Normal thickness

The physical parameters of the cornea change throughout the day, but the thickness in a healthy person varies within 0.06 mm. Large deviations indicate the need for additional examination to identify the type of disease. In the absence of ophthalmological pathology, the following characteristics of the outer shell of the eye should be observed, presented in the table:

How do they check?

Preparatory stage

Before the procedure, it is advisable not to wear lenses for a couple of days.

In order for corneal pachymetry to proceed without complications and accurate results to be obtained, ophthalmologists focus on following the following rules:

• It is necessary to stop wearing optical and decorative lenses 2 days before the examination.
• When collecting anamnesis, it is imperative to report individual drug intolerance. The reaction to local anesthetics and anti-putrefactive agents is especially important.
• You must come to the procedure without any traces of makeup or medicinal cosmetics. Decorative eye cosmetics are completely excluded 2 days before the study.

Ultrasound pachymetry

The technique involves direct contact of the device with the mucous membranes of the eyes. The subject takes a horizontal position, and the local anesthetic drug Inocaine is instilled into the organ of vision. The ophthalmologist carefully moves the nozzle from the ultrasound machine along the cornea. It is important that the procedure is performed by an experienced doctor who applies minimal pressure to the outer part of the eye. Excessive pressure causes injury and poor results.

The data is automatically processed, calculated and displayed on the monitor. To prevent infection, after the examination the mucous membranes of the eyes are treated with antibiotics. The most effective medications include Tsipromed and Albucid. After instillation, it is recommended to close your eyes for 2-3 minutes. and gently massage the eyelids so that the antibacterial substance is evenly distributed throughout the mucous membranes.

The study is carried out by enlarging the cornea with a special device.

The examination takes place without direct contact with the eyes using a special apparatus, thanks to which the cornea is examined under multiple magnification. A nozzle made of 2 parallel pieces of glass, fixed to the slit lamp, makes it possible to measure the diameter of the cornea and its thickness. The subject sits on the side of the device and places his chin on the stand. In this case, the ophthalmologist is on the opposite side of the lamp to examine the cornea. To determine the parameters, the doctor, using a lever, rotates the upper lens and directs light to the lower one. Indicators are assessed using a measuring ruler.

In the absence of the necessary medical equipment or diagnosing contraindications for examination, you can examine the eyes with a coherent apparatus to obtain a tomogram.

1North-Western State Medical University named after. I.I. Mechnikov
2 International Medical Center "SOGAZ"

Relevance

Glaucoma ranks among the leading causes of irreversible blindness, low vision and primary disability in the world. The progress being made in the development of new methods of surgical and, especially, drug treatment of primary open-angle glaucoma (POAG) is obvious, but solving the problem of its early diagnosis still remains a difficult task. Increasing the efficiency of diagnostics, clinical observation of glaucoma patients, individualization of treatment tactics for each specific patient is an urgent problem of modern ophthalmology.

Target

To study the relationship between central corneal thickness and intraocular pressure levels among patients in a healthy population and in patients with POAG in order to improve early diagnosis and monitoring.

Material and methods

According to the data available today, there is no single value for the CTR; in various sources they range from 441 to 664 microns. 291 people were under observation. (509 eyes) aged from 18 to 83 years. Of these, 119 are men and 172 are women. For the study, 2 groups were formed: I - individuals from a healthy population - 100 people (200 eyes); II - patients diagnosed with POAG (duration of the disease from the moment of diagnosis is no more than 5 years) - 191 people. (309 eyes). The study group did not include patients with injuries to the organ of vision, contact lenses, diseases of the cornea, any eye (laser and surgical) operations, suffering from somatic diseases (bronchial asthma, diabetes mellitus, rheumatoid arthritis, etc.), who are taking hormonal medications. In addition to the standard research methods used in ophthalmology (visometry, perimetry, computer perimetry, biomicroophthalmoscopy, tonometry, tonography), all patients underwent CTR measurement. The IOP level was assessed according to Maklakov and Goldman. The thickness of the cornea was studied using an ultrasonic portable pachymeter from TOMAY according to the generally accepted method: after instillation of a local anesthetic (proparacaine hydrochloride - alcaine 0.5%), the thickness of the cornea was determined at 5 points - upper, lower, nasal, temporal and center. After measuring 3 times at each point, the average value was calculated. The pachymeter sensor was held perpendicularly with the patient in the “lying down and looking up” position.

Group I of healthy patients included 100 people. (200 eyes) aged 18 to 79 years. The average age was 41.4±18.1 years. Among them are 61 women and 39 men. Inclusion criteria for this group: 1) corrected visual acuity of at least 0.8; 2) refractive error no more than 3 diopters; 3) astigmatism no more than 1 diopter.

Group II consisted of 191 patients (309 eyes) with one or another stage of the glaucomatous process, but with normalized ophthalmotonus (P0<20 мм рт.ст.). Возраст исследуемых от 39 до 83 лет (80 мужчин и 111 женщин). Средний возраст - 56,7±12,1 лет.

Results and discussion

Taking into account the CTR indicators, all subjects were divided into 5 subgroups depending on the thickness of the cornea: 1)<500 мкм; 2) 501-550 мкм; 3) 551-600 мкм; 4) 601-650 мкм; 5) >651 microns.

The average value of the MD for the group of healthy patients (100 people - 200 eyes) was:

For the right eye (OD) - 532.2±41.0;

For the left eye (OS) - 533.1±41.5.

The average IOP value in this group: OD = 16.5±2.1 mmHg; OS = 17.2±1.9 mmHg. In order to get a more accurate picture of the condition of the cornea in the study, we determined the average thickness of the cornea in 4 quadrants in addition to the center and obtained the following Results: top - 581.43±36.72 microns; bottom - 569.07±33.46 µm; nasal - 579.38±34.24 µm; temporal - 574.77±35.98 µm. Based on the results of the study, high MDG indicators are determined in the upper quadrant, and the lowest MDG indicators are determined in the lower quadrant. This difference in indicators is not yet completely clear to us and requires additional research. Considering that IOP measurement is carried out in the central zone of the cornea, we analyzed the CTR data among different groups of patients.

The data obtained are presented in table. 1.

Analyzing the presented data in Table. 1, it can be seen that the greater the thickness of the cornea, the higher the IOP level. We also examined the dependence of the CTR on gender and age and noted that in age groups up to 40 years in women, a CTR value of >600 μm in the optical zone was determined in 10.71% of cases, and<500 мкм - в 5,37% случаев. В аналогичной выборке мужчин, соответственно, в 5,39% и 7,32% случаев. У категории обследованных в возрасте после 40 лет величины абсолютных значений ЦТР у здоровых мужчин были достоверно выше (p<0,002), чем у женщин. У мужчин ЦТР>600 µm was 2 times less common than in women, and vice versa. The data from our own research practically coincided with the data from similar studies conducted in Russia and abroad. According to the results of our studies, the majority of healthy individuals had a CTP in the range from 520 to 580 μm.

In group II of patients with POAG, 191 people (309 eyes) with various stages of the glaucomatous process were examined. Patients were divided into similar subgroups depending on the thickness of the cornea.

In subgroup I (MDT<500 мкм) обследован 51 чел. (87 глаз). Средняя величина истинного ВГД (P0) = 17,7±1,52 мм рт.ст. Среднее значение ЦТР = 487,2±13,6 мкм.

Stage I - 18 eyes (20.69%); Stage II - 31 eyes (35.63%); Stage III - 34 eyes (39.08%); Stage IV - 4 eyes (4.59%).

In subgroup II (CTR 501-550 µm), 73 people were examined. (119 eyes). Average true IOP (P0) = 18.3±1.56 mmHg. Average value of CTR = 521.09±20.71 µm.

By stages of glaucoma:

Stage I - 39 eyes (32.77%); Stage II - 52 eyes (43.69%); Stage III - 21 eyes (17.65%); Stage IV - 7 eyes (5.88%).

In subgroup III (CTR 551-600 µm), 39 people were examined. (60 eyes). Average true IOP (P0) = 19.3±1.72 mmHg. Average CTR value = 578.63±15.41 µm.

According to the stages of glaucoma, the following was noted:

Stage I - 14 eyes (23.33%); Stage II - 25 eyes (41.66%); Stage III - 19 eyes (31.67%); Stage IV - 2 eyes (3.33%).

In subgroup IV (CTR 601-650 µm), 26 people were examined. (41 eyes). Average true IOP (P0) = 20.1±1.23 mmHg. Average CTR value = 629.21±17.8 µm.

Stage I glaucoma was recorded in 23 eyes (56.09%); Stage II - in 13 eyes (31.71%); Stage III - in 4 eyes (9.75%); Stage IV - in 1 eye (2.44%).

In subgroup V (CTR > 651 µm), 2 people were examined. (2 eyes). Average true IOP (P0) = 21.7±1.19 mmHg. Average CTR value = 653.1±19.3 µm.

The distribution of glaucoma stages was as follows:

Stage I glaucoma was observed in 2 eyes (100%).

A comparative analysis of IOP levels was carried out in healthy patients and patients with POAG (Fig. 1).

The relationship between the CTP and the stage of glaucoma is shown in Fig. 2.

CTR £510 µm CTR>580 µm

The results of the study are reflected in table. 2.

Conclusions

1. According to our study, the thickness of the cornea on average ranges from 510 to 580 microns.

2. A correlation was obtained between corneal thickness and IOP level in the control group. With a corneal thickness of less than 500 µm, the average IOP level was 15.0±2.23 mmHg, while with a corneal thickness of more than 650 µm - 21.1±3.72 mmHg.

3. Our study revealed a dependence of the course of the glaucomatous process on the thickness of the cornea in the group of patients with POAG. In patients with a corneal thickness of less than 500 µm, the incidence of advanced and terminal stages was much higher than in the group with large CTR values.

4. It is necessary to introduce measurement of corneal thickness into the practice of an ophthalmologist, which will greatly contribute to the early diagnosis of POAG and further monitoring of patients, especially from the group with glaucoma and suspicion of it.

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