JP2010068873A - Non-contact ultrasonic tonometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-contact ultrasonic tonometer which appropriately measures an intraocular pressure while ensuring a working distance to a subject's eye. <P>SOLUTION: In the non-contact ultrasonic tonometer equipped with a probe which emits ultrasound entering the subject's eye and detects the ultrasound reflected by the subject's eye and a computation part which acquires the intraocular pressure by processing measurement signals output from the probe for measuring the intraocular pressure of the subject's eye, an appropriate working distance between the subject's eye and the tonometer is set to be longer than at least 10 mm, and the probe has an emission diameter or a shape of an emission surface, which is set, or is equipped with an acoustic absorbent so that an irradiated area with ultrasonic beams in the appropriate working distance fits in an area of opened eyelids of the subject's eye. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-contact ultrasonic tonometer that measures intraocular pressure of a subject's eye in a non-contact manner using ultrasonic waves.

As a device that measures the intraocular pressure of the subject's eye in a non-contact manner compared to the incident wave on the subject's eye and the reflected wave from the subject's eye, the subject's eye (however, the model eye) A probe having a transducer for emitting incident ultrasonic waves and a sensor for detecting ultrasonic waves reflected by the subject's eye is provided, and the probe is arranged in front of the subject's eye, An intraocular pressure measurement device that measures the intraocular pressure of the eye in a non-contact manner has been proposed (see Non-Patent Document 1).
Masayuki Kamide and three others "Fundamental research on non-contact type intraocular pressure measurement system using ultrasonic phase shift method", IEICE technical report Sensor Micromachine Division, 2007, p. 93-96

  However, in the case of the above configuration, the working distance between the eye of the subject and the apparatus is short, and when actually trying to measure the intraocular pressure with respect to the human eye, there is a possibility of contact with the eye of the subject. Yes, it is easy to give fear to the subject.

  In view of the above prior art, an object of the present invention is to provide a non-contact ultrasonic tonometer capable of appropriately measuring intraocular pressure while ensuring a working distance with respect to the subject's eye.

  In order to solve the above problems, the present invention is characterized by having the following configuration.

(1) a probe that emits an ultrasonic wave to be incident on a subject's eye and detects the ultrasonic wave reflected by the subject's eye;
A calculation unit for obtaining intraocular pressure by processing the measurement signal output from the probe;
In a non-contact ultrasonic tonometer that measures the intraocular pressure of the subject's eye,
The appropriate working distance between the subject's eye and the tonometer is set to be longer than at least 10 mm,
The probe has an emission diameter or an emission surface shape, or a sound absorbing material is provided so that an irradiation area of the ultrasonic beam at the appropriate working distance falls within the eye opening area of the subject's eye. It is characterized by being.
(2) In the non-contact ultrasonic tonometer of (1),
The probe includes a piezoelectric element having a resonance frequency and an emission diameter set so that the irradiation area is smaller than the opening area.
(3) In the non-contact ultrasonic tonometer of (2),
The probe is characterized in that a resonance frequency and an emission diameter of the piezoelectric element are set so that a position where the ultrasonic beam emitted from the probe becomes the thinnest is a position of the irradiation area. To do.
(4) In the non-contact ultrasonic tonometer of (3),
In the probe, the resonance frequency and the emission diameter of the piezoelectric element are set so that the position where the ultrasonic beam emitted from the probe turns to the diffusion due to the influence of the spherical wave becomes the position of the irradiation area. It is characterized by being.
(5) The non-contact tonometer of (4) includes an acoustic lens that is disposed in front of the probe and focuses an ultrasonic beam, and the irradiation area is positioned before the focal position of the acoustic lens. It is characterized by being set.
(6) In the non-contact ultrasonic tonometer of (1),
The probe has a sound absorbing material that is disposed between the probe and a subject's eye and absorbs an ultrasonic beam emitted from the probe.
The sound absorbing material is an opening for allowing the ultrasonic beam emitted from the probe to pass therethrough and has an opening smaller than the opening area, and the size of the spherical wave irradiation area and the opening of the sound absorbing material. It has the spherical wave absorption part formed ahead from the position where a magnitude | size becomes substantially the same, It is characterized by the above-mentioned.
(7) In the non-contact ultrasonic tonometer of (1),
A working distance detection system for detecting the working distance between the subject's eye and the tonometer;
Determination means for determining whether or not the working distance detected by the detection system has reached the proper working distance.
(8) In the non-contact ultrasonic tonometer of (1),
The probe is a broadband air-coupled ultrasonic probe that transmits and receives an ultrasonic beam having a broadband frequency component, and the irradiation area of the ultrasonic beam at the appropriate working distance is a corneal area of a subject's eye The emission diameter or the emission surface shape is determined so as to be within the range.
(9) In the ultrasonic tonometer of (8),
The vibrator is characterized in that the shape of the exit surface is concave so that the irradiated ultrasonic beam is converged, or the exit surface is a Fresnel zone plate.

  According to the present invention, it is possible to appropriately measure intraocular pressure while ensuring a working distance with respect to the subject's eye.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining the configuration of a non-contact ultrasonic tonometer according to the present embodiment. The measurement system and the optical system in FIG. 1 are arranged in a housing (not shown) and are movable with respect to the eye E (see Japanese Patent Application No. 2008-120793 by the present applicant). ).

  The probe (transducer) 10 disposed in front of the subject's eye E is reflected by the transducer 11 that emits an ultrasonic wave (incident wave) incident on the subject's eye E and the subject's eye E. And a sensor 13 for detecting ultrasonic waves (reflected waves) for measuring the intraocular pressure of the subject's eye E in a non-contact manner.

  The probe 10 has a configuration in which a PZT element is used as a piezoelectric (piezo) element, and the single piezoelectric element is operated by the vibrator 11 and the vibration detection sensor 13 by the control of the control unit 70. It becomes the composition which serves as both. The probe 10 is not limited to PZT but may be a ceramic piezoelectric probe (piezoelectric material) such as bimorph, unimorph, or PVDF.

  In the present embodiment, a pulse wave is used as an ultrasonic wave incident on the subject's eye E, and the vibrator 11 is used as an ultrasonic wave transmitting unit that emits an ultrasonic wave incident on the subject's eye E. The sensor 13 Is used as an ultrasonic wave receiver that receives ultrasonic waves reflected by the eye E of the subject. A backing material (not shown) is disposed on the back surface of the probe 10. An acoustic lens 16 for converging the ultrasonic wave emitted from the transducer 11 is provided on the subject eye E side (front) of the probe 10.

FIG. 2 is a diagram for explaining a method for setting the resonance frequency and diameter of the piezoelectric element used in the probe 10. When the piezoelectric element of the probe 10 is vibrated in the thickness direction, the diameter of the piezoelectric element is D, the thickness of the piezoelectric element is t, the frequency constant is Nt, the speed of sound in the air is Cair, and the subject's eye If the appropriate working distance (measurement distance) between E and the device is W, the resonance frequency f is
And the wavelength λ is
And the diffusion angle (directivity angle) θs of the spherical wave is
The irradiation area (diameter) S in the case of the measurement distance W is
It is expressed.

In order for a reflected wave from only the cornea Ec to be detected, the irradiation area S must be smaller than the open area K (length from the lower limit portion of the upper eyelid to the upper limit portion of the lower eyelid) (FIG. 2). reference). Therefore, from equation (4)
It is expressed. Here, substituting equation (3) into θs,
It is expressed. Also, if the formula (2) is substituted into λ,
It is expressed. In addition, the measurement distance W needs to be longer than the distance WD1 (for example, about 10 mm) that hardly gives fear to the subject. Therefore, a piezoelectric element having a diameter D and a resonance frequency f that satisfies Expression (7) is used under the condition that W> WD1.

  In addition, it is preferable that the opening area K is set to have a diameter of about 4 mm or less so that an ultrasonic wave is irradiated only to the cornea Ec even if the subject cannot open the eye largely. Further, when the measurement distance W with respect to the subject's eye E is increased, the acoustic intensity of the ultrasonic wave is reduced, and therefore it is necessary to use a piezoelectric element having a diameter D and a resonance frequency f that can obtain an appropriate acoustic intensity.

In addition, the refractive index of an acoustic lens that focuses (converges) an ultrasonic beam (plane wave) in a direction perpendicular to the vibration direction is n, the sound velocity is Cal, the radius of curvature is r, the focal length is F, and the plane wave is converged. If the angle is θf, the refractive index n is
It is expressed. The convergence angle θf is
It is expressed. Here, the radius of curvature r is Snell's law, where F is the focal length,
It is expressed. In the case of the measurement distance W, the irradiation area S is at a position obtained by subtracting W from the focal length.
It is expressed. In order to detect a reflected wave from only the cornea Ec, the irradiation area S of the plane wave focused by the acoustic lens 16 must be smaller than the opening area K. Therefore, from Equation (10) and Equation (11),
It is expressed. Then, substituting equation (9) for θf,
It is expressed. Note that the measurement distance W needs to be longer than the distance WD1 (about 10 mm) at which it is difficult to give fear to the subject. Therefore, here, a piezoelectric element having a diameter D and an acoustic lens having a focal length F and a radius of curvature r satisfying Expression (13) are used under the condition of satisfying W> WD1.
In this case, an irradiation area is set in front of the focal position of the acoustic lens 16 disposed in front of the probe 10 (on the apparatus side). In the present embodiment, the resonance frequency and the emission diameter of the piezoelectric element are such that the position where the beam diameter of the ultrasonic beam emitted from the probe 10 is the thinnest becomes the position of the measurement distance W (position of the irradiation area). Is set. Specifically, the position where the beam distance of the plane wave focused by the acoustic lens 16 and the beam diameter of the spherical wave emitted from the central axis of the acoustic lens 16 coincide is the position of the measurement distance W. ing.

  If the configuration satisfies the above conditions, only the cornea Ec is irradiated with ultrasonic waves emitted from the vibrator 11 in a state where a working distance that does not cause fear to the subject is secured. In the above, the reason why the appropriate working distance between the subject eye E and the device is longer than 10 mm is that when the subject eye E blinks, a part of the device (acoustic lens 16) and the eyelid contact each other. This is to avoid doing.

  In the above configuration, the case where the piezoelectric element is vibrated in the thickness direction has been described as an example. However, the present invention can be applied even when the piezoelectric element is vibrated in the radial direction. When the piezoelectric element is vibrated in the radial direction, the resonance frequency f is determined by Np / D, where Np is the frequency constant in the radial direction and D is the diameter D of the piezoelectric element.

  Here, the probe 10 is sequentially connected to an amplifier 81, a frequency component analysis unit 82, a frequency phase difference specifying unit 83, and a control unit 70. Then, an electric signal corresponding to an incident wave incident on the subject's eye (an outgoing wave emitted from the vibrator 11) and a reflected wave reflected from the subject's eye is an appropriate signal by an amplifier 81. The frequency component analysis unit 82 performs frequency component analysis of the incident wave and the reflected wave, and obtains the spectrum distribution of the phase difference with respect to the frequency for each of the incident wave and the reflected wave.

  Next, the frequency phase difference specifying unit 83 compares the spectrum distribution of the incident wave and the spectrum distribution of the reflected wave, and obtains the phase difference θx that is the difference between the phase of the incident wave and the phase of the reflected wave at each frequency fx. Identified. Here, since the phase difference θx at the frequency fx changes according to the intraocular pressure of the eye E (strictly speaking, the hardness of the cornea due to the intraocular pressure), the control unit 80 includes the frequency phase difference specifying unit 83. The phase difference θx is detected based on the output signal, and the intraocular pressure value of the subject eye E is obtained based on the detection result. For the hardness detection method using the ultrasonic pulse method described above, refer to Japanese Patent Application Laid-Open No. 2002-272743.

  Next, the configuration of the optical system will be described. In this optical system, an optical unit 20 disposed behind the probe 10 and a Z index projection optical system for projecting an alignment detection Z index on the cornea Ec in the front-rear direction (hereinafter, Z direction) which is the working distance direction. A system 50 and a Z index detection optical system 55 that detects an image of the Z index projected onto the cornea Ec are provided.

  The optical unit 20 has a fixation target presenting optical system for fixing the subject's eye E, and an XY index for projecting an XY index for detecting alignment in the horizontal and vertical directions (X and Y directions) onto the cornea Ec. A projection optical system, an observation optical system (XY index detection optical system) for observing the anterior segment of the subject's eye E, and the like are incorporated. The observation optical system is provided with an image pickup device for picking up an image of the anterior segment. The image pickup signal of the image pickup device is output to the control unit 70 and the anterior segment image is displayed on the monitor 72. . Further, the alignment index light beam by the XY index projection optical system is projected from the front onto the cornea Ec and is specularly reflected by the cornea Ec to form an index image i1 that is a virtual image. An opening (not shown) for passing the fixation target light beam and the alignment index light beam is formed at the center of the probe 10 and the acoustic lens 16.

  The Z index projection optical system 50 includes an infrared light source 51 and a projection lens 52, and projects the alignment index onto the cornea Ec. Note that the projection optical axis L4 of the Z index projection optical system 50 intersects the optical axis L1 of the observation optical system at a predetermined angle. Here, the light from the light source 51 is converted into a substantially parallel light beam by the lens 52, then projected from the oblique direction onto the cornea Ec along the projection optical axis L4, and is specularly reflected by the cornea Ec to generate an index image i2 that is a virtual image. Form.

  The Z index detection optical system 55 includes a light receiving lens 56, a filter 57, and a position detection element 58 (for example, a line CCD), and detects an image of an alignment index formed on the cornea Ec by the Z index projection optical system 50. The projection optical axis L5 of the Z index detection optical system 55 and the projection optical axis L4 of the Z index projection optical system 50 are symmetric with respect to the optical axis L1 and intersect each other on the optical axis L1. When the position in the subject eye E (cornea Ec) Z direction changes, the detection position of the index image i2 in the position detection element 58 also changes. Therefore, based on the detection signal from the position detection element 58, the subject eye E is detected. The alignment state in the Z direction of the probe 10 is detected. The Z index detection optical system 55 is set so that the working distance between the subject eye E and the apparatus can be adjusted to the above-described appropriate measurement distance W.

  The control unit 70 is connected to the probe 10, the frequency phase difference specifying unit 83, the light source 51, the position detection element 58, the display monitor 72, the memory 75, etc. Etc.

  The memory 75 stores a table indicating the correlation between the phase difference θx at the frequency fx and the intraocular pressure value of the subject's eye E. The control unit 70 is output from the frequency phase difference specifying unit 83. An intraocular pressure value of the subject eye E corresponding to the phase difference θx is obtained from the memory 75 and the obtained intraocular pressure value is displayed on the monitor 72. The correlation between the phase difference θx and the intraocular pressure value of the subject eye E is, for example, the intraocular pressure value of the subject eye E obtained by a Goldman tonometer and the phase difference θx obtained by the present apparatus. It is possible to set by previously obtaining the correlation between and experimentally. In addition, the memory 75 stores a program for controlling the entire apparatus in addition to a program for measuring the intraocular pressure of the subject's eye E using the probe 10.

  The operation of the apparatus having the above configuration will be described. First, the examiner performs alignment with the subject eye E using a joystick (not shown) while looking at the monitor 72. At this time, as shown in FIG. 3A, the control unit 70 aligns the anterior segment image obtained by the imaging device of the observation optical system and the subject eye E with the reticle LT. And the indicator G are synthesized and displayed on the monitor 72.

  When the index image i2 is detected by the position detection element 58, the alignment state of the apparatus with respect to the subject eye E in the Z direction can be detected. The control unit 70 detects the alignment state in the Z direction based on the detection signal from the position detection element 58, and controls the display of the indicator G based on the detection result.

  The examiner operates a joystick (not shown) so that the index image i1 enters the reticle LT and the indicator G is in a state where alignment is completed (see FIG. 3B). When the alignment in each direction is completed in this way and the measurement start switch (not shown) is pushed by the examiner, the control unit 70 issues a measurement start trigger signal and starts tonometry using the probe 10. To do.

  When a trigger signal for starting measurement is generated (input) as described above, the control unit 70 uses the vibrator 11 to generate ultrasonic waves (incident waves) on the subject's eye E based on the trigger signal. And ultrasonic waves (reflected waves) from the subject's eye E are detected using the sensor 14. Then, as described above, the control unit 70 calculates the intraocular pressure value of the subject eye E based on the output signal from the frequency phase difference specifying unit 83 and displays the measurement result on the monitor 82.

  With the configuration as described above, it is possible to avoid irradiating ultrasonic waves other than the cornea Ec (for example, eyelids, eyelids, etc.) at the time of ultrasonic irradiation. , A decrease in measurement accuracy can be avoided.

  In the above description, the acoustic lens 16 is arranged in front of the probe 10, but a planar matching layer may be used instead of the acoustic lens (concave matching layer). FIG. 4 is a diagram for explaining a method for setting an irradiation area of ultrasonic waves emitted from the probe 10 when a planar matching layer is used.

  The irradiation area S formed by the spherical wave can be obtained using Expression (4). An irradiation area S formed by plane waves corresponds to the diameter D of the piezoelectric element. In order to detect a reflected wave from only the cornea Ec while ensuring a working distance, the irradiation area S must be smaller than the opening area K (see FIG. 4). Accordingly, a piezoelectric element having a diameter D and a resonance frequency f satisfying the expression (7) and D <K under the condition satisfying W> WD1 is used.

  In this case, for example, the resonance frequency and the emission diameter of the piezoelectric element are set so that the position where the ultrasonic beam emitted from the probe 10 turns to the diffusion due to the influence of the spherical wave becomes the position of the irradiation area. Can be considered.

In the above description (see FIGS. 2 and 4), the position where the beam diameter of the ultrasonic beam formed by the plane wave and the spherical wave is the smallest is the position of the measurement distance W. If the irradiation area S can be made smaller than the opening area K while securing the distance WD ₁ that is difficult to give a heart, the front may be set as the position of the measurement distance W.

  In addition, the position behind the position where the beam diameter of the ultrasonic beam becomes the smallest may be the measurement distance position, but the acoustic intensity decreases due to the diffusion of the spherical wave, so it is set within a range where an appropriate acoustic intensity can be obtained. It is necessary to

  Next, a method for limiting an ultrasonic beam using a sound absorbing material will be described. FIG. 5 is a view when a sound absorbing material is disposed between the subject E and the probe 10. In this case, a planar matching layer is provided in front of the probe 10. For this reason, the plane wave beam has a beam shape parallel to the working distance direction.

  Further, a sound absorbing material 30 having a characteristic of absorbing ultrasonic waves is disposed between the probe 10 and the subject's eye E. An opening 31 for allowing ultrasonic waves to pass through is formed at the center of the sound absorbing material 30. For this reason, a part of the ultrasonic wave emitted from the probe 10 is irradiated to the cornea Ec through the opening 31, and a part of the ultrasonic wave emitted from the probe 10 is absorbed by the sound absorbing material 30. Is done. That is, the sound absorbing material 30 in which the opening 31 is formed restricts the shape of the ultrasonic beam emitted from the probe 10.

Here, when the piezoelectric element of the probe 10 is vibrated in the thickness direction, the diameter of the piezoelectric element is D, the thickness of the piezoelectric element is t, the frequency constant is Nt, the speed of sound in the air is Cair, When the appropriate working distance (measurement distance) between the subject's eye E and the apparatus is W, the resonance frequency f is
And the wavelength λ is
And the thickness R of the matching layer is
And the diffusion angle (directivity angle) θs of the spherical wave is
The irradiation area S when the distance from the matching layer to the sound absorbing material is X is
It is represented by

  An irradiation area formed by plane waves corresponds to the diameter D of the piezoelectric element. Here, in order to detect the reflected wave from only the cornea Ec while ensuring the working distance, the irradiation area of the ultrasonic beam (spherical wave and plane wave irradiation area) reaching the cornea Ec is smaller than the opening area K. Must-have.

  Therefore, the sound absorbing material 30 is formed so that the opening diameter H of the opening 31 is smaller than the opening area K (H <K), and the formation position in the working distance direction is substantially equal to the spherical wave irradiation area S and the opening diameter H. It is set to the front (examinee eye side) from the same position (distance X).

  Thereby, the beam diameter of the plane wave that has passed through the opening 31 of the sound absorbing material 30 becomes the same size as the opening diameter H of the opening 31 and consequently becomes smaller than the opening area K. The spherical wave emitted from the probe 10 is absorbed by the sound absorbing material 30. Therefore, the beam shape of the ultrasonic wave that has passed through the sound absorbing material 30 after being emitted from the probe 10 is smaller than the cleavage area K.

  When the sound absorbing material 30 is used, the working distance between the subject eye E and the apparatus is based on the end surface of the sound absorbing material 30 on the subject eye E side. Here, the working distance WD needs to be longer than the distance WD1 (for example, about 10 mm) that hardly gives fear to the subject.

  In this case, it is necessary to use a piezoelectric element having an emission diameter (D) and a resonance frequency f so as to obtain an acoustic intensity capable of measuring intraocular pressure. Further, it is preferable that the opening area K is set to have a diameter of about 4 mm or less so that the ultrasonic wave is irradiated only to the cornea Ec even if the subject cannot open the eye largely. Further, when the opening diameter H of the opening 31 is made smaller than the opening area K, the detected ultrasonic beam decreases as the opening diameter H becomes smaller, so that an acoustic intensity capable of measuring intraocular pressure is obtained. It is necessary to set the size as large as possible.

  That is, in the above configuration, a sound absorbing material is provided between the probe 10 and the subject's eye, and an opening for allowing the ultrasonic beam emitted from the probe 10 to pass therethrough is larger than the opening area. A small opening was provided in the sound absorbing material, and a spherical wave absorbing portion formed in front of the position where the size of the spherical wave irradiation area and the size of the sound absorbing material opening were substantially the same was provided in the sound absorbing material.

  Thereby, the ultrasonic wave emitted from the vibrator 11 can be irradiated only to the cornea Ec in a state in which a working distance that hardly causes fear to the subject is secured. In the case of the configuration using the above sound absorbing material, the ultrasonic energy is attenuated as much as the ultrasonic beam emitted from the probe 10 is limited by the sound absorbing material, but the irradiation area depends on the shape and arrangement of the sound absorbing material. Has the advantage of being easy to set. On the other hand, in the configuration in which the irradiation area is set by the resonance frequency and the emission diameter of the probe 10, since the ultrasonic energy incident on the subject's eye is not attenuated by the sound absorbing material, On the other hand, it has the advantage of being able to irradiate ultrasonic waves efficiently.

  In the above description, when the ultrasonic wave is incident on the subject's eye using the probe 10, the ultrasonic wave incident on the subject's eye is a pulse wave. However, the present invention is not limited to this. A continuous wave may be used.

  In the above description, the intraocular pressure is obtained from the difference in acoustic impedance due to the phase difference between the input phase input to the vibrator 11 and the output phase output from the sensor 13. However, the present invention is not limited to this as long as the intraocular pressure is measured by a calculation process by comparing the incident wave to be detected and the reflected wave detected by the sensor 13. For example, the frequency of the incident wave emitted from the vibrator 11 and the frequency of the reflected wave detected by the sensor 13 may be compared to obtain the intraocular pressure by calculation processing. More specifically, the phase difference is reduced to zero by changing the frequency of the ultrasonic wave generated by the vibrator 11 when a phase difference occurs between the input waveform to the vibrator 11 and the output waveform from the sensor 13. A phase shift circuit for shifting may be provided, and the intraocular pressure may be obtained by detecting a frequency change amount when the phase difference is shifted to zero.

  In the above description, a circular piezoelectric element has been described as an example. However, the present invention is not limited to this, and the resonance is performed so that the irradiation area at the proper working distance of the ultrasonic beam is within the eye opening area of the subject's eye. Any piezoelectric element having a set frequency and emission diameter may be used. In this case, for example, it is conceivable to use a rectangular (rectangular, square, etc.) piezoelectric element. When a square piezoelectric element is used, assuming that the length of the diagonal of the square corresponds to the diameter D described above, the diffusion angle θs of the spherical wave is obtained, and the irradiation area at the proper working distance of the ultrasonic beam is detected. A piezoelectric element that is smaller than the open eye area of the human eye may be selected.

  Further, instead of using a ceramic piezoelectric probe as the probe 10, a broadband air-coupled ultrasonic probe that transmits and receives an ultrasonic beam having a broadband frequency component may be used as the probe 10. Good. In this case, the emission diameter or the emission surface shape of the broadband air-coupled ultrasonic probe is set so that the irradiation area of the ultrasonic beam at an appropriate working distance falls within the cornea area of the subject's eye.

FIG. 6 is a diagram for explaining a main part of the broadband air-coupled ultrasonic probe according to the present embodiment. The probe 10 is a broadband air-coupled transducer that transmits and receives ultrasonic waves having a broadband frequency component, and uses a BAT ^TM transducer of Microacoustic. . The BAT ^TM probe is a capacitor type (capacitance type) sensor.

  More specifically, the probe 10 includes a substrate (back plate) 111 formed with a plurality of fine holes 111a each serving as an air pocket, and a lower portion of the substrate 111 (the substrate 111 is not roughened). The first electrode 113 arranged on the surface side), the second electrode 117 arranged on the upper portion of the substrate 111 (the roughened surface side of the substrate 111), the second electrode 117, and the substrate 111 And an insulating film (or dielectric film) 115 (hereinafter abbreviated as the insulating film 115) disposed therebetween.

  Note that it is only necessary that one (upper) surface of the substrate 111 is roughened to form a small air pocket. The insulating film 115 may be made of an insulating polymer material such as polyethylene or polyimide, or an insulating non-polymer material such as silicon nitride, aluminum oxide, or mica.

  Note that the substrate 111, the insulating film 115, and the second electrode 117 have a concavely curved shape (concave shape) so that the ultrasonic beam irradiated to the subject's eye is converged. It has become. In other words, the probe 10 has an emission surface shape so that the irradiation area of the ultrasonic beam at an appropriate working distance is within the eye opening area of the subject's eye. In this case, for example, the radius of curvature of the concave surface on the exit surface of the probe 10 may be the same as the appropriate working distance between the subject's eye and the tonometer. Thereby, since the irradiation area of the ultrasonic wave can be limited to only the cornea, it is possible to prevent the ultrasonic wave reflected from the eyelid or the like of the subject's eye from becoming noise and reducing the measurement accuracy.

  Here, when a voltage is applied between the first electrode 113 and the second electrode 117, the insulating film 115 is vibrated and ultrasonic waves are generated. Further, when the insulating film 115 is vibrated, the air layer between the insulating film 115 and the substrate 111 is vibrated, and the plurality of fine holes 111a each function as an air pocket. Then, the air in the air pocket, and the insulating film 115 and the second electrode 117 are in a resonance state, so that ultrasonic waves with high propagation efficiency in the air are irradiated toward the subject's eye. In this case, for example, broadband ultrasonic waves having a frequency band from about 200 kHz to 1 MHz are emitted. For details of the broadband air-coupled ultrasonic probe shown in FIG. 6, refer to US Pat. No. 5,287,331, JP 2005-506783, and the like.

  As described above, by using a broadband air-coupled ultrasonic probe as the probe 10, the propagation efficiency of ultrasonic waves in the air can be remarkably increased, so that the working distance to the eye of the subject is increased. Even so, the reflected wave from the subject's eye cornea can be detected with high sensitivity.

  In addition, in the said structure, although the output surface shape of the probe 10 was concave shape, a planar shape may be sufficient. In this case, it is preferable to set the emission surface of the probe 10 so that the ultrasonic wave irradiated to the subject's eye is irradiated only to the subject's eye cornea. For example, it is conceivable to make the emission diameter of the probe 10 smaller than the open area of the subject's eye.

  Further, even when the surface shape of the emission surface of the probe 10 is a planar shape, it is possible to adopt a configuration in which ultrasonic waves are converged. In this case, a configuration (so-called acoustic Fresnel zone plate) in which a part of the second electrode 117 is removed in a ring shape and a concentric multiple ring pattern by the second electrode 117 is formed on the emission surface is considered. It is done. In this case, the ultrasonic waves are converged by the interference between the ultrasonic waves emitted from the respective electrodes 117 formed in a ring shape.

  Further, according to the probe 10 of the present embodiment, since the influence of the spherical wave emitted from the probe 10 can be reduced as compared with the conventional ceramic piezoelectric vibrator, the ultrasonic wave irradiated to the subject's eye. Can be easily avoided from being irradiated to other than the cornea of the subject's eye.

  In the above description, the intraocular pressure of the subject's eye is obtained from the phase difference between the incident wave incident on the subject's eye and the reflected wave reflected from the subject's eye. Instead of this, the acoustic intensity of the reflected wave may be detected to determine the intraocular pressure of the subject's eye. In this case, the higher the intraocular pressure, the greater the difference in acoustic impedance between the cornea and air, so the stronger the acoustic intensity is detected, and the lower the intraocular pressure, the smaller the difference in acoustic impedance between the cornea and air, Is weakly detected.

  For example, it is conceivable to calculate the acoustic impedance of the cornea based on the acoustic intensity of the reflected wave output from the probe 10 and calculate the intraocular pressure of the subject's eye from the calculated acoustic impedance. In this case, the relationship between the acoustic impedance (or acoustic intensity) and the intraocular pressure of the subject's eye may be obtained in advance.

  In the above description, the probe 10 for transmitting and receiving ultrasonic waves is arranged in front of the eye of the subject's eye. However, as shown in FIG. 7, the ultrasonic wave that is incident on the subject's eye E is emitted. A configuration in which the vibrator 11 and the vibration detection sensor 13 for detecting the ultrasonic wave reflected by the subject's eye E are provided at positions symmetrical with respect to the observation optical axis L1.

It is a figure explaining the structure of the non-contact-type ultrasonic tonometer concerning this embodiment. It is a figure explaining the setting method of the resonant frequency and diameter of a piezoelectric element used for a probe. It is an example of the anterior ocular segment observation screen displayed on a monitor. It is a figure explaining the setting method of the irradiation area of the ultrasonic wave radiate | emitted from a probe at the time of using a planar matching layer. It is a figure in case a sound-absorbing material is arrange | positioned between a subject's eye and a probe. It is a figure explaining the principal part of the broadband air coupling ultrasonic probe which concerns on this embodiment. It is a figure at the time of providing a vibrator | oscillator and a vibration detection sensor in the symmetrical position with respect to an observation optical axis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Probe 16 Acoustic lens 50 Z index projection optical system 55 Z index detection optical system 111 Substrate 113 1st electrode 115 Insulating film (or dielectric film)
117 second electrode

Claims (9)

A probe that emits ultrasonic waves incident on the subject's eyes and detects ultrasonic waves reflected by the subject's eyes;
A calculation unit for obtaining intraocular pressure by processing the measurement signal output from the probe;
In a non-contact ultrasonic tonometer that measures the intraocular pressure of the subject's eye,
The appropriate working distance between the subject's eye and the tonometer is set to be longer than at least 10 mm,
The probe has an emission diameter or an emission surface shape, or a sound absorbing material is provided so that an irradiation area of the ultrasonic beam at the appropriate working distance falls within the eye opening area of the subject's eye. A non-contact ultrasonic tonometer characterized by comprising: The non-contact ultrasonic tonometer according to claim 1,
The non-contact ultrasonic tonometer, wherein the probe includes a piezoelectric element having a resonance frequency and an emission diameter set so that the irradiation area is smaller than the opening area. The non-contact ultrasonic tonometer according to claim 2,
The probe is characterized in that a resonance frequency and an emission diameter of the piezoelectric element are set so that a position where the ultrasonic beam emitted from the probe becomes the thinnest is a position of the irradiation area. Non-contact ultrasonic tonometer. The non-contact ultrasonic tonometer according to claim 3,
In the probe, the resonance frequency and the emission diameter of the piezoelectric element are set so that the position where the ultrasonic beam emitted from the probe turns to the diffusion due to the influence of the spherical wave becomes the position of the irradiation area. A non-contact ultrasonic tonometer characterized by comprising: The non-contact tonometer according to claim 4 includes an acoustic lens that is disposed in front of the probe and focuses an ultrasonic beam.
The non-contact ultrasonic tonometer, wherein the irradiation area is set before the focal position of the acoustic lens. The non-contact ultrasonic tonometer according to claim 1,
The probe has a sound absorbing material that is disposed between the probe and a subject's eye and absorbs an ultrasonic beam emitted from the probe.
The sound absorbing material is an opening for allowing the ultrasonic beam emitted from the probe to pass therethrough, and has an opening smaller than the opening area, and the size of the spherical wave irradiation area and the opening of the sound absorbing material. A non-contact ultrasonic tonometer having a spherical wave absorbing portion formed in front of a position having substantially the same size. The non-contact ultrasonic tonometer according to claim 1,
A working distance detection system for detecting the working distance between the subject's eye and the tonometer;
A non-contact ultrasonic tonometer, comprising: a determination unit that determines whether or not the working distance detected by the detection system has reached the proper working distance. The non-contact ultrasonic tonometer according to claim 1,
The probe is a broadband air-coupled ultrasonic probe that transmits and receives an ultrasonic beam having a broadband frequency component, and an irradiation area of the ultrasonic beam at the proper working distance is a cornea area of a subject's eye The non-contact type ultrasonic tonometer is characterized in that the emission diameter or the emission surface shape is determined so as to be within the range. The ultrasonic tonometer according to claim 8.
The vibrator has a non-contact type whose exit surface has a concave shape or a Fresnel zone plate so that the irradiated ultrasonic beam is converged. Ultrasonic tonometer.