The human eye is an amazing optical system that can adapt to different environmental conditions. In twilight and in bright daylight, at near and far distances, a person looks at the world differently. The process of correcting the mechanisms of vision depending on the distance of objects is called the accommodation of the eye.
The structure of the eye
The human organ of vision consists of several refractive and light-conducting structures:
- cornea;
- anterior chamber filled with eye fluid;
- crystalline lens;
- small posterior chamber of the eye;
- vitreous body;
- retina.
Primary processing of the visible image by the nervous system occurs in the retina. It is here that the light rays coming from the external environment are focused.
Correct focusing is ensured by a biconvex lens of the lens. Its main duty is to collect the rays of light into a beam of the desired diameter and direct it at the right angle to the retina.
The rest of the structures of the eye perform auxiliary functions, refracting light, bringing it tolens and passing to the back of the organ of vision.
The quality of vision depends on the characteristics of the processing of the light flux and the ability of the eye to adapt to changes in conditions.
Basics of accommodation
The lens inside the eye is suspended above and below on the ligaments of zon, which, in turn, are connected with the ciliary (ciliary) muscles. In a natural state, these muscles are relaxed, and the ligaments, on the contrary, are tense. Due to their tension, the lens capsule becomes flat, which reduces the refractive power of the lens. Rays of light pass freely through it, focusing almost unchanged on the retina.
This relaxed state of the eye provides high-quality vision at long distances. Therefore, by default, the human eye looks into the distance.
If there is a need to consider something close, the process of accommodation starts. The ciliary muscle tenses, causing relaxation of the ligament of Zinn. Released from its pressure, the lens tends to acquire its natural convex shape. The increased curvature of the lens ensures that images of close objects are properly focused.
During the accommodation of the eye, the optical power of the organ of vision increases by 12-13 diopters.
If the stimulus to tension of the ciliary muscle disappears, it relaxes and the eye again focuses into the distance. This process is called disaccommodation.
Thus, accommodation is the ability of the eye to process light rays coming from near and far differentlyobjects.
Lens curvature control
The work of the visual analyzer is controlled every moment by the sympathetic and parasympathetic divisions of the independent human nervous system. Analyzing the degree of clarity of the image focused on the retina, the brain decides on the need to change the curvature of the lens.
After receiving a signal, the ciliary muscle tenses, acting on the ligaments of zinn, the lens gradually increases its optical power until the image becomes clear enough. At the same time, muscle stimulation stops and the current state of the visual system is recorded.
Indicators of accommodative ability
Accommodation of the human eye is a measurable quantity. The optical power of the lens is usually expressed in diopters. There are also a number of parameters that describe the accommodative ability of the organ of vision:
- Area of accommodation - the absolute distance between the nearest and farthest points of clear vision.
- The volume of accommodation is the difference between the optical power of the lens of the eye at these points.
- Accommodation reserve of the eye - the unused volume of accommodation when fixing vision at a certain point.
With complete relaxation of the ciliary muscle and the absence of accommodative stimuli in the field of view of the eye, one speaks of functional rest of accommodation.
These indicators can be measured for each eye separately and for both together. Under normal conditionsthe quality of vision is closely related to the convergence of the visual axes of the left and right eyes. With different visual acuity and the same angle of convergence, the cost of accommodation of the lens is different.
Disorders of accommodation
Normally, a relaxed eye looks to infinity, and the most intense one looks at a very close object. This condition is called emmetropia.
Disorders of accommodation of the eye can be caused by various reasons. This is:
- inability of the ciliary muscle to fully relax;
- insufficient muscle strength;
- spastic muscle contraction;
- reducing the elasticity of the lens, making it difficult to change its curvature.
Main forms of violation of the accommodative ability of the organ of vision:
- presbyopia - age evolution of the lens associated with the general aging of the body;
- asthenopia - excessive accommodation of the eye during near vision;
- paralysis and paresis;
- Ciliary muscle spasms.
Age changes
With age, the lens of the human eye changes, gradually thickening and losing elasticity. This is a natural process that directly affects the quality of vision. After 40 years, the accommodation of the lens of the eye deteriorates, as the lens hardly takes the desired rounded shape even with the relaxation of the zinn ligaments.
The degree of manifestation of presbyopia largely depends on the initial accommodative ability of the organ of vision. So, with severe myopia, the changes are almost imperceptible, andwith farsightedness, they are felt more strongly.
Age-related changes in the lens are irreversible, deterioration in vision at close distances can be compensated by the selection of optimal corrective means.
Accommodative asthenopia
For any visual impairment, it is extremely important to choose the right correction correctly. Inappropriate glasses can cause asthenopia, a condition in which the lens is more distorted than necessary.
Pathology is accompanied by rapid fatigue when seeing at a short distance, pain, burning and itching in the eyes, headache.
Paralysis and paresis of accommodation
Such disturbances of accommodation of the eye can be caused by a variety of reasons. This is:
- diseases of the nervous system;
- toxic poisoning;
- eye injuries;
- infection;
- exposure to drugs.
With accommodation paralysis, the eye can hardly distinguish small details at close range. The symptoms are especially pronounced in farsighted people, and in myopia, on the contrary, the changes are less noticeable.
Treat such a pathology should be a professional oculist who can determine the exact cause of the disease.
Spasm of accommodation
Spasms of accommodation of the eyes - a pathological condition characteristic of children and adolescents. It is often referred to as "myopia" or "tired eye syndrome".
The problem occurs whenthe ciliary muscle cannot relax even in the absence of accommodative stimuli. Muscle spasm disrupts the mechanism of the visual analyzer and leads to blurry vision both at far and near distances.
Possible causes of ciliary muscle spasm:
- great eye strain;
- prolonged strain when seeing at close distances (reading, working at a computer);
- work in low light;
- physical injury;
- damage caused by exposure to bright light;
- individual features of the functioning of the organ of vision;
- unformed to the end mechanism of accommodation of the eye in children;
- hereditary predisposition;
- violation of accommodation control as a result of diseases of the nervous system;
- general weakening of the body;
- infection, especially in the cranial sinuses;
- weak neck and back muscles;
- circulatory disorders of the head.
Often, spasm of accommodation of the lens manifests itself against the background of other global pathologies:
- metabolic failures;
- exhaustion;
- malnutrition;
- scoliosis;
- congenital pathologies of the visual system;
- lack of immunological reactivity.
A person suffering from accommodation spasms complains of the following symptoms:
- eye fatigue;
- pain and burning sensations;
- redness of mucous membranes;
- lacrimation;
- myopia;
- double vision;
- headaches;
- not feeling well in general.
With early detection and proper treatment, accommodation disturbances resulting from muscle spasms are reversible.
The neglected problem leads to a chronic change in the functioning of the muscles and a gradual deterioration in vision, myopia. To prevent this, children and adolescents should see an ophthalmologist every year.
Treatment of disorders
As in the case of any other disease, the treatment of eye accommodation disorders is the more effective the earlier it is started. The best results are obtained by therapy in children, since the visual apparatus is not yet fully formed and can be easily corrected.
It is very important that an experienced ophthalmologist carry out the diagnosis and prescribe treatment. The eye system has a very fine tuning, it is easy to damage it by unprofessional actions. Recommendations are given only after a comprehensive examination, allowing:
- find out the true causes of the problem, as well as the stage of development;
- detect comorbidities and pathologies;
- identify environmental factors that influence the development of disorders.
Therapy of eye accommodation disorders can go on several fronts at once:
- drug effects (eye drops);
- a variety of training techniques aimed at general strengthening and improvement of the nutrition of the structures of the eye, as well as training the accommodative ability of the lens;
- general improvement of the body, the fight against infectious foci.
Prevention of accommodation disorders
It is always easier to prevent a disease than to deal with its consequences. Prevention of vision pathologies includes:
- eye accommodation training with the help of special exercises and apparatus;
- strengthening joints and blood vessels of the cervical-collar zone;
- a diet rich in trace elements and vitamins;
- general he alth improvement.
Serious visual impairments begin as small, reversible pathologies. Measures taken in time can stop the disease and significantly improve the quality of life.
