Changes in visual acuity near or far.
The following factors may cause refractive error in the eye:
For all refractive errors:
Refraction of the eye is the process of refraction of light rays in the optical system of the eye. The optical system of the eye is quite complex, it consists of several parts: the cornea (the transparent shell of the eye), the moisture of the anterior chamber (this space filled with liquid is located between the cornea and the iris of the eye (the iris determines the color of the eyes)), the lens (a biological transparent lens located behind the pupil) and vitreous(a gelatinous substance that is located behind the lens). Light, passing through all components of the optical system of the eye, hits the retina - the inner layer of the eye, the cells of which convert light particles into nerve impulses, thanks to which an image is formed in the human brain. The refraction of the eye is measured in diopters - these are units of measurement of the refractive power of the lens.
Refraction depends on many characteristics: the radii of curvature of the anterior and posterior surfaces of the cornea (the transparent membrane of the eye) and the lens (biological lens), the distance between them, as well as the distance between back surface lens and retina (inner lining of the eye).
The so-called clinical refraction of the eye is important for a person - i.e. the position of the posterior main focus (the point of intersection of rays passing through the optical system of the eye) in relation to the retina. If the rear main focus lies on the retina, then the person has normal vision.
Ametropia is any refractive error of the eye. When ametropia occurs, visual acuity decreases near or far, depending on the type of refractive error. Visual impairment significantly affects the patient’s quality of life, because we receive 90% of information about the world around us through the organ of vision. A person with ametropia needs to consult an ophthalmologist and correct the existing refractive error.
False myopia is what spasm of accommodation is called. In common parlance, this pathology is called “syndrome tired eyes" As a rule, it occurs in adolescents of preschool and school age.
Caused by heavy strain on the eyes: knitting, sewing, jewelry making, spending a lot of time looking at the monitor.
Externally, the disease is very similar to myopia, the eyes become very tired, farsightedness worsens, and may be accompanied by pain syndromes eye area.
Why is this happening? If we consider the work of the eye, it can be compared with the work of binoculars, where the role of the wheel for focusing the image is played by the lens, which moves with the help of a muscle and selects the correct distance and focus for viewing.
If the object is at a distance, the muscle, called the ciliary muscle, relaxes, allowing the lens to take a flat shape. When viewing objects at close range, the muscle contracts and the lens takes on a convex shape.
If such tension lasts for a long time, then vision deteriorates, this is explained by the “fatigue” of the ciliary muscle. Therefore, the eye is deprived of the ability to react to changes in focus.
Accommodation spasm is a decrease in vision as a result of prolonged overexertion or fatigue. A person develops false myopia, which can develop into real myopia, and as a result, myopia.
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IN healthy eye The cornea and lens have a regular hemispherical shape.
Light passing through them is refracted equally in horizontal and vertical planes.
For astigmatism irregular shape lens or cornea leads to focusing problems.
A ray of light refracted in the eye is not collected at one point on the surface of the retina, as in the eye healthy person, but is scattered over several, behind or in front of the retina.
As a result, the eye cannot focus on objects in the field of view, and the image appears blurry.
In most cases, astigmatism is asymmetrical, which makes it difficult to select means for its correction. In addition, very often it is accompanied by other eye diseases: from microphthalmos to myopia.
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About a quarter of the entire population of the planet is faced with a problem that everyone knows as farsightedness.
Another more scientific name is hypermetropia. This is a vision disorder in which the image is focused behind the retina rather than on it.
To obtain a clear image, it is necessary to increase refraction, and for this you need to strain your eyes.
This is why most people with farsightedness quickly get tired and experience headaches when working at a computer or with documents.
Eat erroneous opinion that farsighted people see well in the distance and poorly see near. In fact, they may have difficulty seeing distant objects.
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Often, among acquaintances or simply in a crowd of passers-by, you can meet a person whose strabismus is noticeable to others.
The reason for this may be astigmatism - a congenital or acquired pathology of the cornea or lens.
Correction of astigmatism is more productive on early stages disease, the choice of treatment depends not only on the stage of visual impairment, but also on the causes leading to impaired visual function.
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There are several deviations in vision that make it difficult to clearly and in detail distinguish objects at close or far distances.
The main role is played not by the power of the optical system itself, but by the proportional ratio of this power to the length of the ocular axis. Of primary importance in human work is the position of the main rear focus point, at which the intersection of lines parallel to the optical axis and passing through the visual system occurs. And also the ratio of this point to .
Refraction– the ability of the eye apparatus to refract a beam of light. Refraction is measured in diopters. In ophthalmology, its types are distinguished: emmetropia, myopia and. The refraction of the eye depends on the state of the refractive media and can change with age.
Experts distinguish three types of refraction. In the first case, the focal point coincides completely with the retina, this state called emmetropia (normal vision). In the second case, the focusing point is located slightly in front of the retina, and a person with a similar feature of the visual apparatus is called myopic (myopia). And in the third case, we'll talk about farsightedness (hypermetropia) caused by the location of the focal point behind the retina.
It is worth noting that each type of refraction imposes certain features on the functioning of the entire visual system person.
The refraction of the eye, in the case of emmetropia, presupposes an exact coincidence of the focal point with the retina, which means that such an eye sees well objects that are at a far distance, but does not see very well what is close to it. For a more detailed examination, such an eye needs to enhance its refraction using the accommodative mechanism.
In the case when the eyeball has an excess of refractive power (myopia), nearby objects are visible quite well, but to improve distance vision it is necessary to use special diverging lenses, which should turn the diverging rays of the light flux reflected from the object into rays located in parallel.
If the focal point is located behind the retina (farsightedness), the eye is, in principle, not adapted to parallel rays, but with the help of an accommodative mechanism it can see perfectly over long distances. To view objects close up, it is necessary to use lenses with a collective property.
All previous types of refraction are of a clinical nature, but in addition there is also a spherical type of refraction, due to the shape of the eyeball, and astigmatic, based on a combination of different types of features of the refraction of the light flux in different directions in one eye.
The refraction of the eye is the main factor that largely determines the functioning of the entire visual apparatus, and any deviation in this area provokes peculiar distortions of the information received through vision or its incompleteness.
The most common disorders include myopia (), hyperopia (farsightedness), and.
With the development of myopia, the eyeball has an irregular, slightly elongated shape, or an increase in the refractive power of the cornea is observed. And sometimes both factors can be present simultaneously.
With farsightedness, on the contrary, the refractive power of the cornea is too weak or the central axis of the eye is too short. Astigmatism, as a rule, is caused by a violation of the natural spherical shape of the cornea, due to which the light ray passing through it has the outline of a straight line rather than a point.
The last violation was due to age-related changes in the eye, of a sclerotic nature, such an abnormal refraction is called presbyopia and is caused by disturbances in the mechanism of accommodation. With this disorder, as with all of the above, vision correction is necessary.
There are two main methods for checking refraction in modern ophthalmology. The objective method is to turn off the accommodative mechanism by instilling special agents into the eye. medical supplies, such as atropine. This diagnostic method is mainly used for children of preschool or primary school age. For older patients, the possibility of its use will depend on the characteristics of the body and lifestyle, so the decision is made in each specific case individually.
The subjective method is based on the selection during the examination of the appropriate lens for vision correction, taking into account the patient’s wishes.
Refraction is an important component of the visual system, therefore, the patient’s eye health and visual acuity depend on its correct determination and successful selection of correction methods.
Along the way, the light beam passes through four refractive surfaces: the posterior and anterior surfaces of the cornea, as well as the posterior and anterior surfaces of the lens. The refractive power it has optical system eyes, on average is 59.92 diopters. For the refraction of the eye, the length of the eye axis is important, that is, the distance from the cornea of the eye to the macula (on average 25.3 millimeters). Thus, the refraction of the eyes is influenced by both the refractive power and the length of the axis, which characterize the optical installation of the eye and the position of the main one in relation to.
There are three types of refraction of the eye: (normal refraction of the eye), . In an emmetropic eye, parallel rays emanating from distant objects intersect at the retinal focus. Such an eye is able to clearly see surrounding objects. To get a clear image up close, the eye increases its own refractive power by increasing the curvature of the lens ().
The farsighted eye has a weak refractive ability, since light rays emanating from distant objects intersect behind the retina. To obtain an image, the far-sighted eye increases the refractive power even when viewing objects located in the distance.
A myopic eye has a strong refractive ability, since rays coming from distant objects intersect in front of the retina.
The higher the degree of farsightedness or myopia, the worse vision, since in these cases the focus is not on the retina, but “behind” or “in front” of it. Farsightedness and myopia come in three degrees: weak (no more than three diopters), medium (4-6 diopters), high (over 6 diopters). There are myopic eyes with 25-30 diopters or even more.
To determine the degree of myopia and farsightedness, a unit of measurement is used, which is used to indicate the refractive power of optical glasses. This unit of refraction is called “Dioptre”, and the procedure is called “” (read more about this in the corresponding section). Diopters calculate the refractive power of convex, concave, scattering and converging lenses. Optical glasses can improve vision for farsightedness and nearsightedness.
The refraction of the patient's eye is also determined using optical glasses or more precise instruments (refractometers). Sometimes one eye combines different refractions or different degrees of one refraction. For example, an eye may have farsighted refraction vertically, and myopic refraction horizontally. This depends on the acquired or congenital differing curvature of the cornea in two different meridians. Vision is significantly reduced. The described optical defect of the eye is called, which is translated from Latin as “absence of a focal point.”
In both eyes, refraction is also not always the same. For example, farsightedness in one eye and nearsightedness in the other can be established. This condition is called anisometropia. This disease, like farsightedness and myopia, can be corrected with glasses with optical lenses or surgery.
Normal vision in both eyes is called binocular (stereoscopic), which provides a clear perception of surrounding objects, as well as correct definition their location in space.
Refraction is a natural process that is characterized by the refraction of light rays in the eye. The condition of the lens and cornea completely determines how strong the refraction should be.
These components of the eye are located at a certain distance from each other. The human light-refracting apparatus has a rather complex structure. Before hitting the retina, the light ray penetrates through the constituent parts of the cornea, as well as two parts of the lens.
Remember that each cavity has its own optical power. There are several refractive errors that cause problems with visual acuity for the patient.
To determine the power of refraction, the patient needs to undergo several diagnostic studies. With their help, it is possible to identify the power of refraction. To indicate this parameter, a unit of measurement is used that determines myopia and farsightedness.
The refractometry procedure is of greatest importance. This is a simple test during which a specialist can determine the refractive power of convex and concave glasses. A special apparatus determines how the eye perceives scattering and collecting rays.
Thanks to properly selected glasses, it is possible to significantly improve visual acuity in people suffering from myopia and farsightedness. In addition, the power of refraction can be determined using other optical glasses.
Cases are often diagnosed when different degrees of this indicator are determined in two eyes. In addition, it may happen that one eye is nearsighted and the other is farsighted.
You also need to take into account some features of the development of this disease: whether it is congenital or acquired.
The above is astigmatism. It requires immediate correction; if it is not corrected, there is a high probability of developing serious complications.
Astigmatism is characterized by the absence of a focal point, which is why the brain cannot correctly perceive the image. Please note that the degree of refraction in different eyes may also be different. This phenomenon is called anisometropia.
It requires correction with glasses or contact lenses. In advanced stages, surgical intervention is performed.
Refraction is a special condition that is characterized by a violation of the refractive power of light rays. There are several varieties of this phenomenon, among them:
Myopia and farsightedness are combined into a single name - ametropia.
This condition characterizes the refractive error of the eye. Much less frequently, patients experience anisometropia, a condition in which the left and right eyes have varying degrees of impairment.
Ametropia also includes astigmatism - a violation of the refractive power in different eyes. It is very important to go through a comprehensive diagnostic examination, which will allow us to determine all the features of the course of this disease.
Can cause refractive errors huge amount factors. Today it is generally accepted that the main causes of the development of the disorder are:
The manifestations of refractive errors depend entirely on the type of anomaly. If the patient suffers from myopia, then the patient may complain of blurred distance vision. The picture is completely blurred; in case of a serious violation, it is impossible to do without glasses.
At the same time, a person can see perfectly close up, no problems arise. To make the picture clearer, the patient begins to stretch his eyes.
If vision correction is not started in a timely manner, a person may experience painful sensations in the forehead and temples.
In addition, myopia can be recognized by excessive sensitivity to light.
Myopia can naturally correct itself after the age of 50-60, when the structure of the eye begins to change. The condition requires mandatory correction, which will help prevent complications from occurring.
Patients who suffer from farsightedness may experience serious problems when working with small objects. A person cannot read without glasses, but no problems arise when performing ordinary manipulations.
Any refractive error requires full and immediate treatment. It is important for the patient to contact the attending physician, who will select effective scheme treatment. If you do not do this, there is a high probability of serious complications.
The greatest danger is carpal degeneration inner shell eyes. This condition can provoke retinal detachment, which in the future requires mandatory surgical intervention.
Due to damage blood vessels hemorrhage may occur in the eye, which often reaches the vitreous.
Patients suffering from stage 3-4 myopia may experience destruction of the gelatinous substance.
In addition, the lack timely treatment Astigmatism often causes the following negative consequences:
Treatment of any deviations in refraction requires a comprehensive and competent approach. It is very important to regularly consult your doctor to prevent any complications from occurring. A specialist will be able to correctly select corrective lenses or glasses for you.
If you have myopia, then diverging lenses are indicated for you - they are prescribed with a minimum optical power, which corrects vision by one. Typically, patients who suffer from myopia need two pairs of glasses. The first is intended for distance, the second for near.
With distance glasses it is possible to correct the refraction of vision by a full unit. Near glasses require less correction and allow you to comfortably work at a computer or read books. For patients with farsightedness, collective lenses of maximum optical power are recommended.
They must also correct their vision by one. If you have presbyopia, a condition that causes age-related degenerative changes in the eye - requires wearing bifocal lenses.
They are made from several stronger glasses so that upper part is intended for remote objects, and the lower one is for reading. If you have astigmatism, you will need to wear special cylindrical lenses.
Surgical treatment of refractive errors is carried out much more often. It's more effective measures, which allow you to quickly return full visual acuity. There is a huge amount various techniques that will help you recover normal work eyeball.
Please note that before the operation you will be sent for an extensive diagnostic examination. It will help determine the exact condition of the eye and identify any abnormalities.
Currently allocated the following types surgical interventions for refractive errors:
Refractive errors are a serious disorder that can cause multiple deviations in visual acuity in a person. To minimize the risk of serious deviations, the following precautions must be observed:
