Types of clinical refraction of the eye. What is eye refraction

The eye is one of the most difficult organized bodies human body. In essence, it is a natural lens with basic optical characteristics. One of these is refraction, which refers to the process of refraction of light when passing from one medium to another.

Many factors of visual perception depend on this characteristic: from visual acuity to the focal length of the eye lens. In other words, the refraction of the eye is most important property eyeball, which depends on the state of the optical system of the eye.

Structure of the eye

The part of the eyeball responsible for the refractive process is called the refractive apparatus. It includes:

A ray of light, penetrating through the light refractive apparatus, falls on the retina. Photoreceptor cones on the retina capture this light, converting it into a stream nerve impulses, thanks to which human brain forms a picture.

The refraction of the eyeball is measured in diopters. The refractive power of the eye depends on the following parameters: the radius of curvature of the surface of the eye, the distance between the lens and the retina. Visual acuity is mainly influenced by clinical refraction. This is the location of the main focus, namely the location of the intersection of the lines of light passing through the lens in relation to the retina.

When the main focus is entirely on the retina, this indicates 100% vision. If it is in front of the retina, it indicates myopia, and when it lies behind, it means a disease such as myopia.

Types of refractions

Doctors divide the refractive power of the eye into 6 types. The first type includes emmetropia– standard level of refraction. In this case, rays of light refracted into eye lens, focus precisely on the retina. A person with emmetropia is able to easily distinguish surrounding objects that are both close to him and at a distance. Such vision is considered to be exemplary; when assessed according to the Golovin-Sivtsev table, it is awarded the highest 100% value.

The second type is myopia (colloquially called myopia). With this type of refraction, the main focus is concentrated in front of the retina, so people suffering from myopia see things nearby clearly, but things in the distance are blurry and illegible. Myopia is divided into 3 categories:

weak – with values up to 3 diopters;
moderate degree - ranging from 3 to 6 diopters;
high – from 6 diopters and above.

People suffering from myopia are recommended to use glasses for vision correction. If the degree of myopia is higher than mild, the recommendations turn into a necessity. With visual acuity of 3 diopters or more, recognizing surrounding objects turns into torture; a person is forced to constantly squint, and this further aggravates the disease.

The next type of refraction is hypermetropia. In this case, the lens directs focus behind the retina. With farsightedness, people see equally poorly both near and far. With hypermetropia, as with myopia, there are 3 degrees:

Interesting fact: all newborns are born with hypermetropia. This is explained by an underdeveloped lens and the small size of the eyeball. Such farsightedness is natural and, as the eye grows, disappears.

Presbyopia is a decrease in near visual acuity, an analogue of farsightedness. The only difference from ordinary hypermetropia is that presbyopia develops in older people. It arises due to age-related changes in the lens, so it loses its former flexibility, mobility and cannot regulate the level of its curvature. As a rule, many people over 40-45 years old have this disease.

Anisometropia is a rare disorder in which the eyes different levels refraction. For example, one eye is nearsighted, and the other is farsighted. Another situation may exist when both eyes have myopia or hypermetropia, but to different degrees. Let's say one eye is -2 diopters, and the other is -7 diopters. This case is also recognized as anisometropia.

Astigmatism is a specific disorder visual functions, in which the lens projects several foci onto the retina. Sometimes in the eye can be combined different degrees one refraction or even several (myopia and farsightedness). This astigmatism is called mixed. Without correction with glasses it is quite difficult to lead a normal life.

Main factors of refractive error

Science still does not know what exact reasons influence the development of certain refractive errors in humans. However, there are known factors whose presence is directly related to disruption of the optical system of the eye. These include:

Methods for diagnosing refractive errors

Visometry is the easiest way to find out clinical refraction. It consists of testing the eye using special tables with letters written on them. A person with perfect vision can see row 10 of this table from a distance of 5 meters.

Automatic refractometry is an examination using a specialized medical device - an automatic refractometer. The essence is as follows: the patient places his head in a special recess of the device, fixing his chin motionless, and the refractometer, sending beams of light into the eyes, measures the degree of refraction.

Cycloplegia is artificial myopia. The patient is injected with a special solution that allows the accommodative muscle to be temporarily disabled. This muscle is responsible for the ability to distinguish objects equally well both near and far. On a short time a person develops false myopia after stopping the effect of the medication healthy person such myopia disappears, and if residual signs are detected, this indicates the presence of real myopia.

Ophthalmometry is a method of measuring clinical refraction by determining the radius of curvature of the cornea and the refractive power of the eye lens.

Ultrasound scanning or ultrasound biometry is an examination of the eye using ultrasound. This study allows you to determine the condition of the anterior eye chamber and lens.

Pachymetry – ultrasound clinical examination cornea of the eye, its thickness and shape. The use of this method helps to find corneal diseases, and is also an auxiliary procedure when planning corneal surgery.

Biomicroscopy is a method of diagnosing eye diseases using a device that is a microscope connected to a lighting lamp. This device allows you to identify many diseases: conjunctivitis, inflammation of the iris, swelling, eye abnormalities, cataracts and glaucoma.

Ophthalmoscopy is a method of examining the fundus of the eyeball using an ophthalmoscope. This device allows you to examine the bottom of the retina, disc optic nerve, as well as fundus capillaries. Thanks to this method already at an early stage it is possible to detect a pathology such as retinal detachment and take the necessary measures.

Study of the ocular cornea using computer keratotopography - an examination method using laser beam. A keratotopograph scans the cornea, the device sends all the data to a computer, where a color image is formed on the monitor with problem areas marked.

Treatment

The treatment process comes down to vision correction (using glasses or lenses) or surgical intervention. Let's take a closer look.

Spectacle vision correction comes down to wearing glasses with specially selected lenses according to the type and degree of refraction. The wearing process can be either constant or periodic - it all depends on the nature of the visual acuity impairment.

Vision correction with contact lenses - the use of special soft hydrogel lenses. The order of wearing lenses can be as follows:

Surgical intervention - extreme degree treatment of eye refraction. It comes down to laser correction of the organ of vision. During this operation, the thickness of the cornea (the outer front shell of the eyeball) is changed, as a result the degree of refraction of light by the eye changes.

Prevention measures

To reduce the risk of refractive errors, you must adhere to the following recommendations:

Always use high-quality lighting, read and watch TV in good source Sveta.
Give your eyes regular rest, and if they become overtired (increased lacrimation, redness), blink, look into the distance, close your eyelids and rest for 10-15 minutes.
Use eye gymnastics – special complex exercises designed to strengthen the ligaments and muscles of the eye. It is advisable to do such gymnastics 2-3 times a day.
Timely and complete vision correction - you should wear only glasses that correspond to your degree of refraction.
Average physical exercise– jogging, walking, skiing, cycling. Avoid weightlifting, bodybuilding, and combat sports.
Balance your diet, it should include sufficient quantities be present essential microelements, vitamins and nutrients.

The human eye is a complex natural lens. All characteristics that determine the properties of other optical systems are applicable to this lens.

One of these characteristics is refraction, on which visual acuity and the clarity of the image received in the eyes depend.

In other words, refraction is the process of refraction of light rays, which is expressed by the etymology of the word (refractio - “refraction” from Latin).

Refraction refers to the manner and degree to which the direction of rays passing through an optical system changes.

Acquaintance

The unified eye system consists of four subsystems: two sides of the lens and two sides of the cornea. Each of them has its own refraction; in their totality they form general level refraction of the organ of vision.

Refraction also depends on the length of the axis of the eye; this characteristic determines whether the rays on the retina will converge at a given refractive power, or whether the axial distance is too large or small for this.

IN medical practice There are two approaches to measuring refraction: physical and clinical. The first method evaluates the system of the cornea and lens on its own, without its connection with other biological subsystems of the eye.

Here, the characteristics of the eyes are assessed by analogy with all other types of physical lenses, without taking into account the specifics human vision. Physical refraction is measured in diopters.

Diopter is a unit of measurement optical power lenses. This value is the inverse of the focal length of the lens (F) - the distance at which the rays refracted by it converge at one point.

This means that with a focal length of one meter the refractive power will be equal to one diopter, and a focal length of 0.1 meters (10 cm) corresponds to a refractive power of 10 diopters (1/0.1).

Average degree healthy refraction human eye is 60 diopters (F=17 mm).

But this characteristic alone is not enough for a full diagnosis of visual acuity. At optimal refractive power eye lens the person may still not see a clear image. This is due to the fact that the structure of the eye plays a big role here.

If it is incorrect, then light rays will not reach the retina even at normal focal length. Because of this, ophthalmology uses a complex parameter - clinical (statistical) refraction; it expresses the relationship of physical refraction with the length of the eye axis and with the location of the retina.

Kinds

Emmetropic

Emmetropic refraction is the refraction of rays in which the length of the axis of the eye and the focal length are equal, therefore, the light rays converge exactly on the retina, and information about a clear image is sent to the brain.

Dot clear vision(the distance from which rays can be focused on the retina) here tends to infinity, that is, a person can easily see distant objects; the possibility of obtaining an image is limited only by their size.

Emmetropia is considered an inherent characteristic healthy eye, measuring visual acuity according to the Sittsev table at such a refraction will give a result of 1.0.

It is easy for an emmetropic eye to view nearby objects by enhancing the refraction of the lens accommodation, but in old age there is a deterioration in close vision due to weakening of the ciliary muscles and loss of elasticity by the lens.

Ametropic

The opposite of emmetropia is ametropia. This common name for all deviations from the norm of statistical refraction. Ametropia is divided into

Such deviations may be caused irregular shape eyeball, impaired physical refraction, or both reasons at once.

Ametropia is measured in diopters, but here this value does not express the physical refraction of the eye itself, but the degree of refraction of the external lens necessary to bring visual acuity to normal.

If the refraction of light by the eye is excessive, then a weakening, diverging lens is needed that reduces the total number of diopters in the optical system, in this case the degree of ametropia is expressed negative number diopter. If refraction is insufficient, an intensifying lens is required, therefore, the number of diopters will be positive.

Myopia

Myopia or myopia is a refractive error in which the point of clear vision is at a close distance and becomes closer as the pathology progresses.

A person without glasses can only see nearby objects, and viewing more distant objects is possible only with very high voltage accommodation, on late stages it's useless too.

The most common reason is a violation of the shape of the eye, elongation of its central axis, due to which the focus of light rays does not reach the retina.

To correct myopia, diverging lenses are needed, so the degree of myopia is expressed as a negative number of diopters. The disease has three stages: weak (up to -3 diopters), moderate (from -3 to -6 diopters), severe (-6 diopters or more)

Hypermetropia

With hypermetropia (farsightedness), the refraction of the eye is too weak, the rays are refracted so that they are focused only behind the retina. This can be caused by too short axial length of the eye, insufficient curvature of the lens, as well as weakness of the muscles of accommodation.

The last reason most often causes senile farsightedness and is not directly related to refraction, since in this case the refractive power of the eye is calm state not broken.

Contrary to its name, farsightedness does not imply a distant location of the point of clear vision; moreover, it is generally imaginary, that is, absent.

The greater ease of viewing distant objects with hypermetropia is not associated with the optimal refraction of the rays emanating from them, but with the relative ease of their accommodation compared to the accommodation of light rays from nearby objects.

Since hypermetropia requires intensifying lenses, the severity of the disorder is expressed in positive diopter values. Stages of the disease: early (up to +3 diopters), moderate (from +3 to +8 diopters), severe (more than +8 diopters).

Astigmatism

Astigmatism is characterized different indicators refraction on the meridians of the eye, that is, a different degree of refraction in each part of the organ of vision. Various combinations are possible: myopia on some meridians and emmetropia on others, different stages myopia or farsightedness on each meridian and so on.

Manifestations of all forms of astigmatism are characteristic - the clarity of vision is impaired when viewing objects of any distance. The degree of pathology is determined by the difference in diopters of maximum and minimum refraction on the meridians.

Diagnostics

To diagnose refractive abilities, it is important to minimize accommodation, which can hide refractive errors in the early stages. This is especially true when diagnosing farsightedness.

The most reliable way to turn off accommodation is cycloplegia, which consists of instilling solutions of atropine or scopolamine into the eyes and then checking visual acuity using standard tables.

If a person is unable to see the image on their own, they are given different lenses until a lens is found that provides a clear picture. The degree of refraction of this lens determines the statistical refraction of the eye.

Sometimes (for example, to check for presbyopia) it becomes necessary to diagnose refraction taking into account accommodation; such refraction will be called dynamic.

Subjective methods have one drawback: the ability to clearly examine an image depends not only on refraction, but also on a number of other factors. Many people remember Sittsev’s tables by heart due to the frequency of checks on them, and even when poor eyesight they will easily name the bottom row of letters, since the brain will complete their outlines from memory.

Objective methods minimize subjective factor and analyze the refraction of the eyes based only on their internal structure. High efficiency among similar methods It measures the refraction of light by the organs of vision using a refractometer. This device sends safe infrared signals into the eye and detects their refraction in the optical medium.

A simpler objective method is skiascopy, in which the ophthalmologist directs light rays into the eye using mirrors and monitors the shadows they cast. Based on this shadow, a conclusion is drawn about statistical refraction.

The most accurate and expensive procedures are presented ultrasound examination and keratopography, using these methods it is possible to examine in detail the refraction on each of the meridians, accurately determine the length of the ocular axis and examine the surface of the retina.

Treatment and prevention

The most basic and necessary treatment method is the selection of corrective external lenses.

This is necessary in all cases, except for a short-term decrease in severity due to overexertion; general preventive measures are sufficient here.

Depending on your aesthetic preferences, you can choose glasses or contact lenses.

More radical methods treatments presented laser correction. More than anything surgical correction Myopia is susceptible, but early stages farsightedness and astigmatism can also be cured with such correction.

Drug treatment is effective as maintenance therapy when using surgical methods.

Prevention of visual acuity disorders consists of proper arrangement of the workplace, ensuring optimal lighting, maintaining a daily and work routine, and preventing overwork. Regular eye exercises are of great benefit, as they relax and tone them. It is important to provide the body with everything essential vitamins and minerals.

In many ways, the health of the eyes is affected by their constant overstrain. This can be avoided by doing gymnastics and special exercises:

Results

Refraction is the refraction of rays optical system. To evaluate the optical system of the human eye, physical and clinical approaches to the measurement of refraction. Physical approach measures the refractive power of the eye without taking into account its relation to internal structure organ.

The clinical approach complements the physical one and evaluates the relationship of refractive power with the length of the eye axis and the structure of the retina. The power of refraction of light is measured in diopters. Refraction has three types: emmetropia, myopia and hypermetropia. Also stands out astigmatism, characterized by varying degrees of refraction in each part of the eye.

Video

We present to your attention the following video:

Ophthalmologist of the first category.

Conducts diagnosis and treatment of astigmatism, myopia, farsightedness, conjunctivitis (viral, bacterial, allergic), strabismus, stye. Performs vision examinations, as well as fitting glasses and contact lenses. The portal describes in detail the instructions for use of eye medications.

Refraction of the eye I Refraction of the eye (Late Lat. refractio refraction)

refractive power of the optical system of the eye, expressed in diopters.

Refraction of the eye physical phenomenon is determined by the radius of curvature of each refractive medium of the eye, the refractive indices of the media and the distance between their surfaces, i.e. due to anatomical features eyes. However, in the clinic it is not the absolute power of the optical (light refractive) apparatus of the eye that matters, but its relationship with the length anteroposterior axis eyes, i.e. the position of the posterior main focus (the point of intersection of rays passing through the optical system of the eye, parallel to its optical axis) in relation to the retina - clinical refraction.

There are three types of clinical refraction. Refraction, in which the rear main focus coincides with the retina, is called commensurate and is designated as ( Fig., b ); when the rear main focus is located in front of the retina, they speak of myopia, or myopia (Myopia) ( Fig., a ); refraction, characterized by the location of the posterior main focus behind the retina, is called hyperopia, or farsightedness ( Fig., in ). The last two types of R. are disproportionate and are called ametropia. Often observed - the difference in the refraction of both, in most cases not exceeding 0.5 diopter.

The emmetropic eye is set to parallel rays coming from infinity, i.e. the refractive power of its optical system corresponds to the length of its axis, the focus of parallel rays coincides exactly with the retina, and such an eye sees well into the distance. For near vision, such an eye needs to enhance its refraction, which can be achieved through accommodation. - the process of changing the refractive power of the eye, allowing it to perceive objects located at different distances. At the core physiological mechanism accommodation lies in the possibility of changing the shape of the lens when tensioning or relaxing the ciliary fibers. In turn, the ability of the lens to change curvature depends on the elasticity of its fibers. With age, it loses elasticity, and therefore the ability to change shape, which leads to a weakening of accommodation - presbyopia (Presbyopia). With myopia, when the eye has, as it were, excessive refractive power, it can see well close at one or another final distance, depending on the degree of myopia. However, to ensure good vision into the distance, it is necessary to use a diverging lens, which turns divergent rays coming from a close distance into parallel ones. With farsightedness, the eyes are not aligned with parallel rays, but subject to accommodation mechanisms, a person is able to see well into the distance. To view closely located objects, the degree of accommodation must be even greater, as a result of which in these cases it is necessary to use a collecting lens of appropriate strength.

With any type of clinical refraction, the eye always has only one most distant point in space to which it is set (the rays emanating from this point are focused on the retina). This point is called the further point of clear vision. For an emmetropic eye, it lies at infinity, with myopia at some finite distance in front of the eye (the closer, the higher the degree of myopia). For a farsighted eye it is imaginary, because in this case, only rays that already have a certain degree of convergence can be focused on the retina, and such rays in natural conditions does not exist. Thus, the position of the further point of clear vision determines the clinical refraction and the degree of ametropia. The degree of ametropia is measured by the power of the lens that compensates for it, and is expressed in diopters. indicated by a number with a minus sign - with a plus sign. Ametropia from ±0.25 to ±3.0 diopter classified as weak, from ±3.25 to ±6.0 diopter- to average and over 6.0 diopter- to high. The refractive power of the eye can increase due to accommodation. Depending on this, the static refraction of the eye is distinguished, i.e. refraction in a state of rest of accommodation, and dynamic refraction when the mechanisms of accommodation are turned on.

Depending on the shape of the optical apparatus of the eye, a distinction is made between spherical refraction, when the refraction of rays in the eye is the same in all meridians, and astigmatic, when in the same eye there is a combination of different refractions, i.e. The refraction of rays is not the same along different meridians. In an astigmatic eye, two main sections of the meridian are distinguished, which are located at right angles: in one of them, the R. g. is the largest, in the other - the smallest. The difference in refraction in these meridians is called the degree of astigmatism. Small degrees astigmatism (up to 0.5 diopter) are quite common, they almost do not impair vision, which is why this type is called physiological.

Often during visual work, especially at close range, the eye () quickly sets in. This condition is called asthenopia. It manifests itself in the fact that the outlines of letters or small items become unclear, occurs in the forehead, near the eyes, in the eyes. This is typical for accommodative asthenopia, which is based on fatigue of the ciliary muscle, which is observed with farsightedness, presbyopia, and astigmatism. With myopia, the so-called muscular myopia develops, caused by defects in the binocular visual system; it manifests itself as pain in the eyes, double vision when working at close range. To eliminate asthenopia, the earliest possible optical correction of ametropia or presbyopia is necessary, creating favorable hygienic conditions visual work, alternating it with rest for the eyes, restorative.

To determine R. in the clinic, two methods are used: subjective and objective. In preschool and school age clinical R. g. is determined in conditions of cycloplegia, i.e. against the background of switching off accommodation by instilling 0.1-1% atropine sulfate solution, 1% scopolamine hydrobromide solution, etc. into each eye. At an older age, the issue of cycloplegia is decided individually.

The subjective method consists of selecting the appropriate corrective lens during the study of visual acuity (Visual acuity); With this method, the patient’s own testimony is used. The expression of refraction and its degree in myopia is the weakest of the diverging lenses, with the help of which a high distance is achieved. For farsightedness, the indicator is the strongest of the collective lenses with the highest possible distance visual acuity. With spherical R., correction is carried out with spherical lenses, with astigmatism - with cylindrical lenses.

Objective methods for determining refraction include skiascopy and eye refractometry. Skiascopy is based on observation of the movement of a light spot in the illuminated pupil during rotation of a concave or (more often) flat ophthalmoscopic mirror (skiascope) located at a distance of 1 m from the subject. With emmetropia, farsightedness and myopia less than 1.0 diopter the light moves in the direction of the mirror if it is flat, and in the opposite direction if it is concave. For myopia greater than 1.0 diopter, the light spot moves in the direction of movement of the concave mirror and in the opposite direction during examination flat mirror. With myopia equal to 1.0 diopter, no movement of the light spot is observed. The degree of refraction is determined using lenses that neutralize the light spot, according to the formula P = ±C + (-1.0), where P is the refraction of the eye under study in diopter; C is the refractive power of the lens with a + or - sign, in diopter, when used, the light spot stops moving. Skiascopy is also used for astigmatism; in this case, the study is carried out separately in the two main meridians, and cylindrical lenses are used to neutralize the movement of the light spot. Refractometry of the eye is carried out using eye refractometers, the principle of which is to find a plane corresponding to the optical installation of the eye, which is achieved by moving the image of a special brand until it is aligned with this plane.

II Refraction of the eye

clinical (refractio oculi; lat. from refringo, refractum to break, refract) - a characteristic of the refractive power of the optical system of the eye, determined by the position of the rear main focus relative to the retina.

Refraction of the eye ametropically(r. oculi ametropica) - R. g., in which the position of the rear main focus of the optical system of the eye does not coincide with the retina.

Dynamic refraction of the eye(g. oculi dynamika) - R. g. in the process of accommodation.

The refraction of the eye is commensurate(r. oculi emmetropica) - see Emmetropic refraction of the eye.

Static eye refraction(r. oculi statica) - R. g. in a state of rest of accommodation.

Spherical refraction of the eye(r. oculi sphaerica) - R. g. without taking into account astigmatism.

Refraction of the eye is emmetropic(r. oculi emmetropica; .: r. eye commensurate, emmetropia) - R. g., in which the position of the rear main focus of the optical system of the eye coincides with the retina.

1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First health care. - M.: Great Russian Encyclopedia. 1994 3. encyclopedic Dictionary medical terms. - M.: Soviet Encyclopedia. - 1982-1984.

See what “Refraction of the eye” is in other dictionaries:

- (from Late Lat. refractio), optical alignment of the eye at rest of accommodation. There are 3 main types of emmetropia ( normal refraction eyes), farsightedness and myopia. * * * REFRACTION OF THE EYE REFRACTION OF THE EYE (from Late Lat.… … encyclopedic Dictionary

- (Late Lat. refractio) characteristic of the refractive power of the optical system of the eye, determined by the position of its total rear main focus relative to the retina. Expressed in diopters. If the main focus of the refracting ... ... Wikipedia

Refraction of the eye- (from Latin refractum - refract). Characteristics of the refractive power of the optical system of the eye, determined by the position of its total posterior main focus relative to the retina. If the main focus of the refractive systems of the eye coincides with the retina... Encyclopedic Dictionary of Psychology and Pedagogy

- (from Late Lat. refraction), optical. installation of the eye during resting accommodation. There are 3 main ones. its type of emmetropia (normal R.G.), farsightedness and myopia... Natural science. encyclopedic Dictionary

- (r. oculi emmetropica) see Refraction of the eye is emmetropic... Big medical dictionary

- (r. oculi emmetropica; synonym: r. eye commensurate, emmetropia) R. g., in which the position of the rear main focus of the optical system of the eye coincides with the retina ... Large medical dictionary

Refraction is the process of refraction of light rays by the optical system of the eye. The refractive power is a quantity that depends on the curvature, as well as the curvature of the cornea, which are refractive surfaces; in addition, it is determined by the magnitude of their distance from each other.

The light refraction apparatus of the human eye is complex. It consists of the lens, cornea, moisture in the chambers of the eye. On the way to retina a ray of light encounters four refractive surfaces: the surfaces of the cornea (posterior and anterior), as well as the surfaces of the lens (posterior and anterior). The refractive power of the human eye is approximately 59.92 diopters. The refraction of the eye depends on the length of its axis - the distance from the cornea to the macula (approximately 25.3 mm). Thus, the refraction of the eyes is determined by both the refractive power and the long axis - the characteristics of the optical installation of the eye, in addition, it is also influenced by the position in relation to the main focus.

Types of refraction

In ophthalmology, it is customary to distinguish three types of eye refraction: emmetropia (normal refraction), (weak refraction), myopia (strong refraction).

In an emmetropic eye, parallel rays reflected from distant objects intersect at the retinal focus. An eye with emmetropia clearly sees surrounding objects. To obtain a clear image at close range, such an eye increases its refractive power by increasing the curvature of the lens - accommodation occurs.

In a far-sighted eye, the refractive power is weak due to the fact that light rays, reflected from objects in the distance, intersect (focus) behind the retina. To obtain a clear image, the far-sighted eye must increase the refractive power even when the object in question is located at a distance.

A myopic eye has a strong refractive ability, because rays reflected from distant objects are focused in front of the retina.

A person’s vision is worse the higher the degree of myopia or hypermetropia, because in these cases the focus does not fall on the retina, but is localized “in front” of it or “behind” it. It is worth mentioning that s have three degrees of severity: weak (up to three diopters), medium (4-6 diopters), high (more than 6 diopters). There are examples of myopic eyes having more than 30 diopters.

Determination of eye refraction

Determination of the degree of myopia and farsightedness is carried out using the unit of measurement that is used to indicate the refractive power for optical glasses. It is called “Diopter”, and the procedure for determining refraction is called “Refractometry”. It is customary to calculate the refractive power of concave, curved, diverging, and converging lenses in diopters. Lenses or optical glasses are a necessary reality for improving vision in farsightedness, as well as myopia.

The refraction of the patient's eyes is also determined using optical glasses or using precision instruments (refractometers). There are cases when one eye can combine different degrees of refraction or even different types of refraction. For example, vertically the eye has farsightedness, and horizontally it has myopia. This depends on genetically determined (congenital) or acquired differences in the curvature of the cornea in two different meridians. At the same time, vision is significantly reduced. Such an optical defect is called, which from Latin can be translated as “lack of a focal point.”

The refraction of both eyes is also not always the same. There are often cases when myopia in one eye and farsightedness in the other are established. Similar condition called anisometropia. This anomaly, like myopia with hyrmetropia, can be corrected with optical glasses, contact lenses or perform surgery.

Normally, a person has stereoscopic (binocular) vision in both eyes, which provides a clear perception of surrounding objects and makes it possible to correctly determine their location in space.

Video about eye refraction

Symptoms of eye refractive error

Decreased visual acuity near or far.
The appearance of visual distortions.
Pain in the eyes.
Diplopia.
Deterioration twilight vision(hemeralopia).

Diseases with refractive error of the eye

Myopia (nearsightedness).
Hypermetropia (farsightedness).
Presbyopia ( presbyopia).
Astigmatism.
Spasm of accommodation (“false myopia”).

Visual organ, with physical point vision, is a combination of lenses. Refraction of the eye means the refraction of rays entering the retina. Light passes through the cornea, the humor of the anterior chamber, the lens and vitreous. The changes that happen to him along this path affect the visualization of near and far objects. Eye strain congenital anomalies developments affect refraction, so it is important to know possible pathologies and their treatment.

What it is?

The refraction of light normally occurs according to the general laws of physics and does not depend on the distance of the object. Focal length cornea means its distance from the surface of the retina and in a healthy person it is 23.5 mm. The optical system of the eye in this case involves directing the rays in such a way that they hit only the surface with the highest concentration of photoreceptors, and a person clearly sees objects at different distances. This difficult process, which functions correctly only when normal operation all structures.

The journal “New in Ophthalmology” in 2017 published the results of a study proving that the refraction of the eye in children is impaired in 96%. This is due to underdevelopment visual analyzer.

What types are there?

Ophthalmology distinguishes the following types of eye refraction:

Refraction is divided into types depending on the strength and location of refraction of the rays, the violation of which leads to the development of pathologies.

Physical or physiological. It is formed as the visual analyzer grows and develops, and subsequently does not change. Measured in diopters.
Clinical. Indicates the place of fixation of rays relative to the retina. Depends on the refractive power. This parameter is taken into account by the ophthalmologist when determining myopia, farsightedness and emmetropia.
Dynamic. It differs from other types of refraction in its dependence on accommodation - a change in the shape of the lens when the viewing angle changes.
Static. Depends on accommodation during the period of relaxation of the ciliary muscle, when the main focus should be on the retina. Normal means the correct intersection of the rays with the surface of the retina.

Refractive errors

Ophthalmologists determine the following changes in the refraction of rays by the optical system of the eye:

myopia;
hypermetropia;
astigmatism;
presbyopia.

Myopia is accompanied by poor focusing and blurry images of distant objects.

The medical name for this pathology is myopia. Such patients clearly see objects that are close, but those that are far away are difficult to see. This is due to the fixation of light rays in front of the retina due to the increase in volume of the eye and strong refractive power. There is weak, moderate and severe myopic refraction, which is important for spectacle correction.

Hypermetropia

Characterized by clear visualization of objects located at a distance, with poor focusing on close objects. Such patients complain of blurring of letters when reading or when it is necessary to see small icons. Another name is farsightedness of the eye. The pathogenesis is based on the fixation of rays behind the retina, as a result of which the refractive surface does not contact photosensitive cells, and the refractive power is weak.

Myopia and farsightedness are not always bilateral. Compensation for violations by the healthy eye often occurs.

Astigmatism

This is a complex refractive error characterized by the presence in one eye different points refraction of light. Each of these focuses has changes that are different from the others. Thus, in different localizations There may be mild or severe degrees of myopia and/or farsightedness. Astigmatism happens different forms, including congenital. Correcting such vision is a complex process that requires detailed diagnostics. Refraction is determined using high-tech techniques.