RU2410998C2 - Method for measuring relative accommodation - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention refers to medicine, namely to ophthalmology and aims at measuring relative accommodation. A patient is presented on a plane at a minimum visual angle with an image of two skew lines with pairs of identical rings unequally distant in pairs with optotype numbers along the whole length of the lines; permanent vergence is monitored by a patient's sensation of a binocular image in the form of three lines middle of which is perceived as vertical by the patient; the patient is set to transfer a central staring along these lines from the nearest pair of optotype numbers to the most distant one. Measuring relative accommodation "+" or "-" is carried out by a dioptric equivalent of a distance to accurate perception of the nearest or most distant optotype number on the vertical line.

EFFECT: invention allows higher accuracy of measurement and effectiveness training of relative accommodation, reduced labour input and cost price of the procedure.

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Description

The present invention relates to medicine, namely to ophthalmology, and is intended to measure relative accommodation.

Relative accommodation is a change in the focusing ability of the eye with a fixed reduction in the eyes - vergence. It is one of the important functional indicators in the study and restoration of the visual system of patients with progressive myopia.

Myopia (myopia) is the most common visual impairment. In the world there are more than a billion short-sighted people. Complicated myopia is one of the main causes of disability due to eye diseases.

In the pathogenesis of progressive myopia, one of the key factors is the mismatch between the strength of accommodation and the visual work performed at close range [Avetisov E.S. Myopia. M .: "Medicine", 1999, p.154]. With weakened accommodation, long-term work at close range becomes an unbearable burden for the eyes. In these cases, the body is forced to change the optical system of the eyes so as to adapt it to work at close range without the strain of accommodation. This is achieved mainly by lengthening the anteroposterior axis of the eye during its growth and the formation of refraction. The weakness of the accommodative apparatus may be due to congenital morphological inferiority of the ciliary muscle, its lack of fitness or the result of exposure to general diseases of the body. The reason for the weakening of accommodation is also insufficient blood supply. It is well known that muscle activity is a powerful activator of blood circulation. With the development of axial myopia, the incentive to accommodation is lost due to the approach of the further point of clear vision, which, in turn, leads to a decrease in the load on the ciliary muscle and the development of its training. Under these conditions, an excessive load on the ciliary muscle during visual work at close range can lead to its spasm. Spasm of accommodation also causes further progression of myopia.

The work of accommodation is characterized by two indicators. The possibility of changing the refraction of each eye individually is measured by absolute accommodation. But when objects are fixed with two eyes in parallel with accommodation, vergence changes (degree of convergence of the eyes: convergence - inside, divergence - outside), so the convergence tension increases the force of absolute accommodation. Since binocular vision is natural for the physiology of visual perception, the degree of change in accommodation with constant, fixed vergence is measured by another indicator - relative accommodation. Thus, relative accommodation (OA) is independent of convergence performance. With nearsightedness, the further point of clear vision approaches the eye, the need for absolute accommodation decreases, and the convergence remains the same - an imbalance in work occurs, so relative accommodation is of greater clinical importance [Avetisov E.S. Myopia. M .: "Medicine", 1999, p.23]. In relative accommodation, two indicators are distinguished: the positive part (OA +) - how much more accommodation can strain (volume, reserve, reserve of accommodation) and the negative part (OA-) - how much accommodation can be relaxed (the spent part of accommodation) when two eyes are fixed on a single object from a distance of 33 centimeters (the average distance of work near).

Monitoring and restoring relative accommodation is one of the key pathogenetic points in the treatment of progressive myopia.

A known method of measuring relative accommodation using a set of trial spectacle lenses [Avetisov ES Myopia. M .: "Medicine", 1999, p.171]. A patient reading line No. 4 (corresponding to visual acuity of 0.7) of the optotypes checklist for close proximity from a distance of 33 centimeters, pairwise to both eyes to lenses that completely correct the lack of refraction into the distance, additionally put scattering (negative, negative) glasses from -0, 5D sequentially with a step of -0.5D to the maximum, still enabling clear binocular (i.e., non-dual) text perception. The optical power of the maximum additionally attached glass, with which a clear perception of the text is still possible, shows the value of the positive part of the relative accommodation (OA +).

To determine the negative part of the relative accommodation, the patient reading line No. 4 of the optotypes check table for close proximity from a distance of 33 centimeters, pairwise to both eyes to the lenses that completely correct the lack of refraction in the distance, additionally collect (positive, plus) glasses from + 0.5D sequentially in increments of + 0.5D to the maximum, still giving the possibility of a clear binocular (i.e., non-dual) text perception. The optical power of the maximum additionally attached glass, with which a clear perception of the text is still possible, shows the value of the negative part of the relative accommodation (OA-).

The disadvantages of the method

1. High complexity and duration: for research, it is necessary to sequentially insert and remove up to 17 pairs of lenses in the spectacle frame, which, together with the study of absolute accommodation and convergence, takes up to 10 minutes.

2. The high cost of research due to the high price of a set of glasses and an apparatus with lenses (phoropter).

3. Low accuracy of the study. Existing sets of test spectacle lenses allow the study to be done only in increments of 0.25D, which is not enough to determine the negative part of the relative accommodation (“-”), showing the possibility of restoring visual acuity in the distance. In addition, the measurement accuracy decreases due to a decrease in the size of the optotype when observing it through a strong negative glass.

4. The impossibility of controlling the binocularity of perception, since reading the text is possible with one eye: often patients do not fix attention on double vision and, with an increase in optical load, continue to read the text with only one eye, which leads to falsification of the research results.

5. The patient’s inability to independently control the amount of relative accommodation (at home) using a set of test glasses.

The objective of the invention is to improve the accuracy of measurement; relative accommodation, cheapening and reducing the complexity, as well as expanding the functionality of the method.

The technical result is achieved by measuring relative accommodation by tension and relaxation of accommodation in a constant state of vergence, characterized in that the patient is shown on a plane at a minimum viewing angle an image of two crossed lines with pairs of equally spaced pairs of identical rings with optotype numbers along the entire length of the lines, while the constant state of vergence is controlled by the patient’s sensation of a binocular image in the form of three lines, the middle of which the patient senses it is located vertically, and cause the patient to translate the central fixation of the gaze along these lines from the nearest pair of optotype numbers to the most distant one; the value of the relative accommodation “+” is determined by the diopter equivalent of the distance to a clear perception of the nearest optotype in the vertically sensed line, and the value of the relative accommodation “-” is determined by the diopter equivalent of the distance to the clear perception of the outermost optotype in the vertically sensed line.

The invention is illustrated by drawings, in which Fig. 1 shows a diagram of a device for measuring relative accommodation, Fig. 2 shows a spatial picture perceived by a patient during preplanar merging of optotypes, Fig. 3 is the same, at a planar merger.

The device (Fig. 1) contains a sheet of paper 2000 × 297 mm in size placed on the table with the image of two straight intersecting lines 1 and 2, the distance between the ends 3 and 4 closest to the patient’s eyes is equal to the average interpupillary distance and is 56 mm. The intersection point of 5 lines is at a distance corresponding to the linear equivalent of 3.0D (diopter) - 333 mm from the patient’s eyes. The observation height is determined empirically as the minimum above the image plane, which makes it possible to observe each of the rings, and is 50 mm. Along the lines, identical rings 6 are arranged in pairs with optotypes placed in them. As optotypes, the proposed method uses numbers (optotype) to denote the value of refraction when they are observed from points 7 and 8 located above points 3 and 4. This allows the accommodation to be determined by the value of a clearly distinguishable optotype. The size of the optotype type in each pair corresponds to 100% visual acuity when observed from a distance corresponding to the indicated refraction. Since the farthest rings are located at an acute angle to the axis of view, which makes it difficult to observe, the upper half of each of the rings with an optotype is cut out and raised above the plane perpendicular to the axis of observation. The distance of each optotype number along line 1 to point 7 and along line 2 to point 8 corresponds to the linear refraction equivalent indicated by this optotype number. In this case, adjacent pairs of rings to point 5 are located at a distance equal to the linear equivalent of 0.5D, and after point 5 - at a distance equal to the linear equivalent of 0.1D. This is established experimentally and is due to a change in the linear equivalent of refraction in the areas of pre- and plane-to-plane merging of optotype numbers.

The method is as follows.

The patient is asked to look with each eye along lines 1 and 2. Since the lines intersect at point 5, corresponding to 3.0 D, this ensures constant convergence, while the patient has a feeling of three lines, with rings “put on” on them, located in front of the image plane (pre-plane fusion zone) - further than point 5 (Fig. 2) and beyond the image plane (plane-fusion zone) - closer to point 5 (Fig. 3).

When preplanar merge (figure 2) the left eye from point 7 feels line 2 tilted to the left, and line 1 - vertical, the right eye from point 8 feels line 1 tilted to the right, and line 2 - vertical. In this case, the sensations of vertical lines from each eye merge into the sensation of a single vertical line 9.

When flatter merging (figure 3), the left eye from point 7 feels line 2 tilted to the left, and line 1 - vertical, the right eye from point 8 feels line 1 tilted to the right, and line 2 - vertical. In this case, the sensations of vertical lines from each eye merge into the sensation of a single vertical line 9.

The sense of "verticality" of the lines guarantees a constant state of vergence. The perception of the near rings with optotypic numbers felt as “lower” 10 occurs with the maximum accommodation voltage, the perception of the distant ones felt as “upper” rings 11 (Fig. 2) - with a minimum.

The measurement of relative accommodation is carried out in two stages.

1. To measure the positive part of the relative accommodation of OA + the patient is asked to name the closest optotype, perceived clearly and without double vision. For the mathematical recalculation of OA + from the absolute accommodation indicator (optotype), you need to subtract 3.0D. Greater measurement accuracy is ensured in the pre-plane fusion section, since the possibility of modern printers provides clearer printing of optotype numbers larger than 1 mm (0.5-3.0D), the linear distance between the optotype numbers in this section is greater than in the non-plane section merging, which makes it possible to measure with an accuracy of 0.1D. Therefore, for a more accurate measurement of OA + is carried out in the area of pre-plane fusion by adding to the optical correction into the distance of the reducing lens -2.5 ... -5,0D. For the mathematical recalculation of OA + with a reducing lens, it is necessary to subtract 3.0D and the power of the reducing lens from the absolute accommodation index. For convenience, in the lower hemisphere of each ring along the line for observation with the right eye, the OA + value for the reducing lens is −5.0D, which makes it possible to measure OA + from 2.5 to 5.0D (physiological indicator of OA + aged 6 to 30 years )

2. To measure the negative part of the relative accommodation of the OA patient, they are asked to name the farthest optotype, which is perceived clearly and without double vision. For the mathematical recalculation of OA-, it is necessary to subtract the value of the absolute accommodation indicator (optotype) from 3.0D. Since the physiological value of OA- is 2.5 ... 3.5D, it is convenient to use a reducing lens + 2.0D to determine its value. For convenience, in the lower hemisphere of each ring along the line for observation by the left eye, the OA-value for a reducing lens + 2.0D is plotted, which makes it possible to measure OA- from 2.0 to 4.5D.

The lines in the images allow you to control the optimal position of the observer relative to the plane of their location: each eye looks along its line, stereo perception should give a feeling of a strictly vertical midline - this is a guarantee of stable vergence. The perception of the adjacent line with each eye gives the sensation of two more lines. Thus, the sensation of three lines is a guarantee of binocular perception. Rings are necessary to enhance the effect of stereo perception due to the inclusion of corresponding receptive fields of the retina, for which the round shape of the object is optimal. The diameters of the rings are selected mathematically so as to give a feeling of the same size of the rings along the entire vertical of the perceived pattern, which helps to simulate the verticality of the midline. The number of rings is maximum, ensuring a minimum change in accommodation when observing each subsequent series of optotype numbers: in the preplanar fusion zone - in 0.1D increments, in the preplanar fusion zone - in 0.5D increments. The difference in 0.5D is more reliable for the objective recording of changes in OA, but for the subjective, the minimum increase in eye strength confidently increases the demonstrativeness in the treatment results. The angle at which the lines intersect with the rings and the optotype is calculated according to the average interpupillary distance of the treated patients - children: 56 mm. When the interpupillary distance is greater or less than 56 mm, the line of sight deviates from the line of optotypes, but the linear distance to the optotypes and, accordingly, the magnitude of OA are maintained. In this case, an error occurs in the magnitude of convergence, but for the same patient with a constant interpupillary distance and, accordingly, constant convergence, this error is leveled out in dynamics and does not affect the value of OA. In principle, it is possible to create separate images for each variant of the interpupillary distance - for individual use at home, but in clinical conditions this will require either arranging several relative accommodometers, which will take up a lot of space, or changing images, which will increase the study time.

The determination of relative accommodation using this method takes about 1 minute, which significantly saves the time of diagnosis and increases the effectiveness of the advisory reception. Observation of the same picture with optotype numbers enables the patient to subjectively assess the state of refraction and accommodation of the eye, which is impossible when measuring it using lenses.

In our practice, not a single patient was encountered who would not be able to perceive stereographic images. For weak convergence, for training in stereographic fusion, we use prisms with a base to the nose or an ophthalmic compensator with a prism and slit-like diaphragm that opens only one line for each eye. Clinical testing was performed on 200 patients. No complications or side effects were detected.

Thus, the proposed invention allows with minor material and labor costs to increase the accuracy of measurement and control of relative accommodation.

Claims (1)

A method of measuring relative accommodation by tension and relaxation of accommodation with a constant state of vergence, characterized in that the patient is shown on a plane at a minimum viewing angle an image of two crossed lines with pairs of equally spaced pairs of identical rings with optotypic numbers along the entire length of the lines, with a constant state of vergence they control the patient’s sensation of a binocular image in the form of three lines, the middle of which the patient feels vertically located, and stagnation they instruct the patient to translate the central fixation of the gaze along these lines from the nearest pair of optotype numbers to the most distant one, and the value of relative accommodation “+” is determined by the dioptric equivalent of the distance to a clear perception of the nearest optotype number on a vertically sensed line, and the value of relative accommodation “-” determined by the diopter equivalent of the distance to a clear perception of the most distant optotype in a vertically sensed line.

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