The human eye is an amazing optical system that can adapt to various environmental conditions. At dusk and in bright daylight, at close and far distances, a person looks at the world differently. The process of adjusting the mechanisms of vision depending on the remoteness of objects is called accommodation of the eye.
Eye structure
The human organ of vision consists of several refracting and light-conducting structures:
- cornea;
- anterior chamber filled with eye fluid;
- the lens;
- small posterior chamber of the eye;
- vitreous body;
- retina.
The 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 provided by a biconvex lens of the lens. Her 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 mesh sheath.
The remaining structures of the eye perform auxiliary functions, refracting light, bringing it to the lens and conducting to the back of the organ of vision.
The quality of vision depends on the features of processing the light flux and the ability of the eye to adapt to changing conditions.
Accommodation Basics
The lens inside the eye is suspended from above and below on the cinnamon ligaments, which, in turn, are associated with 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. The rays of light freely pass through it, almost without changes focusing on the retina.
Such a relaxed state of the eye provides high-quality vision over long distances. Therefore, by default, the human eye looks into the distance.
If there is a need to consider something close, the accommodation process starts. The ciliary muscle tenses, causing relaxation of the zinc ligament. The crystalline lens freed from its pressure tends to acquire its natural convex shape. The increased curvature of the lens ensures the correct focusing of images of close objects.
During accommodation of the eye, the optical power of the organ of vision increases by 12-13 diopters.
If the stimulus to ciliary muscle tension disappears, it relaxes and the eye focuses into the distance again. This process is called de-accommodation.
Thus, accommodation is the ability of the eye to process light rays coming from near and far objects in different ways.
Lens curvature control
The work of the visual analyzer every moment is controlled by the sympathetic and parasympathetic departments of the human independent nervous system. By analyzing the degree of sharpness of the image focused on the retina, the brain makes a decision about the need to change the curvature of the lens.
Having received the signal, the ciliary muscle strains, acting on the cinnamon ligaments, the lens gradually increases its optical power until the image becomes clear enough. In this case, muscle stimulation stops and the current state of the visual system is fixed.
Accommodation Ability Indicators
The 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 accommodation ability of the organ of vision:
- The area of accommodation is 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.
- The reserve of accommodation of the eye is the unused volume of accommodation when fixing vision at a certain point.
With complete relaxation of the ciliary muscle and the absence of accommodation stimuli in the field of vision, they speak of functional rest of accommodation.
These indicators can be measured for each eye separately and for both together. Under normal conditions, the 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 costs of accommodation of the lens are different.
Accommodation Disorders
Normally, a relaxed eye looks into infinity, and as intense as possible at a very close object. This condition is called emmetropia.
Disorders of accommodation of the eye can be caused by various reasons. It:
- inability of the ciliary muscle to complete relaxation;
- lack of muscle strength;
- spastic muscle contraction;
- a decrease in the elasticity of the lens, making it difficult to change its curvature.
The main forms of violation of the accommodative ability of the organ of vision:
- presbyopia is the age-related evolution of the lens associated with general aging of the body;
- asthenopia - excessive accommodation of the eye with near vision;
- paralysis and paresis;
- ciliary muscle spasms.
Age changes
With age, the lens of the human eye changes, gradually compacting 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 worsens, since the lens can hardly take the desired rounded shape even when the zinc ligaments are relaxed.
The degree of manifestation of presbyopia largely depends on the initial accommodative ability of the organ of vision. So, with severe myopia, changes are almost imperceptible, and with farsightedness they are felt more strongly.
Age-related changes of the lens are irreversible, visual impairment 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. Unsuitable glasses can cause asthenopia - a condition in which the lens bends more strongly than necessary.
The pathology is accompanied by rapid fatigue with vision at a short distance, pain, burning and itching in the eyes, headache.
Paralysis and paresis of accommodation
Such disturbances in the accommodation of the eye can be caused by a variety of reasons. It:
- diseases of the nervous system;
- toxic poisoning;
- injuries of the organs of vision;
- infection;
- exposure to drugs.
With paralysis of accommodation, the eyes can hardly distinguish small details at close range. Symptoms are especially pronounced in farsighted people, and with myopia, on the contrary, changes are less noticeable.
A professional optometrist who can determine the exact cause of the disease should treat such a pathology.
Spasm of accommodation
Spasms of eye accommodation - a pathological condition characteristic of children and adolescents. It is often called "imaginary myopia" or "tired eye syndrome."
A problem arises if the ciliary muscle cannot relax even in the absence of accommodation stimuli. Muscle spasm disrupts the working mechanism of the visual analyzer and leads to blurry vision both at long and near distances.
Possible causes of ciliary muscle spasm:
- heavy eye strain;
- long-term tension with vision at close distances (reading, working at a computer);
- work in low light;
- physical injuries;
- damage caused by exposure to bright light;
- individual features of the functioning of the organ of vision;
- incomplete mechanism of eye accommodation in children;
- hereditary predisposition;
- violation of the control of accommodation as a result of diseases of the nervous system;
- general weakening of the body;
- infection, especially in the area of cranial sinuses;
- weak muscles of the neck and back;
- disorders of the blood supply to the head.
Often, a spasm of lens accommodation is manifested against other global pathologies:
- metabolic failures;
- exhaustion;
- eating disorders;
- scoliosis
- congenital pathologies of the visual system;
- lack of immunological reactivity.
A person suffering from accommodation spasms complains of the following symptoms:
- eye fatigue;
- feelings of pain and burning;
- redness of the mucous membranes;
- lacrimation
- myopia;
- double vision
- headache;
- feeling unwell overall.
With early detection and proper treatment, accommodation disorders resulting from muscle cramps are reversible.
A neglected problem leads to a chronic change in muscle functioning and a gradual deterioration in vision, myopia. To prevent this, children and adolescents must visit an ophthalmologist annually.
Treatment of disorders
As in the case of any other disease, the treatment of eye accommodation disorders is more effective the sooner it is started. The best results are given by therapy in children, since the visual apparatus has not yet fully formed and can be easily corrected.
It is very important that the diagnosis and treatment are carried out by an experienced ophthalmologist. 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, which allows:
- find out the true causes of the problem, as well as the stage of development;
- detect concomitant diseases and pathologies;
- identify environmental factors affecting the development of disorders.
Therapy of eye accommodation disorders can go along several fronts at once:
- drug exposure (eye drops);
- various training techniques aimed at the general strengthening and improvement of nutrition of eye structures, as well as at training the accommodative ability of the lens;
- general healing 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 pathologies of vision includes:
- eye accommodation training using special exercises and apparatuses;
- strengthening the joints and blood vessels of the cervical-collar zone;
- a diet rich in trace elements and vitamins;
- general healing of the body.
Serious visual impairment begins with small reversible pathologies. Measures taken on time can stop the disease and significantly improve the quality of life.