Ultrasonic tonometer and ultrasonic tonometer control program

Abstract

To provide an ultrasonic tonometer capable of suitably irradiating a subject eye with ultrasonic waves, and an ultrasonic tonometer control program.SOLUTION: The ultrasonic tonometer for measuring an intraocular pressure of a subject eye by using ultrasonic waves comprises: irradiation means which irradiates the subject eye with converged ultrasonic waves; and Z alignment detection means which detects an alignment state in an actuation distance direction relative to the subject eye. A Z alignment suitable position detected by the Z alignment detection means is set farther than the geometrical focal position of the irradiation means.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to an ultrasonic tonometer that measures intraocular pressure in a subject's eye using ultrasound, and an ultrasonic tonometer control program. [Background technology]

[0002] A typical non-contact tonometer is an air-injection tonometer, which detects the applanation state of the cornea when air is injected onto the cornea and the pressure of the air injected onto the cornea, and converts the air pressure in a predetermined deformation state into intraocular pressure.

[0003] As a non-contact tonometer, an ultrasonic tonometer that measures intraocular pressure using ultrasonic waves has been proposed (see Patent Document 1). The ultrasonic tonometer in Patent Document 1 detects the applanation state of the cornea when ultrasonic waves are irradiated to the cornea and the radiation pressure injected onto the cornea, and converts the radiation pressure in a predetermined deformation state into intraocular pressure.

[0004] Furthermore, as an ultrasonic tonometer, a device has been proposed that measures intraocular pressure based on the relationship between the characteristics (amplitude, phase) of a wave reflected from the cornea and intraocular pressure (see Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 5-253190 [Patent Document 2] Patent Publication No. 2009-268651 Summary of the Invention [Problem to be solved by the invention]

[0006] In the ultrasonic tonometer described above, when the output of the ultrasonic waves increases, the focal position of the ultrasonic waves shifts, and there are cases in which the ultrasonic waves cannot be properly irradiated to the subject's eye.

[0007] In view of the problems of the related art, the present disclosure has as its technical object to provide an ultrasonic tonometer and an ultrasonic tonometer control program that can appropriately irradiate an ultrasonic wave to a subject's eye. [Means for solving the problem]

[0008] In order to solve the above problems, the present disclosure is characterized by having the following configuration.

[0009] (1) An ultrasonic tonometer for measuring the intraocular pressure of a test eye using ultrasound, comprising: an irradiation means for irradiating the test eye with focused ultrasound; a Z alignment detection means for detecting an alignment state in a working distance direction relative to the test eye; and a Z alignment proper position detected by the Z alignment detection means, which is set farther away than the geometric focal position of the irradiation means. (2) An ultrasonic tonometer control program used in an ultrasonic tonometer that uses ultrasound to measure the intraocular pressure of a test eye, characterized in that the ultrasonic tonometer is caused to execute a Z alignment detection step of detecting an alignment state in the working distance direction with respect to the test eye, and a setting step of setting the Z alignment proper position detected in the Z alignment detection step to a position farther away than the geometric focal position of an irradiation means that irradiates focused ultrasound to the test eye. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an external view of an ultrasonic tonometer. [Diagram 2] FIG. 2 is a schematic diagram showing the inside of a housing. [Diagram 3] FIG. 2 is a schematic diagram showing a configuration of an irradiation unit. [Figure 4] FIG. 2 is a block diagram showing a control system. [Diagram 5] 13 is a flowchart showing a measurement operation. [Figure 6] FIG. 2 is a diagram showing an example of an anterior eye image. [Figure 7] FIG. 2 is a diagram showing the positional relationship between an optical system and a maximum position of acoustic radiation pressure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] First Embodiment A first embodiment according to the present disclosure will be described. The ultrasonic tonometer (for example, ultrasonic tonometer 1) of the first embodiment measures the intraocular pressure of the subject's eye using, for example, ultrasonic waves. The ultrasonic tonometer includes, for example, an irradiation unit (for example, irradiation unit 100), an alignment detection unit (for example, optical system 200), and a control unit (for example, control unit 70). The irradiation unit irradiates, for example, ultrasonic waves to the subject's eye. The alignment detection unit has an imaging optical system (for example, observation system 220) that images the anterior segment of the subject's eye, and detects an alignment state with respect to the subject's eye based on an anterior segment image acquired by the imaging optical system. The control unit corrects the alignment information acquired by the alignment detection unit based on, for example, the amount of deviation (for example, the amount of deviation in the up, down, left, and right directions) between the optical axis (for example, optical axis O1) of the imaging optical system and the acoustic axis (for example, acoustic axis L1) of the irradiation unit. This allows the ultrasonic tonometer of the first embodiment to properly irradiate ultrasonic waves to the subject's eye.

[0012] The sound axis is, for example, the central axis of the ultrasonic waves irradiated by the irradiation unit. The sound axis extends, for example, in the direction of propagation of the ultrasonic waves or in the vibration direction of the irradiation unit, and passes through the focal position where the ultrasonic waves output by the irradiation unit are focused. The control unit may correct the alignment information based on, for example, the amount of deviation in the up-down, left-right, and front-rear directions (XY directions) between the optical axis of the imaging optical system and the focal position of the irradiation unit. The control unit may also correct the alignment information based on the amount of deviation between the detection reference position of the alignment detection unit (for example, the focal position of the imaging optical system) and the focal position of the irradiation unit (for example, the amount of deviation in the up-down, left-right, front-rear directions).

[0013] The ultrasonic tonometer may further include a measurement optical system (e.g., measurement optical system 500) that shares an optical axis with the imaging optical system and measures ocular characteristics other than intraocular pressure. In this case, the control unit may switch between correcting the alignment information when measuring ocular characteristics with the measurement optical system and measuring intraocular pressure with the irradiation unit. For example, the control unit may not correct the alignment information when measuring ocular characteristics with the measurement optical system, and may correct the alignment information based on the amount of deviation between the optical axis and the sound axis when measuring intraocular pressure with the irradiation unit. This allows ultrasonic waves to be properly irradiated when measuring intraocular pressure, and allows the measurement of ocular characteristics with the measurement optical system to be performed appropriately.

[0014] The ultrasonic tonometer may further include a drive unit (e.g., drive unit 5) that moves the irradiation unit. In this case, the control unit may control the drive unit based on the corrected alignment information to align the irradiation unit with respect to the subject's eye. This allows the ultrasonic tonometer to automatically perform proper alignment of the irradiation unit with respect to the subject's eye.

[0015] The control unit may display the corrected alignment information on a display unit (for example, the display unit 75). In this case, the examiner can operate an operation unit (for example, the operation unit 76) while checking the alignment information displayed on the display unit, and manually perform proper alignment of the irradiation unit with respect to the subject's eye.

[0016] The control unit may correct the alignment information according to the resonance frequency of the irradiation unit. For example, the amount of deviation between the optical axis of the imaging optical system and the sound axis of the irradiation unit may be stored in a storage unit or the like for each resonance frequency of the irradiation unit, and the alignment information may be corrected based on the amount of deviation according to the resonance frequency of the irradiation unit. This allows for suitable alignment that takes into account the change in the sound axis according to the resonance frequency of the irradiation unit.

[0017] The control unit may execute an ultrasonic tonometer control program stored in a storage unit or the like. The ultrasonic tonometer control program includes, for example, an alignment detection step and a correction step. The alignment detection step is, for example, a step of detecting an alignment state with respect to the subject's eye based on an anterior segment image acquired by an imaging optical system that images the anterior segment of the subject's eye. The correction step is, for example, a step of correcting the alignment information acquired in the alignment detection step based on the amount of deviation between the optical axis of the imaging optical system and the sound axis of the irradiation unit.

[0018] <Second embodiment> A second embodiment according to the present disclosure will be described. The ultrasonic tonometer (for example, ultrasonic tonometer 1) of the second embodiment includes an irradiation unit (for example, irradiation unit 100) and a Z alignment detection unit (for example, Z alignment detection system 280). The irradiation unit irradiates the subject's eye with focused ultrasonic waves. The Z alignment detection unit detects the alignment state in the working distance direction (front-back direction or Z direction) with respect to the subject's eye. In the second embodiment, the Z alignment proper position detected by the Z alignment detection unit is set farther in the working distance direction than the geometric (shape-based) focal position of the irradiation unit. As a result, the ultrasonic tonometer of the second embodiment performs alignment taking into account the focal position shift of the irradiation unit due to high sound pressure, and can properly irradiate ultrasonic waves to the subject's eye.

[0019] The Z alignment proper position may be set based on the relative positions of the Z alignment detection unit and the irradiation unit, or may be set by changing the detection reference position of the Z alignment detection unit. The detection reference position of the Z alignment detection unit may be, for example, the focal position of the Z alignment detection system, or a position a predetermined distance away from the focal position of the Z alignment detection system.

[0020] The ultrasonic tonometer may further include a deformation detection unit (e.g., deformation detection system 260) that detects the deformation state of the cornea of ​​the subject's eye. In this case, the detection position of the deformation detection unit may be set farther away than the Z alignment proper position. This increases the detection sensitivity of the deformation detection unit when the cornea of ​​the subject's eye is pressed, making it easier to detect that the cornea is deformed into a predetermined shape.

[0021] The device may further include a control unit (e.g., control unit 70) that controls the Z alignment detection unit. The control unit may change the Z alignment proper position according to the magnitude of the acoustic radiation pressure or sound pressure. The control unit may also change the Z alignment proper position according to the resonance frequency of the irradiation unit. In this way, the control unit can perform suitable alignment corresponding to the change in the focal position of the ultrasound that changes depending on the output of the irradiation unit by changing the Z alignment proper position according to the output of the irradiation unit.

[0022] The control unit may execute an ultrasonic tonometer control program stored in a storage unit or the like. The ultrasonic tonometer control program includes a Z alignment detection step and a setting step. The Z alignment detection step is, for example, a step of detecting an alignment state in a working distance direction with respect to the subject's eye. The setting step is a setting step of setting a Z alignment proper position detected in the Z alignment detection step to be farther away than a geometric focal position of an irradiation unit that irradiates the subject's eye with focused ultrasound.

[0023] <Example> An embodiment according to the present disclosure will be described below. The ultrasonic tonometer of this embodiment measures the intraocular pressure of the subject's eye in a non-contact manner using, for example, ultrasonic waves. The ultrasonic tonometer measures the intraocular pressure by optically or acoustically detecting, for example, a change in shape or vibration of the subject's eye when ultrasonic waves are irradiated to the subject's eye. For example, the ultrasonic tonometer continuously irradiates a pulse wave or a burst wave to the cornea, and calculates the intraocular pressure based on output information of the ultrasonic waves when the cornea is deformed into a predetermined shape (for example, an applanated state or a flattened state). The output information is, for example, the sound pressure, acoustic radiation pressure, irradiation time (for example, the elapsed time from the input of a trigger signal), or frequency of the ultrasonic waves. When deforming the cornea of ​​the subject's eye, for example, the sound pressure, acoustic radiation pressure, or acoustic streaming of the ultrasonic waves is used.

[0024] 1 shows the external appearance of the device. The ultrasonic tonometer 1 includes, for example, a base 2, a housing 3, a face support unit 4, a drive unit 5, and the like. An irradiation unit 100, an optical system 200, and the like, which will be described later, are arranged inside the housing 3. The face support unit 4 supports the face of the subject's eye. The face support unit 4 is installed on, for example, the base 2. The drive unit 5 moves the housing 3 relative to the base 2, for example, for alignment.

[0025] 2 is a schematic diagram of the main components inside the housing 3. For example, an irradiation unit 100 and an optical system 200 are arranged inside the housing 3. The irradiation unit 100 and the optical system 200 will be described in order with reference to FIG.

[0026] <Irradiation unit> The irradiation unit 100 irradiates, for example, ultrasonic waves to the subject's eye E. For example, the irradiation unit 100 irradiates ultrasonic waves to the cornea to generate acoustic radiation pressure on the cornea. The acoustic radiation pressure is, for example, a force acting in the direction in which sound waves travel. The ultrasonic tonometer 1 of this embodiment uses this acoustic radiation pressure to deform the cornea. The irradiation unit 100 of this embodiment is cylindrical, and an optical axis O1 of the optical system 200 described later is disposed in a central opening 101. The opening 101 is opened, for example, in the direction of the sound axis. The sound axis L1 is, for example, the central axis of the ultrasonic waves irradiated by the irradiation unit 100. The sound axis L1 is an axis extending in the direction in which the ultrasonic waves travel or in the vibration direction of the irradiation unit 100. The sound axis L1 passes through a focal position where the ultrasonic waves output by the irradiation unit 100 are focused. In this embodiment, the optical axis O1 of the optical system 200 and the sound axis L1 of the irradiation unit 100 are approximately coaxial.

[0027] FIG. 3(a) is a cross-sectional view showing a schematic configuration of the irradiation unit 100, and FIG. 3(b) is an enlarged view of the range A1 shown in FIG. 3(a). The irradiation unit 100 of this embodiment is a so-called Langevin type transducer. The irradiation unit 100 includes, for example, an ultrasonic element 110, an electrode 120, a mass member 130, a fastening member 160, and the like. The ultrasonic element 110 generates ultrasonic waves. The ultrasonic element 110 may be a voltage element (for example, piezoelectric ceramics), a magnetostrictive element, or the like. The ultrasonic element 110 of this embodiment is ring-shaped. For example, the ultrasonic element 110 may be a laminate of a plurality of piezoelectric elements. In this embodiment, the ultrasonic element 110 uses two laminated piezoelectric elements (for example, piezoelectric element 111 and piezoelectric element 112). For example, electrodes 120 (electrodes 121 and 122) are connected to the two piezoelectric elements, respectively. The electrodes 121 and 122 of this embodiment are, for example, ring-shaped.

[0028] The mass member 130, for example, sandwiches the ultrasonic element 110. By sandwiching the ultrasonic element 110, the mass member 130, for example, increases the tensile strength of the ultrasonic element 110, enabling it to withstand strong vibrations. This makes it possible to generate high-output ultrasonic waves. The mass member 130 may be, for example, a metal block. For example, the mass member 130 includes a sonotrode (also called a horn or a front mass) 131, a back mass 132, and the like.

[0029] The sonotrode 131 is a mass member disposed in front of the ultrasonic element 110 (on the subject's eye side). The sonotrode 131 propagates ultrasonic waves generated by the ultrasonic element 110 into the air. The sonotrode 131 of this embodiment is cylindrical. A female screw portion 133 is formed in a part of the inner circular portion of the sonotrode 131. The female screw portion 133 is screwed into a male screw portion 161 formed in a fastening member 160 described later. The sonotrode 131 has a shape that focuses ultrasonic waves. For example, the end surface of the sonotrode 131 on the subject's eye side has a spherical shape that focuses on the sound axis L1. The sonotrode 131 may also be a cylinder having a non-uniform thickness. For example, the sonotrode 131 may have a shape in which the outer diameter and the inner diameter change in the longitudinal direction of the cylinder.

[0030] The back mass 132 is a mass member disposed behind the ultrasonic element 110. The back mass 132, together with the sonotrode 131, sandwiches the ultrasonic element 110. The back mass 132 is, for example, cylindrical. A female thread portion 134 is formed in a part of an inner circular portion of the back mass 132. The female thread portion 134 screws into a male thread portion 161 of a fastening member 160, which will be described later. The back mass 132 also includes a flange portion 135. The flange portion 135 is held by an attachment portion 400.

[0031] The fastening member 160 fastens, for example, the mass member 130 and the ultrasonic element 110 sandwiched between the mass member 130. The fastening member 160 is, for example, a hollow bolt. The fastening member 160 is, for example, cylindrical, and has a male thread portion 161 on its outer circular portion. The male thread portion 161 of the fastening member 160 screws into the female thread portions 133, 134 formed on the inside of the sonotrode 131 and the back mass 132. The sonotrode 131 and the back mass 132 are fastened by the fastening member 160 in a direction in which they attract each other. As a result, the ultrasonic element 110 sandwiched between the sonotrode 131 and the back mass 132 is fastened, and pressure is applied.

[0032] The irradiation unit 100 may include an insulating member 170. The insulating member 170 prevents, for example, the electrode 120 or the ultrasonic element 110 from contacting the fastening member 160. The insulating member 170 is disposed, for example, between the electrode 120 and the fastening member 160. The insulating member 170 is, for example, sleeve-shaped.

[0033] <Optical system> The optical system 200 performs, for example, observation or measurement of the subject's eye (see FIG. 2). The optical system 200 includes, for example, an objective system 210, an observation system 220, a fixation target projection system 230, a deformation detection system 260, a dichroic mirror 201, a beam splitter 204, and the like.

[0034] The objective system 210 is, for example, an optical system for taking in light from outside the housing 3 to the optical system 200 or for irradiating light from the optical system 200 to the outside of the housing 3. The objective system 210 includes, for example, optical elements. The objective system 210 may include optical elements such as an objective lens, a relay lens, etc.

[0035] The illumination system 240 illuminates the subject's eye. The illumination system 240 illuminates the subject's eye with, for example, infrared light. The illumination system 240 includes, for example, an illumination light source 241. The illumination light source 241 is disposed, for example, diagonally in front of the subject's eye. The illumination light source 241 emits, for example, infrared light. The illumination system 240 may include a plurality of illumination light sources 241.

[0036] The observation system 220, for example, takes an observation image of the subject's eye. The observation system 220, for example, takes an image of the anterior part of the subject's eye. The observation system 220 includes, for example, a light receiving lens 221, a light receiving element 222, and the like. The observation system 220 receives, for example, light from the illumination light source 241 reflected by the subject's eye. The observation system 220 receives, for example, a reflected light beam from the subject's eye centered on the optical axis O1. For example, the reflected light from the subject's eye passes through the opening 101 of the irradiation unit 100, and is received by the light receiving element 222 via the objective system 210 and the light receiving lens 221. The corneal reflection bright point of the illumination light source 241 received by the light receiving element 222 is used, for example, for alignment in the up, down, left, and right directions (XY alignment). In this case, for example, the illumination system 240 and the observation system 220 function as an XY alignment detection means. Of course, an index projection system that projects an index for XY alignment from the optical axis O1 onto the subject's eye may be provided in addition to the illumination system 240. In this case, since the corneal central bright spot appears in the observation image of the observation system 220, XY alignment may be performed based on this corneal central bright spot.

[0037] The fixation target projection system 230 projects a fixation target on the subject's eye, for example. The fixation target projection system 230 includes, for example, a target light source 231, an aperture 232, a projection lens 233, an aperture 234, and the like. Light from the target light source 231 passes through the aperture 232, the projection lens 233, the aperture 232, and the like along an optical axis O2, and is reflected by the dichroic mirror 201. The dichroic mirror 201, for example, makes the optical axis O2 of the fixation target projection system 230 coaxial with the optical axis O1. The light from the target light source 231 reflected by the dichroic mirror 201 passes through the objective system 210 along the optical axis O1, and is irradiated onto the subject's eye. The subject fixates the target of the fixation target projection system 230, and the subject's line of sight is stabilized.

[0038] The deformation detection system 260 detects, for example, deformation of the cornea of ​​the subject's eye. The deformation detection system 260 includes, for example, a light source 261, a projector lens 262, an aperture 263, a light receiving lens 264, an aperture 265, a light receiving element 266, and the like. Light from the light source 261 passes through the projector lens 262 and the aperture 263 along the optical axis O3, for example, and is irradiated onto the subject's eye. Then, the reflected light reflected by the subject's eye is reflected by the beam splitter 204 along the optical axis O4, passes through the light receiving lens 264 and the aperture 265, and is received by the light receiving element 266. The deformation detection system 260 may detect deformation of the cornea based on, for example, the corneal reflected light received by the light receiving element 266.

[0039] The deformation detection system 260 may detect the deformation state of the cornea based on, for example, the magnitude of the light receiving signal of the light receiving element 266. For example, the deformation detection system 260 may detect that the cornea has entered an applanation state when the amount of light received by the light receiving element 266 becomes maximum. In this case, for example, the deformation detection system 260 is set so that the amount of light received becomes maximum when the cornea of ​​the subject's eye enters an applanation state.

[0040] The deformation detection system 260 may be an anterior segment cross-sectional image capturing unit such as an OCT or Scheimpflug camera, etc. For example, the deformation detection system 260 may detect the amount or speed of deformation of the cornea.

[0041] The Z alignment detection system 280 detects, for example, an alignment state in the Z direction. The Z alignment detection system 280 includes, for example, a light receiving lens 281 and a light receiving element 282. The Z alignment detection system 280 may detect the alignment state in the Z direction, for example, by detecting reflected light from the cornea. For example, the Z alignment detection system may receive reflected light of light from the light source 261 reflected by the cornea of ​​the subject's eye. In this case, the Z alignment detection system 280 may receive, for example, a bright spot formed by the light from the light source 261 being reflected by the cornea of ​​the subject's eye. In this way, the light source 261 may also be used as a light source for Z alignment detection.

[0042] For example, light from the light source 261 reflected by the cornea passes through the beam splitter 204 and the light receiving lens 281 along the optical axis O4, and is received by the light receiving element 282. When the subject's eye and the Z alignment detection system 280 are shifted in the Z direction, the receiving position of the light from the light source 261 reflected by the cornea (for example, the position where the intensity of the received light signal is maximum) shifts on the light receiving element 282. Therefore, the Z alignment detection system 280 may detect the alignment state based on the receiving position of the light from the light source 261 on the light receiving element 282. For example, the Z alignment detection system 280 may detect the alignment state by detecting whether the receiving position of the light from the light source 261 is a predetermined pixel (detection reference position) of the light receiving element 282, or by how many pixels it is shifted from the predetermined pixel.

[0043] <Control Unit> Next, the configuration of the control system will be described with reference to FIG. 4. The control unit 70, for example, controls the entire device and performs arithmetic processing of measured values. The control unit 70 is realized, for example, by a general CPU (Central Processing Unit) 71, a ROM 72, a RAM 73, and the like. The ROM 72 stores various programs for controlling the operation of the ultrasonic tonometer 1, initial values, and the like. The RAM 73 temporarily stores various information. The control unit 70 may be configured by one control unit or multiple control units (i.e., multiple processors). The control unit 70 may be connected to, for example, the drive unit 5, the storage unit 74, the display unit 75, the operation unit 76, the irradiation unit 100, the optical system 200, and the like.

[0044] The storage unit 74 is a non-transient storage medium that can retain stored contents even if the power supply is cut off. For example, a hard disk drive, a flash ROM, a removable USB memory, etc. can be used as the storage unit 74.

[0045] The display unit 75 displays, for example, the measurement results of the subject's eye. The display unit 75 may have a touch panel function.

[0046] The operation unit 76 accepts various operation instructions from the examiner. The operation unit 76 outputs an operation signal according to the input operation instruction to the control unit 70. For the operation unit 76, at least one user interface such as a touch panel, a mouse, a joystick, a keyboard, etc. may be used. When the display unit 75 is a touch panel, the display unit 75 may function as the operation unit 76.

[0047] <Control action> The control operation when measuring intraocular pressure in the ultrasonic tonometer having the above-mentioned configuration will be described with reference to FIG.

[0048] (Step S1: Alignment) First, the control unit 70 performs alignment with respect to the eyes of the subject whose face is supported by the face support unit 4. Fig. 6 shows an example of an anterior eye image 300 captured by the observation system 220. In the example of Fig. 6(a), the alignment is incomplete. The acquired anterior eye image 300 includes, for example, corneal reflection bright points 311, 312, 313, and 314 caused by the light of the illumination light source 241.

[0049] A cross mark 310 indicates the corneal apex position of the subject's eye calculated from the reflected bright point of the illumination light source 241. A cross mark 320 is the optical system center (optical axis O1) of the observation system 220. A cross mark 330 indicates the sound pressure center (sound axis L1) of the ultrasound output by the irradiation unit 100.

[0050] A typical alignment operation is to align the corneal apex position of the subject's eye with the optical axis O1 of the observation system 220, that is, to align the position of the cross mark 310 with the position of the cross mark 320. There is a positional deviation between the cross marks 320 and 330, but this is due to the characteristic variation and assembly error of the ultrasonic element 110 of the irradiation unit 100, and the positional relationship varies from device to device. This deviation can be reduced by using a complex adjustment mechanism or by aligning the characteristics of the ultrasonic element 110, but it is difficult to completely eliminate the amount of deviation.

[0051] Therefore, in this embodiment, the amount of deviation between the optical axis O1 (cross mark 320) and the acoustic axis L1 (cross mark 330) is stored in advance, and when intraocular pressure measurement is performed, alignment is performed so that the corneal apex coincides with the acoustic axis L1. For example, the control unit 70 detects bright points 311, 312, 313, and 314 from the anterior eye image acquired by the light receiving element 222, and obtains the coordinates of the center of the coordinates of the four points as the corneal apex position. Then, the control unit 70 obtains the position of the acoustic axis L1 based on the position of the optical axis O1 and the amount of deviation stored in the memory unit 74, and drives the drive unit 5 so that the corneal apex position and the acoustic axis L1 position coincide. Of course, the control unit 70 may display the cross mark 310 and the cross mark 330 on the display unit 75, and guide the examiner to operate the operation unit 76 or the like to perform manual alignment. FIG. 6(b) shows an anterior eye image when the corneal apex position (cross mark 310) and the acoustic axis L1 (cross mark 330) coincide.

[0052] The amount of deviation between the optical axis O1 and the acoustic axis L1 may be experimentally determined, for example, during calibration of the device, and stored in the storage unit 74. For example, measurements may be performed while shifting the position of the device by the drive unit 5 from a state in which the corneal apex position is aligned with the optical axis O1, and the position at which the amount of light received by the deformation detection system 260 is maximum may be regarded as the position of the acoustic axis L1, and the amount of deviation from the optical axis O1 at that time may be stored. Alternatively, the position at which the sound pressure is maximum may be measured by a microphone, and the amount of deviation from the optical axis O1 may be determined.

[0053] Incidentally, when the sound axis L1 is aligned with the corneal apex, there is a possibility that the optical axes O3, O4 of the deformation detection system 260 may deviate from the corneal apex. However, even if the optical axes O3, O4 of the deformation detection system 260 are deviated to some extent from the corneal apex, the deformation of the cornea can be detected as long as they are within the region where the cornea deforms into a specified shape.

[0054] (Step S2: Ultrasonic irradiation) The control unit 70 generates ultrasonic waves by applying a voltage to the ultrasonic element 110. The ultrasonic waves output from the irradiation unit 100 are irradiated to the subject's eye, and the cornea of ​​the subject's eye is deformed by the acoustic radiation pressure of the ultrasonic waves.

[0055] (Step S3: Deformation detection) The control unit 70 detects the deformation state of the cornea by the deformation detection system 260. For example, the control unit 70 detects that the cornea has been deformed into a predetermined shape (applanation or flattening) based on a light receiving signal of the light receiving element 266.

[0056] (Step S4: Calculate intraocular pressure) The control unit 70 calculates the intraocular pressure of the subject's eye based on, for example, the acoustic radiation pressure (or sound pressure) when the cornea of ​​the subject's eye is deformed into a predetermined shape. The acoustic radiation pressure (or sound pressure) applied to the subject's eye is correlated with the ultrasonic irradiation time, and increases as the ultrasonic irradiation time becomes longer. Therefore, the control unit 70 determines the acoustic radiation pressure (or sound pressure) when the cornea is deformed into a predetermined shape based on the ultrasonic irradiation time. The relationship between the acoustic radiation pressure (or sound pressure) when the cornea is deformed into a predetermined shape and the intraocular pressure of the subject's eye is obtained in advance by experiments or the like, and is stored in the memory unit 74 or the like. The control unit 70 determines the intraocular pressure of the subject's eye based on the acoustic radiation pressure (or sound pressure) when the cornea is deformed into a predetermined shape and the relationship stored in the memory unit 74.

[0057] Of course, the method of calculating the intraocular pressure is not limited to the above, and various methods may be used. For example, the control unit 70 may obtain the amount of deformation of the cornea by the deformation detection system 260, and obtain the intraocular pressure by multiplying the amount of deformation by a conversion coefficient.

[0058] The control unit 70 may measure the intraocular pressure based on the ultrasonic waves reflected by the subject's eye. For example, the control unit 70 may measure the intraocular pressure based on a change in the characteristics of the ultrasonic waves reflected by the subject's eye, or may obtain the amount of deformation of the cornea from the ultrasonic waves reflected by the subject's eye and measure the intraocular pressure based on the amount of deformation.

[0059] As described above, by aligning the corneal vertex position to the acoustic axis L1 based on the deviation between the optical axis O1 and the acoustic axis L1, it is possible to properly irradiate the examinee's eye with ultrasonic waves. This allows the examinee's eye to be measured with the eye sufficiently deformed. In addition, by providing a complex adjustment mechanism to reduce the deviation between the optical axis O1 and the acoustic axis L1 and aligning the characteristics of the ultrasonic elements, it is possible to prevent the device from becoming large or expensive.

[0060] The ultrasonic tonometer 1 may include a measurement optical system for measuring eye characteristics other than intraocular pressure. For example, the ultrasonic tonometer 1 may include a measurement optical system for determining a corneal curvature radius, or a measurement optical system for measuring an eye refractive power. For example, as shown by a dotted line in FIG. 2, the measurement optical system 500 may share the optical axis O1 of the observation system 220 by the beam splitter 202. In this case, when measuring eye characteristics other than intraocular pressure by the measurement optical system 500, the eye characteristics can be measured with high accuracy by performing alignment so that the corneal apex (cross mark 310) coincides with the optical axis O1 (cross mark 320) as shown in FIG. 6(c). In this way, the alignment control may be switched between alignment based on the acoustic axis L1 or alignment based on the optical axis O1 for intraocular pressure measurement and measurement of other eye characteristics.

[0061] In addition, when the resonance frequency of the irradiation unit 100 changes due to a temperature change or the like, the position of the sound axis L1 of the irradiation unit 100 changes, and the deviation amount between the sound axis L1 and the optical axis O1 may change. For this reason, the control unit 70 may perform alignment based on the deviation amount between the sound axis L1 and the optical axis O1 according to the resonance frequency. In this case, the deviation amount between the sound axis L1 and the optical axis O1 according to the resonance frequency may be experimentally obtained in advance and stored in the storage unit 74.

[0062] <Z alignment taking into account focal position shift> Next, Z alignment considering the shift in the focal position of the irradiation unit 100 due to high sound pressure will be described. The focal position of the ultrasound emitted by the irradiation unit 100 shifts farther away when the sound pressure increases. In other words, the focal length of the irradiation unit 100 increases. Therefore, the control unit 70 may perform Z alignment considering the shift in the focal position in the alignment of step S1.

[0063] FIG. 7(a) is a diagram showing the relationship between the Z alignment detection system 280 and the maximum position of the acoustic radiation pressure. As shown in FIG. 7(a), the Z alignment proper position P1 detected by the Z alignment detection system 280 is set farther away than the geometric (shape) focal position F1 of the irradiation unit 100, taking into consideration the focal position shift caused by the high sound pressure. For example, the focal position F1 is the center of the curvature radius of the subject side end face of the irradiation unit 100. The Z alignment proper position P1 is preferably set to the maximum position (focal position after shift) F2 of the acoustic radiation pressure. For example, the control unit 70 controls the drive unit 5 based on the alignment information acquired by the Z alignment detection system 280 so that the position of the subject's eye is aligned with the Z alignment proper position P1 set farther away than the focal position F1.

[0064] As described above, the ultrasonic tonometer 1 of this embodiment can properly irradiate the test eye with ultrasound even if the focal position shifts due to increased sound pressure by aligning the test eye to the proper Z alignment position that is set farther away than the geometric focal position of the irradiation unit 100.

[0065] 7(b) is a diagram showing the relationship between the deformation detection system 260 and the maximum position of the acoustic radiation pressure. As shown in FIG. 7(b), the (intersection of) optical axes O3, O4 of the light projecting and receiving systems of the deformation detection system 260 may be located at a position P2 farther away than the Z alignment proper position P1 or the maximum acoustic radiation pressure position F2 so that the sensitivity of the deformation detection system 260 becomes maximum when the cornea is in a predetermined deformation state (for example, an applanation state).

[0066] In addition, when the light projection system is common to the Z alignment detection system 280 and the deformation detection system 260 as in the above embodiment, the optical axis O3 of the light projection system may be aligned with the Z alignment detection system 280 as shown in FIG. 7(a), or may be aligned with the deformation detection system 260 as shown in FIG. 7(b).

[0067] In the above embodiment, the deformation detection system 260 and the Z alignment detection system 280 are disposed at an angle, but they may be disposed on the front as long as they can detect the alignment state or the deformation state of the cornea. For example, the deformation detection system 260 or the Z alignment detection system 280 may be disposed on the optical axis O1 or on an optical axis branched from the optical axis O1.

[0068] The control unit 70 may change the Z alignment proper position detected by the Z alignment detection system 280 according to the magnitude of the acoustic radiation pressure (or sound pressure). Since the acoustic radiation pressure changes depending on the magnitude of the voltage applied to the ultrasonic element 110 or the application time, these parameters and the corresponding Z alignment proper position may be stored in the storage unit 74 or the like. The control unit 70 may change the Z alignment proper position according to the acoustic radiation pressure by reading out the Z alignment proper position corresponding to the magnitude or application time of the applied voltage from the storage unit 74 and setting it. Of course, the examiner may be allowed to manually adjust the setting of the Z alignment proper position according to the acoustic radiation pressure.

[0069] When the resonance frequency of the irradiating unit 100 changes due to a temperature change or the like, the focal position of the irradiating unit 100 may change, and the maximum acoustic radiation pressure position may change. For this reason, the control unit 70 may perform alignment based on a Z alignment proper position according to the resonance frequency. In this case, the Z alignment proper position according to the resonance frequency may be experimentally obtained in advance and stored in the storage unit 74.

[0070] Although the method of detecting the working distance uses an optical sensor, other sensors such as an ultrasonic sensor may also be used.

[0071] In the above embodiment, an example in which a Langevin transducer is used as the irradiation unit 100 has been described, but the present invention is not limited thereto. The irradiation unit 100 may be configured to generate ultrasonic waves by another method. For example, the irradiation unit 100 may be a parametric speaker in which a plurality of ultrasonic elements are arranged. The parametric speaker may focus ultrasonic waves by, for example, arranging a plurality of ultrasonic elements on a spherical surface that is focused on the surface of the subject's eye. [Explanation of symbols]

[0072] 1. Ultrasonic tonometer 2 Base 3. Chassis 4 Face support 5 Drive unit 6 supporting base 100 Irradiation unit 200 Optical system

Claims

1. An ultrasonic tonometer for measuring intraocular pressure of a subject's eye using ultrasound, an irradiation means for irradiating the subject's eye with focused ultrasound; a Z alignment detection means for detecting an alignment state in a working distance direction with respect to the subject's eye; 2. An ultrasonic tonometer comprising: a Z-alignment proper position detected by the Z-alignment detection means, the Z-alignment proper position being set farther away than a geometric focal position of the irradiation means.

2. a deformation detection means for detecting a deformation state of the cornea of ​​the subject's eye, 2. The ultrasonic tonometer according to claim 1, wherein the detection position of the deformation detection means is set farther away than the proper Z-alignment position.

3. Further comprising a control means for controlling the Z alignment detection means, 3. The ultrasonic tonometer according to claim 1, wherein the control means changes the Z alignment proper position in accordance with the magnitude of an acoustic radiation pressure or a sound pressure.

4. Further comprising a control means for controlling the Z alignment detection means, 3. The ultrasonic tonometer according to claim 1, wherein the control means changes the Z alignment proper position in accordance with a resonance frequency of the irradiation means.

5. 1. An ultrasonic tonometer control program for use in an ultrasonic tonometer that measures intraocular pressure in a subject's eye using ultrasonic waves, comprising: a Z alignment detection step of detecting an alignment state in a working distance direction with respect to the subject's eye; a setting step of setting the Z alignment proper position detected in the Z alignment detection step to a position farther than a geometric focal position of an irradiation means that irradiates the subject's eye with focused ultrasound; The ultrasonic tonometer control program is characterized by causing the ultrasonic tonometer to execute the above-mentioned.

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