Accommodation is an ophthalmological term that refers to the eye's ability to provide clear images. In other words, it is the ability to focus vision and clearly and distinctly distinguish between visible objects. This mechanism sometimes fails, in such cases it is necessary to perform a study of the amount of accommodation to determine the cause of the defect and eliminate it.
Characteristic of accommodation
The concept of "accommodation" (translated from Latin accommodatio) means adaptation. This name already explains the mechanism of action of this property of vision. The eye adjusts to changes in optical conditions in order to ensure image clarity. A similar property in a person is formed already in the first hours after his birth, while the organs of vision gradually get used to joint activity with the brain, transmit information received from outside.
Norma
The accommodation mechanism finally completes its formation after 10-14 days of the baby's life. A common thing is the violation of sharpness, when the gaze is transferred from one object to another, especially when located at different distances from a person. But at the same time, the eye quickly adapts to new conditions, and vision begins to focus immediately after information about the changes arrives in the brain. In a fraction of a second, the lens begins to shrink with a certain effort, and then the sharpness is restored again.
Keep in mind that if this does not happen, then there is some kind of violation that can interfere with the setting of sharpness, and only experienced specialists will be able to determine the root cause.
Let's look at how to determine the amount of accommodation.
Volume determination
What is this research about?
When examining, an important point is to determine the norm of accommodation volume in order to judge the ability of the accommodation apparatus to function, as well as prescribe appropriate therapy.
Volume is determined by the formula APR=AP - (±AR). APR here denotes the desired value. AP is the distance to the nearest point of observation, and AR is the distance to the farthest point. The values are dioptric rather than linear.
Absolute accommodation
The volume of absolute accommodation is the accommodative volume of one eye when the other is turned off from the act of vision. To determine it, you need to knowposition of both points of clear vision.
Measurements of far and near points in diopters are made by the following devices: accommodometers or optometers. Reducing lenses are included in their design. The subject looks with one eye into the lens of the device, and the researcher gradually moves the handle of the device, which in turn moves the test object. The subject shows two positions: the appearance of a clear optotype and then its blurring. These are the positions of the far and near points of clear vision. In diopters, their value is indicated on a scale graduated within +6, 0 - -5, 0 D. The accommodative volume is determined by the algebraic difference between the two indicators on the scale.
Relative accommodation
The relative accommodation volume is the accommodative volume with two eyes open relative to a specific distance. This takes into account convergence. Since the distance to the object is clearly defined (usually 0.33 m is used), it is necessary to put lenses on the eyes - negative for accommodation tension and positive for relaxation.
How is the amount of accommodation determined in this case?
You can use a spectacle frame for lenses, you can use a device that determines visual acuity, a semi-automatic or automatic phoropter with a table for checking near visual acuity, mounted on a rod. Text No. 4 is usually used as a test. The patient looks at the text, which is located onset distance, two eyes. Previously, ametropia is corrected completely. In front of both eyes, sequentially negative and positive lenses of 0.5 D are installed as much as necessary so that the subject cannot read the text. The value of the maximum positive lens shows the spent (negative) part of the accommodation of the relative type. The strength of the maximum of the negative lens determines the accommodative margin or positive part. Its decrease indicates a deterioration in the performance of near vision, an increase in the predisposition to myopia, the progression of the latter, or an increase in visual fatigue.
What does the assessment of the amount of accommodation reflect?
Pathological changes
Accommodation spasm is a false myopia, a violation occurs due to prolonged visual stress and injuries. It is one of the most common violations. This pathology is most often found in students and schoolchildren.
In ophthalmology, there are three types of muscle spasm of the eye:
- Artificial - may occur due to the patient's use of a number of medications.
- Physiological - appears for self-correction of vision with farsightedness or myopia. There is a change in the curvature of the lens of the eye and tension in the ciliary muscle.
- Pathological - this form is characterized by increased refraction of vision, its sharpness is significantly reduced.
- Presbyopia - this process is caused by age-related changes, occurs after fortyyears. In this case, the lens poorly projects light rays and loses elasticity.
- Paralysis is the complete loss of mobility by the ciliary muscle. A person with such a violation cannot read. If the problem is in a neglected state, it will be impossible to restore muscle activity.
- Paresis - Patient has difficulty focusing at close range. Paresis of accommodation is usually the result of poisoning with toxic substances, injuries.
- Asthenopia - a person experiences pain while working at a computer, reading. With such a pathology, special glasses are required.
How does the amount of accommodation change with age?
Changes with age
Spasm in children may develop due to the immaturity of the mechanism of accommodation. For such a state, a characteristic picture is the relaxation of accommodation when looking into the distance, as well as an increase in clinical refraction. Because of this, a person develops false myopia.
In adulthood, accommodation disturbances in people occur due to changes in the lens: elasticity decreases, mass, shape and size change.
Far and near points of clear vision are united by the age of 60-70, the function of accommodation in this state ceases to work completely.
In old age, the deterioration of accommodation occurs not only due to changes in the lens, but also as a result of other factors: a decrease in the contractile activity of the ciliary muscle, processes of degeneration of the zinn ligament.
Studies show that in the ciliary muscle with ageindeed there are changes leading to a decrease in its strength. This usually starts happening between the ages of 30 and 35.
The essence of the changes is based on the cessation of muscle tissue growth, which begins to be replaced by fat and connective fibers.
However, the mechanism of the ciliary muscle, despite this, only weakens, but does not lose functionality. The final stop of the ability to contract is due to age-related changes.
How to return the amount of accommodation to normal?
Treatment of disorders
The main therapies are as follows:
- Magnetotherapy, electrophoresis, color therapy.
- Wearing lenses and eyeglasses to correct deviations.
- Ophthalmologists also prescribe eye drops that dilate the pupils to correct abnormalities. These drugs relax the ciliary ligament. The duration of treatment usually ranges from a week to a month. Before prescribing drops, the doctor should check the pressure inside the eye. And only after that he calculates the duration of administration and dosage.
- Be sure to take vitamin complexes.
- In some cases, laser therapy is required. With the help of this method, vision is restored in a person, the development of pathology slows down.
We examined how the study of the volume of accommodation is carried out, identified the causes of violations and described the main methods of correction.
