Accommodation is an ophthalmology term that refers to the eye’s ability to provide clarity of image. In other words, it is the ability to focus vision and to clearly distinguish visible objects. This mechanism sometimes fails, in such cases it is necessary to carry out a study of the volume of accommodation to establish the cause of the defect and to eliminate it.
Accommodation Characterization
The term "accommodation" (translated from Latin accommodatio) means accommodation. This name already explains the mechanism of action of this property of vision. There is an adjustment of the eye to changes in optical conditions in order to ensure image clarity. A similar property in a person is formed in the first hours after his birth, while the organs of vision gradually get used to working together with the brain, transmit information received from outside him.
Norm
The accommodation mechanism finally completes the formation after 10-14 days of the baby's life. A common occurrence is a violation of sharpness, when the view is transferred from one object to another, especially when located at different distances from a person. But the eye at the same time quickly adapts to new conditions, and vision begins to focus immediately after the receipt of information about changes in the brain. In a split second, the lens begins to contract with a certain effort, and then the sharpness is restored again.
It must be borne in mind that if this does not happen, then there is some kind of violation that can interfere with sharpening, and only experienced specialists can determine the root cause.
Below we consider how to determine the amount of accommodation.
Volume determination
What is this study about?
During the examination, an important point is the determination of the norm of the volume of accommodation in order to judge the ability of the accommodation apparatus to function, as well as prescribe the appropriate therapy.
The volume is determined by the formula APR = AP - (± AR). APR is the desired value. AP is the distance to the closest observation point, and AR is the distance to the farthest point. The values used are diopter, not linear.
Absolute accommodation
The volume of absolute accommodation is the accommodation volume of one eye when the other is turned off from the act of vision. To determine it, you need to know the position of both points of clear vision.
Measurements of the far and near points in diopters are made by the following instruments: accommodameters or optometers. Reducing lenses are included in their design. The examinee 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 researcher shows two positions: the emergence of a clear optotype and then its blur. These are the positions of the far and near points of clear vision. In diopters, their value is indicated on a scale graduated between +6.0 - -5.0 D. The accommodation volume is determined by the algebraic difference between the two indicators on the scale.
Relative accommodation
The relative accommodation volume is the accommodation volume with two eyes open relative to a specific distance. Convergence is taken into account. Since the distance to the object is clearly defined (most often used is 0.33 m), you need to put lenses to the eyes - negative for stress accommodation and positive for relaxation.
How is the volume of accommodation determined in this case?
You can use spectacle frames 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 bar. As a test, text No. 4 is usually used. The patient looks at the text, which is located at a set distance, with two eyes. Preliminary ametropia is fully corrected. In front of two eyes, successively install negative and positive 0.5 D lenses as much as necessary so that the subject could not 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 accommodation reserve or the positive part. Its decrease indicates a deterioration of the near vision, an increase in predisposition to myopia, the progression of the latter or an increase in visual fatigue.
What does the estimate of accommodation reflect?
Pathological changes
Spasm of accommodation is a false myopia, a violation occurs due to prolonged visual load and injuries. It is one of the most common violations. This pathology is most often found in students and schoolchildren.
In ophthalmology, three types of muscle spasm of the eye are distinguished:
- Artificial - may occur due to the use of a number of medications by the patient.
- Physiological - appears for self-correction of vision with hyperopia or myopia. There is a change in the curvature of the lens of the eye and tension of the ciliary muscle.
- Pathological - this form is characterized by increased refraction of vision, its severity is significantly reduced.
- Presbyopia - this process is caused by age-related changes, occurs after forty years. In this case, the lens does not project light rays well and loses elasticity.
- Paralysis - complete loss of mobility function 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 - it is difficult for the patient to focus at close range. Paresis of accommodation is usually the result of poisoning by toxic substances, injuries.
- Asthenopia - a person experiences pain while working at a computer, reading. With this pathology, special glasses are required.
How does accommodation change with age?
Changes with age
Spasm in children can develop due to the immaturity of the accommodation mechanism. For such a condition, a characteristic picture is a relaxation of accommodation when looking away into the distance, as well as increased clinical refraction. In humans, because of this, false myopia appears.
In adulthood in people, accommodation disorders occur due to changes in the lens: elasticity decreases, weight, shape and size change.
Far and near points of clear vision by the age of 60-70 are combined, the accommodation function 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 contractile activity of the ciliary muscle, processes of degeneration of the zinc ligament.
Studies show that in the ciliary muscle, changes do occur with age, leading to a decrease in its strength. This usually starts between 30 and 35 years old.
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 volume of accommodation to normal?
Treatment of disorders
The main methods of therapy are as follows:
- Magnetotherapy, electrophoresis, color therapy.
- Wear lenses and glasses to correct deviations.
- To eliminate violations, oculists also prescribe eye drops that dilate the pupils. 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 calculates the duration of administration and dosage.
- Be sure to take vitamin complexes.
- In some cases, laser therapy is required. In a person using this method, vision is restored, the development of pathology slows down.
We examined how the study of the volume of accommodation is conducted, identified the causes of violations and described the main correction methods.