JP2023141373A - Non contact type eyeball physical property measurement device - Google Patents

Abstract

To provide a non contact type eyeball physical property measurement device capable of minimizing interference of an excitation ultrasonic wave to a detection sensor, in generation and detection of an eyeball surface wave by the ultrasonic wave.SOLUTION: A non contact type eyeball physical property measurement device 1 comprises: an ultrasonic wave radiation unit 1501 for exciting at least one excitation points on an eyeball using a radiation wave for generating a surface wave on an eyeball surface which is an eye to be examined; a reception sensor 1503 for detecting the surface wave generated on the ultrasonic wave radiation unit 1501 on at least one detection point on the eyeball which is different from the excitation point; a surface wave processing part 1507a for analyzing the surface wave detected by the reception sensor 1503; and an eyeball physical property calculation part 1507b for calculating the physical property of the eyeball, on the basis of an analysis result on the surface wave processing part 1507a. The radiation wave generated by the ultrasonic wave radiation unit 1501 is a continuous wave of an aerial ultrasonic wave whose fundamental frequency is 20 KHz or greater and 200 KHz or smaller, or a burst wave of 10 waves or greater of the aerial ultrasonic wave, and satisfies the prescribed formula.SELECTED DRAWING: Figure 15

Description

The present invention relates to an eyeball physical property measuring device that measures the physical properties of an eyeball in a non-contact manner, and particularly relates to an eyeball physical property measuring device that can measure the physical properties such as intraocular pressure of the eyeball and material mechanical properties of the surface tissue of the eyeball.

Conventionally, as a non-contact measurement device for intraocular pressure, an air flow is blown onto the eyeball to deform the cornea without contact, and the pressure of the air flow (Air Puff) is plotted to determine whether the cornea is flattened. A non-contact tonometer that calculates the intraocular pressure value by calculating the correlation between the air ejection pressure at the moment when the pressure reaches the standard and the comparative measurement value measured using a contact applanation tonometer used as a standard intraocular pressure measurement is better. Are known.

For example, when measuring the mechanical properties of the cornea of the eye to be examined and measuring the intraocular pressure, the cornea is deformed by pressing inward with an air puff, and the cornea forms a temporary flattened shape, and this flattened point is detected during the first applanation. called a point. After the cornea reaches its maximum deformation due to further depression, it passes through the flat plane again in the process of returning to its original shape, and this is called the second applanation point.

In Patent Document 1, the air jet pressure is plotted over time during this corneal shape change process, the air jet pressure at the applanation point is measured, and the intraocular pressure is determined from the air jet pressure at the first applanation point and the second applanation point. A method of measuring intraocular pressure has been proposed in which the influence of corneal stiffness on measured values is reduced by determining .

Furthermore, in Patent Document 2, the flattening process of the cornea is photographed as a corneal tomogram using Scheimpflug array illumination and an imaging camera, and the applanation radius and free vibration of the cornea are measured, so that the measured value due to the stiffness of the cornea can be influenced. Systems have been proposed for reduced influence intraocular pressure measurement and analysis of the mechanical material properties of the cornea.

In addition, as a non-contact tonometer method, we use an ultrasonic (acoustic radiation pressure) non-contact tonometer that measures intraocular pressure by irradiating the cornea with ultrasonic waves and deforming or vibrating the cornea using the sound pressure. Several methods have been proposed. For example, Patent Document 3 proposes a system that deforms the cornea using acoustic radiation pressure generated by ultrasound irradiation, detects the amount of deformation, and measures intraocular pressure. Patent Document 4 discloses a system that irradiates the eyeball with powerful ultrasonic waves from a parametric speaker to give vibration to the eyeball, and modulates the frequency of the irradiated ultrasonic wave to detect the natural vibration of the eyeball and measure intraocular pressure. is proposed. Patent Document 5 proposes a system that detects reflected waves from the eyeball surface of ultrasonic waves irradiated to the eyeball and determines intraocular pressure based on the amount of phase shift of the reflected waves with respect to the irradiated waves.

U.S. Patent Publication No. 7,909,765 Patent No. 5314090 Japanese Patent Application Publication No. 2020-5679 Patent No. 6289040 Patent No. 5505684 Japanese Unexamined Patent Publication No. 61-8592 Japanese Patent Application Publication No. 3-60629 Special Publication No. 8-507463 Japanese Patent Application Publication No. 2000-60801 Special Publication No. 6-59272 Japanese Patent Application Publication No. 2011-50445 Japanese Patent Application Publication No. 2012-5835

Direct Experimental Observation of the Crossover from Capillary to Elastic Surface Wave on Soft Gels, October 1998 Physics al Review Letters, Volume 81 Number 15, Francisco Monroe and Dominique Langevin Surface-wave modes on soft gels, The Journal of the Acoustical Society of America, December 1998, Y. Onodera and P. K Choi Investigating soft materials using surface waves, Journal of the Acoustical Society of Japan, Vol. 56, No. 6 (2000), pp. 445-450, Choi Bo-kun Optical coherence elastography assessment of corneal viscoelasticity with a modified Rayleigh-Lamb wave model, Journal of th e Mechanical Behavior of Biomedical Materials, 66 (2017) 87-94, Zhaolong Han et al.

However, in systems such as those disclosed in Patent Document 1 and Patent Document 2, in which the cornea is deformed and measured using an air puff, discomfort to the subject due to noise and air blowing when the air puff is emitted cannot be avoided. Additionally, there is a risk that the air puffs will scatter deposits on the ocular surface, such as tears, and become a source of infection to the surrounding area.

Furthermore, in the case of the above-mentioned ultrasonic excitation type, since the deformation and vibration of the cornea are detected, the ultrasonic output required to excite the eyeball vibration is large. Therefore, in the embodiment of Patent Document 3, a powerful Langevin type vibrator is used as an ultrasonic oscillator for vibration to increase the sound pressure of the ultrasonic waves. In Patent Document 4, it is necessary to obtain strong ultrasonic power using a parametric speaker using a very large number of ultrasonic transducer arrays, and in Patent Document 5, it is necessary to efficiently irradiate ultrasonic waves with an acoustic lens. be. In order to obtain strong ultrasonic power, the ultrasonic oscillator for excitation becomes large and requires a relatively large installation space in front of and near the eye to be examined. There are many constraints on the realization of the device, such as the alignment detection mechanism for the eye to be examined during measurement and the compatibility with a photographing device for photographing eyeball images.

In addition, in these ultrasonic excitation type non-contact tonometers, the focal position of the excitation ultrasonic irradiation onto the eyeball and the detection position of the eyeball vibration or corneal deformation amount approximately coincide on the eyeball. In both cases, the magnitude of the displacement or amplitude caused by the deformation or vibration of the eyeball, or the amount of phase displacement of the reflected wave of the excitation ultrasound due to the vibration of the eyeball, is measured. This is because when the position and the detection position of vibration or displacement are at the same position, the detection sensitivity is maximized and the detection accuracy is optimized.

Therefore, in order to substantially match the focal position of the excitation ultrasonic irradiation and the detection position of the detection device, it is desirable to arrange the irradiation axis of the excitation ultrasonic wave and the detection axis to be coaxial. Alternatively, if coaxiality is not possible, the excitation efficiency deteriorates because the excitation ultrasonic waves are incident obliquely to the eyeball surface. Therefore, it is necessary to compensate for the decrease in measurement sensitivity by increasing the output of the excitation ultrasonic waves even more strongly.

In addition, since the focal position of the ultrasonic irradiation and the detection position substantially match, misalignment of the device with respect to the eye to be examined and deviation in fixation of the eye to be examined can be avoided. This leads to discrepancies and measurement values tend to vary. If the excitation ultrasound is not irradiated to an appropriate position on the eyeball, the amplitude of the eyeball vibration and the displacement of the eyeball deformation become small and unstable, and the detection signal also decreases and becomes unstable, resulting in the measurement value The measurement becomes unstable due to variations in the values, making it impossible to obtain highly reliable measured values.

Furthermore, in Patent Document 3 and Patent Document 4, the intraocular pressure is detected based on the magnitude of displacement and the amplitude of the resonance point, so if the vibration and displacement detection device is not aligned to an appropriate position, the detection sensitivity will decrease and the detection signal will decrease. cannot be obtained stably, so accurate amplitude and displacement cannot be obtained. This becomes a fatal factor when measuring amplitude or displacement, reducing the reliability of the measurement results.

The present invention has been made in view of the above-mentioned problems, and is not based on vibration or displacement of the eyeball or cornea itself, or a phase change due to vibration, as in the past, but is generated at a predetermined position on the surface of the eyeball without contact. When using surface waves to measure intraocular pressure and material mechanical properties of eyeball surface tissues (Young's modulus, shear modulus, viscosity, etc. of eye tissue), interference of excited ultrasonic waves with detection sensors is minimized. The purpose of the present invention is to provide a non-contact type eyeball physical property measuring device that can be used to We also aim to provide a home monitoring system for ocular physical properties that allows patients suffering from glaucoma to detect intraocular pressure values measured by the intraocular pressure physical property measuring device while at home, without placing a large burden on patients. purpose.

In order to achieve the above object, the present invention is a non-contact eyeball physical property measuring device, which uses irradiation waves to generate surface waves on the surface of the eyeball, which is the eye to be examined. an excitation means for exciting an excitation point; a detection means for detecting a surface wave generated by the excitation means at at least one or more detection points on the eyeball different from the excitation point; and a surface wave detected by the detection means. surface wave processing means for analyzing the surface wave processing means, and eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis results in the surface wave processing means, and the irradiation wave emitted by the excitation means has a fundamental frequency of 20 KHz. As described above, it is characterized by being a continuous wave of aerial ultrasound having a frequency of 200 KHz or less, or a burst wave of 10 or more waves of this aerial ultrasound, and satisfying the following [Equation 1].
[Number 1]
Tex+Liw/Va ≦ Lex/Va+Ds/Cs+Ldr/Va
Here, Cs: phase velocity or group velocity of surface waves, Va: sound velocity of airborne ultrasound, Tex: irradiation time of burst wave for excitation of surface waves, Lex: distance between excitation ultrasonic irradiation unit (excitation means) and ocular surface. Distance to the excitation point, Liw: Propagation path length of interference noise of the excitation ultrasonic wave, Ldr: Distance between the surface wave detection point on the eyeball surface and the receiving ultrasonic sensor for surface wave detection (detection means)

In order to achieve the above object, the present invention is a non-contact eyeball physical property measuring device, which uses irradiation waves to generate surface waves on the surface of the eyeball, which is the eye to be examined. an excitation means for exciting an excitation point; a detection means for detecting a surface wave generated by the excitation means at at least one or more detection points on the eyeball different from the excitation point; and a surface wave detected by the detection means. surface wave processing means for analyzing the surface wave processing means, and eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis results of the surface wave processing means, and the irradiation wave emitted by the excitation means has a fundamental frequency of 50 KHz. The above is continuous pulsed light from a light source of coherent light or incoherent light having a frequency of 50 MHz or less, and further includes modulation means for amplitude modulating the pulsed light with a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than the fundamental frequency. , the excitation means continuously irradiates amplitude-modulated continuous pulsed light obtained by amplitude-modulating the continuous pulsed light at a frequency lower than its fundamental frequency by the modulation means, or a burst wave of 10 cycles or more of this amplitude-modulated continuous pulsed light. and the excitation means controls the pulse time and pulse period of the continuous pulsed light to match the phase of the continuous photoacoustic waves generated in the tissue by the continuous pulsed light.

In this eyeball physical property measuring device, the pulse time of the continuous pulsed light emitted from the excitation means is set within a range of 10 ns to 1000 ns, and the pulse period of the continuous pulsed light is set to 0.00 ns at the frequency of the photoacoustic wave. It is preferable that the frequency satisfies the range of 5 MHz to 50 MHz and has the same period as the frequency or an integer fraction thereof.

This eyeball physical property measuring device preferably further includes communication means for transmitting the physical properties of the eyeball obtained by the eyeball physical property calculation means to an external device via a wide area network.

In order to achieve the above object, the present invention provides a home monitoring system for eyeball physical properties using a non-contact eyeball physical property measuring device installed in a patient's home, the non-contact eyeball physical property measuring device comprising: In order to generate a surface wave on the surface of the eyeball, which is the eye to be examined, an excitation means for exciting at least one or more excitation points on the eyeball using an irradiation wave; a detection means for detecting at least one or more detection points on the eyeball different from the above, a surface wave processing means for analyzing the surface waves detected by the detection means, and a surface wave processing means for analyzing the surface waves detected by the detection means; An eyeball physical property calculation means for calculating physical properties, and a communication means for transmitting the physical properties of the eyeball obtained by the eyeball physical property calculation means to an external device via a wide area network, and the irradiation wave emitted by the excitation means is The external device is a continuous wave of aerial ultrasound having a fundamental frequency of 20 KHz or more and 200 KHz or less, or a burst wave of 10 waves or more of this aerial ultrasound, and the external device calculates the physical properties of the patient's eyeball calculated by the physical property calculation means of the eyeball. an eyeball physical property analysis unit that analyzes the degree of progression of a patient's symptoms based on the data regarding the eyeball physical properties; an eyeball physical property data storage unit that accumulates data regarding the eyeball physical properties; and a patient information storage section in which the analysis results of the section and information related to the patient are stored.

In order to achieve the above object, the present invention provides a home monitoring system for eyeball physical properties using a non-contact eyeball physical property measuring device installed in a patient's home, the non-contact eyeball physical property measuring device comprising: In order to generate a surface wave on the surface of the eyeball, which is the eye to be examined, an excitation means for exciting at least one or more excitation points on the eyeball using an irradiation wave; a detection means for detecting at least one or more detection points on the eyeball different from the above, a surface wave processing means for analyzing the surface waves detected by the detection means, and a surface wave processing means for analyzing the surface waves detected by the detection means; An eyeball physical property calculation means for calculating physical properties, and a communication means for transmitting the physical properties of the eyeball obtained by the eyeball physical property calculation means to an external device via a wide area network, and the irradiation wave emitted by the excitation means is Continuous pulsed light from a coherent light or incoherent light source with a fundamental frequency of 50 KHz or more and 50 MHz or less, and the pulsed light is further amplitude-modulated by a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than the fundamental frequency. The excitation means includes a modulation means, and the excitation means continuously irradiates the continuous pulsed light with an amplitude modulated continuous pulsed light obtained by modulating the continuous pulsed light at a frequency lower than the fundamental frequency by the modulating means, or irradiates the continuous pulsed light with 10 cycles of the amplitude modulated continuous pulsed light. The above burst wave is irradiated, and the external device includes a transmitting/receiving unit that receives data regarding the physical properties of the patient's eyeball calculated by the physical property calculating means, and analyzes the degree of progress of the patient's symptoms based on the data regarding the physical properties of the patient's eyeball. an eyeball physical property analysis unit that stores data related to the eyeball physical properties, an eyeball physical property data storage unit that stores data related to the eyeball physical properties, and a patient information storage unit that stores analysis results of the eyeball physical property analysis unit and information related to the patient. Features.

In order to achieve the above object, the present invention is a non-contact method for measuring physical properties of the eyeball, which uses irradiation waves to generate surface waves on the surface of the eyeball, which is the eye to be examined. an excitation step of exciting an excitation point; a detection step of detecting the surface waves generated in the excitation step at at least one or more detection points on the eyeball different from the excitation point; and a surface wave detected in the detection step. and an eyeball physical property calculation step that calculates the physical properties of the eyeball based on the analysis results in the surface wave processing step, and the irradiation wave emitted in the excitation step has a fundamental frequency of 20 KHz. As described above, it is characterized by being a continuous wave of aerial ultrasound having a frequency of 200 KHz or less, or a burst wave of 10 or more waves of this aerial ultrasound, and satisfying the following [Equation 1].
[Number 1]
Tex+Liw/Va ≦ Lex/Va+Ds/Cs+Ldr/Va
Here, Cs: phase velocity or group velocity of surface waves, Va: sound velocity of airborne ultrasound, Tex: irradiation time of burst wave for surface wave excitation, Lex: distance from excitation ultrasonic irradiation unit to excitation point on the eyeball surface. Distance, Liw: Propagation path length of interference noise of excitation ultrasonic waves, Ldr: Distance between the surface wave detection point on the eyeball surface and the receiving ultrasonic sensor for surface wave detection

In order to achieve the above object, the present invention is a non-contact method for measuring physical properties of the eyeball, which uses irradiation waves to generate surface waves on the surface of the eyeball, which is the eye to be examined. an excitation step of exciting an excitation point; a detection step of detecting the surface waves generated in the excitation step at at least one or more detection points on the eyeball different from the excitation point; and a surface wave detected in the detection step. and an eyeball physical property calculation step that calculates the physical properties of the eyeball based on the analysis results in the surface wave processing step, and the irradiation wave emitted in the excitation step has a fundamental frequency of 50 KHz. The above is continuous pulsed light from a light source of coherent light or incoherent light having a frequency of 50 MHz or less, and further includes a modulation step of amplitude modulating the pulsed light with a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than its fundamental frequency. , in the excitation step, continuous irradiation with amplitude-modulated continuous pulsed light obtained by amplitude-modulating the continuous pulsed light at a frequency lower than its fundamental frequency in the modulation step, or a burst of 10 cycles or more of this amplitude-modulated continuous pulsed light; irradiating a wave, and in the excitation step, controlling the pulse time and pulse period of the continuous pulsed light to match the phase of the continuous photoacoustic wave generated in the tissue by the continuous pulsed light. do.

The non-contact eyeball physical property measuring device according to the present invention includes an ultrasound irradiation unit that excites at least one or more excitation points on the eyeball using irradiation waves to generate surface waves on the surface of the eyeball, which is the eye to be examined. , a receiving sensor that detects the surface waves generated in the ultrasonic irradiation unit at at least one detection point on the eyeball different from the excitation point, a surface wave processing unit that analyzes the surface waves detected by the receiving sensor, and a surface wave processing unit that analyzes the surface waves detected by the receiving sensor. An eyeball physical property calculation unit that calculates the physical properties of the eyeball based on the analysis results in the wave processing unit. The irradiation wave emitted by the ultrasound irradiation unit is a continuous wave of aerial ultrasound whose fundamental frequency is 20 KHz or more and 200 KHz or less, or a burst wave of 10 waves or more of this aerial ultrasound, and satisfies a predetermined formula. With this configuration, in the present invention, interference of excited ultrasonic waves with the detection sensor can be minimized in generating and detecting surface waves by ultrasonic waves. Furthermore, the device according to the present invention can be made lightweight and compact, allowing patients to take measurements at remote clinics or at home, and even if patients and medical institutions are far apart, data can be easily exchanged by connecting to the Internet. It is possible to perform this, and has great effects in diagnosis through telemedicine and home medical care.

FIG. 2 is a diagram illustrating the basic configuration of a surface wave excitation unit and a detection unit for the cornea of a subject's eye, which are included in the eyeball physical property measuring device according to the present embodiment. It is a functional block diagram of the eyeball physical property measuring device same as the above. It is a figure which shows an example of the waveform which amplitude-modulated the excitation ultrasonic wave of a surface wave using the modulation part with which the eyeball physical property measuring device is equipped. FIG. 4 is a diagram illustrating generation of low-frequency sound pressure using a parametric speaker system, using a plurality of transducers as the ultrasonic transducer for excitation of surface waves provided in the eyeball physical property measuring device. FIG. 6 is an explanatory diagram of a case in which a surface wave is generated on the surface of a subject's eye by the photoacoustic effect of pulsed light in the excitation unit included in the ocular physical property measuring device. FIG. 6 is a diagram showing an example of a generation pattern of modulated pulsed light for generating a surface wave by pulsed light using the modulation unit same as the above. It is a figure which shows an example of the case where the external modulation method of a laser pulse light is used in the modulation part same as the above. It is a figure which shows an example of the case where the direct modulation method of a laser diode is used in the modulation part same as the above. It is a figure which shows an example of the surface wave detection by an ultrasonic reflection method in the detection part with which the eyeball physical property measuring apparatus same as the above is equipped. It is a figure which shows an example of surface wave detection by optical triangulation in the detection part same as the above. It is a figure which shows an example of the surface wave detection by the confocal method of the optical multi-wavelength coaxial light beam in the detection part same as the above. It is a figure which shows an example of the surface wave detection by phase detection of the optical heterodyne type Fourier domain optical interferometer in the detection part same as the above. It is a figure which shows an example of the surface wave detection by optical heterodyne type laser Doppler measurement in the detection part same as the above. It is a figure which shows an example of the sound field and directivity of the ultrasonic wave for excitation which generate|occur|produces in the excitation part same as the above. FIG. 6 is a diagram showing an example of the path and positional relationship of interference noise given to the receiving sensor for detecting excitation ultrasonic waves in the surface wave excitation ultrasonic unit and surface wave detection sensor unit provided in the eyeball physical property measuring device. FIG. 3 is a diagram illustrating an example of how the continuous pulsed light is intensity-modulated in the excitation pulsed light provided in the eyeball physical property measuring device, and a surface wave having a frequency lower than the frequency of the generated photoacoustic wave is excited on the eyeball surface. It is a figure which shows an example of the relationship between the pulse time of the pulsed light in the pulsed excitation light source with which the eyeball physical property measuring apparatus is equipped, and the wavelength of the photoacoustic wave generated. It is a figure which shows an example of the relationship between the pulse time of the pulsed light in the pulsed excitation light source with which the eyeball physical property measuring apparatus is equipped, and the wavelength of the photoacoustic wave generated. FIG. 2 is a diagram showing an example of a case where irradiation is performed in accordance with the frequency of a photoacoustic wave that generates a pulse period of continuous pulsed light in an excitation pulsed light source provided in the eyeball physical property measuring device. FIG. 6 is a diagram showing an example of a case where the amplitude of a surface wave is maximized by controlling the pulse time and pulse period of a light pulse of a pulsed light source provided in the eyeball physical property measuring device. FIG. 2 is a diagram illustrating a home monitoring system for eyeball physical properties that connects the eyeball physical property measuring device same as above to the Internet, accumulates measurement data, and analyzes the accumulated data to provide information for diagnosis by a doctor. It is a figure which shows an example of the functional block of each processing part of the home monitoring system of eyeball physical properties same as the above.

(Embodiment)
Here, embodiments of the present invention will be described in the following order.
(1) Basic configuration of measurement method (2) Surface waves generated on the ocular surface (3) Configuration of excitation means for generating surface waves (4) Configuration of detection means for detecting surface waves (5 ) Configuration of excitation/detection means to minimize interference of excited ultrasonic waves with the detection sensor when generating and detecting surface waves using ultrasonic waves (6) To efficiently generate surface waves using optical energy (7) Output means and analysis means for measured intraocular pressure values and material mechanical properties of ocular tissue (home monitoring system for ocular physical properties)

(1) Basic configuration of the measurement method The present invention utilizes the ocular surface waves of the eye to be examined and determines the phase velocity of the waves to determine the intraocular pressure in the eye to be examined and the material properties of the eye tissue to be examined. When each point is located at one location, the propagation of the surface wave cannot be measured unless the detection point is located at a location different from the excitation point. However, this does not apply when there are multiple excitation points or detection points.

FIG. 1 shows the simplest configuration in which the non-contact eyeball physical property measuring device according to the present embodiment has one excitation point 104 and one detection point 105. The excitation unit 102 and the detection unit 103 are arranged such that the excitation irradiation axis 107 and the detection axis 108 are substantially coaxial with each other on the normal line of the detection point 104 and the detection point 105, respectively. The intersection point on the extended line of the excitation irradiation axis 107 and the detection axis 108 substantially coincides with the center of corneal curvature. The ultrasonic waves or pulsed light (preferably continuous pulsed light from a coherent light or non-coherent light source is used) irradiated onto the eyeball surface by the excitation unit 102 arranged in this way has an amplitude in the direction perpendicular to the eyeball surface. Excite a surface wave 106 having . The surface waves 106 propagate along the ocular surface with the excitation point at the center at a frequency and phase velocity determined by the excitation means, like the ripples generated on the water surface when a stone is thrown onto the water surface. By detecting the waves at a predetermined position, the frequency and phase velocity of the surface waves can be determined.

Here, surface waves will be explained. Waves that propagate in soft tissue include body waves that propagate within the tissue, and surface waves and guided waves that propagate along the surface of the tissue. Here, surface waves or guided waves are collectively referred to as the propagation of waves appearing on the tissue surface.

Body waves include longitudinal elastic waves and transverse shear waves, and even in living tissues, imaging equipment uses ultrasound as longitudinal elastic waves, and tissue stiffness can be diagnosed by measuring transverse shear waves. It is applied to ultrasonic elastography, etc.

There are Rayleigh waves as surface acoustic waves where restoring force due to shear elasticity acts on surface waves, surface tension waves due to the restoring force of surface tension, and leaky surface tension waves which propagate due to the combined action of shear elasticity and surface tension. Regarding these surface waves, measurement examples such as hardness measurement of gel-like substances are known.

Furthermore, Lamb waves are known as waves that propagate in a plate-like medium, and unlike Rayleigh waves that propagate in a semi-infinite medium, Lamb waves are generated when the outside of both interfaces of the plate is in a mechanical state such as air or a vacuum state. It propagates through the plate-like medium in such a way that it satisfies the boundary condition of being free.

However, ocular tissues such as the cornea, conjunctiva, and sclera have a layered structure; for example, the outer surface of the cornea is in contact with air, and the inner boundary surface is a thin layer in contact with the anterior aqueous humor. . The boundary conditions for each interface are different, and it is necessary to consider the case where one of the interfaces is in contact with a liquid substance. In such cases, the Rayleigh-Lam model is known as a guided wave that takes into account the boundary conditions with other materials in contact at the boundary.

From Rayleigh waves and Rayleigh-Lamb waves, the shear modulus G and viscosity η of the medium can be determined from the phase velocity Cr and the density ρ. Further, from the surface tension wave, its phase velocity Cc and density can be determined as ρ, and the surface tension γ of the medium can be determined from the angular frequency ω. Further, from the leaky surface tension wave, the surface tension γ can be determined from its phase velocity Cl, shear modulus G, density ρ, and angular frequency ω.

From the above, it is possible to determine the shear modulus G and viscosity modulus η by measuring the phase velocity of the Rayleigh-Lamb wave on the tissue surface, and by measuring the phase velocity of the surface tension wave or leaky surface tension wave, the surface tension By determining γ, it is possible to determine the internal pressure, that is, the intraocular pressure in the case of an eyeball, from the surface curvature radius and surface tension using Laplace's law.

Here, the surface waves that propagate on the surface of the eyeball are not vibrations of the eyeball or cornea themselves, but are waves that are localized and propagated only near the surface of the tissue, and the power to generate this surface wave is not the vibration of the eyeball or cornea itself. Compared to the power needed to vibrate, surface waves can be generated with smaller power. Furthermore, since what is detected is the propagation velocity, phase, or frequency spectrum of the surface waves, there is little influence from changes in the amplitude of the surface waves, and stable measurement is possible against various external influences in clinical practice.

Next, the functional configuration of the non-contact eyeball physical property measuring device 1 according to the present embodiment will be described with reference to FIG. 2. FIG. 2 shows an example of the eyeball physical property measuring device 1, in which an excitation unit 201 that excites the eyeball surface generates a surface wave by exciting the eyeball surface, and a detection unit 202 detects the surface wave. The excitation unit 201 is driven by a drive circuit 203, and the drive circuit 203 is controlled by a transmission control section 210 of a control unit 211. The excitation unit 201 includes a modulation section 201a for amplitude modulating an ultrasonic wave or pulsed light using a modulation frequency lower than its oscillation frequency. The detection unit 202 has a detection transmitting section and a receiving section integrated, and the transmitting section driven by the detection transmitting circuit 204 sends a detection transmission signal to the ocular surface, and the signal is reflected from the ocular surface and returned. The receiving section receives the signal and sends the detection signal to the detection receiving circuit 205. In the detection receiving circuit 205, for example, an amplified received wave is converted into a digital signal by an A/D converter 207 and sent to the control unit 211 side. A surface wave processing section 208 in the control unit 211 processes the received waves, identifies components of the surface waves in the received waves, and measures the phase and delay time of the surface waves. The eyeball physical property calculation unit 209 calculates the phase velocity from the phase and delay time of the surface waves, and calculates the intraocular pressure or the material properties of the eye tissue.

As the excitation unit 201 that excites the surface waves, there are an excitation method using ultrasonic waves and an excitation method using pulsed light. In the ultrasonic method, the ocular surface is vibrated by the sound pressure of the ultrasonic waves irradiated to a predetermined position on the ocular surface to generate surface waves. In the method using optical energy, short pulsed light is irradiated onto the ocular surface, and the tissue at the focal point of the irradiated pulsed light absorbs the light energy, causing its temperature to rise and instantaneous thermal expansion, causing ultraviolet radiation to be generated within the tissue. Generate sound waves. The generated ultrasound propagates to the tissue surface and excites surface waves.

As will be described later, methods for detecting surface waves include a detection method using an ultrasonic reflection method, a minute displacement detection method using optical triangulation, a multi-wavelength coaxial confocal method, and an optical heterodyne method. The ultrasonic reflection method uses ultrasonic waves with a frequency several times higher than the frequency of the generated surface waves to be sent to and received from the surface wave detection point, and the returned reflected waves are demodulated and detected to detect the surface waves on the ocular surface. To detect. Optical trigonometry irradiates a detection point with a light beam and detects the light reflected from the detection point using multiple light receiving elements or one-dimensional or two-dimensional imaging devices, resulting from periodic changes in the reflection angle due to surface vibration. Surface waves are detected from changes in the output of the light receiving element and changes in the bright spot position of the image sensor. In the differential detection method of multiple wavelength light beams, multiple light beams with different wavelengths are coaxially irradiated onto the ocular surface, and the optical design is such that the focal position of the light beams of each wavelength is slightly shifted, and the focal position area is aligned with the cornea. When aligned so that the surface is included, the intensity of reflected light of each wavelength fluctuates due to the vibration of the ocular surface, and the reflected light intensity of each wavelength is differentially amplified to detect a surface wave. Optical heterodyne methods include a method that measures phase changes due to minute fluctuations on the ocular surface detected by a Fourier domain optical interferometer, and a method that detects surface waves by detecting minute vibrations on the ocular surface using a laser Doppler vibrometer.

To detect the phase velocity of the surface wave, measure the phase difference between the detected surface wave signal and the drive signal of the excitation unit drive circuit 203, and calculate the phase velocity from the phase difference and the distance from the excitation point to the detection point. I can do it. If there are multiple detection points, the phase of the surface wave at each detection point can be detected, and the phase velocity can be calculated from the phase difference and the distance between the detection points.

Once the phase velocity of the Rayleigh wave or Rayleigh-Lamb wave is determined, the shear modulus, Young's modulus, and viscosity of the tissue can be calculated using the equations described below.

Once the phase velocity of the surface tension wave or leakage surface tension wave on the corneal surface is determined, the tension on the corneal surface can be determined using the formula described later, and the internal pressure, or intraocular pressure, is calculated using Laplace's law from the average curvature of the ocular surface and the surface tension. be able to.

(2) Surface waves generated on the ocular surface Surface waves generated on the surface of living tissues are elastic waves, and include Rayleigh waves and Rayleigh-Lamb waves in which shear elasticity and viscosity act as restoring forces in the propagation process, and surface tension waves. There are surface tension waves that act as a restoring force, and leakage surface tension waves that act as a restoring force that is a mixture of shear elasticity, viscosity, and surface tension. For example, in the case of Rayleigh-Lamb waves generated on the corneal surface, the zeroth order of the asymmetric mode can be observed. The zero-order phase velocity is relatively slow, about 1 to 5 m/sec, and there is frequency dispersion, so the phase velocity differs depending on the frequency. It is possible to detect frequencies from about 200 Hz to 5 KHz, and when the frequency is outside this range, the attenuation increases and detection becomes difficult. This measurable frequency varies depending on the Young's modulus of the eye tissue and the thickness of the tissue layer, so it is necessary to measure at multiple frequencies.

In the case of surface tension waves and leaky surface tension waves, in order for surface tension to become dominant as a restoring force, the wavelength must be short and the waves must be at a relatively high frequency that is localized to the biological surface, resulting in Rayleigh waves and Rayleigh-Lamb waves. It can be detected at a relatively high frequency. In the case of the cornea, the frequency of surface tension waves is shorter than the thickness of the cornea, and can be detected at a frequency of 20 KHz or higher (for example, 20 to 50 KHz), where the influence of Rayleigh-Lamb waves is small.

(3) Configuration of excitation means for generating surface waves As excitation means for surface waves, excitation means using ultrasonic waves and excitation means using optical energy can be considered.
In the case of aerial ultrasound, the frequency can range from about 20 KHz to about 1 MHz, but in order to obtain effective power for excitation, it is appropriate to range from about 20 KHz to about 100 KHz. In the case of an airborne ultrasonic transducer of 100 KHz or more, not only the radiated sound pressure is low, but also the attenuation due to air propagation is large. When ultrasonic waves propagate through the air, the attenuation coefficient is 1× ¹⁰⁻¹¹ ×f ² (m ⁻¹ ), where f is the frequency of ultrasonic waves, and is proportional to the square of the frequency, and at 100 KHz, the attenuation coefficient is 0. 1 (m ^-1 ), and the attenuation increases exponentially.

Airborne ultrasonic transducers, which are generally used as ultrasonic sensors, may not have enough sound pressure with one transducer. In such cases, sufficient ultrasonic output can be obtained by driving multiple ultrasonic transducers. Furthermore, by controlling the phase of each drive signal of multiple ultrasonic transducers, a phased array transducer is configured to control the phase of the ultrasonic waves and control the focal position on the ocular surface to an arbitrary position. It can also be used as a control. Even when a plurality of ultrasonic transducers are used, the sound pressure of the ultrasonic waves is not as high as that of vibration detection using corneal vibration, so the number of transducers when configuring an ultrasonic transducer array is not large and is limited.

Furthermore, in order to excite Rayleigh waves or Rayleigh-Lamb waves on the ocular surface, the ocular surface must be locally excited at a frequency in the audible range lower than that of ultrasound. Therefore, by amplitude-modulating a high-frequency ultrasonic wave with a low frequency, it is possible to generate a sound pressure wave with the same low frequency as the amplitude modulation frequency near the focal position. FIG. 3 shows how the modulation unit 201a is used to superimpose a modulation signal of a low frequency on the oscillation frequency of an ultrasonic transducer to perform amplitude modulation and generate amplitude-modulated ultrasonic waves. Furthermore, by using multiple ultrasound transducers to perform phased array control and frequency amplitude modulation, low-frequency sound waves are generated only near the focal point while maintaining sharp directivity, selectively targeting the ocular surface. A predetermined position can be excited with an amplitude modulation frequency. This is the well-known principle of parametric speakers. FIG. 4 shows the generation of low frequency sound pressure near the focal point of the ultrasound beam due to the parametric speaker configuration. For example, a modulated ultrasonic wave Mw is transmitted from a transducer array 401 made up of a plurality of ultrasonic transducers in the excitation unit 201, and the ultrasonic wave is focused at a focal position F, resulting in a sound wave with a modulated frequency component having a low frequency. This indicates that Mc occurs locally. It is also possible to control the focus position by changing the drive signal phase of each individual transducer in the transducer array 401 to control the focus position back and forth.

When the excitation means is optical energy, excitation using short pulsed light is possible. FIG. 5 shows the excitation of surface waves by pulsed light. The ocular surface is irradiated with continuous pulses of pulsed light from the light source 501, and the irradiated pulsed light energy is absorbed by molecules near the heat point Hp at the focal position, causing the tissue to thermally expand and contract momentarily. Ultrasound waves are generated into the intraocular tissues just below the ocular surface. The ultrasonic waves reach the surface and excite surface waves. A method of generating ultrasonic waves in a living body using light is known as the photoacoustic effect, and image diagnostic apparatuses using photoacoustic imaging using this principle are known.

The pulsed light used for the photoacoustic effect is very short, on the order of nanoseconds. The frequency of ultrasonic waves generated within a living body as a photoacoustic effect due to pulsed light is approximately 1 MHz to 10 MHz. Therefore, ultrasonic waves generated by simple continuous pulses cannot excite surface waves at low frequencies on the order of KHz. In order to solve this problem, the pulsed light uses continuous pulses of 100 KHz or more, and modulates the intensity at the same low frequency as the frequency of the surface wave that generates the continuous pulsed light, thereby superimposing sound pressure changes at low frequencies. to excite surface waves. FIG. 6 shows that continuous pulsed light having a fundamental pulse frequency is modulated by a modulation frequency signal to produce modulated pulsed light. That is, it is necessary to continuously irradiate amplitude-modulated continuous pulsed light in which the power intensity of the optical pulse is amplitude-modulated by a modulation means, or to irradiate a burst wave of 10 cycles or more of this amplitude-modulated continuous pulsed light.

As a light intensity modulation method, FIG. 7 shows an external direct modulation method in which a CW laser 201b provided in an excitation unit 201 is directly turned ON/OFF by a modulator 201a that receives an electrical adjustment signal from a controller 201c. FIG. 8 shows a direct modulation method in which the driving current of a semiconductor light source LD (semiconductor laser, SLD, light emitting diode, etc.) 201d is modulated by a current control section 201e in the excitation unit 201.

Light sources for pulsed light include light emitting diodes, semiconductor lasers, fiber lasers, and superluminescence diodes. The wavelength of the light source is preferably a wavelength at which the optical absorption rate of the ocular surface tissue is high. However, the cornea is a transparent tissue and has low light absorption in the region from 380 nm to 1400 nm, and high absorption at other wavelengths, so ultraviolet and near-infrared rays are candidates, but considering biosafety, the ultraviolet region Since the optical power cannot be increased due to the large invasion of living organisms, the wavelength is preferably from the near-infrared region around 1400 nm to the infrared region around 3000 nm. Opaque tissues other than the cornea have a high absorption rate of light from the visible light range of 400 nm or more to the near-infrared region, and the absorption rate of blood hemoglobin in particular increases rapidly at wavelengths of 600 nm or less, so it is difficult to absorb light on the ocular surface. Efficient excitation can be achieved by using pulsed light of 400 nm to 600 nm using the capillaries as heat points. When using a surface tissue other than the cornea, such as the conjunctiva, as an excitation point, pulse light is irradiated to the capillaries of the conjunctiva as a heat point Hp, and surface waves are excited on the conjunctival surface, and the surface waves propagated to the cornea are detected on the cornea. This enables efficient measurement.

Regarding the excitation method for generating surface waves, we have mainly shown excitation using continuous waves, but excitation using burst waves is also possible. However, in the case of a burst wave, in order to stabilize the output of the excitation means and further stabilize the amplitude of the surface wave, it is necessary to output continuous waves of a certain constant wave number. For example, in the case of excitation by ultrasonic waves, a certain amount of time is required for the sound pressure of the ultrasonic transducer to reach its peak, and in the case of excitation by pulsed light, time is also required for the surface waves to rise. For this reason, in the case of surface wave excitation using burst waves or burst pulses, ultrasonic waves, modulated ultrasonic waves, or modulated pulsed light are transmitted at a transmission time such that the number of surface waves that can be detected is at least 10 waves (10 cycles or more). . The transmission time of the burst wave depends on the characteristics of the ultrasonic transducer, pulsed light source, etc., and is therefore determined according to the characteristics.

(4) Configuration of detection means for detecting surface waves Detection means for detecting surface waves include an ultrasonic reflection method, an optical triangulation method, an optical multi-wavelength coaxial confocal method, an optical heterodyne method, and the like.

When the detection means is an ultrasonic reflection method, detection is performed using continuous ultrasonic waves or burst ultrasonic waves of 100 or more waves. The ultrasonic waves transmitted from the transmitting ultrasonic transducer reach the ocular surface, are reflected and scattered, and then return. When the ultrasound waves reflect off the ocular surface, they are modulated by surface wave vibrations and return to the receiving ultrasound transducer with the surface wave vibration components superimposed on them. By demodulating and detecting this reflected wave, it is possible to demodulate the vibration frequency component modulated by the surface wave vibration on the eye surface. By measuring the frequency and phase of this demodulated wave, the phase and frequency of the surface wave can be calculated.

FIG. 9 shows one example of surface wave detection using ultrasonic waves. In this embodiment, a transmitting ultrasonic transducer 901 and a receiving ultrasonic transducer 902 are provided separately. By using separate ultrasonic transducers for transmission and reception, it is possible to use continuous ultrasonic waves for detection, which has the advantage of always detecting surface waves. A digital value for controlling the oscillation frequency of the voltage variable oscillator 905 is output by the control CPU 903 to the D/A converter 904, and a control voltage corresponding to the digital value is output from the D/A converter 904 to the voltage variable oscillator 905. The voltage variable oscillator oscillates at a frequency corresponding to the voltage. The oscillated signal is amplified by a transmission amplifier 906, drives a transmission ultrasound transducer 901, and transmits detection ultrasound to the ocular surface. The ultrasonic waves reflected and returned from the ocular surface are modulated at the surface wave frequency by surface wave vibrations on the ocular surface. A receiving ultrasonic transducer 902 receives the returned ultrasonic waves, and a received signal amplified by a receiving amplifier 907 is input to a multiplier 908 . Since the transmission signal output from the voltage variable oscillator 905 is also used as a reference signal to demodulate the reception signal, a reference signal filtered by a reference signal band-pass filter 909 that passes only the transmission frequency band is generated and received by the multiplier 908. By demodulating the received signal by multiplying it by the signal, the surface wave component included in the received signal is demodulated. A demodulated signal band-pass filter 910 removes frequency components other than surface waves, and an A/D converter 911 converts the signal into a digital value, which is input to a control/arithmetic CPU 903 for calculation processing. At this time, the control/calculation CPU 903 is placed in the control unit 211 shown in FIG. 2, and here calculates the physical property values of the surface waves such as surface tension, and the intraocular pressure of the eyeball based on these physical property values.

If the ultrasonic transmission for detection is made into a burst wave, the ultrasonic transducer can be used for both transmission and reception, and surface wave vibrations can be detected with one transducer. It is also possible to digitally convert the returned received signal without demodulating or detecting it using an A/D converter, input it to the arithmetic CPU, and calculate the frequency spectrum and phase change of the surface wave component by Fourier transform.

Here, it is desirable that the frequency of the ultrasonic waves for detection be at least about 10 times the frequency of the surface waves excited by the excitation means. This is necessary for demodulation/detection and Fourier transform processing to completely separate the fundamental frequency of the ultrasonic wave and the frequency components of the surface wave and to accurately detect the surface wave. Therefore, the reason why the detection burst waves are set to 100 waves or more is because at least 10 waves or more of surface wave components are detected and analyzed in order to increase the phase detection accuracy of the surface waves. This is because the number of waves is about 100 times.

Next, the case where the detection means for surface wave detection is detected by optical triangulation will be described with reference to FIG. 10. In this case, the detection point is irradiated with a detection light beam, and the light reflected and scattered from the detection point and returned is detected by a plurality of light receiving elements, an optical position sensor, an optical line sensor, or the like. When the detection point surface vibrates due to surface wave vibration, the angle and intensity distribution of the light returning from the detection point will change, and the imaging position on the light-receiving side image-forming surface will also change. Vibrations can be detected by differentially amplifying output changes, and in the case of optical position sensors and optical line sensors, changes in the imaging position itself can be detected, so the position changes can be detected as surface wave vibrations. FIG. 10 is an example of detection means using optical triangulation. The light emitted from the surface wave detection light source 1001 reaches the eye surface via the objective lens 1002, and the light reflected at the detection point enters the light receiving element A1004 and the light receiving element B1005 via the imaging lens 1003. When the detection point vibrates due to surface waves, the optical axis angle of the light reflected at the detection point changes in accordance with the vibration, so the amount of light incident on each of the light receiving element A 1004 and the light receiving element B 1005 changes relatively. The surface wave vibration at the detection point is detected by differentially amplifying the electric signals output from the light receiving element A1004 and the light receiving element B1005 by the differential amplifier 1006.

Next, a case will be described with reference to FIG. 11 regarding a case in which the detection means uses a confocal method of optical coaxial light beams having multiple wavelengths. In this case, the measurement light beam is irradiated with a light source of multiple wavelengths or white light, and an optical system is created that has a chromatic aberration focus in which the focal position shifts little by little depending on the wavelength. When micro vibrations due to surface waves occur at the detection point on the eye surface, the amount of reflected light of each wavelength whose focal position differs slightly changes in accordance with the vibration, and the reflected light of wavelengths close to the focal position is strong, while the reflected light of wavelengths whose focal position is far apart changes. The reflected light becomes weaker. Furthermore, the confocal optical system allows a sharper reflection peak to be obtained near the focal point of each wavelength, so when the reflected and returned light is split into multiple wavelengths and detected by a photodetector, each wavelength is incident on the photodetector. The amount of light changes significantly even with minute vibrations. By differentially amplifying the electrical signals from the light-receiving elements of each wavelength, it is possible to detect vibrations at the detection point due to surface waves. FIG. 11 shows an embodiment of a multi-wavelength coaxial confocal system. A light beam emitted from a light source 1101 passes through a fiber collimator 1102, a fiber coupler 1103, and a fiber collimator 1104, and is irradiated onto a detection point on the eye surface by a chromatic aberration focusing lens 1105, with the focus of each wavelength being slightly shifted. In this example, the focus of wavelength A, wavelength B, and wavelength C is slightly shifted from the detection point, so the detection peak of each wavelength shifts, and when the detection point position on the ocular surface shifts, the amount of reflected light of each wavelength changes. It has been shown that The light beam reflected at the detection point is incident on a spectral detection unit 1107 via a chromatic aberration lens 1105, a fiber collimator 1104, and a fiber collimator 1106. The light beam incident on the spectroscopic detection unit is split into wavelength A, wavelength B, and wavelength C by hot mirror 1107a and hot mirror 1107b, and imaging lens A, imaging lens B, which becomes confocal for each wavelength, The light enters a photodetector 1107c, a photodetector 1107d, and a photodetector 1107e via an imaging lens C. Surface wave vibrations are detected by differentially amplifying the electrical signals output from each photodetector.

Next, a case where the detection means is phase detection of a Fourier domain optical interferometer using an optical heterodyne method will be described with reference to FIG. 12. In this case, a light beam emitted from a low-coherence light source such as a superluminescence diode or a wavelength-swept laser light source is divided into a light beam that irradiates the measurement target and a light beam that serves as a reference light within the optical interferometer. The light beam irradiated onto the object to be measured is irradiated onto the ocular surface by the interferometer, reflected by the ocular surface, and then enters the optical interferometer again. The light beam incident on the optical interferometer interferes with the reference light inside the interferometer and is detected as a spectral distribution waveform with an interference spectral distribution and a beat signal with a beat frequency. By Fourier transforming these spectral distribution waveforms and beat signals, the interference peak and phase of the light rays reflected from the eye surface and returned are calculated. Microfluctuations caused by surface waves are detected as changes in phase, and surface waves can be detected.

FIG. 12 shows an embodiment of a Fourier domain interferometer using the spectral domain method. A light beam emitted from a superluminescence diode (SLD) light source has low coherence and a wide wavelength band. This light beam enters a fiber coupler 1202 via an optical fiber and is split into two optical paths. One is projected onto the reference mirror 1205 via the fiber collimator 1203 and the achromatic lens 1204, is reflected, and returns to the fiber coupler 1202 via the achromatic lens 1204 and the fiber collimator 1203 again. The other branched light is sent from a fiber coupler through a fiber collimator 1206 and an aperture 1207, and then the light beam is waved or set at a predetermined angle by a galvano mirror 1108 for scanning, and then passed through an objective lens 1209 to the ocular surface. is projected on. The light beam reflected from the eye surface returns to the fiber coupler 1202 via the objective lens 1209, galvanometer mirror 1208, aperture 1207, and fiber collimator 1206. In the fiber coupler, the reference light and the reflected light returning from the eye surface are superimposed to form interference light. The interference light is projected onto CCD 1214 via fiber connector 1210, relay lens 1211, diffraction grating 1212, and achromatic lens 1213. . The CCD 1214 outputs spectral distribution data separated by the diffraction grating 1212. This spectral data is Fourier-transformed by an arithmetic circuit to calculate the interference peak and phase to detect minute vibrations caused by surface waves. In this embodiment, a spectrum domain optical interferometer is used as a detection interferometer, but a swept source (light source wavelength swept) type optical interferometer may be used.

Next, a case where the detection means is a laser Doppler interferometer using optical heterodyne will be described with reference to FIG. 13. In this case, the beam emitted from the laser light source is split into two, one beam is irradiated onto the ocular surface, and the other beam is modulated by an acousto-optic modulator at a constant carrier frequency fm. The light beam reflected on the ocular surface undergoes a Doppler shift of frequency fd due to the surface wave vibration of the ocular surface, and returns to the interferometer again, where it interferes with the light modulated by the acousto-optic modulator to generate a beat frequency of fm±fd. . Since fm of this beat frequency is a constant frequency, only the Doppler shift frequency fd changes due to surface wave vibration. Surface wave vibrations can be detected by FM demodulating this frequency change.

FIG. 13 shows an example of a laser Doppler interferometer. A light beam emitted from a laser light source 1301 having an optical frequency fo is split by a polarization beam splitter 1302 into two light beams, S-polarized light and P-polarized light. The S-polarized light beam is reflected by a polarizing beam splitter 1302 and enters an acousto-optic modulator (AOM) 1305 via a mirror 1304. The frequency is modulated by an acousto-optic modulator to fo+fm, reflected by a polarizing beam splitter 1303 and a polarizing beam splitter 1308 via a mirror 1307, reflected by a reference mirror 1310 via a quarter-wave plate 1309, and returned. The light passes through the quarter-wave plate 1309 again, becomes P-polarized light, and enters the polarization beam splitter 1308. On the other hand, the P-polarized light beam that has passed through the polarizing beam splitter 1302 further passes through the polarizing beam splitters 1303 and 1308, is reflected by a mirror 1311, and is irradiated onto the eye surface via a quarter-wave plate 1312. The irradiated light beam is reflected on the ocular surface and returns at a frequency of fo+fd due to Doppler shift frequency fd due to surface wave vibration. It becomes S-polarized light by the quarter-wave plate 1312 and is reflected by the polarizing beam splitter 1308. The light beam from the reference mirror 1310 and the light beam from the eye surface interfere and enter the photodetector 1313 . A signal with a frequency fm+fd is output from the photodetector 1313, and by FM demodulating the modulation component of the Doppler shift frequency fd that changes due to vibration, phase modulation and frequency modulation components are obtained, and surface vibration due to surface waves can be detected. can.

(5) Configuration of excitation/detection means to minimize interference of excited ultrasonic waves with the detection sensor when generating and detecting surface waves by ultrasonic waves Figure 15 shows the excitation means for surface waves by ultrasonic waves and the generated In the case where surface waves are detected by the ultrasonic reflection method, an embodiment is shown for minimizing the interference noise caused by the surface wave excitation ultrasonic waves to the surface wave detection ultrasonic sensor.

Generally, the ultrasonic waves emitted by the ultrasonic excitation means form a sound field having a sound pressure peak at the center of the beam as shown in FIG. Therefore, ultrasound not only irradiates a strong peak sound pressure at the excitation point, but also irradiates relatively weak sound waves around the excitation point. The ultrasonic waves spread around the area are reflected on the surface of the measuring eye and interfere with the detection ultrasonic sensor, so they are superimposed as noise on the surface wave detection waveform. This configuration shows a configuration for minimizing the interference of acoustic noise on the detection sensor due to this excitation ultrasonic wave.

As shown in FIG. 15, the ultrasonic wave for surface wave excitation is emitted as the burst wave from an ultrasonic irradiation unit (excitation means) 1501, and a surface wave is generated around an excitation point on the surface of the eye to be examined. From the excitation point, the surface wave propagates on the eye surface at a phase velocity (or group velocity) Cs and reaches the detection point. The arriving surface waves are detected by a detection ultrasonic sensor unit. In the case of FIG. 15, an example is shown in which the detection ultrasonic sensor unit is divided into a transmitting sensor 1502 and a receiving sensor 1503 (detection means), but the transmitting sensor and the receiving sensor may be the same. .

The control unit 1507 outputs a drive signal to the drive circuit 1504, and the drive circuit drives the ultrasound irradiation unit 1501 according to the drive signal to irradiate excitation ultrasound to an excitation point on the ocular surface. A transmitting sensor 1502 of the ultrasonic sensor unit for detection transmits ultrasonic waves for surface wave detection to a detection point on the surface of the eye to be examined, and a receiving sensor 1503 receives the ultrasonic waves reflected at the detection point. The control unit 1507 outputs a transmission signal to the transmission circuit 1506, and demodulates the ultrasonic signal received from the reception sensor 1503 and amplified by the reception circuit using the ultrasonic detection method as shown in FIG. 9 to generate surface wave components. Extract and analyze. The control unit 1507 includes a surface wave processing section 1507a that analyzes the surface waves detected by the receiving sensor 1503, and an eyeball physical property calculation section 1507b that calculates the physical properties of the eyeball based on the analysis results in the surface wave processing section 1507a.

In the configuration shown in Figure 15, the distance from the ultrasound irradiation unit to the excitation point is Lex, the distance on the ocular surface from the excitation point to the detection point is Ds, the distance from the receiving sensor to the detection point is Ldr, and the distance from the transmitting sensor to the detection point is Let the distance to Ldt be Ldt. Ldr and Ldt may be the same or different, but if the receiving sensor and the transmitting sensor are the same, the distances will of course be the same.

Further, the interference wave component of the ultrasonic wave emitted from the ultrasonic irradiation unit 1501 to the detection sensor is reflected on the eye surface and reaches the reception sensor 1503, and its path length is defined as Liw. The angle of reflection on the eye surface is such that the incident angle and the exit angle are the same with respect to the normal to the eye surface. The timing at which the detection reception sensor 1503 detects the surface wave component is set to be outside the time when the interference component due to the excitation ultrasonic wave reaches the reception sensor 1503 as interference noise (i.e. Only the surface waves after the interference components of the ultrasonic waves have reached the receiving sensor 1503 are detected). acoustic noise interference can be minimized.

At this time, the phase velocity or group velocity of the surface wave is Cs, the sound velocity of the airborne ultrasound is Va, the irradiation time of the burst wave of the excitation ultrasound is Tex, and the excitation ultrasound irradiation unit (excitation means) is used to excite the eyeball surface. If the distance to the point is Lex, the propagation path length of the interference noise of the excitation ultrasonic wave is Liw, and the distance between the surface wave detection point on the eyeball surface and the receiving ultrasonic sensor (detection means) for surface wave detection is Ldr, then the following is obtained. When [Equation 1] is satisfied, the influence of acoustic noise can be minimized.
[Number 1]
Tex+Liw/Va ≦ Lex/Va+Ds/Cs+Ldr/Va

(6) Configuration of excitation means for efficiently generating surface waves using optical energy As shown in FIG. As already mentioned, surface waves having a frequency lower than that of photoacoustic waves are excited on the eye surface by continuously generating the continuous pulsed light and modulating the intensity of the continuous pulsed light. Furthermore, in order to make the sound pressure of the photoacoustic waves efficiently act as surface wave excitation on the ocular surface, it is necessary to control the pulse time and period of the continuous pulsed light in accordance with the phase of the photoacoustic waves.

Photoacoustic waves are a phenomenon in which thermoelastic waves are generated by adiabatic expansion of substances that absorb the energy of light when pulsed light is irradiated onto living tissue, etc., and the pulse time is sufficiently shorter than the heat dissipation time of the tissue. The acoustic pressure P is expressed by the following [Equation 2]. The Grüneisen coefficient is the efficiency with which irradiated light energy is converted into acoustic wave energy, F0 is the light energy density, and μa is the tissue absorption coefficient.
[Number 2]
P=Γ×μa×F0×exp(-μa×z)
Here, P: acoustic pressure, Γ: Grüneisen coefficient, μa: absorption coefficient of tissue, F0: optical energy density, z: tissue depth And the pulse time of pulsed light satisfies the generation conditions of photoacoustic waves by the following formula: This is [Math. 3].
[Number 3]
τp < τstr
Here, τp: optical pulse time, τstr: tissue heat dissipation time

The photoacoustic wave generated by the photoacoustic effect is a steep pressure change caused by short pulse light, and its spectral band is wide. Photoacoustic waves produce temporal changes in pressure due to the effects of tissue thermal conductivity, stress dissipation time, bulk modulus, density, etc., and the frequency of the generated photoacoustic waves also changes, but within the stress dissipation time It has a change depending on the pulse time of the light pulse. 17 and 18 show the pulse time of the optical pulse and the wavelength change of the generated photoacoustic wave.

Pulsed light is irradiated continuously, but by setting the irradiation period to the same frequency as the frequency of the photoacoustic wave generated by the pulsed light or an integer fraction thereof, each pulsed light is superimposed and continuous. Not only does this result in an acoustic wave, but also an increase in amplitude (amplification) can be obtained due to the superimposed components. Figure 19 shows that by irradiating the pulse irradiation period of pulsed light to match the center frequency of the photoacoustic wave, the phases of each photoacoustic wave (1901, 1902, 1903,...) match, and the sound pressure waveform is A superimposed waveform 1904 appears, indicating that the sound pressure increases.

The frequency of photoacoustic waves generated in living bodies is generally about 0.5 MHz to 50 MHz, and the pulse time of pulsed light is set within the range of 10 ns to 1000 ns to adjust the center frequency or peak spectral frequency of the photoacoustic waves. control. Furthermore, in order to match the phase of each acoustic wave generated, the pulse period of the pulsed light is set to the same period as the frequency of the photoacoustic wave (that is, in the range of 0.5 MHz to 50 MHz), or an integer fraction thereof. The photoacoustic waves are aligned in phase and superimposed to maximize sound pressure. By controlling the pulse time and pulse period of pulsed light, it is also possible to detect the pulse time and pulse period at which the amplitude of the surface wave is maximum.

Furthermore, in order to obtain the optimal pulse time and pulse period of the light pulse, the light pulse time is set to a plurality of pulse times in the range from short-time pulses to long-time pulses, for example, from 10 nsec to 1000 nsec, before measuring the physical properties of the eyeball for the eye to be examined. By further sweeping the pulse period of the pulsed light for each pulse time, the pulse time and pulse period at which the surface wave amplitude on the surface of the eye to be examined detected by the surface wave detection unit is the highest are detected and obtained. By driving the optical pulse at the optimum value, the most efficient surface wave excitation can be achieved.

FIG. 20 shows an example for controlling the pulse time and pulse period of a light pulse and measuring the physical properties of the eyeball at a pulse time and pulse period that maximize the amplitude of the surface wave. Although this embodiment shows surface wave detection as an example of detection using the ultrasonic reflection method, detection may also be performed using the optical triangulation method, the optical multi-wavelength coaxial confocal method, or the optical heterodyne method.

The optical pulse light source (excitation means) 2001 is driven by a light source drive circuit 2002, and the time of the drive pulse output from the light source drive circuit 2002 is set in the pulse signal generation circuit 2005 by the control unit 2008. The control unit 2008 sequentially sweeps the pulse period within a predetermined range according to the set pulse time. The amplitude of the surface wave detected by the detection ultrasonic sensor unit (detection means) is sequentially measured in accordance with the sweep of the pulse period, and the pulse period having the maximum amplitude is determined. The sweep of the pulse period is repeated by sequentially changing the pulse time to a plurality of preset values. As a result, it becomes possible to compare the maximum values of the obtained surface wave amplitudes and determine the optimal pulse time and pulse period of the pulsed light irradiated to the eyeball.

(7) Output means and analysis means for measured intraocular pressure values and material mechanical properties of eyeball tissue (home monitoring system for eyeball physical properties)
Ocular physical properties such as measured intraocular pressure values and material mechanical properties of ocular tissues are used as important parameters in the diagnosis of eye diseases such as glaucoma and keratoconus, which require long-term observation, diagnosis, and treatment. Therefore, it is important that measured values are accumulated smoothly and can be easily checked during diagnosis. Additionally, in recent years, the need for telemedicine and home medical care has increased, and the need for measurements at clinics and at home has also increased.

FIG. 21 shows the overall configuration of a home monitoring system S for ocular physical properties. The intraocular pressure value of the eye to be examined 2101 and the mechanical material properties of the eyeball surface measured by the eyeball physical property measuring device 2102 are connected to the Internet 2110 through one of a plurality of connection means. Connection means include a method via a router 2103 connected to a wired local area network (LAN), a method via a wireless router 2104 using short-range wireless such as wireless LAN or Bluetooth (registered trademark), and a mobile terminal 2105 such as a smartphone. It is connected to the Internet (WAN) by means such as via mobile communication. Measurement data transmitted from the eyeball physical property measuring device is stored in a cloud service 2106 or a fixed server 2111 on the Internet. On the other hand, a medical personnel 2109 such as a doctor can check and analyze data at any time using a terminal device 2108 such as a personal computer, tablet computer, or smartphone.

Furthermore, the cloud service 2106 and fixed server 2111 have built-in applications that analyze the accumulated data, providing data analysis through statistical processing, data analysis and future predictions through artificial intelligence (AI) and deep learning. It becomes possible to do so. These analysis data can be confirmed by the medical officer 2109 as data necessary for diagnosis, and can also be sent to the eyeball physical property measuring device 2102 or smartphone 2105 for confirmation by the subject.

FIG. 22 shows a mechanical configuration diagram of each processing unit (the eyeball physical property measuring device 2102, the mobile terminal 2105, the fixed server 2111, and the terminal device 2108) of the home monitoring S of the eyeball physical properties. The eyeball physical property measuring device 2102 used in this home monitoring system S is a small, low-cost device that is installed in a patient's home and is specialized for the function of measuring the patient's eyeball physical properties such as intraocular pressure.

The eyeball physical property measuring device 2102 includes an excitation unit 102 that excites at least one excitation point on the eyeball using an irradiation wave in order to generate a surface wave on the surface of the eyeball, which is an eye to be examined; A detection unit 103 that detects a surface wave at at least one detection point on the eyeball different from the excitation point, a surface wave processing unit 208 that analyzes the surface wave detected by the detection unit 103, and an analysis in the surface wave processing unit 208. An eyeball physical property calculation unit 209 that calculates the physical properties of the eyeball based on the results, and a communication unit 301 that transmits the physical properties of the eyeball obtained by the eyeball physical property calculation unit 209 to an external device (here, the fixed server 2111) via a wide area network. and. The communication unit 301 is a communication module that enables communication connection with the Internet via, for example, wireless/wireless communication.

The mobile terminal 2105 includes a control unit 2105a that uses a processor such as a CPU and memory to control the components of the mobile terminal 2105 to realize various functions, a storage unit 2105b that is a memory such as RAM, and a communication network such as the Internet. It includes a communication processing unit 2105c that realizes communication connection, a screen display unit 2105d such as a liquid crystal panel or an organic EL display, and an operation input unit 2105e such as a touch panel.

The fixed server (external device) 2111 includes a transmitting/receiving unit 2111a that receives information regarding the physical properties of the eyeball such as intraocular pressure measured by the measuring device 2102, and a control unit that returns response information when a request is received from the mobile terminal 2105 or the terminal device 2108. 2111b, an eyeball physical property analysis unit 2111c that determines the progression of glaucoma etc. based on AI based on the data received from the measurement device 2102, and an eyeball physical property data storage unit 2111d that is a database that accumulates data regarding the eyeball physical properties of patients (users). , and a patient information storage section 2111e in which patient (contractor) analysis results, subscriber ID, password, etc. are stored.

The terminal device 2108 uses an input unit 2108a such as a keyboard to receive input from a doctor, an application execution unit 2108b that executes a dedicated application on a web browser, etc., and an input unit 2108a to display the ocular physical properties of the patient's eye and the results of AI analysis. It includes a request generation unit 2108c that performs acquisition, a transmission/reception unit 2108d, a storage unit 2108e, and the like.

With such a home monitoring system S for ocular physical properties, a patient suffering from glaucoma or the like can monitor the intraocular pressure value measured by the intraocular pressure physical property measuring device 2102 while remaining at home without placing a large burden on the patient. As a result, patients can detect symptoms such as glaucoma at an early stage while staying at home, and a doctor with the terminal device 2108 can prompt the patient to see an ophthalmologist based on the detected data in a timely manner. can prevent the progression of symptoms.

Note that the present invention is not limited to the configuration of the above-described embodiments, and various modifications can be made without changing the spirit of the invention. In addition, in order to achieve the object of the present invention, the present invention is realized as an eyeball physical property measuring method that has characteristic constituent means included in the eyeball physical property measuring device as steps, or as a program that includes those characteristic steps. You can also. The program can not only be stored in a ROM or the like, but can also be distributed via a recording medium such as a USB memory or a communication network.

1,2102 Eyeball physical property measuring device S Home monitoring system for eyeball physical properties 101 Eyeball surface 102 Excitation unit (excitation means)
103 Detection unit (detection means)
104 Excitation point 105 Detection point 106 Surface wave 107 Irradiation axis 108 Detection axis 201 Excitation unit 201a Modulation section (modulation means)
202 Detection unit 208, 1507a, 2008a Surface wave processing section (surface wave processing means)
209, 1507b, 2008b Eyeball physical properties calculation unit (eyeball physical properties calculation means)
210 Transmission control section 211 Control unit 301 Communication section (communication means)
1501 Ultrasonic irradiation unit (excitation means)
1502 Transmission sensor (detection means)
1503 Receiving sensor (detection means)

Claims (8)

A non-contact eyeball physical property measuring device,
Excitation means for exciting at least one or more excitation points on the eyeball using irradiation waves in order to generate surface waves on the surface of the eyeball, which is the eye to be examined;
detection means for detecting the surface waves generated by the excitation means at at least one or more detection points on the eyeball different from the excitation point;
surface wave processing means for analyzing the surface waves detected by the detection means;
eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis results in the surface wave processing means,
The irradiation wave emitted by the excitation means is a continuous wave of aerial ultrasound whose fundamental frequency is 20 KHz or more and 200 KHz or less, or a burst wave of 10 or more waves of this aerial ultrasound, and the following [Equation 1] is satisfied. An eyeball physical property measuring device that satisfies the following.
[Number 1]
Tex+Liw/Va ≦ Lex/Va+Ds/Cs+Ldr/Va
Here, Cs: phase velocity or group velocity of surface waves, Va: sound velocity of airborne ultrasound, Tex: irradiation time of burst wave for excitation of surface waves, Lex: distance between excitation ultrasonic irradiation unit (excitation means) and ocular surface. Distance to the excitation point, Liw: Propagation path length of interference noise of the excitation ultrasonic wave, Ldr: Distance between the surface wave detection point on the eyeball surface and the receiving ultrasonic sensor for surface wave detection (detection means) A non-contact eyeball physical property measuring device,
Excitation means for exciting at least one or more excitation points on the eyeball using irradiation waves in order to generate surface waves on the surface of the eyeball, which is the eye to be examined;
detection means for detecting the surface waves generated by the excitation means at at least one or more detection points on the eyeball different from the excitation point;
surface wave processing means for analyzing the surface waves detected by the detection means;
eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis results in the surface wave processing means,
The irradiation wave emitted by the excitation means is continuous pulsed light from a coherent light or non-coherent light source whose fundamental frequency is 50 KHz or more and 50 MHz or less,
Furthermore, it comprises a modulation means for amplitude modulating the pulsed light with a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than its fundamental frequency,
The excitation means continuously irradiates amplitude-modulated continuous pulsed light obtained by amplitude-modulating the continuous pulsed light at a frequency lower than its fundamental frequency by the modulation means, or generates a burst wave of 10 cycles or more of this amplitude-modulated continuous pulsed light. irradiate,
The apparatus for measuring physical properties of an eyeball is characterized in that the excitation means controls the pulse time and pulse period of the continuous pulsed light, and adjusts the phase of the continuous photoacoustic waves generated in the tissue by the continuous pulsed light. . The pulse time of the continuous pulsed light emitted from the excitation means is set within a range of 10 ns to 1000 ns, and the pulse period of the continuous pulsed light satisfies a frequency range of 0.5 MHz to 50 MHz of the photoacoustic wave. 3. The eyeball physical property measuring device according to claim 2, wherein the period is the same as the frequency or an integer fraction thereof. The eyeball physical properties according to any one of claims 1 to 3, further comprising communication means for transmitting the eyeball physical properties obtained by the eyeball physical properties calculation means to an external device via a wide area network. measuring device. A home monitoring system for ocular physical properties using a non-contact ocular physical property measuring device installed in a patient's home,
The non-contact eyeball physical property measuring device includes:
Excitation means for exciting at least one or more excitation points on the eyeball using irradiation waves in order to generate surface waves on the surface of the eyeball, which is the eye to be examined;
detection means for detecting the surface waves generated by the excitation means at at least one or more detection points on the eyeball different from the excitation point;
surface wave processing means for analyzing the surface waves detected by the detection means;
Eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis results in the surface wave processing means;
a communication means for transmitting the physical properties of the eyeball obtained by the eyeball physical property calculation means to an external device via a wide area network,
The irradiation wave emitted by the excitation means is a continuous wave of aerial ultrasound whose fundamental frequency is 20 KHz or more and 200 KHz or less, or a burst wave of 10 waves or more of this aerial ultrasound,
The external device is
a transmitting/receiving unit that receives data regarding the patient's eyeball physical properties calculated by the eyeball physical property calculation means;
an eyeball physical property analysis unit that analyzes the degree of progression of the patient's symptoms based on the data regarding the eyeball physical properties;
an eyeball physical property data storage unit that stores data regarding the eyeball physical properties;
A home monitoring system for eyeball physical properties, comprising: a patient information storage unit in which the analysis results of the eyeball physical property analysis unit and patient-related information are stored. A home monitoring system for ocular physical properties using a non-contact ocular physical property measuring device installed in a patient's home,
The non-contact eyeball physical property measuring device includes:
Excitation means for exciting at least one or more excitation points on the eyeball using irradiation waves in order to generate surface waves on the surface of the eyeball, which is the eye to be examined;
detection means for detecting the surface waves generated by the excitation means at at least one or more detection points on the eyeball different from the excitation point;
surface wave processing means for analyzing the surface waves detected by the detection means;
Eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis results in the surface wave processing means;
a communication means for transmitting the physical properties of the eyeball obtained by the eyeball physical property calculation means to an external device via a wide area network,
The irradiation wave emitted by the excitation means is continuous pulsed light from a coherent light or non-coherent light source whose fundamental frequency is 50 KHz or more and 50 MHz or less,
Furthermore, it comprises a modulation means for amplitude modulating the pulsed light with a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than its fundamental frequency,
The excitation means continuously irradiates amplitude-modulated continuous pulsed light obtained by amplitude-modulating the continuous pulsed light at a frequency lower than its fundamental frequency by the modulation means, or generates a burst wave of 10 cycles or more of this amplitude-modulated continuous pulsed light. irradiate,
The external device is
a transmitting/receiving unit that receives data regarding the patient's eyeball physical properties calculated by the eyeball physical property calculation means;
an eyeball physical property analysis unit that analyzes the degree of progression of the patient's symptoms based on the data regarding the eyeball physical properties;
an eyeball physical property data storage unit that stores data regarding the eyeball physical properties;
A home monitoring system for eyeball physical properties, comprising: a patient information storage unit in which the analysis results of the eyeball physical property analysis unit and patient-related information are stored. A non-contact method for measuring physical properties of the eyeball,
an excitation step of exciting at least one or more excitation points on the eyeball using the irradiation wave in order to generate a surface wave on the eyeball surface of the eye to be examined;
a detection step of detecting the surface waves generated in the excitation step at at least one or more detection points on the eyeball different from the excitation point;
a surface wave processing step of analyzing the surface waves detected in the detection step;
an eyeball physical property calculation step of calculating the physical properties of the eyeball based on the analysis results in the surface wave processing step,
The irradiation wave emitted in the excitation step is a continuous wave of aerial ultrasound whose fundamental frequency is 20 KHz or more and 200 KHz or less, or a burst wave of 10 waves or more of this aerial ultrasound, and the following [Equation 1] is satisfied. A method for measuring physical properties of an eyeball, which satisfies the following.
[Number 1]
Tex+Liw/Va ≦ Lex/Va+Ds/Cs+Ldr/Va
Here, Cs: phase velocity or group velocity of surface waves, Va: sound velocity of airborne ultrasound, Tex: irradiation time of burst wave for surface wave excitation, Lex: distance from excitation ultrasonic irradiation unit to excitation point on the eyeball surface. Distance, Liw: Propagation path length of interference noise of excitation ultrasonic waves, Ldr: Distance between the surface wave detection point on the eyeball surface and the receiving ultrasonic sensor for surface wave detection A non-contact method for measuring physical properties of the eyeball,
an excitation step of exciting at least one or more excitation points on the eyeball using the irradiation wave in order to generate a surface wave on the eyeball surface of the eye to be examined;
a detection step of detecting the surface waves generated in the excitation step at at least one or more detection points on the eyeball different from the excitation point;
a surface wave processing step of analyzing the surface waves detected in the detection step;
an eyeball physical property calculation step of calculating the physical properties of the eyeball based on the analysis results in the surface wave processing step,
The irradiation wave emitted in the excitation step is continuous pulsed light from a coherent light or non-coherent light source whose fundamental frequency is 50 KHz or more and 50 MHz or less,
Furthermore, it includes a modulation step of amplitude modulating the pulsed light with a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than its fundamental frequency,
In the excitation step, the continuous pulsed light is amplitude-modulated at a frequency lower than its fundamental frequency in the modulation step, or a burst wave of 10 cycles or more of this amplitude-modulated continuous pulsed light is continuously irradiated. irradiate,
Further, in the excitation step, the pulse time and pulse period of the continuous pulsed light are controlled to match the phase of the continuous photoacoustic waves generated in the tissue by the continuous pulsed light. Method.