RU2723598C1 - Device for determining visual acuity - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to medical equipment. Software-hardware system for determining visual acuity of a person being tested during video nystagmography comprises a mask with a means of fixation on the head of the person being tested and a set of corrective lenses, information output device configured to demonstrate an optotype in the form of a moving object with a variable structural framework, and data processing software configured to determine parameters of projected moving objects with variable structural structure and pupil detection with subsequent plotting of motion. Mask is equipped with an IR illumination system, two dichroic reflecting infrared mirrors, and two infrared video cameras detecting movement of eyes in the infrared range, and configured to record eye movements and are directly connected to the IR illumination module. Infrared video cameras are configured to transmit a projection of the image of the area of interest of the person being tested to the data processing device. IR illumination system and infrared video camera are located on the mask so that they are beyond the field of vision of the person being tested, and dichroic mirrors transmitting visible light and reflecting infrared light are fixed relative to chambers on the suspension common to them.

EFFECT: use of the invention enables higher accuracy of determining visual acuity with correction and without correction, based on the results of video nystagmography.

5 cl, 11 dwg

Description

FIELD OF THE INVENTION

The invention relates to medical equipment, in particular to diagnostic equipment, namely to ophthalmology, and is intended to determine objective visual acuity based on the fixation and recording of specific eye movements.

State of the art

A system for determining visual acuity based on the determination by a medical specialist of the moment of occurrence of optokinetic nystagmus, including a mechanical device (rotating drum), and accessories (replaceable, pre-created optotypes, lenses). Disadvantages of the system: the need for manual change of optotypes, a limited set of optotypes, the subjectivity of assessing visual acuity, both on the part of the patient and the operator.

A device for controlling visual acuity is known (RF patent No. 21644074, 09/10/2000, IPC АВВ 3/02). The device includes a light source, a plate with groups of characters of the same size placed on it, an information converter with a memory unit, an indication unit, and a command generation unit. These blocks are connected with the information converter for alternately highlighting a group of characters. The light source is made in the form of a matrix of light emitters, each of which is connected through an inclusion unit to the output of the information converter, while the information converter contains an optical system that is located in close proximity to the eye being examined. The device is configured to change the distance between the plate and the optical system and is equipped with a measurement scale.

The prior art device for determining visual acuity (RF patent No. 2269921, 10.27.2005, IPC АВВ 3/032). The device includes optotype tables with a step of 0.05, different contrast and background color. Tables are placed in a wooden box open in front, the walls of which are lined with mirrors from the inside. The device also has two sensors: the illumination of tests and the illumination of the surrounding field, two dimmers: the surrounding field and tests, an illumination indicator that measures illumination in digital terms, and a light source, which is a halogen lamp that allows you to achieve illumination of up to 1000 lux.

The disadvantages of these devices include the static nature of optotypes, which makes the devices unsuitable for assessing dynamic visual acuity.

Also known from the prior art is a method and apparatus for determining dynamic visual acuity by computer testing [Kubarko A.I., Lukashevich I.V. Analysis of the mechanisms of dynamic visual acuity // Minsk; BSMU, Medical Journal. - 2007. - No. 1 (19)], selected by the authors for the prototype. The method consists in the fact that subjects in a completely darkened room, after ten minutes of adaptation to darkness, were asked to recognize the direction of the Landolt ring defect while it was moving across the dark monitor screen, the minimum recognition time being an indicator of dynamic visual acuity.

In the above analogues of devices for recording and recording specific eye movements and video histograms, there is no possibility of an objective assessment of visual acuity based on registration of optokinetic nystagmus using IR video cameras, the recording was carried out using slit lamps by a subjective physician, photo and video cameras operating in the visible range. The use of radiation in the infrared range eliminates the negative impact on the determination of the position of the pupil of the eye glare, spurious illumination in the optical range, eliminates the interfering effect of visible light on the reaction of the patient’s eyes during the determination of visual acuity.

SUMMARY OF THE INVENTION

The objective of the claimed invention is to provide a device designed to record and analyze specific eye movements for professional use by a qualified medical professional with an objective determination of visual acuity.

The technical result of the claimed invention is to increase the accuracy of determining visual acuity with and without correction, based on the results of video histogram.

The technical result of the claimed invention is achieved through a device for determining the visual acuity of a test subject, comprising a mask with a set of corrective lenses, an information output device configured to demonstrate a moving object with a variable structural structure, and a data processing device configured to determine the parameters of projected moving objects with variable structural structure and pupil detection with subsequent construction of a motion schedule, while the mask has an IR illumination system, two dichroic mirrors reflecting infrared light, and two IR cameras recording eye movements in the infrared range, and made with the ability to record movements the eye and are directly connected to the IR illumination module, whereby the IR video cameras are configured to transmit a projection image of the subject's area of interest in the information processing device, while the IR illumination system and the IR video camera are located on the mask so that it is outside the field of view of the subject, and dichroic mirrors transmitting visible light and reflecting infrared light are stationary relative to the cameras on the suspension, common with them.

In the particular case of the implementation of the claimed technical solution, the mask is made in the form of spectacle frames and is made with the ability to adjust and fix the individual characteristics of the subject's face.

In the particular case of the implementation of the claimed technical solution, the set of corrective lenses contains aspherical lenses.

In the particular case of the implementation of the claimed technical solution, the set of corrective lenses contains positive and negative spherical and cylindrical lenses, apertures, color filters of red and green colors, as well as occluders.

In the particular case of the implementation of the claimed technical solution, the set of corrective lenses contains spherical lenses having a biconvex or biconcave shape.

In the design of the device for determining visual acuity, mirrors are used that transmit visible light and reflect infrared radiation, as well as video cameras that record the occurring eye movements (optokinetic nystagmus) in the IR range, and an information processing device that recalculates the sizes of the optotype based on data entered by the user and simulates their movement similar to the drum used to call optokinetic nystagmus (OKN).

In the process of demonstrating animation with the movement of the optotype, video recording of the movement of the pupil is conducted. Since the size of the optotype is designed for a certain visual acuity, only an individual with sufficient vision can distinguish it. Based on the technology of machine vision, an analysis of the movements of the pupil is carried out, and visualization is built according to these parameters - the curves on the graph. Visualization allows a specialist doctor to confirm whether the patient monitored the movement of the optotype during the animation or not, thereby establishing objectively, without the participation of the patient, the fact of the ability to distinguish an object of a certain angular size from a certain distance. Offering various test variants with different optotypes, it is possible to establish on which variant of the optotype the subject ceases to follow the animation on the screen. To confirm the test, it is proposed to insert a corrective lens and apply the optotype size corresponding to higher visual acuity in the test, where the subject will track smaller optotypes that he could not distinguish without correction. Thus, the subjective assessment of the subject's ability to distinguish elements on the screen is excluded, which makes the method objective and more resistant to attempts to mislead a specialist doctor.

Brief Description of the Drawings

Details, features, and also advantages of the present invention follow from the following description of embodiments of the claimed technical solution using the drawings, which show:

FIG. 1 - appearance of the mask;

FIG. 2 - front view of the mask;

FIG. 3 is a side view of the mask (glasses) of the video histogram;

FIG. 4 - appearance of the mask (glasses) of the video histogram;

FIG. 5 - projection of a visible image;

FIG. 6 - human eye;

FIG. 7 is a graph of the study of the OKN;

FIG. 8 is a description of the components of the nystagmus cycle using the example of a single cycle consisting of slow and fast phases;

FIG. 9 is a block diagram of the operation of the device;

FIG. 10 is a block diagram of the operation of the device;

FIG. 11 - examples of objects with variable structure.

The following positions are indicated in the figures:

1 - earhook; 2 - locking screw; 3 - holder; 4 - adjustment wheel; 5 - cable clamp; 6 - casing of an IR video camera; 7 - IR video camera; 8 - dichroic mirror; 9 - C-Mount adapter with IR illumination; 10 - a plastic base; 11 - nose nose; 12 - focus ring; 13 - the frame of the lens; 14 - corrective lens, or light filter or occluder; 15 - contour of the palpebral fissure; 16 - axis of the palpebral fissure; 17 - contour of the free edge of the eyelid; 18 - contour of the iris; 19 - eye protein; 20 - lacrimal meat; 21 - contour of the upper eyelid; 22 - contour of the lower eyelid; 23 - eye opening width; 24 - the inner corner of the eye; 25 - the outer corner of the eye; 26 - top of the free edge of the lower eyelid; 27 - the length of the palpebral fissure; 28 - top of the free edge of the upper eyelid.

In the figures are also indicated: t - time; ϕ is the angle of rotation of the eye; A is the amplitude; T is the duration; s is a sign of belonging to the slow phase of the cycle (slow); f - sign of belonging to the fast phase of the cycle (fast).

Disclosure of invention

A video nystagmograph is a hardware-software complex consisting of a mask, a set of corrective lenses, a monitor projecting optotypes of a certain size, and software that allows you to determine the parameters of the projected optotypes and conduct pupil detection with subsequent construction of a motion graph.

The sizes of contrast elements of optotypes are calculated on the basis of the well-known position of Donders-Snellen that the determination of visual acuity requires the use of signs visible to the patient with an angular size of the order of one minute. These sizes are determined from the geometric dependence tan α = x / h, where x is the linear size of the contrast element, h is the distance from the eye to the projected optotype. From this it turns out, for example, that an element with a linear size of 1 mm has an angular size of 1 angular minute if it is projected from a distance of 3.5 m. Based on this dependence, the sizes of the contrast elements are calculated for the actual study. Also, when calculating visual acuity, the dependence V = d / D is used, where V is the visual acuity, d is the distance from the eye to the optotype, and D is the distance from which the element is visible as having an angular size of 1 angular minute.

To determine visual acuity during video nystagmography, a device is used to demonstrate a moving object with a variable structural structure - an optotype, while the eyes make involuntary movements rhythmically with the patient's ability to distinguish the structure of objects. Optotypes correspond to a certain visual acuity. Optotypes correspond with the values of visual acuity of the Sivtsev table and the specified parameters in accordance with the previously established order. Examples of objects with a variable structure are shown in FIG. eleven.

The mask of the device for determining visual acuity is a modified form of a standard spectacle frame. The mask of the device for determining visual acuity is equipped with a plastic base with movable arms, removable nose pads, two removable holders with mirrors that reflect infrared light and IR video cameras, magnetic lens clamps that make it easy to change corrective lenses, rotate them, and install with a package consisting of two lenses and a remote spacer; IR illumination, located on the back of the magnetic clips, providing uniform illumination of the eye and eliminating flare, spurious reflections when working with lenses.

The mask is made with the possibility of adjustment / fixing under the individual characteristics of the subject's face. To register the parameters of the eyes, a mask is worn on the subject so as to ensure complete capture of the area of interest of the study.

The need to use lenses of different diopter levels imposes certain conditions on the design of the mask of a video histogram: the presence of guides for fixing the lens, positioning the corrective lens at a certain vertex distance not exceeding 15 ± 1 mm.

When registering eye movement, the possibility of observing moving objects with a variable structural structure gives the researcher video recording in the IR spectrum, which is invisible to the human eye. An additional advantage is the small influence of external illumination of the visible spectrum on the registration result.

IR illumination system illuminates the palpebral fissure. The IR illumination system consists of LEDs located on the mask from the side of the subject’s face on both sides of each eye and emitting towards the eye. The operation of the device does not affect the human perception of the visible spectrum and is safe for health, assuming that the level of safe radiation energy in this spectrum is not exceeded.

In order for the backlight and construction elements not to introduce significant deterioration in the subject's field of vision of the ability to track moving objects, a dichroic mirror was used. The dichroic mirror reflects, at angles close to 45 °, the infrared waves, but does not refract or distort the rays of the visible spectrum. This property of dichroic mirrors makes it possible to construct a refraction system so as to remove the IR illumination and the IR video camera outside the field of view of the subject. The light of the spectrum invisible to the human eye is reflected from the surface of the eye with different intensities, which allows you to get an image of the eye, including: the inner and outer corners of the eyes, the free edges of the upper and lower eyelids, the contour of the palpebral fissure, the contour of the free edge of the eyelids, the contours of the iris, pupil sclera eyes.

Dichroic mirrors transmitting visible light and reflecting infrared light are located motionless relative to the cameras on the suspension, common with them. These mirrors are necessary to separate the reflection of the subject’s eye (with further video recording by IR cameras) and the light entering the patient’s eye from the optotypes displayed on the screen.

IR video cameras that record specific eye movements (optokinetic nystagmus) in the IR range allow you to record the patient’s eye movements and work in direct connection with the IR illumination module. An IR video camera allows you to transfer the resulting projection of the image of the region of interest to a computer program for further processing.

To increase the accuracy of recording parameters of the eye, the device should have the means of reliable fixation on the head of the subject. This is achieved by using the design of the earhooks and nose pads. The earhooks include fastenings for a tightening system with a latch. To provide an opportunity to increase the research time and minimize the impact on the fatigue of the test subject, the design is designed to minimize the weight and comfort of the test subject when fixing the device. The device does not block the airways, does not put pressure on the nose and in the temple area. The presence in the mask of a video histogramograph of polymer naso-pads of various sizes allows us to make the mask universal, suitable for use in a wide range of patients.

A set of corrective lenses is a selection of positive and negative spherical and cylindrical lenses, diaphragms of various sizes (1, 3, 4 mm), color filters in red and green, as well as occluders. The kit includes spherical lenses for correcting myopia and hyperopia, as well as cylindrical lenses for correcting astigmatism of varying degrees. Corrective lenses are used by the doctor as necessary, the order of their location is important when they are installed in the device holder, and determined by the doctor.

Spherical lenses with a biconvex or biconcave shape are included in standard corrective sets. The diameter of the lenses used corresponds to the average size of the length of the palpebral fissure, which allows not to violate the quality of shooting the eye and further detection of the pupil.

Taking into account the necessity of using IR video cameras, the minimal image distortion present in the optical system "IR video camera - IR mirror - corrective lens - eye" is important.

To implement this solution, we proposed the use of a specific lens design - aspherical (the lens has one flat surface, and the second, respectively, diopters - convex or concave) with different refractive indices (increasing in accordance with an increase in the lens diopter). Compliance with these conditions allows you to achieve a minimum change in eye size and, as a result, does not affect the quality of shooting and detection of the pupil.

The method of video nystagmography is based on the graphic registration of induced optokinetic nystagmus (OKN). To implement this technique, a device is used that demonstrates a moving object with a variable structural structure - an optotype, for example, an animated optotype, while the eyes make involuntary movements rhythmically with the patient's ability to distinguish the structure of objects.

A computer program presents data on the called OKN on the operator’s monitor in the form of a specific graph. The figure 7 shows an example of a study graph, which shows: visual acuity of 0.1 when moving an object with a variable structure from right to left (speed: 8 rpm, optotype: vertical lines).

The animation output to the display and the process of capturing frames from the corresponding camera in the mask are activated. In the process of research, a quick analysis of the position of the pupil is performed. After the test time has elapsed, the procedure for saving the recording is called.

After the analysis is completed, a graph is displayed illustrating the movement in the corresponding direction.

Depending on the settings, several search strategies are selected:

1) a frame is received, smoothing is performed, the dark regions are united by the threshold color value.

2) the most suitable area is selected, a mask is produced from it to calculate the estimated position of the pupil, the area is passed through predictors that confirm whether the object is a pupil or not. Uses the Canny and Hough methods. A search may be affected by a previous frame, which gives an area of interest for the intended search.

3) a frame is received, transmitted to the trained classifier on a special sample, the classifier transfers the area similar to the pupil to the predictors. Predictors confirm the result.

4) 2 and 1 method sequentially, the transition to the next is carried out depending on the result of the check by the predictor of the previous one. First, the region of interest is processed, if necessary, the entire frame.

5) the relative displacement is calculated relative to the first frame with a successfully recognized pupil. After starting the program, the driver is initialized to the cameras built into the mask. During the initialization process, the affiliation of the IR cameras to the entered license key is checked. In the event of a mismatch, the controls for interacting with the device are blocked.

Claims (9)

1. A hardware-software complex for determining the visual acuity of a subject during video nystagmography, containing a mask with means for fixing it on the subject’s head and a set of corrective lenses, an information output device configured to demonstrate the optotype in the form of a moving object with a variable structural structure, and data processing software configured to determine the parameters of projected moving objects with a variable structural structure and detect a pupil with subsequent construction of a motion graph, the mask contains an IR illumination system, two dichroic mirrors reflecting infrared light, and two IR video cameras recording eye movements in the IR range and made with the ability to record eye movements and directly connected to the IR illumination module, moreover, the IR video cameras are capable of transmitting the projection of the image of the subject’s area of interest to the data processing device, while the IR illumination system and the IR video camera are located on the mask so that they are outside the subject’s field of view, and dichroic mirrors transmitting visible light and reflecting infrared light, are stationary relative to the cameras on the suspension, common with them. 2. The device according to claim 1, characterized in that the mask is made in the form of spectacle frames and is configured to adjust and fix to the individual characteristics of the subject’s face, while the means of fixation on the subject’s head are made in the form of earhooks and nose pads. 3. The device according to claim 1, characterized in that the set of corrective lenses contains aspherical type lenses. 4. The device according to claim 1, characterized in that the set of corrective lenses contains positive and negative spherical and cylindrical lenses, apertures, color filters in red and green, as well as occluders. 5. The device according to claim 1, characterized in that the set of corrective lenses contains spherical lenses having a biconvex or biconcave shape.

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