Accommodation of the eye: types, causes and treatment methods

These include:

• Myopia (nearsightedness).
• Hypermetropia (farsightedness).
• Astigmatism.

Ametropia may be due to the structure of the eye. In this case, this condition is permanent (often congenital), the eye requires correction (glasses/lenses).

However, there are acquired conditions that are reversible. But if there is no proper treatment or correction, this condition can turn from transient to permanent, or lead to an increase in already existing ametropia.

Myopia (nearsightedness)

With myopia, the eye is enlarged in the anteroposterior segment (longer) and, as a stronger, “convex” lens, refracts the light entering the eye more strongly. This causes the focal length to be projected in front of the retina when looking into the distance.

Diverging (minus) lenses help to “pull” the focus back onto the retina and restore clear vision. Since myopia is a permanent condition (remember that this is a feature of the structure of the eye), glasses / soft contact lenses are constantly prescribed. At the age of up to 40 years, they are prescribed for constant wear (for near, distant). After 40 years, these glasses are only worn when looking into the distance, because presbyopia comes into force - an age-related decrease in distance vision, but more on that a little later.

Laser vision correction (LASIK technique) helps to achieve the effect of constantly wearing glasses/lenses, i.e. it allows you to see well without the use of optical correction.

How does PINA differ from myopia?

Let's figure out how to distinguish a spasm of accommodation from true myopia. The first manifests itself in a temporary loss of clarity of vision. With myopia, the ability to see well is lost for a long time and is rarely restored by itself. However, with false myopia, spasms can reach a force that impairs vision by as much as 3 diopters.

But there is something in common between them: with both ailments, there is a blurring of vision and a feeling of blurriness of distant objects. If you confuse PINA with myopia and buy glasses without consulting a doctor, you can develop true myopia.

Astigmatism

It is a structural feature of the cornea that leads to vision distortion and/or double vision. It can be present either isolated in the eye or accompany myopia or myopia. For the purpose of correction, glasses with a cylindrical component in the lens or soft contact lenses (SCL) are prescribed. Externally, these glasses are no different from ordinary ones. Performing LASIK can correct the structure of the cornea, and the patient will forget about astigmatism.

It is important to understand that properly selected glasses do not worsen your vision! It is a myth.

Over the past decade, devices designed to simplify our lives and communications have become firmly established in our everyday life. Wearable electronics come in a variety of shapes, sizes and purposes. People have been using a personal computer for even longer. And it’s hard to calculate how long a person has been using printed publications.

An increase in tasks that require long-term visual load, as well as the emergence of new professions where the main activity is performed at the computer, leads to an increase in disorders associated with increased visual load.

These conditions can be acute, subacute, become chronic, or lead to changes in the structure of the eye:

• Presbyopia.
• Spasm of accommodation.
• PINA (habitual excess tension of accommodation).
• Paresis and paralysis of accommodation.
• Accommodative asthenopia.

Refractive errors of the eye

The human eye is a complex optical system. Like any optical system, it has a refractive ability - refraction. In relation to the eye, there are two types of refraction - physical and clinical. All real optical systems have optical errors - aberrations. There are monochromatic (spherical and astigmatic) and chromatic aberrations. Chromatic aberration is a consequence of unequal refraction of light rays of different wavelengths, so they are collected at different points on the optical axis.

The optical system of the human eye has some imperfections:

• non-spherical refractive surfaces;
• decentration of refractive surfaces - the centers of curvature of the various refractive surfaces of the eye do not lie exactly on the same straight line;
• uneven density of refractive media, especially the lens.

Together they create an optical error in the eye, which is called physiological astigmatism . Its essence is that rays emanating from a point source of light are collected not at a point, but into a certain zone on the optical axis of the eye - the focal area, as a result of which a circle is formed on the retina. The focal area is characterized by diameter and depth. The smaller the diameter of the focal area, the clearer the image and the higher the visual acuity. Its depth depends on the width of the pupil. The focal area allows the eye to see clearly at different distances even in the absence of a lens.

To obtain a clear image on the retina, the ability of the eye's optical system to focus rays precisely on the retina is important. Depending on this, two types of clinical refraction are distinguished: emmetropia and ametropia. Emmetropia (from the Greek, emmetros - proportionate, ops - vision) - proportionate refraction. The power of the optical system of such an eye corresponds (commensurate) to the anterior-posterior size of the eye and the main focus of parallel rays is on the retina. Emmetropia is the most advanced type of clinical refraction of the eye. The further point of clear vision of the emmetrope lies in infinity. The visual acuity of such an eye is 1.0 or higher. Emmetropes have good distance and close-up vision. Ametropia is disproportionate refraction. The main focus of parallel rays in such an eye does not coincide with the retina, but is located in front of or behind it. Ametropia can be of two types: myopia and farsightedness. Myopia or myopia (myopia, from the Greek muo - squint, ops - vision) is a strong refraction. The parallel rays come to focus in front of the retina, resulting in a blurred image on the retina. Visual acuity in myopes is always below 1.0; they see poorly at distance and well at near. Non-progressive myopia is a refractive error that is clinically manifested by decreased distance vision, is easily corrected and does not require treatment. An increase in the degree of myopia by more than 1.0 diopters over the course of a year is considered progressive myopia. Continuous progression (the degree of myopia continues to increase throughout life) is called malignant myopia, or myopic disease. This is a disease that requires treatment and leads to visual impairment. Farsightedness or hypermetropia (hypermetropia, from the Greek hypermetros - excessive), is a weak type of refraction. The focus of parallel rays is behind the retina, the image on the retina is unclear, and the visual acuity of such an eye is below 1.0. Equality of clinical refraction in both eyes is called isometropia, inequality is called anisometropia.

Emmetropia, myopia and hypermetropia are spherical refractions. The refractive surfaces of the optical system of such eyes have a spherical shape (the cornea is a convex concave sphere, the lens is a biconvex sphere), the refractive power in different meridians is the same and the main focus of parallel rays is a single point.

There are eyes in which the refractive surfaces of the optical system are aspherical and their refractive power in different meridians is not the same. There is more than one main focus of parallel rays in such eyes; There are several of them and they occupy different positions in relation to the retina, as a result of which it is impossible to obtain a clear image. This anomaly of the optical system is called astigmatism. Astigmatism (from the Greek a - negation, stigma - point) is characterized by different refractive powers of the optical media of the eye in mutually perpendicular meridians (axes). If the refractive power is the same throughout the meridian, then astigmatism is called correct, if it is different, it is called incorrect.

Correct direct astigmatism with a difference in refractive power in the main meridians of 0.5-0.75 diopters is considered physiological and does not cause subjective complaints.

For normal human life, a clear vision of objects at different distances is necessary. The ability of the eye to focus the image of objects under consideration on the retina, regardless of the distance at which the object is located, is called accommodation. Thus, accommodation is the ability of the eye to see well both far and near. In the human eye, accommodation occurs due to changes in the curvature of the lens, which results in a change in the refractive power of the eye. Two components are involved in the accommodation process: active - contraction of the ciliary muscle and passive - due to the elasticity of the lens.

The refraction of the eye in a state of rest of accommodation is called static, and when it is stressed - dynamic. Accommodation is characterized by the area and volume of accommodation. The area (length) of accommodation is the space within which clear vision is possible at different distances, thanks to accommodation. The further point of clear vision is the point in space at which clear vision is maintained with maximum relaxation of accommodation, and the nearest point of clear vision is the point at which clear vision is maintained with maximum tension of accommodation. The segment between them is the area, or length of accommodation. It is determined in linear measures by the difference in the values ​​of the far and near points of clear vision.

Pathology of accommodation (spasm, paresis and paralysis)

Palsy of accommodation occurs when the oculomotor nerve is damaged due to disease, poisoning, injury or exposure to medications. Overload of the accommodative apparatus leads to accommodative asthenopia or spasm of accommodation. Accommodative asthenopia (visual fatigue) is observed with uncorrected hyperopia, astigmatism and presbyopia. It occurs as a result of paresis ( paresis of accommodation ) of the ciliary muscle, which is accompanied by a decrease in the volume of accommodation. Accommodative asthenopia is characterized by the appearance of pain in the bridge of the nose and temples when working at close range, headache, blurred vision when reading and looking at objects; sometimes there are general phenomena in the form of nausea and even vomiting. Accommodation spasm occurs as a result of prolonged tension of the ciliary muscle and is manifested by increased refraction of the eye - false emmetropia or myopia develops. Accommodation spasm is characterized by decreased distance visual acuity, headache, and fatigue when reading.

Presbyopia

The eye's ability to accommodate weakens with age. This process begins immediately after birth, gradually intensifies and becomes noticeable in adulthood. The weakening of the ability to accommodate is associated with the physiological involution of the lens and a change in its physicochemical composition. The amount of moisture in the lens decreases, it becomes denser (it begins to form at the age of 20, and by the age of 40 this process is completed), its elasticity decreases. By the age of 60, the compaction of the lens almost ends. An age-related change in accommodation is called presbyopia (presbyopia, from the Greek presbys - old man, ops - vision) - senile farsightedness. Presbyopia appears after 40 years of age and is characterized by the distance of the nearest point of clear vision further than the distance at which the person works, writes, etc. (further than 33 cm), and the patient begins to experience difficulty working at close range. When looking at small objects, you have to move them further and further away from the eye instead of bringing them closer

Presbyopia

When the ciliary muscle is tense, the ligaments of Zinn, to which the lens capsule is attached, relax. As a result, the lens becomes more convex, slightly lowered, and the pupil narrows, providing clearer near vision. As the lens becomes more convex, it gains additional optical power, thereby bringing the focal length closer to the eye. However, after 40-45 years, the lens loses its elasticity and cannot fully take on a convex shape. The ciliary muscle also loses its strength with age, and presbyopia gradually increases.

This condition is not a pathology, but a physiological norm. It cannot be excluded, but it can be delayed for several years.

The onset of presbyopia is accelerated due to:

• long absence of rest,
• stressful situations,
• chronic lack of sleep,
• deficiency of vitamins A, B, C,
• abnormal visual loads.

When presbyopia has already set in, the most correct decision would be to select glasses for correction. These glasses are prescribed only for close work (reading, writing or working on a PC).

Everyone is susceptible to presbyopia: nearsighted, farsighted and emmetropic (lack of ametropia). But it manifests itself in different ways.

• Emmetropia
  . In this case, presbyopia proceeds in the usual way with manifestation at 40-45 years and the prescription of weak positive glasses.
• Farsightedness.
  Since in this case the patient already needs plus glasses for distance, the optical power of the glasses for near is added to the power of the glasses for distance. The need for glasses for near vision may appear as early as 35 years of age.
• Myopia.
  Patients use minus distance glasses. But we remember that the correction for near is added to the necessary correction for distance. Therefore: either the patient needs weaker minus glasses, or (with weak myopia) presbyopic glasses will be needed much later than usual.

How to prevent accommodation disorders

In ophthalmology, the best ways to prevent accommodation are:
A balanced diet containing all the vitamins and minerals the body needs.

• Taking special vitamins for vision during periods of vitamin deficiency (for example, winter and spring).
• Long walks in the fresh air, playing sports.
• Proper equipment of the work area (you must adhere to recommendations regarding the distance to the monitor, back position, viewing angle, etc.).
• Using programs to relieve eye strain or performing eye exercises.
• Regular breaks during significant visual stress.
• Timely treatment of colds, neurological, mental diseases.

Spasm of accommodation

An acute condition in which distance vision is significantly reduced. In this condition, the ciliary muscle is sharply spasmed, the eye acquires a pronounced myopic refraction, but with maximum correction it is not possible to bring the eye to vision 1.0 (100%).

It most often occurs at the age of 12-18 years, appears abruptly, perhaps due to stress, the patient begins to see nearby objects (eyelashes, for example). There may also be pain in the area of ​​the brow ridge.

Causes: stress, poisoning with organophosphorus compounds, use of cholinomimetics (pilocarpine hydrochloride).

In the treatment of accommodation spasm, drugs that relax the ciliary muscle are used. For persistent conditions, drugs are prescribed for a longer period. In some cases, treatment by a psychotherapist is necessary.

Habitually excessive tension of accommodation (PINA)

This is a chronic overstrain of the ciliary muscle, leading to the appearance of myopic refraction (false myopia - pseudomyopia).

The following features are noteworthy:

• school age, adolescence,
• complaints of decreased distance vision,
• develops gradually
• the appearance is associated with an increase / intensification of visual load.

Many clinical and experimental studies have proven the connection between accommodation disorders and childhood myopia, as well as the progression of myopia. PINA is inextricably linked with myopia, so it makes sense to remember what factors influence the appearance and progression of myopia.

The chain is built as follows: heredity, trauma to the cervical spine, unfavorable environmental conditions, excessive visual load -> pseudomyopia, PINA -> true myopia, PINA -> progression of myopia -> complications of myopia.

PINA is most often caused by prolonged, abnormal visual load at the wrong distance.

Myopia appears (but this is false myopia), which completely corrects vision to 1.0 (100%)

The mistake in this case would be to immediately prescribe glasses. After a course of treatment with drugs that relax the ciliary muscle, and a visual load determined by the doctor, glasses may not be needed. There are cases when, after a course of treatment, false myopia turns into farsightedness.

The sooner a child starts using tablet computers and similar electronic devices, the sooner and more likely he will develop PINA, which turns into myopia.

Diagnosis and treatment

Diagnosis of paralysis of accommodation is carried out on the basis of an ophthalmological examination, vasometry, study of accommodation reserves, and study of eye refraction. Treatment of accommodation paralysis is based on eliminating the cause of the pathological process and vision correction with the selection of glasses with appropriate diopters. Contact lenses have a positive effect on improving the quality of vision, not only correcting vision, but also protecting the eyes from external irritations.

Paralysis of accommodation that occurs against the background of traumatic injuries is practically not treated, but over time they can go away on their own. Paralysis caused by nervous disorders is cured as the underlying disease is treated.

The general course of treatment is aimed at eliminating changes in refraction, reducing visual stress, proper nutrition, and improving lighting conditions in workplaces. In the treatment of paralysis, laser-magnetic effects on the eye muscle and other corrective measures are used.

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Weakness of accommodation

A condition in which accommodation is difficult (near vision). This is a long-term condition that is often accompanied by PINA. If accommodation is weak, the ciliary muscle cannot remain in a tense state for a long time; it weakens.

Patients complain of fatigue and fatigue when reading and writing. The closest point of clear vision approaches the eye. In this case, the ciliary muscle must be stimulated. The drug of choice is Irifrin 2.5%. Weakness of accommodation can also lead to the appearance or intensification of existing myopia.

Signs of a PIN

Since this disorder is detected mainly in adolescents, parents should be alert to the following characteristic signs:

• Rapid general fatigue.
• Headaches in the evening.
• Eye fatigue, discomfort, pain.
• Decreased visual acuity.

If you detect several of the listed points, you should definitely visit an ophthalmologist. At this stage, it is still possible to return good vision without myopic refraction in the future.

Paralysis and paresis of accommodation

This is an acute or subacute condition in which the eye loses the ability to see an object located at close range.

There are disorders of the central

or
peripheral
origin.

Peripheral genesis is a consequence of the use of m-anticholinergics (Atropine).

Central - may be a consequence of an acute illness: intoxication, influenza, scarlet fever, diphtheria, poisoning with carbon disulfide, lead, injury or tumor of the central nervous system, severe stress. Well corrected with plus glasses.

In this case, it is possible to assign:

• temporary plus points,
• the drug pilocarpine,
• acupuncture, laser stimulation of the ciliary muscle.

Accommodative asthenopia

This is a symptom complex that includes discomfort, fatigue during prolonged work, and decreased vision at distance and near. Patients report pain.

During the examination, there may be slight refractive errors (myopia, hypermetropia), which are either not corrected at all or incorrectly corrected.

It is necessary to use adequate optical correction, stimulate the ciliary muscle, and use adrenergic agonists.

If you feel that your vision has deteriorated - this is interfering with work, reading, etc., you should consult an ophthalmologist to determine the cause. The doctor can make the right decision based on the examination and examination: what measures to take, whether to prescribe treatment or choose glasses for temporary or permanent wear.

Symptoms of false myopia. How to diagnose it

False myopia may appear suddenly or develop gradually and may last for several years. Its symptoms are very similar to those of true myopia:

• it becomes difficult to view distant objects
• unpleasant symptoms occur, such as pain, burning, stinging, scleral hyperemia, photosensitivity, lacrimation;
• eyes get tired quickly;
• the person becomes inattentive and loses the ability to concentrate;
• headaches appear.

In addition, experts call increased sweating of the palms one of the symptoms of false myopia.

Additional symptoms include trembling of the eyelids, differences in the size of the pupils, and involuntary movements of the eyeballs.

If you notice symptoms of visual impairment in yourself or your children - they begin to constantly squint, often rub their eyes - be sure to consult an ophthalmologist for a diagnosis and treatment. You should undergo a full examination including checking visual acuity, ultrasound diagnostics of the condition of the eyeball, measuring intraocular pressure and examining the fundus for light reflection.