RU2485879C1 - Method of measuring intraocular pressure - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to field of medicine, in particular to the field of ophthalmology for measurement of intraocular pressure. Method lies in performing pneumatic impulse on eye with simultaneous illumination of its surface by laser. After that, reflected signal is transferred into autodyne signal, its power is registered, then, the signal is digitised and analysed. Ratio of deflection value ΔZ and acceleration a, with which membrane is moving, is used as an information parameter. To find said parameters autodyne signal P(t) is analysed. Deflection value ΔZ is determined as a result of recovery of function of motion Z(t) by means of reverse function: θ+4π/λ0·Z(t)=±arccos(P(t))+2πn, where n=0,±1,±2, …; θ is advance of autodyne signal phase, λ0 is wavelength of laser irradiation. Acceleration is determined from solution of reverse problem of obtained as a result of determination of functional minimum, determined as the sum of squares of deviations of experimental Pexp and theoretical Pther of autodyne signal P(t) for different time intervals: $$S(\theta ,а)={\displaystyle \sum _i{(Р\exp (t_i)-Рther(t_i,\theta ,а))}^2}.$$

Intraocular pressure is determined by the obtained ratio ΔZ/a with application of calibration curve.

EFFECT: application of the invention will make it possible to increase accuracy of measurement of intraocular eye pressure in contactless way.

2 cl, 5 dwg

Description

The invention relates to the field of medicine and healthcare. In particular, this development can be used in ophthalmology to measure intraocular pressure (IOP) in vivo. The proposed method will allow to evaluate the IOP non-contact.

A known method of measuring intraocular pressure, which consists in using a variable frequency sound generator, a transmitting element, a receiving element, an amplifying circuit, and a computer. The method consists in the fact that when measuring the IOP, the vibration of the studied eyeball is provided by means of vibration. The vibration of the studied eyeball is measured by means of non-contact measurement of the quality factor (Q) of the resonance of the studied eyeball. The intraocular pressure is calculated depending on the Q value. The vibration tool and the measuring device are located on the eyelid of the eyeball (see patent for IZ No. 2290856 IPC A61B 3/16).

The disadvantage of this method and its implementing devices is the need for contact between the eyelid, the receiving and transmitting element, causing additional loading of the eyeball and a change in true IOP.

A known method of measuring pressure, in which the intraocular pressure is measured using a contact means that comes in contact with the eyelid, means of vibration that vibrates when voltage is applied, means of applying alternating current to the means of vibration, means of measuring the value of the flowing current through the means of vibration, information processing means. The method for measuring intraocular pressure is based on bringing the vibrating means into contact with the eyelid through the contact means, applying voltage to the vibrating means, measuring the value of the current flowing through the vibrating means, and measuring the pressure from the current value in the region of the resonance point calculated using the information processing means on based on the change in current value, which is caused by a change in the frequency of vibration (see patent for IZ No. 2372021 IPC A61B 3/16).

The disadvantage of this method is that the measurement of IOP is carried out through the eyelid. The search for the resonant frequency can be complicated by various values of the eyelid thickness, because for each person, these indicators will be individual.

Closest to the proposed solution is a non-contact method for measuring intraocular pressure, implemented using a radiation source, the optical axis of which is located at an angle to the optical axis of the eye, installed in series along the beam of light reflected from the cornea of the eye, a slit diaphragm and a photodetector, the output of which is connected to a recording device , and a device for pneumatic impact, made in the form of a hollow tapering channel, the diameter of the output window of which is commensurate with the size of the horns The window and the window are located close to it, and the input window is aligned with the plane of the low-frequency acoustic speaker diffuser installed in the housing and connected to the low-frequency signal generator, and the diameter of the channel input window is not less than the diameter of the diffuser, photodetector, and diaphragm, which can be moved in a plane perpendicular the direction of propagation of the light beam reflected from the cornea. The method consists in illuminating the center of the cornea of the eye with a narrow beam of light directed at an angle to the optical axis of the eye, deforming the cornea by means of pneumatic action periodically in the sound frequency range, changing by moving the diaphragm and photodetector perpendicular to the propagation direction of the magnitude of the electric signal amplitude reflected from the cornea to the maximum value, measuring the value of the amplitudes of the received signal, finding the average value of these amplitudes, according to which the pre-constructed calibration dependence determines the desired value of the intraocular pressure (see patent for IZ No. 2067845 IPC A61B 3/16).

The disadvantage of this method is that this method is associated with measuring the amplitude of the reflected signal and does not take into account the structural features of the cornea and the thickness of the cornea, which ultimately affects the accuracy of the measurement of true IOP.

The objective of the present invention is to provide the ability to measure the internal pressure of the spherical shell of the eye (intraocular pressure) in a non-contact manner and to obtain information about the dynamic properties of the shell, comparing the results with the results of a test measurement of internal pressure.

The technical result consists in increasing the accuracy of measuring the internal pressure of the eye in a non-contact manner by using a semiconductor laser operating in autodyne mode.

The specified technical result is achieved by the fact that the sclera of the eye is affected by a pneumatic pulse, while it is illuminated by laser radiation, the reflected signal is converted into an autodyne signal, its power is recorded, after which the signal is digitized and analyzed. As information parameters, parameters of the shell motion and the amount of deflection are used, which correspond to the pressure inside the eye, measured using an eye tonometer. The method is characterized in that the signal reflected from the eye is converted into an autodyne signal, its power is recorded, after which the signal is digitized using a digital autodyne signal P (t):

$$P(t)=\cos \left(\theta +\frac{\mathrm{four}\pi }{{\lambda }_0}Z(t)\right),\text{(one)}$$

where θ is the phase incursion of the autodyne signal, λ ₀ is the wavelength of the laser radiation, t is the time interval of the observed autodyne signal in different parts of the movement, Z (t) is a function that describes the longitudinal displacements of the object.

To determine the magnitude of the displacement, it is necessary to restore the object's motion function Z (t). The object’s motion function Z (t) can be determined by the normalized variable component of the interference signal P (t) using the inverse function, i.e.:

$$\theta +\frac{\mathrm{four}\pi }{{\lambda }_0}Z(t)=\pm \arccos (P(t))+2\pi n,\text{(2)}$$

where n = 0, ± 1, ± 2, ...

The unknown parameter shell acceleration a is determined by solving the inverse problem of finding the resulting functional minimum S (θ, a), defined as the sum of the squared deviations of the experimental and theoretical P P _{exp theor} autodyne signal magnitudes (1) for various time intervals:

$$S(\theta ,\mathrm{but})={\displaystyle \sum _i{(R_{\mathrm{uh}\mathrm{to}\mathrm{from}P}(t_i)-R_{te\mathrm{about}R}(t_i,\theta ,\mathrm{but}))}^2}.\text{(3)}$$

When finding the minimum of functional (3), we determined the region of the global minimum, the exact value of which was found by the descent method using the sought-for parameters θ and a . The calculated values of the acceleration and the magnitude of the deflection of the shell ΔZ, correspond to the pressure inside the eye, measured using an eye tonometer.

The method is implemented as follows.

Computer simulation of the autodyne signal of a semiconductor laser is carried out with oscillations of the external reflector. The variable component of the autodyne signal in the proposed model is written in the form:

$$P(t)=\cos \left(\theta +\frac{\mathrm{four}\pi }{{\lambda }_0}Z(t)\right),\text{(one)}$$

where θ is the phase incursion of the autodyne signal, λ ₀ is the wavelength of the laser radiation, t is the time interval of the observed autodyne signal in different parts of the movement, Z (t) is a function that describes the longitudinal displacements of the object.

To determine the magnitude of the displacement, it is necessary to restore the object's motion function Z (t). The object’s motion function Z (t) can be determined by the normalized variable component of the interference signal P (t) using the inverse function, i.e.:

$$\theta +\frac{\mathrm{four}\pi }{{\lambda }_0}Z(t)=\pm \arccos (P(t))+2\pi n,\text{(2)}$$

where n = 0, ± 1, ± 2, ...

The unknown parameter shell acceleration a is determined by solving the inverse problem of finding the resulting functional level (3), defined as the sum of the squared deviations of the experimental and theoretical P P _{exp theor} autodyne signal magnitudes (1) for various time intervals:

$$S(\theta ,\mathrm{but})={\displaystyle \sum _i{(R_{\mathrm{uh}\mathrm{to}\mathrm{from}P}(t_i)-R_{te\mathrm{about}R}(t_i,\theta ,\mathrm{but}))}^2}.\text{(3)}$$

When finding the minimum of functional (3), we determined the region of the global minimum, the exact value of which was found by the descent method using the sought-for parameters θ and a . The calculated values of the acceleration and the magnitude of the deflection of the shell ΔZ correspond to the pressure inside the eye, measured using an eye tonometer.

To obtain the values of P (t), the eyes are illuminated by laser radiation from a semiconductor laser operating in the autodyne mode. The autodyne signal is recorded by a photodetector integrated into the laser, while the output autodyne signal from the photodetector is amplified, converted into a digital code and stored in the computer's memory for subsequent processing.

To simulate the deformation of the eyeball under the action of an air stream, a model was used, which was a rubber ball filled with a gel with different internal pressure. The pressure inside the layout was changed by introducing an additional volume of gel. The sample had a diameter of 24 mm.

Figure 1 shows the block diagram of the experimental setup. The radiation from a semiconductor laser 1 stabilized by a current source 3 was directed to the model of the eye. Air pulses from the compressor 2, powered by a current source 4, were sent through a flexible hose and a plastic tube to the mantle shell surface illuminated by a laser. Part of the radiation reflected from the surface was returned to the cavity of the semiconductor laser, the change in the output power of which was recorded by the built-in photodetector 5. The signal from the photodetector was fed through amplifier 6 to analog-to-digital converter 7. The digital signal from the ADC was stored in computer memory 8 for subsequent processing.

Experimental studies were carried out to determine the magnitude of the deformation and acceleration of the shell and layout under the influence of a pneumatic pulse. A Roteri RCC-90 type compressor with a power of 120 W was used to affect the analyzed area of the eye model. During the experiments, various compressor operation modes were used. Using an external power source, the pressure of the air pulses was changed. To measure deformations of the eye model, an RLD-650 semiconductor laser diode with a radiation power of up to 1 mW was used. The test measurement of the internal pressure was carried out according to the Maklakov method with a load of 10 g.

Experimental studies were carried out to determine the magnitude of the deformation and acceleration of the shell and eyes on his model. Experimental studies were carried out with three different forces. Deformation of the surface of the layout led to a change in the magnitude of the autodyne signal of a semiconductor laser. The displacement and motion parameters were determined by the autodyne signal according to the methods described above.

The measured autodyne signals obtained by reflection from the surface of the model of the eye with an internal pressure of 24 mm Hg are shown in FIG. 2, FIG. 3, FIG. 4.

Table 1 No. Shell acceleration a , m / s ² × 10 ^-2 Shell displacement ΔZ, m × 10 ^-6 The ratio ΔZ / a , s ² × 10 ^-4 Jet pressure p, Pa VD layout, mm Hg one 0.93 1.71 1,823 0.018 16 2 1.28 2,35 1,827 0,082 3 1,67 3.05 1,823 0.158 four 1,07 1.53 1,430 0.018 twenty 5 1.49 2.15 1,442 0,082 6 1.95 2.80 1,435 0.158 7 1,04 1.30 1,252 0.018 24 8 1,57 1.95 1,254 0,082 9 2.07 2.60 1,258 0.158 10 1.06 1.12 1,047 0.018 thirty eleven 1.68 1.76 1,044 0,082 12 2,31 2.43 1,048 0.158 13 1.01 0.95 0.932 0.018 33 fourteen 1.71 1,59 0.929 0,082 fifteen 2.48 2,31 0.93 0.158

From table 1 it can be seen that the ratio of the displacement of the shell ΔZ and the acceleration of the shell a with an internal pressure of 24 mm Hg changes as follows: for p ₁ = 0.01873 Pa, the deviation from the average value was 0.207%, for p ₂ = 0.08272 Pa - 0.047%, for p ₃ = 0.15806 Pa - 0.27%. Similar results were obtained in the case of VD mock 16, 20, 30 and 33 mm Hg. Thus, we can conclude that the ratio ΔZ / a weakly depends on the pressure of the air stream.

ΔZ and a were also measured at different distances between the source of pneumatic pulses and the object (Δx). The deflection and acceleration of the shell a were measured for three different distances: 5, 10, and 15 mm. The measurement results are shown in table 2.

table 2 No. Δx, mm Shell acceleration a , m / s ² × 10 ^-2 Shell displacement ΔZ, m × 10 ^-6 The ratio ΔZ / a , s ² × 10 ^-4 VD layout, mm Hg one 5 1,63 2.98 1,824 16 2 10 1,07 1.95 1,823 3 fifteen 0.70 1.32 1,825 four 5 1.95 2.80 1,435 twenty 5 10 1.22 1.75 1,433 6 fifteen 0.84 1.21 1,432 7 5 2.04 2,55 1,251 24 8 10 1.14 1.43 1,255 9 fifteen 0.65 0.82 1,253 10 5 2.23 2,34 1,047 thirty eleven 10 1.65 1.72 1,044 12 fifteen 1,08 1.13 1,048 13 5 2.41 2.25 0.932 33 fourteen 10 1.73 1,61 0.929 fifteen fifteen 1.12 1,04 0.93

The results presented in table 2 indicate that when the distance between the source of pneumatic pulses and the object of study, within the same pressure, ΔZ / a changes slightly.

The obtained features can be used to eliminate possible errors associated with the inconsistency of pressure that creates an air stream during pneumatic shock. In addition, the construction of many calibration curves describing the dependence of the deflection - internal pressure is not required. For these purposes, it will be possible to use a universal dependence based on the constancy of the ratio of the magnitude of the deflection and acceleration of the shell a . Figure 5 shows a calibration curve obtained from experimental data.

The proposed method was implemented by the example of determining the unknown internal pressure of the eye using calibration curves. The studies were carried out using an RLD-650 laser diode on quantum-dimensional structures with a diffraction-limited single spatial mode and characteristics: radiation power <1 mW, wavelength 654 nm. A pneumatic pulse compressor with a power of 2 W, a pressure of 0.01 MPa and an air pulse frequency of 1 Hz was used to apply an air pulse to the eye; the diameter of the air jet at a distance of 10 mm from the object was 3 mm. The measured ΔZ / a ratio was 1.91 × 10 ^-4 s ^-2 , which corresponds to a pressure value of 16 mm Hg on the calibration curve (Fig. 5). Checking the value of the internal pressure of the eye was carried out using a non-contact pneumotometer Canon Full Auto Tonometr. The measured pressure value was 15 ± 3.5 mm Hg. Thus, the proposed method is consistent with the generally accepted one, but, unlike it, allows measurements to be made with high accuracy.

Claims (2)

1. A method for measuring intraocular pressure by the amount of eye deformation by applying a pneumatic pulse to the eye while simultaneously illuminating its surface with a laser, characterized in that the signal reflected from the eye is converted into an autodyne signal, its power is recorded, and then the signal is digitized using a digital autodyne signal P ( t) restore the function of the eye section Z (t) using the inverse function:
θ + 4π / λ ₀ · Z (t) = ± arccos (P (t)) + 2πn, where n = 0, ± 1, ± 2, ...; θ is the phase incursion of the autodyne signal, λ ₀ is the wavelength of the laser radiation; the value of eye deformation ΔZ is determined by the function Z (t), the shell acceleration a is determined from the solution of the inverse problem, obtained by finding the minimum functional, defined as the sum of the squared deviations of the experimental P _exp and theoretical P _{theory of the} autodyne signal P (t) for different time intervals :
$$S(\theta ,a)={\displaystyle \sum _i{(R_{\mathrm{uh}\mathrm{to}\mathrm{from}P}(t_i)-R_{te\mathrm{about}R}(t_i,\theta ,\text{a}))}^2};$$

the ratio of the deflection of the shell ΔZ to the value of the acceleration of the shell a, using the calibration curve that describes the dependence of the pressure inside the eye model, measured using a manometer or eye tonometer, on the ratio ΔZ / a, determines the intraocular pressure. 2. The method according to claim 1, characterized in that the calibration curve is obtained by illuminating the eye model with a laser, which is a spherical shell of elastic material filled with an incompressible fluid, while simultaneously applying a pneumatic pulse to it, the reflected signal is converted into an autodyne signal, and its power is recorded , after which the signal is digitized, the function of the eye section Z (t) is restored using the digital autodyne signal P (t) using the inverse function θ + 4π / λ ₀ · Z (t) = ± arccos (P (t)) + 2πn, where n = 0, ± 1, ± 2, ...; θ is the phase incursion of the autodyne signal, λ ₀ is the wavelength of the laser radiation; the function Z (t) determines the amount of eye deformation ΔZ, the shell acceleration a is determined by finding the minimum of the functional $$S(\theta ,\text{a})={\displaystyle \sum _i{(R_{\mathrm{uh}\mathrm{to}\mathrm{from}P}(t_i)-R_{te\mathrm{about}R}(t_i,\theta ,\text{a}))}^2};$$

ΔZ / a ratio, the pressure inside the model is measured according to a pressure gauge or an eye tonometer.

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