RU2436496C1 - Method of applying optic system for determination of vision acuity - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to medicine, namely to ophthalmology and can be used for determination of vision acuity. In order to determine small angular distances observation of objects is performed via reducing optic system, which contains short-focus objective and long-focus eye-piece. Visual angle, at which virtual image of objects is seen, corresponds to visual angle of eye. Method can be used in research work and practical work of ophthalmologists for reliable measurement of vision acuity.

EFFECT: method makes it possible to test vision acuity in angular measures.

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Description

The invention relates to medicine, namely to ophthalmology, and can be used to determine visual acuity.

The study of visual acuity is one of the most important in determining the functions of vision.

Visual acuity is the sensitivity of the visual analyzer, reflecting the ability to distinguish between boundaries and details of visible objects; determined by the minimum angular distance between two points at which they are perceived separately [1, 2, 3].

Visual acuity is inversely proportional to the angular limit of resolution (angle of view). Signs have been used to determine visual acuity. When developing signs, the size of the informative section corresponding to the angular distance is taken into account. Signs are tabulated. The most widespread tables with a decimal step differences in the rows of the table. Based on the tables of signs, the distances between the table and the subject, the level of illumination, the contrast of the tables, national standards for recording visual acuity are developed [2, 3].

Known devices for subjective research of visual acuity by the method of presenting signs: on a illuminator of printed tables, transparency devices, devices for projecting signs and collimator devices. In collimator devices, a simple optical system (single magnifier) is used [6, 7], in the focal plane of which test marks are set in the form of transparencies. The device is used for mass preventive examinations of the population [3].

The preserved historical information on research in visual acuity is of research interest. The first ideas about visual acuity are found in the sources of ancient Greece and ancient Egypt. To determine the suitability for military service of Imperial Rome, the applicant was invited to consider the double star system in the constellation Ursa Major: Horse and Horseman (Mizar and Alcor). Astronomical observations of stellar objects laid the foundation for the study of the function of vision: visual acuity as an angular magnitude, fields of vision, color, and photosensitivity. Practical infinite remoteness, proximity to the mathematical definition of the “point” of astronomical objects meets the ideal conditions for the study of vision functions [4].

From the theory of optical systems, the ratio of the main focal lengths of the objective Fob to the eyepiece Fok determines the angular changes in the optical system [5].

In complex optical systems, including a large number of optical elements, two components can be distinguished that are equivalent to two lenses and carry the function of an objective and an eyepiece [7].

In optical instruments designed to increase the angle of view when observing large objects that are far away (telescopes, telescopes), it is assumed to install a telephoto lens and a short focus eyepiece, and the distance between the components satisfies the relation [5].

The laws of geometric optics, calculation formulas are universal in nature, are used in the description of optical devices. To calculate angular values, trigonometric functions are used [2, 3, 4, 5, 6, 7].

In the known methods for determining visual acuity, there are disadvantages. Registration of visual acuity using tables of signs involves the determination of relative visual acuity. The norm is the value of average measurements of visual acuity of a limited group. The decimal step in the size of the signs (10%) does not allow us to determine the intermediate data of visual acuity. The existing method for determining visual acuity using tables of signs is indicative of the indicator method of measurement, significantly different from reliable methods of measurement in other branches of technology. The method is far from the declared method for recording angular values of view in degree or radian measure. The method of registering visual acuity using tables, devices largely depends on the type and quality of the tests presented, the ability to memorize test signs or recognize them by any secondary signs, measurement conditions, patient intelligence [2, 3]. The use of astronomical observations to study the functions of vision is limited, depending on weather, geographic and other conditions. The method can be applied for an individual study of the researcher’s vision.

The ability to register visual acuity in angular measurements is associated with objective difficulties in modeling angular values of one or less minutes. Changing the angular magnitude of vision by known methods: removing an object over significant distances, reducing the size of the object, leads to an increase in negative moments and significantly affects the technical feasibility of the method.

To overcome the limitations when registering small angular values of the angle of view, it is proposed to use a reducing optical system.

The optical effect of angular reduction (opposite to angular magnification) is achieved if the optical system uses a short-focus lens and a long-focus eyepiece, and the distance between the components satisfies the relations. Figure 1 shows a diagram of the proposed method. Two point objects 3 are located at a distance L from the eye of the studied (optical system of the eye) 2. The objects are examined through a decreasing optical system 1. An imaginary, reduced, distant image of objects is formed 4. When reducing point objects 3, the images of objects are reduced 4. Achieving the minimum angle B, at which points are perceived separately, is the goal. Angle B is the desired angle of view, which determines the visual acuity of the subject. Angle A is the angle of view between point objects. The distance H is measured between two point objects. For the calculation, two measurements L and N are necessary. The calculation is made according to the formulas:

Angle B is less than angle A by the angular change in the optical system. The change in the optical system is determined by the ratio of the focal lengths of the lens and eyepiece. For a decreasing optical system, the change is less than unity. Respectively:

Optical removal of imaginary objects eliminates the impulse for accommodation (myopization) in the subject under study. Increasing the difference between the focal lengths of the lens and the eyepiece allows increasing the reduction ratio of the optical system, correspondingly increasing the distance H between objects, decreasing the distance L, and improving the recording conditions for small angular dimensions. The method can be implemented in standard rooms of medical institutions. It is convenient to use small luminous objects as point objects: diode bulbs, fiber optics; use apertures, filters, etc. Due to the optical reduction of the system, the imaginary images of objects are also reduced, which eliminates the negative effects of using point light sources. The size, brightness, color of objects should provide overcoming the threshold of excitability of the visual analyzer.

The effect of image reduction in the optical system in the prior art was not used. Using a reducing optical system solves the technical problem of determining visual acuity in angular quantities.

The method can practically be implemented using well-known optical devices: telescope, telescope, binoculars. Observation is performed when the instruments are rotated 180 degrees through the “standard lens”, the “standard eyepiece” is directed towards the object (figure 2). The applied characteristic of optical devices, which reflects the magnification of the optical increase, for example, × 9 (nine-fold increase), corresponds to the optical decrease of the same device (nine-fold decrease).

An example of using the method. Researched S., 45 years old, higher education. Monocular examination of the right eye. Visual acuity of the right eye according to medical documents 1.0, according to the tables of signs Golovin-Sivtsev - 1.5, by the projector of signs - 2.0. Research conditions: a darkened room of 10 m, two trinkets with diode bulbs diaphragmed 0.5 mm; as an optical system, a telescope was used, the optical change ratio was 9. When reducing objects to a distance of 12 mm, the minimum angle of separate image perception was achieved.

The calculation.

According to the Bradis table, angle A = 4 min, angle B = angle A / 9 = 27 s.

To calculate small angular distances, it is convenient to use the radian measure of angles; with sufficient accuracy, the angular measure is converted to the radian measure. 1 min = 0.000291 rad. 1 s. = 0.000005 rad. You can take into account that a radian measure of an angle of less than two degrees corresponds to the tangent of this angle.

The result of the study.

Visual acuity of the right eye of the researched S. is 27 p., Translated into relative values - 2.25 units. or 225% of the view.

The proposed method for determining visual acuity using a reducing optical system allows you to explore visual acuity in angular measures. The method can be used in research activities and the practical work of ophthalmologists for reliable measurement of visual acuity.

BIBLIOGRAPHY

1. Ch. Ed. Petrovsky B.V. Encyclopedic dictionary of medical terms. T.2, M., Soviet Encyclopedia. 1983. S. 275.

2. P.Romer. Guide to eye diseases. T.2, St. Petersburg. Practical medicine (V.S. Ettinger). 1913.p. 705-711.

3. Urmacher L.S., Aizenshtat L.I. Ophthalmic devices. Textbook. M., Medicine. 1988.p. 12-33, p. 174-181.

4. Vygodtsky M.Ya. Handbook of elementary mathematics. M., State Publishing House of technical and theoretical literature. 1955.p.38-39, p.115-116, p.328-331, 334-335, 367-368.

5. Zhdanov L.S., Maranjan V.A. Physics course. Part two. M., Science. 1968.S. 438-455.

6. Avetisov E.S. Myopia. M., Medicine. 1986. p. 5-7.

7. Sergienko N.M. Ophthalmic optics. M., Medicine. 1991.S. 15-21.

Claims (1)

A method for determining visual acuity, including recording the minimum angular distance between two point objects, characterized in that, in order to determine small angular distances, the objects are monitored through a reducing optical system containing a short-focus lens and a long-focus eyepiece, an angle of view under which an imaginary image of objects corresponds to the angle of view of the eye and is determined by the following ratios:

where angle A is the angle between point objects and the eye, angle B is the angle between imaginary images of objects under which they are perceived separately, corresponds to visual acuity; L is the distance from the eye to point objects; H is the distance between point objects; Fob - the focal length of the lens of the optical system; Foc. - the focal length of the eyepiece of the optical system.

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