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Methods for the study of accommodation
Last reviewed: 23.04.2024
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It is necessary to distinguish between absolute and relative accommodation.
Absolute accommodation is the accommodation of one (isolated) eye when turned off from the act of seeing the other. The mechanism of relative accommodation implies the accommodation of two eyes simultaneously while fixing a common object.
Absolute accommodation is characterized by two points on the visual axis: a further point of clear vision PR (punctum remotum) and the closest point of clear vision PP (punctum proximum). PR - the point of the best vision in space, the position of which actually depends on the clinical refraction. PP - the point of best vision at a close distance at the maximum accommodation voltage. Thus, the volume of absolute accommodation can be calculated by the formula:
A = R - PP,
Where A - the volume of absolute accommodation, R - clinical refraction, RR - the closest point of clear vision (all values in diopters). Refraction of points close to the eye is usually denoted with a "-" sign, since these points conditionally correspond to myopic refraction. For example, with the magnitude of clinical refraction equal to myopia 1.0 dpt, and the location of the nearest point of clear vision at 20 cm from the eye, the absolute accommodation volume will be:
A = -1.0 - (- 1 / 0.2) = -1.0 - (-5.0) = 6.0 (diopter).
Approximate age norms of the reserve of relative accommodation (A)
|
Age, years |
A, D |
|
7-9 |
3 |
|
10-12 |
4 |
|
13-20 |
5 |
|
21-25 |
4 |
|
26-30 |
3 |
|
31-35 |
2 |
|
36-40 |
1 |
|
41-45 |
0 |
To determine the position of the nearest point of clear vision, use special devices (proximeters or akkomodometry).
The determination of the relative accommodation is carried out as follows. The patient is asked to binocularly (ie, with two eyes) to read the text of the table to verify visual acuity near. In the trial frame consistently (with an interval of 0.5 D) insert first positive and then negative lenses until the subject can still read. In this case, positive lenses will compensate for the already expended tension of accommodation, and negative ones, on the contrary, will cause this voltage. The values of the maximum positive and maximum negative lenses will indicate respectively the negative, i.e., consumed, and positive, i.e., remaining in the reserve, part of the relative accommodation. The sum of these indicators will amount to the volume of relative accommodation.
For an objective assessment of the condition of the accommodative apparatus of the eye, ergography is used . The essence of the method is to determine the performance of the ciliary muscle in visual work at close range. The results of the study are recorded as a graphical curve. It is proposed to distinguish 4 types of ergographic curves: the first characterizes the normal performance of the ciliary muscle, the rest - the increasing decrease in accommodative capacity.
From the practical point of view, the value of the reserve of relative accommodation, i.e., the indicator that serves as an indirect indication of the potential capabilities of the accommodation apparatus, is important. There is evidence that a decrease in the logotype indicates a predisposition to the onset of myopia.
For a long quiet work at close range it is necessary that the positive part of the relative accommodation be 2 times more negative.
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