WO2008072527A1

WO2008072527A1 - Intraocular pressure measuring device

Info

Publication number: WO2008072527A1
Application number: PCT/JP2007/073512
Authority: WO
Inventors: Sadao Omata; Yoshinobu Murayama
Original assignee: Nihon University
Priority date: 2006-12-08
Filing date: 2007-12-05
Publication date: 2008-06-19
Also published as: JPWO2008072527A1; JP5505684B2

Abstract

An intraocular pressure measuring device (10) comprising a probe (20) provided with a concave acoustic lens (22) at the tip end side facing and spaced apart from an eyeball (8) and with a probe element (24) having a vibrator and a vibration detection sensor laminated therein, a probe moving mechanism (30) for regulating the position of the probe (20) respective to the eyeball (8), and a body unit (60) connected with the probe (20) to calculate and output an intraocular pressure. The body unit (60) includes a phase shift circuit connected in series with the probe (20) along with an amplifier to change its frequency, when the phase difference between an input waveform to the vibrator and an output waveform from the vibration detection sensor occurs, and compensate the phase difference to zero, and an intraocular pressure calculating unit that determines in advance the relation between a frequency change amount and an intraocular pressure when a phase difference is compensated to zero, and calculate an intraocular pressure from a frequency change amount compensating to zero an phase difference occurring when ultrasonic wave is allowed to enter an eyeball.

Description

Specification

Tonometry device

Technical field

[0001] The present invention relates to an intraocular pressure measurement device, and more particularly to an intraocular pressure measurement device that measures intraocular pressure using ultrasonic waves.

Background art

[0002] Tonometers are widely used to measure intraocular pressure. The tonometer blows air onto the eyeball, optically measures how the eyeball is distorted by the air pressure, and measures the intraocular pressure based on the magnitude of the distortion.

[0003] Since the tonometer blows air onto the eyeball, it is not accurate due to the influence of the pulsation of the air pressure. In addition, since air is directly injected into the eyeball tissue such as the cornea, a load is applied to the subject. Thus, for example, in Patent Document 1, a probe is placed on the heel and appropriately pressurized, and the change in the depth of the anterior chamber at that time is detected by ultrasonic waves. Here, an ultrasonic wave is incident, a reflected sound bundle is detected, and the time axis within one sweep of the ultrasonic detection signal is converted into a distance by the biological sound velocity of the anterior ocular segment for a waveform called ultrasonic A mode. The depth of the anterior chamber is detected by a general distance measurement principle.

[0004] As disclosed in Patent Document 2, the present inventor has developed a method capable of accurately measuring the hardness of an object using a phase shift method. In this technology, vibration is incident on the measurement object from the vibrator, the reflected wave from the measurement object is detected by the vibration detection sensor, and the measurement object is between the incident wave and the reflected wave according to the hardness of the measurement object. By changing the frequency of the generated phase difference using a phase shift circuit, the phase difference is compensated to zero, and the hardness of the measured object is obtained from the amount of frequency change that compensates for the phase difference to zero. According to this method, the force of measuring the hardness of an object to be measured is measured by a contact method in which vibration is input to the object to be measured and a reflected wave is detected.

Patent Document 1: Japanese Patent Laid-Open No. 8-322803

Patent Document 2: JP-A-9 145691 Disclosure of the invention

Problems to be solved by the invention

[0006] As described above, the tonometer applies air pressure to the eyeball, and also presses the eyeball through the eyelid in the method of Patent Document 1. As described above, in the conventional technique, pressure is applied to the eyeball by an external force, and the magnitude of the intraocular pressure is determined from the distortion of the eyeball due to the pressure. Further, according to the phase shift method described in Patent Document 2 by the inventor of the present application, the hardness of the measurement object can be measured by inputting vibration to the measurement object and detecting the reflected wave. When the object to be measured is an eyeball, the hardness is related to the intraocular pressure, so this method makes it possible to measure the intraocular pressure without applying external force. multiply. Therefore, if the intraocular pressure can be measured without touching the eyeball, the burden on the subject can be reduced, which is convenient.

[0007] An object of the present invention is to provide an intraocular pressure measuring device capable of measuring intraocular pressure without contacting the eyeball.

Means for solving the problem

[0008] In the present invention, vibration is incident on the eyeball in a non-contact manner, a reflected wave from the eyeball is detected, and whether or not the phase shift method can be applied to the phase difference generated between the incident wave and the reflected wave has been confirmed. Based on experiments. According to experiments, it was found that if the tip shape of the probe facing the eyeball is adjusted, there is a correlation between the intraocular pressure and the frequency difference that compensates for the phase difference to zero. Based on this experiment, the following measures can be taken.

[0009] An intraocular pressure measurement device according to the present invention includes a probe having a transducer that makes ultrasonic waves incident on an eyeball in a non-contact manner, and a vibration detection sensor that detects a reflected wave from the eyeball. When a phase difference force S occurs between the input waveform to the transducer and the output waveform from the vibration detection sensor, connected to the probe in series with the amplifier, and a concave acoustic lens with a concave surface facing the eyeball. The phase shift circuit that changes the frequency to compensate for the phase difference to zero, the relationship between the frequency change amount when the phase difference is compensated to zero and the intraocular pressure are obtained in advance, and the concave acoustic lens is attached to the eyeball. A frequency variation force that compensates for the phase difference that occurs when ultrasound is incident on the eyeball facing away from each other, and an intraocular pressure calculation unit that calculates intraocular pressure. . [0010] In addition, the intraocular pressure measurement device according to the present invention preferably includes a probe moving mechanism that can vary the distance between the concave acoustic lens and the eyeball of the measurement object.

[0011] In addition, the intraocular pressure measurement device according to the present invention preferably includes curved surface shape changing means capable of changing the curved surface shape of the concave acoustic lens.

The invention's effect

[0012] With the above configuration, the intraocular pressure measurement apparatus uses a probe having a concave acoustic lens whose surface facing the eyeball is a concave surface, and separates the concave acoustic lens from the eyeball so as to face the eyeball. Is incident. Then, the relationship between the frequency change amount and the intraocular pressure when the phase difference is compensated to zero is obtained in advance, and the frequency change force that compensates the phase difference generated when the ultrasonic wave is incident on the eyeball to zero is calculated. calculate. Therefore, the intraocular pressure can be measured without touching the eyeball.

[0013] Further, since the distance between the concave acoustic lens and the eyeball of the measurement object can be varied, it is possible to detect the reflected wave by injecting vibration while focusing on the eyeball.

[0014] Further, since the curved surface shape of the concave acoustic lens can be varied, it is possible to detect the reflected wave by injecting the vibration while focusing on the eyeball.

Brief Description of Drawings

FIG. 1 is a diagram showing a configuration of an intraocular pressure measurement device according to an embodiment of the present invention.

FIG. 2 is a diagram extracting and showing a configuration of a probe element, a concave acoustic lens, and a portion of an intraocular pressure measurement unit included in a main body part in an embodiment according to the present invention.

FIG. 3 is a diagram showing a state of selection of an oscillation frequency in which the circuit constant of the phase shift circuit is set in the embodiment according to the present invention.

FIG. 4 is a diagram showing the shape dimensions of the simulated objects A and B used to obtain the correspondence relationship between the amount of frequency change and the acoustic impedance in the embodiment according to the present invention.

FIG. 5 is a diagram showing a correspondence relationship between the amount of change in frequency and acoustic impedance in the embodiment according to the present invention.

FIG. 6 is a diagram showing a state of an eyeball model used for obtaining a correspondence relationship between a frequency change amount and intraocular pressure in the embodiment according to the present invention.

FIG. 7 shows the correspondence between frequency variation and intraocular pressure in the embodiment of the present invention. FIG.

Explanation of symbols

[0016] 8 eyeballs, 10 intraocular pressure measuring device, 20 probe, 22 concave acoustic lens, 24 probe element, 26 transducer, 28 vibration detection sensor, 30 probe moving mechanism, 32 fixed base, 34 movable base , 36 Operation knob, 38 Probe mounting part, 40 Intraocular pressure measurement part, 42, 44, 46 terminals, 48 amplifier, 50 Phase shift circuit, 52 Frequency change calculation part, 54 Intraocular pressure calculation part, 60 Main body part , 70 eyeball model, 72 base part, 74, 75, 76 curved part, 80 pressurizer, 82 pressure gauge.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Below, as a means for bringing the probe closer to the person to be measured, the force described as mounting the probe on a movable table movable with respect to the floor may be used. For example, the probe may be mounted on a support base fixed in relation to the head of the subject. In the following, the probe may be a force described as a laminate of a transducer and a vibration detection sensor, or any other arrangement method. For example, the vibrator and the vibration detection sensor may be arranged concentrically, or the vibrator and the vibration detection sensor may be separately arranged in parallel.

FIG. 1 is a diagram showing a configuration of the intraocular pressure measurement device 10. FIG. 1 shows an eyeball 8 that is not a constituent element of the intraocular pressure measurement device 10 but is an intraocular pressure measurement target. The intraocular pressure measurement device 10 is connected to the probe 20, a probe moving mechanism 30 for adjusting the position of the probe 20 with respect to the eyeball, and the probe 20 via a signal line. And a main body 60 that calculates and outputs the value.

The probe moving mechanism 30 includes a fixed base 32 fixed to the floor surface and a movable base 34 that can move linearly with respect to the fixed base 32, and a probe is attached to the movable base 34. Part 38 is provided. As the fixed base 32 and the movable base 34, for example, a conversion mechanism between a rotational motion and a linear motion by a pinion and a rack can be used. In this case, there is an operation node 36 force S connected to the pinion, and by rotating the operation handle 36, the pinion provided on the fixed base 32 rotates, and the rack that meshes with this moves linearly. , Movable table with rack mounted 34 You can power to move. Of course, a linear motor or the like that can be moved by controlling electric signals may be used as a mechanism between the fixed base 32 and the movable base 34! /.

[0020] The probe 20 is a probe having an elongated cylindrical shape, and is provided with a concave acoustic lens 22 and a probe element 24 on the tip side facing and spaced apart from the eyeball 8, and one end side of the probe element 24 is connected to the probe element 24. The signal line to be connected is connected to the main body 60 on the other end side.

FIG. 2 is a diagram showing an extracted configuration of the probe element 24, the concave acoustic lens 22, and the intraocular pressure measurement unit 40 included in the main body 60.

[0022] The probe element 24 includes a transducer 26 that makes an ultrasonic wave incident on an eyeball 8 that is a measurement object via a concave acoustic lens 22, and a vibration detection sensor 28 that detects a reflected wave from the eyeball 8. And have. In the example of FIG. 2, the vibrator 26 and the vibration detection sensor 28 are stacked and connected in series, and the connection point is grounded. Specifically, two disk-shaped piezoelectric elements each provided with electrodes are stacked using two, and the middle two electrodes are integrated into a ground electrode, and the stacked upper surface side electrode and lower surface electrode are integrated. One side of the side electrode is used as the input electrode of the vibrator 26, and the other side is used as the output electrode of the vibration detection sensor 28. In the example of FIG. 2, the surface on the input electrode side of the vibrator 26 is bonded and fixed to the flat back surface of the concave acoustic lens 22. A commercially available PZT element can be used as the piezoelectric element.

[0023] The concave acoustic lens 22 focuses the ultrasonic wave radiated from the probe 24 on the measurement object, and efficiently collects the reflected waves radiated from the measurement object. It is an element that has a function to transmit to 24. The concave acoustic lens 22 is formed in a concave surface having a predetermined curved surface on the surface facing the eyeball 8 as a measurement object, and the back surface on the opposite side of the concave surface is formed on, for example, a flat surface to connect to the probe element 24. Is done. The concave acoustic lens 22 may be made of a suitable plastic material or ceramic, glass or the like molded into a predetermined shape.

[0024] The concave curved surface shape of the concave acoustic lens 22 is preferably a shape corresponding to the curved surface shape of the eyeball 8 to be measured. In short, the force S can be configured as a part of a spherical surface having a certain radius of curvature. In this case, the radius of curvature can be the radius of curvature at a site suitable for measuring intraocular pressure, or the average radius of curvature of the eyeball. For example, the force S can be set to a radius of curvature of several millimeters. The concave surface shape of the concave acoustic lens 22 can be formed into a fixed shape by molding an appropriate material as described above. For example, the concave acoustic lens 22 has a fixed end on the outer periphery of a cylindrical support portion. This is a variable-shape concave acoustic lens that has a flexible curved membrane, injects pressurized fluid into the cylindrical support, and changes the shape of the concave surface by changing the fluid pressure. As the fluid, it is preferable to use a fluid that easily propagates ultrasonic vibrations, and fluid silicone rubber can be used.

FIG. 2 shows the configuration of the intraocular pressure measurement unit 40. The intraocular pressure measurement unit 40 includes a terminal 42 that receives an output signal corresponding to the reflected wave from the vibration detection sensor 28, a terminal 44 that outputs an input signal corresponding to the incident wave to the transducer 26, and the main body shown in FIG. A terminal 46 for outputting an intraocular pressure value to an output section such as a display screen of the section 60; The inside of the intraocular pressure measurement unit 40 is configured as follows.

[0027] The terminal 42 connected to the vibration detection sensor 28 is connected to the amplifier 48 via an appropriate DC cut capacitor. The amplifier 48 is an electronic circuit that appropriately amplifies the reflected wave signal detected by the vibration detection sensor 28, and a known amplifier circuit can be used.

The output of the amplifier 48 is input to the phase shift circuit 50, and the output of the phase shift circuit 50 is connected to the vibrator 26 via the terminal 44. Therefore, transducer 26—concave acoustic lens 2 2-(atmosphere) — (eyeball 8)-(atmosphere) —concave acoustic lens 22—vibration detection sensor 28—amplifier 48—phase shift circuit 50—closed loop of transducer 26 Composed. Therefore, by appropriately setting the contents of the phase shift circuit 50, the force S can be used to generate self-excited oscillation in this closed loop.

[0029] The function of the phase shift circuit 50 is to change the oscillation frequency of the closed loop when a phase difference occurs between the input signal input to the phase shift circuit 50 and the output signal output in this closed loop. Thus, the phase difference is compensated to zero. Then, the frequency when the phase difference is compensated to zero is output to the frequency change amount calculation unit 52.

[0030] The frequency variation calculation unit 52 generates a closed loop oscillation frequency f when self-oscillation occurs due to the action of the phase shift circuit 50 when the measurement target is not included in the closed loop, When the self-excited oscillation occurs due to the action of the phase shift circuit 50 when the measurement object is included, the closed-loop oscillation frequency f is received and the frequency change therebetween It has a function to calculate the quantity A f = f — f. That is, the frequency variation calculation unit 52

twenty one

This function detects the oscillation frequency f when the measurement object is not included in the closed loop and stores it once, and then detects the oscillation frequency f when the measurement object is included in the closed loop. This is also memorized once and the two memorized frequencies f and f are read.

2 1 2 This is a series of processing that calculates the amount of frequency change that is the difference between the two.

In the examples of FIGS. 1 and 2, the amount of frequency change between the frequency f of the self-oscillation in the closed loop when the eyeball 8 is not present and the frequency f of the self-oscillation in the closed loop when the eyeball 8 is present.

2

A f = f — f is obtained by the frequency variation calculation unit 52 and output to the intraocular pressure calculation unit 54.

twenty one

The Note that the specific configuration and detailed operation of the force and phase shift circuit 50 are disclosed in Patent Document 2 above.

[0032] In order to maintain the closed-loop self-oscillation, the phase shift circuit 50 has a closed-loop frequency when a phase difference occurs between the output signal of the vibration detection sensor 28 and the input signal to the vibrator 26. To compensate for the phase difference to zero. Therefore, as for the frequency of the self-oscillation of the closed loop, the difference in the physical properties of the measurement object becomes easier when the frequency change amount when compensating for the phase difference to zero is large. Therefore, the circuit constants, which are the circuit contents of the phase shift circuit 50, are set so that the frequency change amount when the phase difference is compensated to zero becomes a stable and large oscillation frequency for the target closed loop. In other words, in the frequency-phase characteristics of the probe element 24, a force with a large number of oscillation frequencies, among which the oscillation is stable, and changing the phase difference causes a frequency change of an appropriate magnitude. An oscillation frequency satisfying the above condition is selected, and the circuit constant of the phase shift circuit 50 is set for the selected oscillation frequency.

FIG. 3 is a diagram showing a state of selection of an oscillation frequency at which the circuit constant of the phase shift circuit 50 is set. FIG. 3 shows the frequency-phase characteristics of the probe element 24. As shown in FIG. 3, the characteristic of the probe element 24 has a plurality of peaks. Peak B is the peak with the sharpest oscillation characteristics and stable oscillation. Conversely, due to its strong stability, there is almost no frequency change even if the phase difference is changed. Peak C is unstable in oscillation. [0034] Therefore, it is assumed that the peak A causes the oscillation to be properly stabilized, and the force and the frequency change of an appropriate magnitude according to the change of the phase difference. It can be selected as a peak suitable for detection. That is, the circuit constant of the phase shift circuit 50 is set to be suitable around 350 kHz in the frequency band.

The intraocular pressure calculation unit 54 has a function of calculating intraocular pressure based on the frequency change amount output from the frequency change amount calculation unit 52. In order to calculate intraocular pressure with respect to the frequency variation force, the relationship between the frequency variation and the intraocular pressure is obtained in advance, and the frequency variation calculated by the frequency variation calculator 52 is applied to the relationship. The

FIG. 4 to FIG. 7 are diagrams for explaining the state of an experiment for determining the relationship between the amount of change in frequency and the intraocular pressure for compensating for the phase difference generated when an ultrasonic wave is incident on the eyeball to zero. These figures show the frequency change amount A f of the frequency f force when there is no simulated object, with respect to the frequency f when the phase difference is compensated to zero by applying ultrasonic waves to the simulated object modeling the eyeball. Seeking

twenty one

Therefore, this is correlated with the acoustic impedance of the simulated object or the pressure corresponding to the intraocular pressure. In the following description, the reference numerals in FIGS. 1 and 2 are used.

[0037] Figures 4 and 5 show simulated objects A and B with different shapes, and the distance from the concave acoustic lens 22 to the tips of the simulated objects A and B is 4000 m, that is, 4 mm. FIG. 4 is a diagram for explaining a state in which a relationship between Δf and acoustic impedances of simulated objects A and B is obtained. FIG. 4 shows the geometric dimensions of the simulated objects A and B. The shapes of the simulated objects A and B approximate the outer shape of the eyeball 8, and have a curved surface that is gentler than the hemisphere. From the dimensions in Fig. 4, the radius of curvature at the tip of simulated objects A and B can be evaluated as about 4 mm to about 6 mm. For each of the simulated objects A and B, silicon rubber is mixed in an appropriate medium and the concentration is changed to 40%, 60%, 80%, and 100%. A sample was created.

[0038] For these samples, the acoustic impedance corresponding to the hardness was measured.

In addition, as described above, in the frequency band of about 350 kHz, the frequency change amount A f that is the change amount of the oscillation frequency between when the simulated objects A and B are present and not present was obtained. Figure 5 shows the result of associating the calculated acoustic impedance with the calculated frequency change. As can be seen from Fig. 5, the frequencies of simulated objects A and B with different shapes are There is a correlation between the change A f and the acoustic impedance. According to Fig. 5, the correlation is almost linear, but the correlation varies depending on the shape of the simulated object!

[0039] As shown in FIG. 5, since there is a correlation between the frequency change amount A f when the phase shift method is used and the hardness of the measurement object, the component force, that is, the frequency change amount is described next. Figures 6 and 7 show the experiment of correlating Af with the pressure corresponding to intraocular pressure. Here, a silicone rubber eyeball model 70 having a shape shown in FIG. 6 and having a cavity inside is used as a simulated object modeling the eyeball. The eyeball model 70 is configured to include a base portion 72 and a curved surface portion 74 that can bulge and change its outer shape by pressurizing the inside, and the pressurizer 80 supplies water or an appropriate fluid to the inside of the eyeball model 70. The shape of the curved surface portion 74 can be changed by injecting under pressure. The pressure of the internal fluid in the curved surface portion 74 can be detected by a pressure gauge 82 such as a manometer. FIG. 6 shows how the curved surface portion 74 expands and changes to curved surface portions 75 and 76 as the pressure is increased.

FIG. 7 is a diagram showing the relationship between the frequency variation A f and the pressure of the eyeball model 70 when the distance from the concave acoustic lens 22 to the tip of the eyeball model 70 is 2000 m, ie, 2 mm. . As can be seen from FIG. 7, there is a clear linearity between the pressure of the eyeball model 70 and the frequency change Δf in the phase shift method.

Accordingly, by storing the correspondence relationship as shown in FIG. 7 in a memory or the like in advance, the intraocular pressure of the eyeball 8 can be obtained by the intraocular pressure measurement device 10 shown in FIG. The correspondence relationship of “A f—intraocular pressure” is stored in a format in which the intraocular pressure is output by inputting A f. Specifically, it may be stored in the form of a calculation formula that may be stored in the form of a conversion table such as a lookup table.

[0042] The operation of the intraocular pressure measurement apparatus 10 having the above-described configuration will be described below as a procedure for obtaining intraocular pressure.

In the following, description will be made using the reference numerals in FIGS.

First, by the action of the phase shift circuit 50, self-excited oscillation is generated in the absence of the eyeball 8, and the oscillation frequency at that time is output to the frequency change amount calculation unit 52 as f. In the above example, f is about 350 kHz because it is the frequency of peak A in Fig. 3. The absence of the eyeball 8 can be realized by providing a sufficiently large space between the eyeball 8 and the tip of the concave acoustic lens 22. Next, the concave acoustic lens 22 is brought closer to the eyeball 8 using the probe moving mechanism 30. The approaching distance is preferably a distance force between the eyeball 8 and the tip of the concave acoustic lens 22 and a representative radius of curvature of the concave acoustic lens 22. Alternatively, by changing the distance, a position where the variation in oscillation frequency at that time is reduced can be used as an interval for measurement. That is, if the distance between the eyeball 8 and the concave acoustic lens 22 is too narrow or too wide, the ultrasonic waves diverge or do not concentrate on the curved surface of the concave acoustic lens 22.

[0045] When the interval between the eyeball 8 and the concave acoustic lens 22 is set at an appropriate interval, the oscillation frequency at that position is output to the frequency variation calculation unit 52 as f. Frequency change calculation

2

The unit 52 calculates A f = f − f as the frequency change amount and outputs it to the intraocular pressure calculation unit 54.

twenty one

. The magnitude of A f is about 100 Hz in the examples of Figs.

[0046] The intraocular pressure calculation unit 54 reads the pre-stored “A f—intraocular pressure” correspondence, and applies the frequency change amount A f given from the frequency change amount calculation unit 52 to the correspondence relationship. Calculates and outputs the intraocular pressure. The output intraocular pressure value is displayed and output on the main body 60 by an output means such as a display or a printer. In the example of Fig. 7, if A f = 120Hz, the corresponding intraocular pressure will be calculated and displayed as approximately 1. lkPa.

Claims

The scope of the claims

[1] A probe having a transducer that makes ultrasonic waves incident on the eyeball in a non-contact manner and a vibration detection sensor that detects reflected waves from the eyeball;

A concave acoustic lens, which is provided at the tip of the probe and has a concave surface facing the eyeball, is connected to the probe in series with an amplifier, and the input waveform to the transducer and the vibration detection sensor force When a phase difference occurs, a phase shift circuit that changes the frequency to compensate for the phase difference to zero,

The relationship between the amount of change in frequency and the intraocular pressure when the phase difference is compensated to zero is obtained in advance, and the position that occurs when an ultrasonic wave is incident on the eyeball with the concave acoustic lens facing away from the eyeball. An intraocular pressure measurement device comprising: an intraocular pressure calculation unit that calculates an intraocular pressure to compensate for a phase difference to zero.

[2] In the intraocular pressure measuring device according to claim 1,! /,

An intraocular pressure measuring device comprising a probe moving mechanism capable of varying a distance between a concave acoustic lens and an eyeball of a measurement object.

[3] In the intraocular pressure measuring device according to claim 1,! /,

An intraocular pressure measuring device comprising curved surface shape changing means capable of changing a curved surface shape of a concave acoustic lens.