Non-contact eyeball physical property measuring device

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

[Technical Field]

[0001] 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 in particular to an eyeball physical property measuring device that can measure the physical properties such as intraocular pressure and material mechanical properties of the eyeball surface tissue. [Background technology]

[0002] A well-known conventional non-contact tonometer for measuring intraocular pressure is one that blows air onto the eyeball to deform the cornea without contact, plots the air puff pressure, and calculates the correlation between the air puff pressure at the point where the cornea becomes flat and a comparative measurement value measured using a contact applanation tonometer, which is used for standard intraocular pressure measurement, to obtain an intraocular pressure value.

[0003] For example, when measuring the mechanical properties and intraocular pressure of the cornea of a test eye, an air puff is used to press the cornea inward, causing it to deform, resulting in a temporary flattened shape, and this flattened point is detected and called the first applanation point. After the cornea further concaves and reaches its maximum deformation, it passes through the flat surface again in the process of returning to its original shape, and this point is called the second applanation point.

[0004] Patent Document 1 proposes a method of measuring intraocular pressure that reduces the effect of corneal rigidity on the measurement value by plotting the air ejection pressure over time during this corneal shape change process, measuring the air ejection pressure at the applanation point, and determining the intraocular pressure from the air ejection pressure at the first and second applanation points.

[0005] Furthermore, Patent Document 2 proposes a system for measuring intraocular pressure and analyzing the mechanical material properties of the cornea, which reduces the effect of corneal rigidity on the measurement value by capturing the corneal flattening process as a corneal tomogram using illumination with a Scheimpflug array and an imaging camera, and measuring the corneal applanation radius and free vibration.

[0006] Additionally, several non-contact ultrasonic (acoustic radiation pressure) tonometers have been proposed, which measure intraocular pressure by irradiating the cornea with ultrasound and causing the cornea to deform or vibrate due to the acoustic pressure. For example, Patent Document 3 proposes a system that measures intraocular pressure by deforming the cornea with acoustic radiation pressure generated by ultrasound irradiation and detecting the amount of deformation. Patent Document 4 proposes a system that measures intraocular pressure by irradiating the eyeball with powerful ultrasound from a parametric speaker, causing the eyeball to vibrate, and modulating the frequency of the irradiated ultrasound to detect the eyeball's natural vibrations. Patent Document 5 proposes a system that detects reflected waves from the surface of the eyeball of ultrasound irradiated to the eyeball, and determines intraocular pressure based on the phase shift of the reflected waves relative to the irradiated waves. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent Publication No. 7,909,765 [Patent Document 2] Patent No. 5314090 [Patent Document 3] Japanese Patent Application Publication No. 2020-5679 [Patent Document 4] Patent No. 6289040 [Patent Document 5] Patent No. 5505684 [Patent Document 6] Japanese Patent Application Publication No. 61-8592 [Patent Document 7] Japanese Patent Application Publication No. 3-60629 [Patent Document 8] Special Publication No. 8-507463 [Patent Document 9] Japanese Patent Application Laid-Open No. 2000-60801 [Patent Document 10] Special Publication No. 6-59272 [Patent Document 11] Japanese Patent Application Laid-Open No. 2011-50445 [Patent Document 12] Japanese Patent Application Laid-Open No. 2012-5835 [Non-patent literature]

[0008] [Non-Patent Document 1] Direct Experimental Observation of the Crossover from Capillary to Elastic Surface Wave on Soft Gels, October 1998 Physical Review Letters, Volume81 Number15, Francisco Monroy and Dominique Langevin [Non-patent document 2] Surface-wave modes on soft gels, The Journal of the Acoustical Society of America, December 1998, Y.Onodera and PK Choi [Non-patent document 3] Investigating soft materials with surface waves, Journal of the Acoustical Society of Japan, Vol. 56, No. 6 (2000), pp. 445-450, Choi Bok-gon [Non-patent document 4] Optical coherence elastography assessment of corneal viscoelasticity with a modified Rayleigh-Lamb wave model, Journal of the Mechanical Behavior of Biomedical Materials, 66(2017)87-94, Zhaolong Han et al. Summary of the Invention [Problem to be solved by the invention]

[0009] However, in systems that use an air puff to deform the cornea for measurement, such as those described in Patent Documents 1 and 2, the noise and air produced when the air puff is emitted inevitably cause discomfort to the subject. Also, the air puff can scatter particles such as tears on the ocular surface, which can become a source of infection for those around them.

[0010] Furthermore, in the case of the ultrasonic excitation method described above, since deformation and vibration of the cornea are detected, a large ultrasonic output is required to excite eyeball vibration. Therefore, in the example of Patent Document 3, a powerful Langevin-type transducer is used as the ultrasonic oscillator for excitation to increase the sound pressure of the ultrasound. Patent Document 4 requires a parametric speaker using an array of a large number of ultrasonic transducers to obtain powerful ultrasonic power, while Patent Document 5 requires efficient irradiation of ultrasound using an acoustic lens. To obtain powerful ultrasonic power, the ultrasonic oscillator for excitation becomes large, requiring a relatively large installation space in front of and near the subject's eye. Therefore, in all of the examples of Patent Documents 3, 4, and 5, there are many constraints on the realization of the device, such as the need for a mechanism for detecting alignment with the subject's eye during measurement and a camera for capturing eyeball images.

[0011] Furthermore, in these ultrasonic vibration-type non-contact tonometers, the focal position of the irradiation of the vibrating ultrasonic waves onto the eyeball and the detection position of the eyeball vibration or corneal deformation amount are approximately the same on the eyeball. This is because they all measure the magnitude of displacement or amplitude caused by deformation or vibration of the eyeball, or the amount of displacement in phase of the reflected wave of the vibrating ultrasonic waves caused by eyeball vibration, and therefore detection sensitivity is maximized and detection accuracy is optimized when the irradiation position of the vibrating ultrasonic waves and the detection position of the vibration or displacement are the same.

[0012] Therefore, in order to approximately align the focal position of the excitation ultrasound irradiation with the detection position of the detection device, it is desirable to arrange the irradiation axis of the excitation ultrasound and the detection axis of the detection so that they are coaxial. Alternatively, if they cannot be coaxial, the excitation ultrasound will be incident obliquely on the surface of the eyeball, which will reduce excitation efficiency. Therefore, it is necessary to compensate for the decrease in measurement sensitivity by increasing the output of the excitation ultrasound.

[0013] Furthermore, since the focal position of the ultrasonic irradiation and the detection position are approximately the same, misalignment of the device with respect to the eye to be examined or misalignment of the eye to be examined leads to a mismatch between the ultrasonic vibration irradiation position and the detection position, which tends to cause variations in the measurement values. If the ultrasonic vibration 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 further the detection signal also decreases and becomes unstable, which causes variations in the measurement values, making it impossible to obtain highly reliable measurement values.

[0014] Furthermore, in Patent Documents 3 and 4, intraocular pressure is detected from the magnitude of displacement and the magnitude of the amplitude of the resonance point, so if the vibration and displacement detection device is not aligned in an appropriate position, the detection sensitivity will decrease and a stable detection signal will not be obtained, making it impossible to obtain accurate amplitude or displacement. This can be a fatal factor when measuring amplitude or displacement, reducing the reliability of the measurement results.

[0015] The present invention has been made in view of the above-mentioned problems, and aims to provide a non-contact ocular physical property measuring device that can minimize interference with a detection sensor of excitation ultrasonic waves when measuring intraocular pressure and the material mechanical properties of ocular surface tissue (such as Young's modulus, shear modulus, and viscosity of ocular tissue) using surface waves generated at a predetermined position on the surface of the ocular ball in a non-contact manner, rather than being based on vibration or displacement of the eyeball or cornea itself or phase changes due to vibration as in conventional devices. Another aim is to provide a home monitoring system for ocular physical properties that allows patients with glaucoma or other conditions to monitor intraocular pressure values and other measurements made by the intraocular pressure physical property measuring device while at home, without imposing a significant burden on the patient or the like. [Means for solving the problem]

[0016] In order to achieve the above object, the present invention provides a non-contact eyeball physical property measuring device, comprising: excitation means for exciting at least one or more excitation points on the eyeball using an irradiation wave to generate a surface wave on the surface of the eyeball, which is the eye to be examined; detection means for detecting the surface wave 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 wave detected by the detection 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, wherein the irradiation wave emitted by the excitation means is a continuous wave of airborne ultrasonic waves having a fundamental frequency of 20 KHz or more and 200 KHz or less, or a burst wave of 10 or more waves of this airborne ultrasonic waves, and satisfies the following [Equation 1]: [Number 1] Tex+Liw / Va ≦ Lex / Va+Ds / Cs+Ldr / Va where Cs is the phase velocity or group velocity of the surface wave, Va is the sound speed of the airborne ultrasound, Tex is the irradiation time of the burst wave for exciting the surface wave, Lex is the distance from the excitation ultrasound irradiation unit (excitation means) to the excitation point on the surface of the eyeball, Liw is the propagation path length of the interference noise of the excitation ultrasound, and Ldr is the distance between the detection point of the surface wave on the surface of the eyeball and the receiving ultrasound sensor for detecting the surface wave (detection means).

[0017] In order to achieve the above object, the present invention provides a non-contact eyeball physical property measuring device, comprising: excitation means for exciting at least one or more excitation points on the eyeball using an irradiation wave in order to generate a surface wave on the surface of the eyeball, which is the eye to be examined; detection means for detecting the surface wave 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 wave detected by the detection 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, wherein the irradiation wave emitted by the excitation means is a coherent light or is continuous pulsed light emitted from a light source of incoherent light, and further comprises a modulation means for amplitude-modulating the pulsed light at a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than the fundamental frequency of the pulsed light, and the excitation means continuously irradiates amplitude-modulated continuous pulsed light obtained by amplitude-modulating the continuous pulsed light at a frequency lower than the fundamental frequency by the modulation means, or irradiates burst waves of this amplitude-modulated continuous pulsed light with 10 or more periods, and the excitation means controls 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.

[0018] In this eyeball physical property measuring device, it is preferable that the pulse time of the continuous pulsed light irradiated from the excitation means is set within a range of 10 nsec to 1000 nsec, and the pulse period of the continuous pulsed light satisfies the frequency range of 0.5 MHz to 50 MHz of the photoacoustic wave and is the same period as the frequency or an integer fraction thereof.

[0019] It is preferable that this eyeball physical property measuring device further comprises a communication means for transmitting the eyeball physical properties obtained by the eyeball physical property calculation means to an external device via a wide area network.

[0020] In order to achieve the above object, the present invention provides a home monitoring system for eyeball physical properties using a non-contact type eyeball physical property measuring device installed in a patient's home, the non-contact type eyeball physical property measuring device including: excitation means for exciting at least one or more excitation points on the eyeball using an irradiation wave in order to generate a surface wave on the surface of the eyeball, which is the eye to be examined; detection means for detecting the surface wave generated by the excitation means at at least one or more detection points on the eyeball different from the excitation points; surface wave processing means for analyzing the surface wave detected by the detection means; eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis result of the surface wave processing means; and eyeball physical property calculation means for calculating the physical properties of the eyeball obtained by the eyeball physical property calculation means. and a communication means for transmitting the physical properties of the patient's eye to an external device via a wide area network, wherein the irradiation wave emitted by the excitation means is a continuous wave of airborne ultrasonic waves having a fundamental frequency of 20 KHz or more and 200 KHz or less, or a burst wave of 10 or more waves of the airborne ultrasonic waves, and the external device is characterized by comprising: a transceiver unit for receiving data regarding the patient's eyeball physical properties calculated by the eyeball physical properties calculation means; an eyeball physical properties analysis unit for analyzing the progression of the patient's symptoms based on the data regarding the eyeball physical properties; an eyeball physical properties data storage unit for accumulating the data regarding the eyeball physical properties; and a patient information storage unit for storing the analysis results of the eyeball physical properties analysis unit and information related to the patient.

[0021] In order to achieve the above object, the present invention provides a home monitoring system for eyeball physical properties using a non-contact type eyeball physical property measuring device installed in a patient's home, the non-contact type eyeball physical property measuring device comprising: excitation means for exciting at least one or more excitation points on the eyeball using an irradiation wave in order to generate a surface wave on the surface of the eyeball which is the eye to be examined; detection means for detecting the surface wave 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 wave detected by the detection means; eyeball physical property calculation means for calculating the physical properties of the eyeball based on the analysis result of the surface wave processing means; and 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, wherein the irradiation wave emitted by the excitation means is a coherent wave having a fundamental frequency of 50 KHz or more and 50 MHz or less. the external device is characterized in that the external device is continuous pulsed light emitted from a light source of coherent light or incoherent light, and further comprises a modulation means for amplitude-modulating the pulsed light at a modulation frequency of 200 Hz or more and 100 KHz or less which is lower than the fundamental frequency of the pulsed light, the excitation means continuously irradiates amplitude-modulated continuous pulsed light obtained by amplitude-modulating the continuous pulsed light at a frequency lower than the fundamental frequency by the modulation means, or irradiates burst waves of this amplitude-modulated continuous pulsed light with 10 or more periods, and the external device is characterized in that it comprises: a transceiver unit that receives data on the patient's ocular properties calculated by the ocular property calculation means; an ocular property analysis unit that analyzes the progression of the patient's symptoms based on the data on the ocular properties; an ocular property data storage unit that accumulates the data on the ocular properties; and a patient information storage unit that stores the analysis results of the ocular property analysis unit and information related to the patient.

[0022] In order to achieve the above object, the present invention provides a non-contact eyeball physical property measurement method, which includes an excitation step of exciting at least one or more excitation points on the eyeball using an irradiation wave to generate a surface wave on the surface of the eyeball, which is the eye to be examined; a detection step of detecting the surface wave 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 wave detected in the detection step; and an eyeball physical property calculation step of calculating the physical properties of the eyeball based on the analysis result in the surface wave processing step, wherein the irradiation wave emitted in the excitation step is a continuous wave of airborne ultrasonic waves having a fundamental frequency of 20 KHz or more and 200 KHz or less, or a burst wave of 10 or more waves of this airborne ultrasonic waves, and satisfies the following [Equation 1]: [Number 1] Tex+Liw / Va ≦ Lex / Va+Ds / Cs+Ldr / Va where Cs is the phase velocity or group velocity of the surface wave, Va is the sound speed of the airborne ultrasound, Tex is the irradiation time of the burst wave for exciting the surface wave, Lex is the distance from the excitation ultrasound irradiation unit to the excitation point on the eyeball surface, Liw is the propagation path length of the interference noise of the excitation ultrasound, and Ldr is the distance between the detection point of the surface wave on the eyeball surface and the receiving ultrasound sensor for detecting the surface wave.

[0023] In order to achieve the above object, the present invention provides a non-contact eyeball physical property measuring method, which includes an excitation step of exciting at least one or more excitation points on the eyeball using an irradiation wave in order to generate a surface wave on the surface of the eyeball, which is the eye to be examined; a detection step of detecting the surface wave 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 wave detected in the detection step; and an eyeball physical property calculation step of calculating the physical properties of the eyeball based on the analysis result in the surface wave processing step, wherein the irradiation wave generated in the excitation step is a coherent wave having a fundamental frequency of 50 KHz or more and 50 MHz or less. The excitation step is characterized in that the continuous pulsed light is continuous pulsed light emitted from a light source of coherent light or non-coherent light, and further includes a modulation step of amplitude-modulating the pulsed light at a modulation frequency of 200 Hz or more and 100 KHz or less, which is lower than the fundamental frequency of the pulsed light, and in the excitation step, the continuous pulsed light is amplitude-modulated at a frequency lower than the fundamental frequency by the modulation step, and the amplitude-modulated continuous pulsed light is continuously irradiated, or a burst wave of this amplitude-modulated continuous pulsed light having 10 or more periods is irradiated, and 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 wave generated in the tissue by the continuous pulsed light. [Effects of the Invention]

[0024] The non-contact ocular physical property measuring device according to the present invention comprises an ultrasound irradiation unit that excites at least one excitation point on the eyeball using an irradiation wave to generate a surface wave on the surface of the eyeball (the subject's eye); a receiving sensor that detects the surface waves generated by the ultrasound 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 an ocular physical property calculation unit that calculates the physical properties of the eyeball based on the analysis results of the surface wave processing unit. The irradiation wave emitted by the ultrasound irradiation unit is a continuous airborne ultrasound wave with a fundamental frequency of 20 kHz or more and 200 kHz or less, or a burst wave of 10 or more waves of this airborne ultrasound, and satisfies a predetermined formula. With this configuration, the present invention can minimize interference of the excitation ultrasound with the detection sensor when generating and detecting surface waves using ultrasound. Furthermore, the device according to the present invention can be lightweight and compact, allowing patients to perform measurements at remote clinics or at home. Even when the patient and the medical institution are far apart, data can be easily exchanged via an internet connection, making it highly effective in telemedicine and home medical diagnosis. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a diagram showing the basic configuration of an excitation unit and a detection unit for a surface wave applied to a cornea of a subject eye, which is provided in an eyeball physical property measuring device according to the present embodiment. FIG. [Figure 2] FIG. 2 is a functional block diagram of the eyeball physical property measuring device. [Figure 3] 10 is a diagram showing an example of a waveform obtained by amplitude-modulating an ultrasonic wave for exciting a surface wave using a modulation unit provided in the eyeball physical property measuring device. FIG. [Figure 4] This is a diagram explaining the generation of low-frequency sound pressure using a parametric speaker system, using multiple ultrasonic transducers for exciting surface waves in the eyeball physical property measuring device. [Figure 5] 10 is an explanatory diagram of a case where a surface wave is generated on the surface of the subject's eye by the photoacoustic effect of pulsed light in an excitation unit provided in the same eyeball physical property measuring device. FIG. [Figure 6]10A and 10B are diagrams showing an example of a generation pattern of modulated pulsed light for generating a surface wave by pulsed light using the modulation section of the same. [Figure 7] 10 is a diagram showing an example of a case where an external modulation method of laser pulse light is used in the modulation section of the same. FIG. [Figure 8] 10 is a diagram showing an example of a case where a direct modulation method of a laser diode is used in the modulation section of the same. FIG. [Figure 9] 10 is a diagram showing an example of surface wave detection by an ultrasonic reflection method in a detection unit provided in the eyeball physical property measuring device. FIG. [Figure 10] 10A and 10B are diagrams showing an example of surface wave detection by optical triangulation in the detection unit of the same. [Figure 11] 10A and 10B are diagrams showing an example of surface wave detection by a confocal method using optical coaxial light beams of multiple wavelengths in the detection unit of the same embodiment. [Figure 12] 10 is a diagram showing an example of surface wave detection by phase detection of an optical heterodyne Fourier domain interferometer in the detection unit of the embodiment. FIG. [Figure 13] 10A and 10B are diagrams showing an example of surface wave detection by optical heterodyne laser Doppler measurement in the detection unit of the same. [Figure 14] 3A and 3B are diagrams showing an example of the sound field and directivity of excitation ultrasonic waves generated in the excitation unit. [Figure 15] 10 is a diagram showing an example of the path and positional relationship of interference noise that is given to a detection receiving sensor of the exciting ultrasonic wave in the surface wave exciting ultrasonic unit and surface wave detection sensor unit provided in the eyeball physical property measuring device. FIG. [Figure 16] FIG. 10 is a diagram showing an example of how a surface wave having a frequency lower than the frequency of a photoacoustic wave generated by intensity-modulating continuous pulsed light is excited on the surface of the eyeball in the excitation pulsed light provided in the eyeball physical property measuring device. [Figure 17] 10 is a diagram showing an example of the relationship between the pulse time of pulsed light in an excitation pulse light source provided in the eyeball physical property measuring device and the wavelength of the generated photoacoustic wave. FIG. [Figure 18]10 is a diagram showing an example of the relationship between the pulse time of pulsed light in an excitation pulse light source provided in the eyeball physical property measuring device and the wavelength of the generated photoacoustic wave. FIG. [Figure 19] FIG. 10 is a diagram showing an example of irradiation in which the pulse period of continuous pulsed light in the excitation pulse light source provided in the eyeball physical property measuring device is adjusted to the frequency of the photoacoustic wave that generates the light. [Figure 20] 10 is a diagram showing an example of maximizing the amplitude of a surface wave by controlling the pulse time and pulse period of a light pulse from a pulsed light source provided in the eyeball physical property measuring device. FIG. [Figure 21] FIG. 10 is a diagram showing a home monitoring system for eyeball physical properties in which the above-mentioned eyeball physical property measuring device is connected to the Internet, measurement data is accumulated, and the accumulated data is analyzed to provide information for a doctor's diagnosis. [Figure 22] FIG. 2 is a diagram showing an example of functional blocks of each processing unit of the home monitoring system for eyeball physical properties. DETAILED DESCRIPTION OF THE INVENTION

[0026] (Embodiment) Here, the embodiments of the present invention will be described in the following order. (1) Basic configuration of the measurement method (2) Surface waves generated on the surface of the eye (3) Configuration of excitation means for generating surface waves (4) Configuration of the detecting means for detecting surface waves (5) Configuration of excitation and detection means for minimizing interference of excitation ultrasonic waves with the detection sensor when generating and detecting surface waves using ultrasonic waves. (6) Configuration of excitation means for efficiently generating surface waves using optical energy (7) Means for outputting and analyzing measured intraocular pressure values and the material mechanical properties of ocular tissues (home monitoring system for ocular physical properties)

[0027] (1) Basic configuration of the measurement method In the present invention, the intraocular pressure of the subject's eye and the material properties of the subject's eye tissue are determined by determining the phase velocity of the ocular surface wave of the subject's eye, and therefore when there is only one excitation point and one detection point, the propagation of the surface wave cannot be measured unless the detection point is measured at a position different from the excitation point. However, this does not apply when there are multiple excitation points or detection points.

[0028] 1 shows the simplest configuration of a non-contact eyeball physical property measuring device according to this embodiment, with one excitation point 104 and one detection point 105, and the excitation unit 102 and detection unit 103 are arranged so that an excitation irradiation axis 107 and a detection axis 108 are approximately coaxial with the normals to the excitation point 104 and the detection point 105, respectively, with respect to the eyeball surface 101. The intersection of the extensions of the excitation irradiation axis 107 and the detection axis 108 approximately coincides with the center of corneal curvature. Ultrasound or pulsed light (it is preferable to use continuous pulsed light from a coherent or non-coherent light source) irradiated onto the eyeball surface by the excitation unit 102 arranged in this manner excites a surface wave 106 having an amplitude perpendicular to the eyeball surface. The surface wave 106 propagates across the surface of the eye, like the fine waves that appear on the surface of water when a stone is thrown into the water, with the excitation point as the center and the frequency and phase velocity determined by the excitation means. Therefore, the frequency and phase velocity of the surface wave can be determined by detecting the wave at a predetermined position.

[0029] Here, we will explain about surface waves. Waves that propagate through 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 and guided waves are collectively referred to as surface waves, as they are waves that appear on the surface of the tissue.

[0030] Body waves include longitudinal elastic waves and shear elastic waves, and are used in imaging diagnostic devices that use ultrasound as longitudinal elastic waves in biological tissue, and in ultrasound elastography to diagnose tissue stiffness by measuring shear elastic waves.

[0031] There are three types of surface waves: Rayleigh waves, which are surface acoustic waves that are affected by the restoring force of shear elasticity; capillary waves, which are caused by the restoring force of surface tension; and leaky capillary waves, which propagate due to the combined action of shear elasticity and surface tension. These surface waves have been used in measurements such as measuring the hardness of gel-like materials.

[0032] Furthermore, Lamb waves are known as waves that propagate through plate-like media. Unlike Rayleigh waves, which propagate through semi-infinite media, Lamb waves propagate through plate-like media so as to satisfy boundary conditions where the outsides of both boundary surfaces of the plate are mechanically free, like air or a vacuum.

[0033] However, ocular tissues such as the cornea, conjunctiva, and sclera have a layered structure. For example, the cornea has a thin layer structure with its outer surface in contact with air and its inner boundary surface in contact with aqueous humor. The boundary conditions at each boundary surface are different, and it is necessary to consider the case where one of the boundaries is in contact with a liquid material. In such cases, the Rayleigh-Lamb model is known as a guided wave model that takes into account the boundary conditions with the other material in contact at the boundary.

[0034] From Rayleigh waves and Rayleigh-Lamb waves, the shear modulus G and viscosity η of the medium can be calculated from their phase velocity Cr and density ρ. From capillary waves, the surface tension γ of the medium can be calculated from their phase velocity Cc, density ρ, and angular frequency ω. Furthermore, from leaky capillary waves, the surface tension γ can be calculated from their phase velocity Cl, shear modulus G, density ρ, and angular frequency ω.

[0035] As described above, by measuring the phase velocity of the Rayleigh-Lamb waves on the tissue surface, it is possible to determine the shear modulus G and the viscosity η, and by measuring the phase velocity of the capillary wave or leaky capillary wave, it is possible to determine the surface tension γ, and then, using Laplace's law, it is possible to determine the internal pressure, or in the case of the eyeball, the intraocular pressure, from the surface radius of curvature and surface tension.

[0036] The surface waves propagating on the surface of the eye are not vibrations of the eyeball or cornea itself, but waves that propagate only in the vicinity of the surface of the tissue, and the power required to generate these surface waves is smaller than the power required to vibrate the cornea or eyeball itself. Furthermore, because what is detected is the propagation velocity, phase, or frequency spectrum of the surface wave, there is little effect from changes in the amplitude of the surface wave, making stable measurements possible despite various external clinical influences.

[0037] Next, the functional configuration of a non-contact eyeball physical property measuring device 1 according to this 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 excites the eyeball surface to generate surface waves, and a detection unit 202 detects the surface waves. The excitation unit 201 is driven by a drive circuit 203, which is controlled by a transmission control unit 210 of a control unit 211. The excitation unit 201 includes a modulation unit 201a for amplitude-modulating ultrasound or pulsed light at a modulation frequency lower than the oscillation frequency of the ultrasound or pulsed light. The detection unit 202 integrates a detection transmitter and receiver. The transmitter, driven by a detection transmitter circuit 204, transmits a detection transmission signal to the eye surface, and the receiver receives the signal reflected back from the eye surface and sends the detection signal to a detection receiver circuit 205. In the detection receiver 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. The surface wave processing unit 208 in the control unit 211 processes the received waves, identifies the surface wave components 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.

[0038] The excitation unit 201 for exciting surface waves can be either an ultrasound excitation method or a pulsed light excitation method. In the ultrasound excitation method, the sound pressure of ultrasound irradiated at a predetermined position on the ocular surface vibrates the ocular surface, generating surface waves. In the optical energy method, a short pulsed light is irradiated onto the ocular surface, and the tissue at the focal position of the irradiated pulsed light absorbs the light energy, causing a temperature rise and instantaneous thermal expansion, generating ultrasound within the tissue. The generated ultrasound propagates to the tissue surface, exciting surface waves.

[0039] As described below, methods for detecting surface waves include ultrasonic reflection detection, optical triangulation microdisplacement detection, multi-wavelength coaxial confocal detection, and optical heterodyne detection. Ultrasonic reflection detection uses ultrasound with a frequency several times higher than the frequency of the generated surface wave to transmit and receive ultrasound waves to a detection point, and the returned reflected waves are demodulated and detected to detect surface waves on the ocular surface. Optical triangulation irradiates a light beam onto the detection point, and the light reflected from the detection point is detected using multiple light-receiving elements or one- or two-dimensional image sensors. Surface waves are detected from changes in the output of the light-receiving elements or changes in the bright spot position of the image sensor, which occur due to periodic changes in the reflection angle caused by surface vibration. Multi-wavelength light beam differential detection irradiates the ocular surface with multiple light beams of different wavelengths on a coaxial axis. The optical design ensures that the focal positions of each light beam are slightly shifted. When aligned so that the corneal surface is within the focal position, the reflected light intensity of each wavelength fluctuates due to vibration of the ocular surface. This differential amplification of the reflected light intensity of each wavelength is used to detect surface waves. Optical heterodyne methods include measuring phase changes caused by minute fluctuations on the ocular surface detected by a Fourier domain optical interferometer, and detecting surface waves by detecting minute vibrations on the ocular surface using a laser Doppler vibrometer.

[0040] To detect the phase velocity of the surface wave, the phase difference between the detected surface wave signal and the drive signal of the excitation unit drive circuit 203 is measured, and the phase velocity can be calculated from this phase difference and the distance from the excitation point to the detection point. If there are multiple detection points, the phase of the surface wave at each detection point is detected, and the phase velocity can be calculated from the phase difference and the distance between the detection points.

[0041] If the phase velocity of the Rayleigh wave or Rayleigh-Lamb wave can be determined, the shear modulus, Young's modulus, and viscosity of the tissue can be calculated using the equations described below.

[0042] If the phase velocity of the capillary wave or leaky capillary wave on the corneal surface can be determined, the tension on the corneal surface can be determined using the formula described below, and the internal pressure, or intraocular pressure, can be calculated from the mean curvature and surface tension of the ocular surface using Laplace's law.

[0043] (2) Surface waves generated on the surface of the eye Surface waves generated on the surface of biological tissues are classified as elastic waves. These include Rayleigh and Rayleigh-Lamb waves, in which shear elasticity and viscosity act as restoring forces during propagation; capillary waves, in which surface tension acts as a restoring force; and leaky capillary waves, in which shear elasticity, viscosity, and surface tension act as a combined restoring force. For example, in the case of Rayleigh-Lamb waves generated on the surface of the cornea, the asymmetric zeroth-order mode can be observed. The zeroth-order phase velocity is relatively slow, approximately 1–5 m / sec, and exhibits frequency dispersion, resulting in different phase velocities depending on frequency. Frequencies from 200 Hz to 5 kHz can be detected; frequencies outside this range exhibit significant attenuation, making detection difficult. Because the measurable frequency varies depending on the Young's modulus of the ocular tissue and the thickness of the tissue layer, measurements at multiple frequencies are required.

[0044] In the case of capillary waves and leaky capillary waves, the wavelength is short and the frequency is relatively high, confining the wave to the surface of the living body, because surface tension is the dominant restoring force, and they can be detected at higher frequencies than Rayleigh waves and Rayleigh-Lamb waves. In the case of the cornea, the wavelength of capillary waves is short compared to the thickness of the cornea, and they can be detected at frequencies above 20 kHz (for example, 20 to 50 kHz), where the influence of Rayleigh-Lamb waves is small.

[0045] (3) Configuration of excitation means for generating surface waves Possible means for exciting the surface waves include an excitation means using ultrasonic waves and an excitation means using optical energy. In the case of airborne ultrasonic waves, frequencies from 20KHz to 1MHz are possible, but in order to obtain effective power for excitation, frequencies from 20KHz to 100KHz are appropriate. Airborne ultrasonic transducers above 100KHz not only have low radiated sound pressure, but also suffer from significant attenuation due to propagation through the air. The attenuation coefficient when ultrasonic waves propagate through the air is 1 x 10, where f is the frequency of the ultrasonic waves. ー11 ×f 2 (m ー1 ) and is proportional to the square of the frequency, and at 100 kHz the damping coefficient is 0.1 (m ー1 ) and the decay increases exponentially.

[0046] Airborne ultrasonic transducers, which are generally used as ultrasonic sensors, may not produce sufficient sound pressure with a single transducer. In such cases, sufficient ultrasonic output can be obtained by driving multiple ultrasonic transducers. Furthermore, by controlling the phase of the drive signal for each of the multiple ultrasonic transducers, the phase of the ultrasound can be controlled, and a phased array transducer can be constructed to control the focal position on the surface of the eye to any position. Even when multiple ultrasonic transducers are used, the sound pressure of the ultrasound is not as high as that of vibration detection using corneal vibration, so the number of transducers required to construct an ultrasonic transducer array is limited.

[0047] To excite Rayleigh or Rayleigh-Lamb waves on the ocular surface, localized excitation of the ocular surface is required at frequencies in the audible range lower than those of ultrasound. Therefore, amplitude-modulating high-frequency ultrasound at a low frequency can generate sound pressure waves at the same low frequency as the amplitude-modulation frequency near the focal point. Figure 3 shows how amplitude-modulated ultrasound is generated by superimposing a low-frequency modulation signal on the oscillation frequency of the ultrasound transducer using the modulation unit 201a. Furthermore, by using multiple ultrasound transducers for phased array control and frequency amplitude modulation, low-frequency sound waves can be generated only near the focal point while maintaining sharp directionality, allowing for selective excitation of specific locations on the ocular surface at the amplitude-modulated frequency. This principle is well known as a parametric speaker. Figure 4 illustrates the generation of low-frequency sound pressure near the focal point of an ultrasound beam using a parametric speaker configuration. For example, it shows that modulated ultrasonic waves Mw are transmitted from a transducer array 401 consisting of multiple ultrasonic transducers in the excitation unit 201, and the ultrasonic waves are focused at a focal position F to locally generate sound waves Mc of a modulated frequency component, which is a low frequency. It is also possible to control the focal position back and forth by changing the phase of the drive signal for each individual transducer in the transducer array 401.

[0048] When the excitation means is optical energy, excitation using short pulsed light is possible. Figure 5 shows the excitation of surface waves using pulsed light. Pulsed light is irradiated onto the surface of the eye as a continuous pulse from a light source 501. 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 instantaneously, generating ultrasound waves in the intraocular tissue just below the surface of the eye. These ultrasound waves reach the surface and excite surface waves. The method of generating ultrasound waves inside a living body using light is known as the photoacoustic effect, and diagnostic imaging devices using photoacoustic imaging based on this principle are known.

[0049] The pulsed light used in the photoacoustic effect is extremely short, on the order of nanoseconds. The frequency of ultrasound generated in living tissue by the photoacoustic effect of pulsed light is approximately 1 MHz to 10 MHz. Therefore, ultrasound generated by a simple continuous pulse cannot excite surface waves with low frequencies on the order of kHz. To solve this problem, continuous pulses of 100 kHz or higher are used, and the intensity is modulated at a low frequency equal to the frequency of the surface waves generating the continuous pulsed light, thereby superimposing low-frequency sound pressure changes and exciting surface waves. Figure 6 shows how continuous pulsed light at a basic pulse frequency is modulated with a modulation frequency signal to produce modulated pulsed light. In other words, it is necessary to continuously irradiate amplitude-modulated continuous pulsed light, in which the power intensity of the light pulses is amplitude-modulated by a modulation means, or to irradiate burst waves of this amplitude-modulated continuous pulsed light with 10 or more cycles.

[0050] As a light intensity modulation method, Fig. 7 shows an external direct modulation method in which a modulator 201a that receives an electrical adjustment signal from a controller 201c directly turns on / off a CW laser 201b provided in an excitation unit 201. Fig. 8 shows a direct modulation method in which a drive current of a semiconductor light source LD (semiconductor laser, SLD, light emitting diode, etc.) 201d in the excitation unit 201 is modulated by a current control unit 201e.

[0051] Pulsed light sources include light-emitting diodes, semiconductor lasers, fiber lasers, and superluminescent diodes. The wavelength of the light source is preferably one with high optical absorption by ocular surface tissue. However, the cornea is a transparent tissue with low optical absorption in the 380 to 1400 nm range and high absorption at other wavelengths. Therefore, ultraviolet and near-infrared light are candidates. However, considering biosafety, the ultraviolet range is too invasive to the body and does not allow for high light power. Therefore, wavelengths ranging from the near-infrared range around 1400 nm to the infrared range around 3000 nm are desirable. Opaque tissues other than the cornea have high optical absorption from the visible light range to the near-infrared range above 400 nm. In particular, hemoglobin in blood rapidly absorbs light at wavelengths below 600 nm. Therefore, pulsed light from 400 to 600 nm can be used to efficiently excite the capillaries on the ocular surface as a heat point. When using surface tissue other than the cornea, such as the conjunctiva, as the excitation point, pulsed light is irradiated onto the capillaries of the conjunctiva as the heat point Hp, exciting a surface wave on the conjunctival surface, and the surface wave that propagates to the cornea is detected on the cornea, enabling efficient measurement.

[0052] While excitation using continuous waves has been mainly discussed as a method for generating surface waves, excitation using burst waves is also possible. However, in the case of burst waves, in order for the output of the excitation means to stabilize and for the amplitude of the surface waves to stabilize, it is necessary to output a continuous wave of a certain wave number. For example, in the case of excitation using ultrasound, it takes a certain amount of time for the sound pressure of the ultrasonic transducer to reach a peak, and in the case of excitation using pulsed light, it also takes time for the surface waves to rise. For this reason, when exciting surface waves using burst waves or burst pulses, ultrasound, modulated ultrasound, or modulated pulsed light is transmitted with a transmission time that will result in at least 10 detectable surface waves (10 cycles or more). The transmission time of the burst wave depends on the characteristics of the ultrasonic transducer and pulsed light source, and is therefore determined based on those characteristics.

[0053] (4) Configuration of the detecting means for detecting surface waves The detection means for detecting surface waves include ultrasonic reflection method, optical triangulation method, optical multiple wavelength coaxial confocal method, and optical heterodyne method.

[0054] When the ultrasonic reflection method is used as the detection method, it is detected by continuous ultrasound or a burst ultrasound of 100 waves or more. After the ultrasound transmitted from the transmitting ultrasound transducer reaches the surface of the eye, it is reflected and scattered and returns. When the ultrasound is reflected from the surface of the eye, it is modulated by the surface wave vibration and returns to the receiving ultrasound transducer with the surface wave vibration components superimposed. By demodulating and detecting this reflected wave, it is possible to demodulate the vibration frequency components modulated by the surface wave vibration of the eye surface. By measuring the frequency and phase of this demodulated wave, the phase and frequency of the surface wave can be calculated.

[0055] Figure 9 shows one example of ultrasonic surface wave detection. In this example, a transmitting ultrasonic transducer 901 and a receiving ultrasonic transducer 902 are separately provided. Separate ultrasonic transducers for transmission and reception allow for continuous ultrasonic detection, which has the advantage of enabling constant detection of surface waves. A control CPU 903 outputs a digital value to a D / A converter 904 to control the oscillation frequency of a voltage-variable oscillator 905. A control voltage corresponding to this 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 this voltage. The oscillated signal is amplified by a transmission amplifier 906 and drives the transmitting ultrasonic transducer 901, which transmits ultrasonic waves for detection to the surface of the eye. The ultrasonic waves reflected back from the surface of the eye are modulated at the frequency of the surface waves due to the surface wave vibrations on the surface of the eye. The receiving ultrasonic transducer 902 receives the returned ultrasonic waves, and the received signal, amplified by a reception amplifier 907, is input to a multiplier 908. The transmission signal output from voltage variable oscillator 905 is also used as a reference signal to demodulate the received signal, so a reference signal filtered by reference signal bandpass filter 909, which passes only the transmission frequency band, is generated, and this reference signal is multiplied by the received signal in multiplier 908 to demodulate the received signal, thereby demodulating the surface wave component contained in the received signal. Frequency components other than surface waves are removed by demodulated signal bandpass filter 910, and the digital value is converted by A / D converter 911 and input to control / calculation CPU 903 for calculation processing. In this case, control / calculation CPU 903 is located in control unit 211 shown in Fig. 2, where physical properties of surface waves such as surface tension and intraocular pressure of the eyeball are calculated based on these physical properties.

[0056] If the ultrasonic wave transmission for detection is a burst wave, the ultrasonic transducer can be used for both transmission and reception, and surface wave vibrations can be detected with a single transducer.In addition, the returned received signal can be directly converted to digital form by an A / D converter without demodulation or detection, and input to a calculation CPU, where the frequency spectrum and phase change of the surface wave component can be calculated by Fourier transform.

[0057] Here, it is desirable that the frequency of the ultrasonic waves used for detection be at least 10 times the frequency of the surface waves excited by the excitation means. This is necessary to completely separate the fundamental frequency of the ultrasonic waves from the frequency components of the surface waves and accurately detect the surface waves when performing demodulation, detection, and Fourier transform processing. Therefore, the reason for using 100 or more detection burst waves is that in order to improve the accuracy of surface wave phase detection, at least 10 or more surface wave components must be detected and analyzed, so the ultrasonic waves used for detection are approximately 10 times the surface wave frequency, or 100 waves.

[0058] Next, a detection method for detecting surface waves using optical trigonometry will be described with reference to FIG. 10. In this case, a detection light beam is irradiated onto the detection point, and the light reflected and scattered from the detection point is detected using multiple light-receiving elements, optical position sensors, optical line sensors, etc. When the surface at the detection point vibrates due to surface wave vibration, the angle and intensity distribution of the light returning from the detection point change, and the imaging position on the light-receiving side imaging plane also changes. In the case of multiple light-receiving elements, vibration can be detected by differentially amplifying the output changes of each light-receiving element. In the case of optical position sensors or optical line sensors, the change in imaging position itself can be detected, and this position change can be detected as surface wave vibration. FIG. 10 shows an example of a detection method using optical trigonometry. Light emitted from a surface wave detection light source 1001 reaches the surface of the eye via objective lens 1002, and the light reflected at the detection point enters light-receiving element A 1004 and light-receiving element B 1005 via 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, causing a relative change in the amount of light incident on light receiving element A 1004 and light receiving element B 1005. The electrical signals output from light receiving element A 1004 and light receiving element B 1005 are differentially amplified by differential amplifier 1006 to detect the surface wave vibration at the detection point.

[0059] Next, we will explain the case where the detection means uses a confocal system with multiple wavelength coaxial light beams. In this case, the measurement light beam is emitted from a light source of multiple wavelengths or white light, and an optical system with a chromatic aberration focus is used, with the focal position shifting slightly depending on the wavelength. When minute vibrations due to surface waves occur at the detection point on the surface of the eye, the amount of reflected light at each wavelength, which has a slightly different focal position, also changes in accordance with the vibration. The reflected light at wavelengths with close focal positions is strong, while the reflected light at wavelengths with farther focal positions is weak. Furthermore, the confocal optical system produces sharper reflection peaks near the focal positions of each wavelength. When the reflected light is separated into multiple wavelengths and detected by a light-receiving element, the amount of light incident on each wavelength's light-receiving element changes significantly even with minute vibrations. By differentially amplifying the electrical signals from the light-receiving elements for each wavelength, vibrations at the detection point due to surface waves can be detected. Figure 11 shows an example of a multi-wavelength coaxial confocal system. A light beam emitted from light source 1101 passes through fiber collimator 1102, fiber coupler 1103, and fiber collimator 1104 and is then incident on a detection point on the surface of the eye, with the focus of each wavelength being shifted slightly by chromatic aberration focusing lens 1105. In this example, the focus of wavelengths A, B, and C is shifted slightly relative to the detection point, which shifts the detection peak of each wavelength. As the position of the detection point on the surface of the eye shifts, the amount of reflected light of each wavelength changes. The light beam reflected at the detection point passes through chromatic aberration lens 1105, fiber collimator 1104, and fiber collimator 1106 and enters spectroscopic detection unit 1107. The light beam incident on the spectroscopic detection unit is split into wavelengths A, B, and C by hot mirrors 1107a and 1107b, and then enters photodetector 1107c, photodetector 1107d, and photodetector 1107e via imaging lenses A, B, and C, which are confocal, corresponding to the respective wavelengths. The electrical signals output from the respective photodetectors are differentially amplified to detect the vibration of the surface waves.

[0060] Next, a case where the detection means is a Fourier-domain optical interferometer using the optical heterodyne method for phase detection will be described with reference to FIG. 12. In this case, light emitted from a low-coherence light source such as a superluminescence diode or a wavelength-swept laser light source is split into a light beam to be irradiated onto the measurement object and a light beam used as a reference beam within the optical interferometer. The light beam to be irradiated onto the measurement object is irradiated onto the ocular surface by the interferometer, reflected from the ocular surface, and re-enters the optical interferometer. The light beam entering the optical interferometer interferes with the reference beam within the interferometer and is detected as a spectral distribution waveform having an interference spectral distribution or a beat signal having a beat frequency. These spectral distribution waveforms and beat signals are Fourier-transformed to calculate the interference peak and phase of the light beam reflected back from the ocular surface. Minute fluctuations due to the surface wave are detected as a phase change, allowing the surface wave to be detected.

[0061] Figure 12 shows an embodiment of a Fourier domain interferometer using the spectral domain method. The light beam emitted from a superluminescence diode (SLD) light source is low-coherent and has a wide wavelength band. This light beam is incident on a fiber coupler 1202 via an optical fiber and split into two optical paths. One path passes through a fiber collimator 1203 and an achromatic lens 1204, is projected onto a reference mirror 1205, is reflected, and returns to the fiber coupler 1202 via the achromatic lens 1204 and the fiber collimator 1203. The other branched light beam passes through a fiber coupler, passes through a fiber collimator 1206, and passes through an aperture 1207. The beam is deflected or set at a predetermined angle by a galvanometer mirror 1108, which deflects and scans the beam, and is projected onto the surface of the eye via an objective lens 1209. The light reflected from the ocular 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 from the ocular surface are superimposed to form interference light, which is projected onto a CCD 1214 via a fiber connector 1210, a relay lens 1211, a diffraction grating 1212, and an achromatic lens 1213. The CCD 1214 outputs spectral distribution data obtained by dispersion by the diffraction grating 1212. An arithmetic circuit performs a Fourier transform on this spectral data to calculate the interference peak and phase, thereby detecting minute vibrations due to surface waves. Note that, although a spectrum-domain optical interferometer is used as the detection interferometer in this embodiment, a swept-source (light source wavelength swept) type optical interferometer may also be used.

[0062] Next, a case where the detection means is a laser Doppler interferometer using optical heterodyne will be described with reference to Figure 13. In this case, a light beam emitted from a laser light source is split into two, one of which is directed onto the surface of the eye, and the other is modulated by an acousto-optic modulator at a constant carrier frequency fm. The light beam reflected by the surface of the eye is Doppler-shifted to a frequency fd by the surface wave vibrations of the eye, and this beam returns to the interferometer. This beam interferes with the light modulated by the acousto-optic modulator, generating a beat frequency of fm±fd. Of these beat frequencies, fm is a constant frequency, so only the Doppler shift frequency fd changes due to the surface wave vibrations. This frequency change can be detected by FM demodulating the surface wave vibrations.

[0063] Figure 13 shows an embodiment of a laser Doppler interferometer. A beam of light emitted from a laser light source 1301 with an optical frequency fo is split by a polarizing beam splitter 1302 into two beams, one S-polarized and one P-polarized. The S-polarized beam is reflected by the polarizing beam splitter 1302 and enters an acousto-optic modulator (AOM) 1305 via mirror 1304. The frequency of the S-polarized beam is modulated to fo+fm by the acousto-optic modulator, and the beam is reflected by polarizing beam splitters 1303 and 1308 via mirror 1307, then by a quarter-wave plate 1309 and reference mirror 1310 before returning. It passes through the quarter-wave plate 1309 again, becomes P-polarized, and enters the polarizing beam splitter 1308. Meanwhile, the P-polarized light beam that passed through polarizing beam splitter 1302 further passes through polarizing beam splitters 1303 and 1308, is reflected by mirror 1311, and is then irradiated onto the ocular surface via quarter-wave plate 1312. The irradiated light beam is reflected by the ocular surface and returns at a frequency of fo+fd due to the Doppler shift frequency fd caused by surface wave vibration. It becomes S-polarized by quarter-wave plate 1312 and is reflected by polarizing beam splitter 1308. The light beam from reference mirror 1310 and the light beam from the ocular surface interfere and enter photodetector 1313. A signal with frequency fm+fd is output from photodetector 1313, and by FM demodulating the modulated component of Doppler shift frequency fd, which changes due to vibration, phase-modulated and frequency-modulated components are obtained, making it possible to detect surface vibration caused by surface waves.

[0064] (5) Configuration of excitation and detection means for minimizing interference of excitation ultrasonic waves with the detection sensor when generating and detecting surface waves using ultrasonic waves. FIG. 15 shows an embodiment for minimizing interference noise from the ultrasonic waves used to excite the surface waves in an ultrasonic sensor for detecting the surface waves, in the case where the generated surface waves are detected by the ultrasonic reflection method using means for exciting the surface waves using ultrasonic waves.

[0065] Generally, ultrasonic waves emitted by an ultrasonic excitation means form a sound field with a sound pressure peak at the center of the beam, as shown in Figure 14. Therefore, not only does the ultrasonic wave irradiate the excitation point with a strong peak sound pressure, but relatively weaker sound waves are also irradiated around it. This ultrasonic wave that spreads to the periphery is reflected by the surface of the eye to be measured and interferes with the ultrasonic sensor used for detection, resulting in it being superimposed as noise on the detected waveform of the surface wave. This configuration is intended to minimize the acoustic noise interference caused by this excitation ultrasonic wave with the detection sensor.

[0066] As shown in Figure 15, ultrasonic waves for exciting surface waves are emitted as burst waves from an ultrasonic wave emission unit (excitation means) 1501, generating surface waves centered on the excitation point on the surface of the subject's eye. From the excitation point, the surface waves propagate across the eye surface at a phase velocity (or group velocity) Cs and reach the detection point. The surface waves that have arrived are detected by a detection ultrasonic sensor unit. Figure 15 shows an example in which the detection ultrasonic sensor unit is divided into a transmission sensor 1502 and a reception sensor 1503 (detection means), but the transmission sensor and reception sensor may be the same.

[0067] The control unit 1507 outputs a drive signal to the drive circuit 1504, and the drive circuit drives the ultrasound irradiation unit 1501 in accordance with the drive signal to irradiate the excitation ultrasound to the excitation point on the surface of the eye. The transmission sensor 1502 of the detection ultrasound sensor unit transmits ultrasound for detecting surface waves to the detection point on the surface of the subject's eye, and the ultrasound reflected at the detection point is received by the receiving sensor 1503. The control unit 1507 outputs a transmission signal to the transmission circuit 1506, and demodulates the ultrasound signal received by the receiving sensor 1503 and amplified by the receiving circuit using the ultrasound detection method shown in Fig. 9 to extract and analyze the surface wave component. The control unit 1507 includes a surface wave processing unit 1507a that analyzes the surface wave detected by the receiving sensor 1503, and an eyeball physical property calculation unit 1507b that calculates the physical properties of the eyeball based on the analysis results of the surface wave processing unit 1507a.

[0068] 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 Ldt. Ldr and Ldt may be the same or different, but if the receiving sensor and transmitting sensor are the same, they will of course be the same distance.

[0069] Furthermore, the interference wave component of the ultrasound emitted from the ultrasound emission unit 1501 to the detection sensor is reflected by the surface of the eye and reaches the receiving sensor 1503, and the path length is Liw. The reflection angle on the surface of the eye is such that the angle of incidence and the angle of emergence are the same with respect to the normal to the surface of the eye. The interference of acoustic noise caused by the excitation ultrasound can be minimized by arranging the ultrasound emission unit 1501, the receiving sensor 1503, and the distance between the excitation point and the detection point so that the timing at which the detection receiving sensor 1503 detects the surface wave component does not coincide with the time when the interference component caused by the excitation ultrasound reaches the receiving sensor 1503 and arrives as interference noise (i.e., only the surface wave after the interference component of the excitation ultrasound has finished reaching the receiving sensor 1503 is detected).

[0070] In this case, if the phase velocity or group velocity of the surface wave is Cs, the sound speed of the airborne ultrasound is Va, the irradiation time of the burst wave of the excitation ultrasound is Tex, the distance from the excitation ultrasound irradiation unit (excitation means) to the excitation point on the surface of the eyeball is Lex, the propagation path length of the interference noise of the excitation ultrasound is Liw, and the distance between the detection point of the surface wave on the surface of the eyeball and the receiving ultrasound sensor for surface wave detection (detection means) is Ldr, the influence of acoustic noise can be minimized when the following [Equation 1] is satisfied. [Number 1] Tex+Liw / Va ≦ Lex / Va+Ds / Cs+Ldr / Va

[0071] (6) Configuration of excitation means for efficiently generating surface waves using optical energy As already mentioned, in excitation of surface waves by pulsed light, photoacoustic waves generated by pulsed light are continuously generated by continuous pulsed light, and the continuous pulsed light is further intensity-modulated to excite surface waves at a frequency lower than that of the photoacoustic waves on the surface of the eye, as shown in Figure 16. Furthermore, in order to efficiently use the sound pressure of the photoacoustic waves to excite surface waves on the surface of the eye, it is necessary to control the pulse duration and period of the continuous pulsed light in accordance with the phase of the photoacoustic waves.

[0072] Photoacoustic waves are a phenomenon in which thermoelastic waves are generated when a material that absorbs light energy when pulsed light is irradiated onto biological tissue undergoes adiabatic expansion, and are generated when the pulse time is sufficiently shorter than the heat dissipation time of the tissue, and the resulting acoustic pressure P is expressed by the following [Equation 2]. The Gruneisen 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 absorption coefficient of the tissue. [Number 2] P=Γ×μa×F0×exp(-μa×z) where P: acoustic pressure, Γ: Gruneisen coefficient, μa: tissue absorption coefficient, F0: light energy density, z: depth within tissue The pulse duration of the pulsed light satisfies the generation condition of the photoacoustic wave as shown in the following equation (3). [Number 3] τp < τstr where τp: light pulse time, τstr: tissue heat dissipation time

[0073] Photoacoustic waves generated by the photoacoustic effect are abrupt pressure changes caused by short pulsed light, and their spectral bandwidth is wide. Photoacoustic waves produce temporal changes in pressure due to factors such as the thermal conductivity, stress dissipation time, bulk modulus, and density of tissue, and the frequency of the generated photoacoustic waves also changes, but as long as it is within the stress dissipation time, there is a change depending on the pulse time of the light pulse. Figures 17 and 18 show the change in wavelength of the generated photoacoustic waves as a function of the pulse time of the light pulse.

[0074] The pulsed light is irradiated continuously, but by setting the irradiation period to the same period as the frequency of the photoacoustic wave generated by the pulsed light or a period that is an integer fraction of that period, not only are the pulsed light superimposed to form a continuous acoustic wave, but the superimposed components also result in an increase in amplitude (amplified). Figure 19 shows that by irradiating the photoacoustic wave with a pulsed light irradiation period that matches the center frequency of the photoacoustic wave, the phases of the photoacoustic waves (1901, 1902, 1903, ...) are matched, resulting in a superimposed sound pressure waveform 1904, and an increase in sound pressure.

[0075] The frequency of photoacoustic waves generated in living tissue is generally approximately 0.5 MHz to 50 MHz, and the pulse duration of the pulsed light is set within the range of 10 nsec to 1000 nsec to control the center frequency or peak spectral frequency of the photoacoustic waves. Furthermore, to align the phases of the generated acoustic waves, the pulse period of the pulsed light is set to the same period as the photoacoustic wave frequency (i.e., in the range of 0.5 MHz to 50 MHz) or an integer fraction thereof, thereby aligning the phases of the photoacoustic waves and superimposing them to maximize the sound pressure. By controlling the pulse duration and pulse period of the pulsed light, it is also possible to detect the pulse duration and pulse period that maximize the amplitude of the surface wave.

[0076] Furthermore, in order to obtain the optimal pulse time and pulse period of the light pulse, multiple pulse times are set before measuring the ocular properties of the test eye, ranging from short pulses to long pulses, for example, in a range from 10 nsec to 1000 nsec, and the pulse period of the pulsed light is further swept for each pulse time, thereby detecting the pulse time and pulse period at which the amplitude of the surface wave on the test eye surface detected by the surface wave detection unit is highest, and driving the light pulse at the obtained optimal value enables the most efficient excitation of the surface wave.

[0077] 20 shows an embodiment for measuring eyeball physical properties by controlling the pulse time and pulse period of the light pulse to maximize the amplitude of the surface wave. While this embodiment shows the detection of the surface wave as an example of detection using the ultrasonic reflection method, it is also possible to use the optical triangulation method, the optical multiple wavelength coaxial confocal method, or the optical heterodyne method.

[0078] 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 a pulse signal generation circuit 2005 by a control unit 2008. The control unit 2008 sequentially sweeps the pulse period within a predetermined range in accordance with 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 resulting in the maximum amplitude is determined. The pulse time is sequentially changed to a plurality of predetermined values, and the sweep of the pulse period is repeated. As a result, the maximum values of the obtained surface wave amplitude are compared, making it possible to determine the optimal pulse time and pulse period of the pulsed light to be irradiated onto the eyeball.

[0079] (7) Means for outputting and analyzing measured intraocular pressure values and the material mechanical properties of ocular tissues (home monitoring system for ocular physical properties) Measured ocular properties such as intraocular pressure and the material mechanical properties of ocular tissues are used as important parameters in the diagnosis of glaucoma and keratoconus, which are eye diseases that require long-term observation, diagnosis, and treatment. Therefore, it is important that measured values are smoothly accumulated and can be easily confirmed at the time of diagnosis. In addition, with the increasing need for telemedicine and home medical care in recent years, there is also an increasing need for measurements in clinics and at home.

[0080] FIG. 21 shows the overall configuration of a home monitoring system S for ocular physical properties. The intraocular pressure value of a subject's eye 2101 and the mechanical material properties of the ocular surface measured by an ocular physical property measuring device 2102 are connected to the Internet 2110 by one of a number of connection means. The connection means may be via a router 2103 connected to a wired local area network (LAN), via a wireless router 2104 using short-range wireless communication such as wireless LAN or Bluetooth (registered trademark), or via mobile communication using a mobile terminal 2105 such as a smartphone, for connection to the Internet (WAN). The measurement data transmitted from the ocular physical property measuring device is stored in a cloud service 2106 on the Internet or in a fixed server 2111. Meanwhile, a doctor or other medical professional 2109 can check and analyze the data at any time using a terminal device 2108 such as a personal computer, tablet computer, or smartphone.

[0081] Furthermore, an application for analyzing the accumulated data is incorporated into the cloud service 2106 and the fixed server 2111, and it becomes possible to provide data analysis and future predictions using statistical processing, artificial intelligence (AI), and deep learning. This analysis data can be confirmed by medical officers 2109 as data necessary for diagnosis, and can also be sent to the eyeball physical property measuring device 2102 or smartphone 2105 so that the subject can confirm it.

[0082] 22 shows a structural diagram of each processing unit (ocular physical property measuring device 2102, mobile terminal 2105, fixed server 2111, terminal device 2108) of home monitoring system S for 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 the patient's home and is specialized for measuring the patient's eyeball physical properties such as intraocular pressure.

[0083] The eyeball physical property measuring device 2102 includes an excitation unit 102 that excites at least one or more excitation points on the eyeball using an irradiation wave to generate a surface wave on the surface of the eyeball, which is the eye to be examined, a detection unit 103 that detects the surface wave generated by the excitation unit 102 at at least one or more detection points on the eyeball that are different from the excitation points, a surface wave processing unit 208 that analyzes the surface wave detected by the detection unit 103, an eyeball physical property calculation unit 209 that calculates the physical properties of the eyeball based on the analysis result in the surface wave processing unit 208, 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, a fixed server 2111) via a wide area network. The communication unit 301 is a communication module that enables communication connection with the Internet, for example, wirelessly.

[0084] 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, a communication processing unit 2105c that realizes communication connection to a communication network such as the Internet, a screen display unit 2105d such as an LCD panel or an organic EL display, and an operation input unit 2105e such as a touch panel.

[0085] The fixed server (external device) 2111 includes a transmitter / receiver 2111a that receives information regarding ocular physical properties such as intraocular pressure measured by the measuring device 2102, a control unit 2111b that returns response information when a request is received from the mobile terminal 2105 or the terminal device 2108, an ocular physical property analysis unit 2111c that determines the progression of glaucoma and other conditions based on AI using data received from the measuring device 2102, an ocular physical property data storage unit 2111d that is a database that accumulates data regarding the ocular physical properties of patients (subscription contract holders), and a patient information storage unit 2111e that stores the analysis results of the patient (subscription contract holder), the subscription contract holder ID, password, etc.

[0086] The terminal device 2108 includes an input unit 2108a such as a keyboard that accepts input from a doctor, an application execution unit 2108b that executes a dedicated application using a web browser or the like, a request generation unit 2108c that acquires the ocular properties of the patient's eye to be examined and the results of AI analysis via the input unit 2108a, a transmission / reception unit 2108d, and a memory unit 2108e.

[0087] Such an ocular physical property home monitoring system S allows patients with glaucoma and the like to monitor intraocular pressure values measured by the intraocular pressure physical property measuring device 2102 while at home, without placing a significant burden on the patient. As a result, the patient can detect symptoms of glaucoma and the like early on while at home, and a doctor with the terminal device 2108 can urge the patient to visit an ophthalmologist based on the detected data, thereby preventing the progression of the symptoms in a timely manner.

[0088] The present invention is not limited to the configurations of the above-described embodiments, and various modifications are possible within the scope of the invention. Furthermore, in order to achieve the object of the present invention, the present invention can be realized as an eyeball physical property measuring method having steps corresponding to characteristic constituent means included in an eyeball physical property measuring device, or as a program including those characteristic steps. The program can be stored in a ROM or the like, or can be distributed via a recording medium such as a USB memory or a communication network. [Explanation of symbols]

[0089] 1,2102 Eyeball property measuring device S Home monitoring system for eyeball physical properties 101 Ocular surface 102 Excitation unit (excitation means) 103 Detection unit (detection means) 104 excitation points 105 detection points 106 Surface waves 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 property calculation unit (eyeball property calculation means) 210 Transmission control section 211 Control Unit 301 Communications Department (Communication Means) 1501 Ultrasonic irradiation unit (excitation means) 1502 Transmitting sensor (detection means) 1503 Receiving sensor (detection means)

Claims

1. A non-contact eyeball physical property measuring device, an excitation means for exciting at least one excitation point on the eyeball using an irradiation wave to generate a surface wave on the surface of the eyeball, which is the eye to be examined; a detection means for detecting the surface wave generated by the excitation means at at least one detection point on the eyeball different from the excitation point; 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 of the eyeball based on the analysis result of the surface wave processing means, an ocular physical property measuring device, wherein the irradiation wave emitted by the excitation means is a continuous wave of airborne ultrasonic waves having a fundamental frequency of 20 KHz or more and 200 KHz or less, or a burst wave of 10 waves or more of the airborne ultrasonic waves, and satisfies the following [Equation 1]: [Equation 1] Tex+Liw / Va ≦ Lex / Va+Ds / Cs+Ldr / Va where Cs is the phase velocity or group velocity of the surface wave, Va is the sound speed of the airborne ultrasound, Tex is the irradiation time of the burst wave for exciting the surface wave, Lex is the distance from the excitation ultrasound irradiation unit (excitation means) to the excitation point on the surface of the eyeball, Liw is the propagation path length of the interference noise of the excitation ultrasound, and Ldr is the distance between the detection point of the surface wave on the surface of the eyeball and the receiving ultrasound sensor for detecting the surface wave (detection means).

2. 2. The eyeball physical property measuring device according to claim 1, further comprising a communication means for transmitting the eyeball physical property obtained by said eyeball physical property calculation means to an external device via a wide area network.

3. A non-contact eyeball physical property measuring method, comprising: an excitation step of exciting at least one excitation point on the eyeball using an irradiation wave to generate a surface wave on the surface of the eyeball, which is the eye to be examined; a detection step of detecting the surface wave generated in the excitation step at at least one detection point 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 physical properties of the eyeball based on the analysis result in the surface wave processing step, an ocular property measuring method, characterized in that the irradiation wave emitted in the excitation step is a continuous wave of airborne ultrasonic waves having a fundamental frequency of 20 KHz or more and 200 KHz or less, or a burst wave of 10 waves or more of the airborne ultrasonic waves, and satisfies the following [Equation 1]: [Equation 1] Tex+Liw / Va ≦ Lex / Va+Ds / Cs+Ldr / Va where Cs is the phase velocity or group velocity of the surface wave, Va is the sound speed of the airborne ultrasound, Tex is the irradiation time of the burst wave for exciting the surface wave, Lex is the distance from the excitation ultrasound irradiation unit to the excitation point on the surface of the eyeball, Liw is the propagation path length of the interference noise of the excitation ultrasound, and Ldr is the distance between the detection point of the surface wave on the surface of the eyeball and the receiving ultrasound sensor for detecting the surface wave.

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