What does the concept of "ametropia" include: all ophthalmic pathologies and their treatment. "Topographically oriented PRK" in the correction of secondary ametropia What is eye ametropia

Ametropia is a violation of the refraction of the eyeball, in which the refracted light rays are focused not on the retina (as it should be in the norm), but behind or in front of it. As a result, a person sees the world around him fuzzy and blurry. This is a common ophthalmic pathology.

Forms of ametropia

Causes and risk factors

The disease can be either congenital or acquired. The causes of congenital ametropia are presumably adverse factors affecting the fetus during fetal development. These include:

• viral diseases of a pregnant woman (flu, chicken pox);
• ionizing radiation;
• smoking, drinking alcohol or drugs during pregnancy;
• bad ecology.

The main manifestations of ametropia are a decrease in visual acuity, a deterioration in its quality and clarity.

The causes of acquired ametropia can be traumatic damage to the structures of the eye, inflammatory processes. But most often, acquired ametropia develops due to age-related changes in eye tissues or as a result of prolonged and frequent overstrain of vision.

Forms of the disease

There are four forms of ametropia:

1. Myopia (nearsightedness). Difficulties arise when viewing distant objects, which is associated with the focusing of light rays not in the retina, but in front of it. Myopia is quite widespread among children and adolescents, which is associated with their violation of the rules of visual hygiene.
2. Hypermetropia (farsightedness). The plane of focus is located behind the retina, as a result, closely spaced objects are not clearly perceived.
3. Astigmatism. Light rays traveling along different meridians are refracted with different strengths, which is why all objects are perceived fuzzy and with deformed contours.
4. Presbyopia (age-related farsightedness). Occurs in people over 40 years of age. It is associated with an age-related decrease in the elasticity of the lens, which is why it does not change the curvature to the required extent. As a result, visual acuity decreases, and this process progresses.

Stages of the disease

Depending on the number of diopters by which it is necessary to reduce or increase the refractive power of the eyeball in order to achieve the correct focusing of the refracted light rays, myopia and hypermetropia are divided into several degrees:

• weak - up to 3 diopters;
• medium - up to 6 diopters;
• strong - over 6 diopters.

To prevent the development or progression of ametropia, attention must be paid to visual hygiene.

The degrees of astigmatism are determined by other values:

• weak - up to 2 diopters;
• medium - up to 4 diopters;
• strong - over 4 diopters.

Symptoms

The main manifestations of ametropia are a decrease in visual acuity, a deterioration in its quality and clarity. It is these symptoms that make patients seek medical help.

Diagnostics

To determine the degree of ametropia are used:

• skiascopy;
• refractometry;
• subjective measurement of ametropia.

Also, if necessary, a number of auxiliary techniques are used.

Treatment

Treatment of ametropia is aimed at restoring the correct refraction of the eyeball. The most common way to correct vision is the selection of glasses or contact lenses, but surgical treatment is also used:

• implantation of intraocular lenses;
• installation of an artificial lens;
• conductive keratoplasty;
• keratotomy.

Modern methods of correction make it possible to normalize visual dysfunctions caused by ametropia.

Possible complications and consequences

In the absence of correction, ametropia can lead to the development of the following complications:

• amblyopia;
• strabismus;
• conjunctivitis;
• retinal dystrophy;
• retinal disinsertion.

Forecast

The prognosis for ametropia is generally favorable. Modern methods of correction make it possible to normalize the existing violations of visual function.

Prevention

To prevent the development or progression of ametropia, attention must be paid to visual hygiene. This concept includes:

• the correct mode of illumination of the workplace;
• inadmissibility of excessive visual loads;
• performing gymnastics for the eyes;
• regular examinations by an ophthalmologist;
• correction of existing visual impairments;
• training of the eye muscles responsible for the process of accommodation.

To maintain vision, it is important to lead a correct lifestyle, play sports, eat a balanced diet and give up bad habits.

Video from YouTube on the topic of the article:

1-11-2012, 19:40

Description

emmetropic eye

Gulstrand in his scheme of eye optics attributed to each of its parameters the average of the measured or otherwise found values ​​of this parameter for real human eyes.

The parameters of the eyes of each person can be very different from those indicated in the diagram. For example, the length of the eye can be more or less than 24 mm. However, this difference does not necessarily lead to visual impairment. A longer eye may have less optical power, and a shorter one more. As a result, a clear image of distant objects can in all cases be obtained on the retina and ensure their good visibility. In these cases, the changes in parameters compensate each other, the eye remains proportionate or, to use the accepted term, emmetropic.

Glasses allow for vision correction, i.e. correct ametropia. Let us put a diverging lens (negative) in front of the myop's eye, such that its focus coincides with point R in Fig. 10. The lens will make parallel rays coming from a distant object diverge, and exactly as if they come from point R. Therefore, the rays will gather on the retina and the myope will clearly see the distant object. If the lens is located close to the eye, then its focal length f? lr and, therefore, the refraction of the lens is equal to ametropia. Thus, determining the ametropia of the eye, thereby determining the strength of the corrective lens. If the eye is hyperopic, the focus of the corrective lens should be aligned with the hyperopic R point. Since lR is positive for it, the lens must also be positive (collective) and its optical power must be equal to the ametropia of the eye. Of course, the spectacle lens is some, albeit a small, distance from the eye. Therefore, strictly speaking, there must be some difference between ametropia and the optical power of the lens that corrects it. But it has to be taken into account only with strong ametropias, when the segment lr is small.

The standard distance of the lens from the eye is 12 mm. All spectacle corrective lenses are designed for this distance. If for some reason the lens needs to be placed at a different distance from the eye, its optical power should be calculated separately. Such recalculations have been carried out, and there are tables that indicate the ametropia of the eye and the corresponding optical powers of corrective lenses, depending on their distances from the eye.

However, there are often eyes that cannot be corrected with conventional lenses with spherical surfaces. We have already mentioned astigmatism oblique beams. But quite often the optical system of the eye and on the axis does not give a point image either on the retina, or in front of it, or behind it. This deficiency of the eye is called astigmatism: ametropia of the astigmatic eye in different meridians is different. In this case, two meridians are found with the smallest (sometimes equal to zero) and the largest ametropia. Correcting astigmatism is necessary with a lens that is also astigmatic, for example, one in which one surface is spherical and the other cylindrical.

Of significant importance lens shape. Now the use of biconvex or biconcave lenses has been abandoned, although they give a fairly good image on their axis. But it is taken into account that the eye is very mobile, and when it looks not through the central part of the lens, strong aberrations appear, mainly astigmatism of oblique beams. The outlines of objects are blurred, and in order to see them clearly, the owner of the glasses has to turn his head instead of turning his eyes. Now mainly used meniscus lenses: convex-concave and concave-convex. Their shape, determined by complex calculations, largely corrects the astigmatism of oblique beams and expands the field of view. To correct astigmatism, lenses with toric surfaces are usually used, that is, surfaces with two different radii of curvature in two mutually perpendicular planes. Complicated calculations have been carried out for lenses of various refractions, and forms have been found that reduce aberrational distortions to a minimum. A person with glasses sees well both directly in front of him and to the sides, if only the glasses are correctly appointed and made.

Measurement of ametropia

For the appointment of glasses, that is, mainly for determining ametropia and astigmatism, there are several methods. Let's name the most common of them:

• subjective definition of ametropia;
• measurement with an eye refractometer;
• skiascopy.

First method called subjective because the physician has to rely on the patient's feelings and responses. The patient is seated at a distance of five meters from the well-lit table of Golovin-Sivtsov test tests (Fig. 11).

Rice. eleven. Table Golovin - Sivtsov

The table is divided into two halves: letters are printed on one side, and Landolt's ring on the other (Fig. 12).

Rice. 12. Landolt ring

Numbers from 0.1 to 2 are placed next to each line, indicating visual acuity. Landolt rings are the main test for determining visual acuity. If the gap size h is taken as one, then the thickness of the ring is also equal to one, the outer diameter is five, and the inner diameter is three. The doctor puts a trial frame on the patient and inserts a shield into it that covers one of the patient's eyes. The patient must tell the doctor on which line he still sees how the Landolt rings are turned: with a gap up, down, right or left. As a rule, the patient can also read the letters on the same line. Thus, the visual acuity of one eye is determined. Then the shield is rearranged and the other eye is examined. If the visual acuity of at least one eye is less than one, the doctor begins to insert lenses from a set of spectacle glasses into the frame in front of the eye. If none of the anastigmatic (spherical) lenses can bring visual acuity to unity, the doctor turns to astigmatic lenses. Here you have to not only put the lens, but also rotate it in the frame in the proper way. As a result, the doctor can write out a prescription that looks, for example, as in Fig. 13.

Rice. 13. prescription for glasses

In addition to the main optical power of the lenses (sphere), the optical power of the cylindrical part (cyl.) and the angle between the horizontal plane and the axis of the cylinder (axis) are indicated. The axes are also shown graphically.

It is very important that the patient receives not only the correct prescription, but also that its execution is accurate: the distance between the centers of the lenses corresponding to the interpupillary distance is observed, the axes of the cylinders are correctly rotated, the frame provides the necessary distance from the cornea to the glass. And of course, so that the optical powers of the lenses are the same as indicated in the prescription. The optical power of the lens is measured with a diopter, which, in addition, allows you to find and mark the center of the lens and the axis of the cylinder, if the lens is astigmatic.

The idea of ​​the eye refractometer device is that the doctor can see how sharply the test object is focused on the patient's retina. The scheme of the eye refractometer is shown in fig. 14.

Rice. 14. Diagram of an eye refractometer

Lamp And with the help of a condenser K illuminates a matte plate with a test figure applied on it - brand T. After two reflections from the faces of the prism P, the light rays enter the lens L. The prism P can approach the lens L or move away from it, and the position of the prism is marked by an arrow C on the W scale. The main position of the prism P (arrow C at zero) is such that the mark T is in the focal plane of the lens L and parallel beams of rays exit the lens from each point of the mark. Reflected from mirror 3, they fall into the examined eye of patient D and form an image on his retina. If the eye is emmetropic, parallel beams (without accommodation) gather on the retina and produce a sharp image of the mark. The doctor using a telescope (objective B, eyepiece R - F) sees the patient's retina and the image of the mark and, if it is clear, makes sure that the eye is emmetropic. If the image is blurred, the doctor shifts the P prism, making the rays from the T mark converge or diverge and achieve a sharp image of the mark on the retina. When this has been achieved, the doctor looks at the W scale, calibrated in diopters of the patient's ametropy. When the prism moves, the F lens moves, providing good focusing of the patient's retina for the doctor's eye.

It should be noted that the eye refractometer does not measure the refraction of the eye: only the ametropia of the eye is measured by the device, which, however, is of the greatest practical interest.

Skiascopy is another objective method that is extremely widely used by ophthalmologists when prescribing eyeglasses, since it requires fairly simple equipment. First of all, you need a mirror with a small hole or a translucent mirror.

We are used to the fact that the pupils of the eyes are always black. But we simply cannot look into the eye in the same direction as the light falls on it. An ophthalmic mirror allows you to do this. The doctor puts the lamp behind and somewhat to the side of the patient and, directing the light from the lamp - a bunny - into his pupil with a mirror, looks through the mirror at the same pupil. The doctor sees the pupil as a glowing reddish light reflected from the retina. Turning the mirror, the doctor leads the bunny over the patient's eye, due to which the illuminated spot moves along the retina. At the edge of the pupil, the doctor notices a shadow that moves as the mirror is turned and finally covers the entire pupil. has diagnostic value. shadow movement direction: whether it moves in the same direction as the bunny, or in the opposite direction. It all depends on whether the doctor's eye is closer or farther than the patient's further point. After all, if an object located at a further point focuses on the retina, then, therefore, the points of the retina are focused at a further point. At a further point, the rays that have passed through the pupil intersect, which explains the change in the direction of the shadow movement visible to the doctor. With some skill, the doctor quite accurately finds the position of the stop of the shadow (the pupil either shines all over, or the whole goes out) and, having measured the distance to the patient's eye, determines lR and, consequently, ametropia AR.

True, the further point can be located at a great distance from the eye (for the emmetrop, lR = -?) and even behind the eye. But any eye can be made nearsighted by placing a sufficiently strong positive lens in front of it. A skiascopic ruler with a set of lenses helps the doctor in his work. Usually the doctor places his eye at a fixed, familiar distance, for example, 80 cm, and brings a skiascopic ruler to the patient's eye, and, moving its slider, changes the lenses in it until he stops the shadow. The patient's ametropia is equal to the algebraic sum of the refraction of the lens and the reciprocal of the distance between the eyes of the doctor and the patient (at a distance of 80 cm, the addition is -1.25 diopters).

In the case of an astigmatic eye, skiascopy becomes more complicated, but there are methods for quite accurately determining both astigmatism and the main meridians using the skiascopic method.

Skiascopy and measurement with an eye refractometer are called objective methods in the sense that they do not require asking questions to the patient. But these methods also depend on the feelings and assessments of the doctor. Recently, devices have appeared in which ametropia and astigmatism are measured quite objectively, without the influence of the assessments of both the patient and the doctor. Several models of automatic ophthalmic refractometers have been created, such as, for example, the Bausch and Lomb ophthalmetron (USA) and the Coherent Radiation (USA) dioptron.

In automatic eye refractometers, the doctor's eye is replaced by a photocell and the brain is replaced by a computing device. After taking measurements, the device gives the result either in the form of a graph of the dependence of ametropia on the meridian, or immediately prints a prescription for a spectacle lens. However, such a recipe must be verified by subjective testing.

Glasses that correct ametropia are usually called distance glasses. However, vision correction with glasses does not always give good results. So, for example, sometimes due to injury or illness, the damaged cornea distorts the shape of the light wave so that an incorrect, blurry image of objects appears on the retina. This is where contact lenses can help.

Contact lenses

contact lens placed directly on the cornea of ​​the patient's eye. The surface of the lens that faces the eye corresponds to the shape of the cornea. The gap between the cornea and the lens is filled with tear fluid, due to which both surfaces in the optical sense almost cease to exist: light passes through them without refraction, reflection and scattering. The outer surface of the lens is shaped to correct eye ametropia. As a result, visual acuity is fully restored.

Contact lenses are essential with a large difference in ametropia of both eyes. After removal of the lens (removal of the cataract), the hypermetropia of the operated eye increases by 10-12 diopters. When correcting ametropia with spectacle lenses, clear images of the object are obtained on the retina of both eyes, but the scale of these images is different. The disparity of images in the eyes is called aniseikonia. If it is large, a person cannot merge two images into one image at all. With less aniseikonia, the images can be merged, but with a certain tension, which can cause fatigue, headache, etc. The contact lens is placed, although not in the place of the removed lens, but much closer to where it was. Therefore, replacing the lens with a contact lens introduces much less distortion throughout the eye system than a spectacle lens and, therefore, changes the image scale less.

Contact lenses are useful for workers in some professions for whom glasses are inconvenient, they are good in cosmetic terms. However, not everyone tolerates contact lenses well. Few people are able to wear them all day without a break.

The appointment of a contact lens requires an accurate determination of the shape of the cornea. The device has been around for a long time keratometer, which allows you to determine the radius of curvature of the cornea in any meridian. However, the keratometer gives only the average value of the radius, and it, as a rule, is different at different points of the cornea, even in the same meridian. In addition, local features of the shape of the cornea are often found. Therefore, for its study it was necessary to create special devices. In 1978, a domestic model of such a device appeared - photokeratometer.

The main part of the photokeratometer is a camera, the lens of which is surrounded by an annular flash lamp. On a spherical surface, the diameter of which coincides with the axis of the lens, a number of concentric reflective rings are fixed. When the lamp flashes, they are reflected in the cornea of ​​the patient's eye and an image of the rings is obtained in the photograph. If the cornea were exactly spherical, the photographic film would show a series of regular concentric circles, the distances between which would make it possible to determine the radius of the cornea. In reality, it is often not circles that are obtained, but more complex curves, the distances between which are different in different places. Measurement of a photograph and further calculations allow determining the shape of the cornea with the accuracy necessary for prescribing a contact lens.

Presbyopia

So far, we have only associated spectacles with ametropia. But the emmetrope, when he begins to approach fifty years, requires glasses. With age, the volume of accommodation inevitably and monotonously decreases. On fig. 15

Rice. 15. Dependence of accommodation volume APR and distance to the nearest point lP on age

the average dependence of the volume of accommodation on age is shown. The abscissa axis shows the age in years, along the ordinate axis on the left - the volume of accommodation in diopters, on the right - the distance to the nearest point for the emmetrop. The graph highlights the age at which an emmetrop should wear glasses for work. The reference book on ophthalmology provides a formula for the optical power of glasses that should be assigned to a person whose age in years is expressed by the number T, and whose ametropia is AR:

Glasses for work in prescriptions of doctors are called glasses for near. A significant loss of accommodation volume, leading to the need to work with glasses, is called presbyopia, that is, senile vision. The often used name "senile farsightedness" is incorrect, since there is no improvement in the visibility of distant objects in older people.

To measure the volume of accommodation, a special device has been created, mass-produced in the USSR - accomodometer. This is a portable desktop device. The test object is placed in the focal plane of a lens serving as a collimator. The patient looks with one eye (the other is closed with a shutter) and says which line of the test chart he distinguishes. Thus, its visual acuity for distant objects is determined (test object in the focal plane of the collimator). Then shifting the object to one side or the other from the focal plane, two positions are found in which visual acuity is close to maximum, i.e., the distances to the farthest and nearest points are determined. The difference between the reciprocals gives the volume of accommodation in diopters. Trial glasses, in particular astigmatic glasses, can be installed in front of the patient's eye, which allows glasses to be prescribed by the selection method. Thus, the accommodometer is used to quickly determine visual acuity, to measure ametropia and to prescribe glasses for both distance and near. Near glasses with an accommodometer are prescribed more reasonably than according to formula (25), which is based on statistical data and does not take into account the individual characteristics of the patient.

Article from the book: .

The human eye is designed in such a way that light rays passing through the lens, cornea and vitreous body are refracted and combined on the surface of the retina. And with the help of visual pathways, we see a clear image of the world around us.

However, there are many different pathologies of the organs of vision, up to malignant neoplasms. Among all diseases, the most common is ametropia. This concept means a violation of refraction (refractive power) of the eye.

In simple terms, in the ametropic eye, the image is focused either in front of or behind the retina, due to which a blurry spot is seen instead of a clear object. So, the main varieties of ametropia are and.

In a nearsighted eye, the reflected rays from a distant object converge in front of the retina, and then diverge. So, an object located far away is not visible, and an object located near at a certain distance is visible. Exactly the opposite happens in the far-sighted eye. This boundary distance at which good visibility is maintained is called the furthest point of the eye. The reciprocal distance from this point to the surface of the organ (in meters) is the value of ametropy - diopter.

Depending on the magnitude of the diopter, the severity of the disease is distinguished:

• weak (
• medium (3.25-6.0 diopters);
• strong (>6.0 diopters).

Another common type of ametropia is. In this case, the shape of the eye is not round, therefore, the image is curved. Ametropia is often combined with farsightedness or nearsightedness.

What are the causes of the development of the disease?

This pathology can be congenital or acquired during any period of life. The main cause of impaired visual acuity obtained at birth is unfavorable conditions for the normal development of the visual apparatus.

Acquired refractive changes may be associated with any trauma or inflammatory process. However, a common cause of visual impairment in adults is constant overstrain associated with the peculiarities of labor activity.

In particular, with myopia, the cause is an increase in the eyeball, with hyperopia - its reduction and weakening of the lens, with astigmatism - pathological changes in the cornea.

Forms of ametropia

There are the following forms of the disease:

1. Mixed - the values ​​​​of the optical axis and refractive power are outside the norm.
2. Combined - the indicators are normal, but their combination negatively affects refraction.
3. Refractive - normally only the length of the optical axis.
4. Axial - on the contrary, normally only the magnitude of the refractive power.

Treatment Methods

The most common way to improve vision is to wear glasses with specially selected lenses either. However, this implies their frequent or constant wearing, which is not always convenient. Therefore, other methods have been developed. These are ophthalmic surgeries that often use a laser. Subsequently, wearing glasses is no longer required.

Today, such operations are carried out as:

• keratotomy;
• conductive keratoplasty;
• replacement of the lens with a donor one;
• implantation of special intraocular lenses.

All such types of surgical intervention are paid and require high professionalism of doctors. Therefore, having decided on such a method of treatment, you should carefully select a clinic working in this area.

Can focus rays that are reflected from distant objects onto the retina. In the event that the rays from such objects are not located in the plane, then the eye is called ametropic, and this condition is called ametropia.

In the case when the focus is located in front of the retina, and in the very plane with the receptors the rays already diverge, we are talking about a long eyeball, characteristic of. The eye itself is called myopic. In this case, only an object that is located at a certain distance and no further can clearly focus on the retina. This point is called the further point of the eyeball. In this case, the distance from the anterior main point to the far point of the eye determines the degree of myopia. The smaller this distance, the more pronounced the degree. The reciprocal of this value is called ametropia. Due to the fact that the point R with myopia is located in front of the eyeball, the value of ametropia has a negative value.

If the axis of the eyeball is too short and there is no accommodation, the image from a distant object is focused behind the plane of the retina. As a result, on the retina itself, the image is represented not by a dot, but by a blurry spot. Remote point R for does not exist, it can only be obtained by using corrective lenses. As a result, ametropia for the far-sighted eye is positive. Such an eyeball is called hypermetropic, that is, farsighted.

With myopia, a person is not able to clearly recognize objects that are located further than his R point. The name of negative ametropia, myopia, is associated with this feature.

With farsightedness, the patient has difficulty perceiving both near and far objects. Even rays that are reflected from an infinitely distant point cannot focus properly on the retina. Rays from close objects are generally very blurred. Therefore, it cannot be said that a far-sighted patient has some kind of superpowers. In the event that the severity is not very high, then the patient can see a distant object, but at the same time he will be forced to resort to the help of accommodation.

Glasses for ametropia

To correct ametropia, it is customary to use the simplest method - glasses. To do this, it is necessary to select lenses in such a way that the focus from the image coincides with the plane of the retina. When the lens is close to the eyeball, its focal length coincides with the distance from the anterior eye point to the main point of the eyeball. That is, the lens coincides with the value of ametropia. Thus, in order to determine the required strength of the corrective lens, it is enough to set the value of the ametropia of the eyeball.

With farsightedness, the focus of the corrective device should be aligned with the R point of the eyeball. Due to the fact that ametropia is positive, then the lens should be the same, that is, collecting. The lens power value must match the ametropia value.

Due to the fact that the lens inserted into the frame is some distance away from the eyeball, there should be a slight corrective difference between its strength and the degree of ametropia. However, it makes sense to take into account this difference only in the case of a serious deviation from the norm of the refractive power of the eye.

Usually the distance from the corrective lens to the surface of the eyeball is 12 mm. This distance is standard, therefore, when changing the parameter, it is necessary to calculate the optical power of the lens in a special way. To facilitate this task, special tables have already been developed, which, depending on the size of the ametropia of the eye and the distance of the lens from the surface, show the necessary optical power for correction.

In some cases, conventional spherical corrective lenses are not enough to correct ametropia. This is due to the presence of oblique beams in the patient. Often the optical system of the eyeball is generally unable to focus the rays at any point, regardless of its location. This condition is called astigmatism. This is due to the fact that in different meridians of the eyeball, the magnitude of ametropia is different. To correct this pathology, it is necessary to find two meridians that have the greatest and least ametropia, respectively. Next, a special astigmatic corrective lens is selected, which has surfaces of various shapes (spherical and cylindrical, for example).

The shape of the corrective lens itself is also of great importance. At present, biconcave or biconvex lenses are practically not used in ophthalmic practice, despite the fact that they give a good image along their axis. Modern doctors take into account the mobility of the eyeball, that is, the gaze is not always directed through the central part of the lens. As a result, serious aberrations may appear, the outlines of objects become fuzzy. In order to avoid such a situation, a person is forced to turn not only his eyes, but his entire head to the side.

Currently, meniscus lenses are more commonly used, which have a concave-convex or convex-concave shape. The lens surface itself is the result of a series of complex calculations that contribute to the expansion of the fields of view and the elimination of the phenomenon of oblique astigmatism.

Patients with astigmatism benefit from using toric lenses for vision correction. These lenses have two different radii in perpendicular meridians. Mathematical calculations are used to minimize aberrations. In such glasses, the patient normally sees both in front of him and to the sides. The main condition for the effectiveness of such glasses is the correct selection and manufacture.

It is important not only to get the correct ophthalmological examination and obtain the correct prescription, but also the fine manufacturing of custom-made lenses. In this case, it is necessary to observe the distance between the central points of the lenses (exactly corresponds to the interpupillary size), the correct arrangement of the cylinders. Not unimportant factor is the frame, which must have a given distance from the surface of the cornea to the lens. To measure the optical power of a corrective lens, a dioptriometer is used, which is also necessary to identify the central point of the lens, the axis of the cylinder.

At rest of accommodation, the emmetropic eyeball can focus rays that are reflected from distant objects onto the retina.

Measurement of ametropia

To correctly select corrective glasses, it is necessary to determine the degree of ametropia and astigmatism. To do this, several methods are used, among which the most common are:

• Subjective measurement of ametropia.

Contact lenses for ametropia

Ametropia can also be corrected with the help of those that are directly adjacent to the surface of the cornea. The surface of the lens, which is placed on the cornea, must correspond to the shape of the latter. Between the cornea and the lens, a small layer is formed, filled with tear fluid. As a result, light waves pass through both of these surfaces without being refracted, scattered or reflected. The outer surface of the contact lens changes depending on the form of ametropia. Through the use of corrective lenses, you can completely restore normal

Whatever the eye disease, it is imperative to devote time to it. After all, any complication is fraught with loss of vision. To avoid this, you should immediately consult a doctor at the first manifestations of any disease.

About the disease

The ratio between the focal length of the eye and the distance between the retina and the corneal coating is the clinical refraction. When it is in the "correct" stage, the focus is on the retina. In the eye, the length of the optical axis corresponds to physical refraction.

A change in this ratio is ametropia. It is of two types:

• Myopia. Physical refraction is essential: parallel rays are focused in front of the retina.
• Farsightedness. The refractive power of the eye is small to focus on the retina, so this point is behind it.

In any case, the picture of a point light source looks like a spot on the retina.

Causes

Why does ametropria occur? There are various reasons. With axial ametropia, the axis of the eye is either greater or less than normal. With refractive ametropia - weaker or stronger in comparison with the norm.

Newborns are usually farsighted. The growth of the eye contributes to the lengthening of its axis, resulting in the development of clinical refraction. If there is no congenital farsightedness, then with age you may encounter the development of myopia. Such a problem - the eye cannot focus objects that are far away on the retina. Thus, in order to better see the object, you need to bring it as close as possible.

Kinds

Ametropia can be of the following types:

• myopia of any degree;
• farsightedness of varying degrees;
• astigmatism of any degree;
• age-related farsightedness.

Myopia

Also called myopia. Focusing of the visible object occurs in front of the retina.

There are three degrees:

• more than -6D - strong;
• up to -6D - medium;
• up to -3D - weak.

As a rule, as a result of myopia, the eyeball enlarges.

The reasons may be such factors:

• Wrong nutrition. The body may simply lack some elements that play an important role in the development of scleral tissues.
• genetic predisposition. In the presence of myopia in parents, children in 50 percent of cases suffer from such an ailment. Statistics show that in healthy parents, children have such a diagnosis only in 8 percent.
• Eye strain. Constant work in front of the monitor or excessively long watching TV, poor lighting - all this puts a lot of strain on the organs of vision.
• Poor quality correction. If there was no timely treatment or errors occurred during its implementation, then significant deviations can be observed.
• Weakness of the muscles of the organs of vision. Basically, this is an innate feature.

Increasingly, myopia is observed in children, even younger ones. Moreover, this disease develops in them much faster than in adults.

For treatment, correction is used with contact lenses and glasses. In this case, there is no question of any elimination of the problem. These devices only improve the standard of living, but do not relieve myopia.

One of the methods can also be used:

• keratoplasty;
• lens replacement;
• introduction of lenses;
• radial keratotomy;
• laser correction.

farsightedness

Farsightedness is the opposite of nearsightedness. Three degrees are also distinguished here, but the cut does not occur at -6D and -3D, but at +5D and +2D, respectively.

In this case, the patient does not see objects nearby: the picture is focused behind the retina. The disorder has two causes: a weakening of the lens or a new shape of the eyeball.

At birth, most children have farsightedness, as they grow, the size of the eyeball increases, and muscles strengthen. The focus gradually shifts to the retina, which leads to the "alignment" of the child's vision.

If the child is more than seven years old, and farsightedness persists, it is necessary to solve this problem together with the doctor.

For the treatment of farsightedness in children, correction lenses, glasses are used. Any action must be agreed with the ophthalmologist.

Astigmatism

This is another kind of ametropia. It can be caused by refraction of the eye, which makes it difficult to focus the image on the retina. Similar to myopia and hyperopia, three degrees of the disease are distinguished, only the division occurs along + 4D and + 2D.

Astigmatism is not treated, but corrected. But for this, its timely detection is important. Otherwise, visual acuity may decrease sharply, even strabismus may occur. In children, astigmatism can be observed even in infants up to a year old. Cases of congenital forms are known.

It should be noted that a similar defect that causes astigmatism is observed in all people, but it is within the normal range - 0.5D.

With such a disease, the eyes turn red, watery. There may be a headache. In children, this problem can be identified by observing their behavior. With astigmatism, the child will squint to see the object.

Contact lenses and glasses are used for treatment. Laser correction may be applied.

Correction methods

Let's summarize how ametropia can be corrected. Based on the above recommendations for the correction of farsightedness, myopia and astigmatism, the following methods can be distinguished:

• contact correction;
• correction using glasses;
• surgical intervention.

Finally, we emphasize once again: self-medication is dangerous; at the first symptoms of ametropia, it is necessary to contact a qualified specialist. Only timely appeal guarantees stabilization of the situation.