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 ultrasonic waves; detection means which includes an imaging optical system for imaging the anterior eye part of the subject eye and detects an alignment state relative to the subject eye based on the image of the anterior eye part acquired with the imaging optical system; and control means which on the basis of the deviation between an optical axis of the imaging optical system and a sound axis of the irradiation means, corrects alignment information acquired by the detection means.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to an ultrasonic tonometer that measures the intraocular pressure of an eye to be examined using ultrasonic waves, and an ultrasonic tonometer control program.

Background Art

[0002] As a non-contact tonometer, an air-jet tonometer is common. The air-jet tonometer converts the air pressure in a predetermined deformed state into the intraocular pressure by detecting the flattened state of the cornea when air is jetted onto the cornea and the air pressure jetted onto the cornea.

[0003] Further, as a non-contact tonometer, an ultrasonic tonometer that measures the intraocular pressure using ultrasonic waves has been proposed (see Patent Document 1). The ultrasonic tonometer of Patent Document 1 converts the radiation pressure in a predetermined deformed state into the intraocular pressure by detecting the flattened state of the cornea when ultrasonic waves are radiated onto the cornea and the radiation pressure jetted onto the cornea.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the ultrasonic tonometer as described above, due to variations in the characteristics of the ultrasonic element or assembly errors, etc., the optical axis of the optical system for alignment detection and the acoustic axis of the ultrasonic irradiation unit may be misaligned. In such a case, even when the alignment with respect to the eye to be examined is optically correct, the focusing position of the ultrasonic waves is shifted, and the ultrasonic waves cannot be properly irradiated onto the eye to be examined.

[0007] In view of the conventional problems, an object of the present disclosure is to provide an ultrasonic tonometer capable of properly irradiating ultrasonic waves onto an eye to be examined, and an ultrasonic tonometer control program.

Means for Solving the Problems

[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 an eye to be examined using ultrasonic waves, comprising irradiation means for irradiating ultrasonic waves onto the eye to be examined, a photographing optical system for photographing the anterior segment of the eye to be examined, alignment detection means for detecting the alignment state with respect to the eye to be examined based on the anterior segment image acquired by the photographing optical system, and control means for correcting the alignment information acquired by the alignment detection means based on the deviation amount between the optical axis of the photographing optical system and the acoustic axis of the irradiation means. , the control means corrects the alignment information based on the amount of deviation according to the change in the resonance frequency of the irradiation means It is characterized by this. (2) An ultrasonic tonometer control program used in an ultrasonic tonometer for measuring the intraocular pressure of an eye to be examined using ultrasonic waves, which, when executed by the control means of the ultrasonic tonometer, includes an alignment detection step for detecting the alignment state with respect to the eye to be examined based on the anterior segment image acquired by the photographing optical system for photographing the anterior segment of the eye to be examined, and the optical axis of the photographing optical system and irradiate the eye to be examined with ultrasonic waves the acoustic axis of the irradiation means , according to the change in the resonance frequency of the irradiation means Based on the deviation amount, a correction step for correcting the alignment information acquired in the alignment detection step, and causing the ultrasonic tonometer to execute the correction step. It is characterized by this.

Brief Description of the Drawings

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

Mode for Carrying Out the Invention

[0011] <First Embodiment> The 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 eye to be examined 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 the eye to be examined with ultrasonic waves, for example. The alignment detection unit has an imaging optical system (for example, observation system 220) that photographs the anterior eye segment of the eye to be examined, and detects the alignment state with respect to the eye to be examined based on the anterior eye 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 deviation amount (for example, the deviation amount in the vertical and horizontal 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. As a result, the ultrasonic tonometer of the first embodiment can irradiate the eye to be examined with ultrasonic waves appropriately.

[0012] Note that the acoustic axis is, for example, the central axis of the ultrasonic waves irradiated by the irradiation unit. The acoustic axis extends, for example, in the propagation direction of the ultrasonic waves or 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 vertical and horizontal directions (XY direction) between the optical axis of the imaging optical system and the focal position of the irradiation unit. Further, the control unit may correct the alignment information based on the amount of deviation (for example, the amount of deviation in the vertical, horizontal, front, and rear directions) 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.

[0013] Note that the ultrasonic tonometer may further include a measurement optical system (for example, the measurement optical system 500) that shares the optical axis with the imaging optical system and measures eye characteristics different from intraocular pressure. In this case, the control unit may switch whether to correct the alignment information between the measurement of the eye characteristics by the measurement optical system and the measurement of the intraocular pressure by the irradiation unit. For example, the control unit may not correct the alignment information when measuring the eye characteristics by the measurement optical system, and may correct the alignment information based on the amount of deviation between the optical axis and the acoustic axis when measuring the intraocular pressure by the irradiation unit. Thereby, ultrasonic waves can be appropriately irradiated during intraocular pressure measurement, and the measurement of eye characteristics by the measurement optical system can also be suitably performed.

[0014] Note that the ultrasonic tonometer may further include a drive unit (for example, the 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 perform alignment of the irradiation unit with respect to the eye to be examined. Thereby, the ultrasonic tonometer can automatically perform appropriate alignment of the irradiation unit with respect to the eye to be examined.

[0015] Note that the control unit may cause the display unit (for example, the display unit 75) to display the corrected alignment information. In this case, the examiner can also manually perform appropriate alignment of the irradiation unit with respect to the eye to be examined by operating the operation unit (for example, the operation unit 76) while checking the alignment information displayed on the display unit.

[0016] Note that 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 acoustic 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 corresponding to the resonance frequency of the irradiation unit. Thereby, suitable alignment considering the change in the acoustic axis according to the resonance frequency of the irradiation unit can be performed.

[0017] Note that 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 a step of detecting the alignment state with respect to the subject eye based on a front-eye image acquired by an imaging optical system that images the anterior eye part of the subject eye. The correction step is a step of correcting the alignment information acquired in the alignment detection step based on, for example, the amount of deviation between the optical axis of the imaging optical system and the acoustic axis of the irradiation unit.

[0018] <Second Embodiment> The second embodiment according to the present disclosure will be described. The ultrasonic tonometer of the second embodiment (for example, the ultrasonic tonometer 1) includes an irradiation unit (for example, the irradiation unit 100) and a Z alignment detection unit (for example, the Z alignment detection system 280). The irradiation unit irradiates the subject eye with focused ultrasonic waves. The Z alignment detection unit detects the alignment state in the operating distance direction (front-rear direction or Z direction) with respect to the subject eye. In the second embodiment, the Z alignment appropriate position detected by the Z alignment detection unit is set farther in the operating distance direction than the geometric (shape) focal position of the irradiation unit. Thereby, the ultrasonic tonometer of the second embodiment performs alignment considering the focal position shift of the irradiation unit accompanying the increase in the high sound pressure, and can irradiate the subject eye with ultrasonic waves appropriately.

[0019] Note that the proper position of the Z alignment may be set according to the arrangement relationship between 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 at a predetermined distance from the focal position of the Z alignment detection system.

[0020] Note that the ultrasonic tonometer may further include a deformation detection unit (for example, the deformation detection system 260) that detects the deformation state of the cornea of the eye to be examined. In this case, the detection position of the deformation detection unit may be set farther away than the proper position of the Z alignment. As a result, when the cornea of the eye to be examined is pushed in, the detection sensitivity of the deformation detection unit increases, so that it becomes easier to detect that the cornea is deformed into a predetermined shape.

[0021] Note that a control unit (for example, the control unit 70) for controlling the Z alignment detection unit may be further provided. The control unit may change the proper position of the Z alignment according to the magnitude of the acoustic radiation pressure or the sound pressure. Further, the control unit may change the proper position of the Z alignment according to the resonance frequency of the irradiation unit. In this way, the control unit can perform a suitable alignment corresponding to the change in the focal position of the ultrasonic wave that changes due to the output of the irradiation unit by changing the proper position of the Z alignment according to the output of the irradiation unit.

[0022] Note that 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 the alignment state in the operating distance direction with respect to the eye to be examined. The setting step is a setting step of setting the proper position of the Z alignment detected in the Z alignment detection step farther away than the geometric focal position of the irradiation unit that irradiates focused ultrasonic waves on the eye to be examined.

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

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

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

[0026] <Irradiation portion> The irradiation unit 100 irradiates the eye to be examined E with, for example, ultrasonic waves. For example, the irradiation unit 100 irradiates the cornea with ultrasonic waves to generate an acoustic radiation pressure on the cornea. The acoustic radiation pressure is, for example, a force acting in the direction in which the sound wave travels. The ultrasonic tonometer 1 of the present embodiment deforms the cornea by utilizing, for example, this acoustic radiation pressure. Note that the irradiation unit 100 of the present embodiment is cylindrical, and the optical axis O1 of the optical system 200 described later is arranged in the central opening 101. The opening 101 is opened, for example, in the acoustic axis direction. The acoustic axis L1 is, for example, the central axis of the ultrasonic waves irradiated by the irradiation unit 100. The acoustic axis L1 is an axis extending in the traveling direction of the ultrasonic waves, the vibration direction of the irradiation unit 100, or the like. The acoustic axis L1 passes through the focal position where the ultrasonic waves output by the irradiation unit 100 are focused. In the present embodiment, the optical axis O1 of the optical system 200 and the acoustic axis L1 of the irradiation unit 100 are substantially coaxial.

[0027] FIG. 3(a) is a cross-sectional view showing a schematic configuration of the irradiation unit 100, and FIG. 3(b) shows an enlarged view of the range A1 shown in FIG. 3(a). The irradiation unit 100 of the present embodiment is a so-called Langevin type vibrator. The irradiation unit 100 includes, for example, an ultrasonic element 110, electrodes 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, a piezoelectric ceramic) or a magnetostrictive element. The ultrasonic element 110 of the present embodiment is ring-shaped. For example, the ultrasonic element 110 may be formed by laminating a plurality of piezoelectric elements. In the present embodiment, two laminated piezoelectric elements (for example, piezoelectric element 111 and piezoelectric element 112) are used as the ultrasonic element 110. For example, electrodes 120 (electrode 121, electrode 122) are connected to the two piezoelectric elements, respectively. The electrodes 121 and 122 of the present embodiment are, for example, ring-shaped.

[0028] The mass member 130 sandwiches, for example, the ultrasonic element 110. By sandwiching the ultrasonic element 110, the mass member 130, for example, strengthens the tensile strength of the ultrasonic element 110 so that it can withstand strong vibrations. As a result, high-output ultrasonic waves can be generated. The mass member 130 may be, for example, a metal block. For example, the mass member 130 includes a sonotrode (also referred to as 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 side of the eye to be examined). The sonotrode 131 propagates the 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 partially formed in the inner circular portion of the sonotrode 131. The female screw portion 133 engages with a male screw portion 161 formed on a fastening member 160 described later. Note that the sonotrode 131 has a shape that focuses ultrasonic waves. For example, the end face of the sonotrode 131 on the side of the eye to be examined has a spherical shape that forms a focal point on the acoustic axis L1. Also, the sonotrode 131 may 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 sandwiches the ultrasonic element 110 together with the sonotrode 131. The back mass 132 is, for example, cylindrical. A female screw portion 134 is partially formed in the inner circular portion of the back mass 132. The female screw portion 134 engages with the male screw portion 161 of the fastening member 160 described later. Also, the back mass 132 includes a flange portion 135. The flange portion 135 is held by the mounting portion 400.

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

[0032] Note that 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 clamping member 160. The insulating member 170 is disposed, for example, between the electrode 120 and the clamping 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 eye to be examined (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, etc.

[0034] The objective system 210 is, for example, an optical system for taking in light from outside the housing 3 into the optical system 200 or irradiating light from the optical system 200 outside 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 and a relay lens.

[0035] The illumination system 240 illuminates the eye to be examined. The illumination system 240 illuminates, for example, the eye to be examined with infrared light. The illumination system 240 includes, for example, an illumination light source 241. The illumination light source 241 is disposed, for example, obliquely in front of the eye to be examined. 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 captures, for example, an observation image of the eye to be examined. The observation system 220 captures, for example, an anterior segment image of the eye to be examined. The observation system 220 includes, for example, a light receiving lens 221, a light receiving element 222, etc. The observation system 220 receives, for example, the light from the illumination light source 241 reflected by the eye to be examined. The observation system 220 receives, for example, the reflected light beam from the eye to be examined centered on the optical axis O1. For example, the reflected light from the eye to be examined 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 spot of the illumination light source 241 received by the light receiving element 222 is used, for example, for alignment in the vertical and horizontal directions (XY alignment). In this case, for example, the illumination system 240 and the observation system 220 function as XY alignment detection means. Of course, separately from the illumination system 240, an indicator projection system that projects an indicator for XY alignment from the optical axis O1 onto the eye to be examined may be provided. In this case, since the corneal center bright spot appears in the observation image of the observation system 220, XY alignment may be performed based on this corneal center bright spot.

[0037] The fixation target projection system 230 projects a fixation target onto the eye to be examined, 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, etc. The light from the target light source 231 passes along the optical axis O2 through the aperture 232, the projection lens 233, the aperture 232, etc. and is reflected by the dichroic mirror 201. The dichroic mirror 201 makes the optical axis O2 of the fixation target projection system 230 coaxial with the optical axis O1, for example. 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 irradiates the eye to be examined. When the fixation target of the fixation target projection system 230 is fixated by the subject, the subject's line of sight is stabilized.

[0038] The deformation detection system 260 detects, for example, the deformation of the cornea of the eye to be examined. The deformation detection system 260 includes, for example, a light source 261, a projection lens 262, a diaphragm 263, a light receiving lens 264, a diaphragm 265, a light receiving element 266, and the like. The light from the light source 261 passes through the projection lens 262 and the diaphragm 263 along the optical axis O3, for example, and irradiates the eye to be examined. Then, the reflected light reflected by the eye to be examined is reflected by the beam splitter 204 along the optical axis O4, and then passes through the light receiving lens 264 and the diaphragm 265 and is received by the light receiving element 266. The deformation detection system 260 may detect the 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 deformed state of the cornea based on, for example, the magnitude of the light reception signal of the light receiving element 266. For example, the deformation detection system 260 may detect that the cornea is in a flattened state when the amount of light received by the light receiving element 266 is maximum. In this case, for example, the deformation detection system 260 is set such that the amount of light received is maximum when the cornea of the eye to be examined is in a flattened state.

[0040] Note that the deformation detection system 260 may be an anterior eye segment imaging unit such as an OCT or a Scheimpflug camera. For example, the deformation detection system 260 may detect the amount of deformation or the deformation speed of the cornea.

[0041] The Z alignment detection system 280 detects, for example, the 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 by detecting, for example, the reflected light from the cornea. For example, the Z alignment detection system may receive the reflected light of the light from the light source 261 reflected by the cornea of the eye to be examined. In this case, the Z alignment detection system 280 may receive, for example, the bright spot formed by the reflection of the light from the light source 261 by the cornea of the eye to be examined. Thus, the light source 261 may also be used as a light source for Z alignment detection.

[0042] For example, the 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 eye to be examined and the Z alignment detection system 280 are displaced in the Z direction, the light receiving position of the light from the light source 261 reflected by the cornea (for example, the position where the intensity of the light receiving signal is maximum) is displaced on the light receiving element 282. Therefore, the Z alignment detection system 280 may detect the alignment state based on the light 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 light receiving position of the light from the light source 261 is at a predetermined pixel (detection reference position) of the light receiving element 282, or by detecting how many pixels it is displaced 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 performs, for example, overall control of the apparatus, arithmetic processing of measurement values, and the like. The control unit 70 is realized by, for example, a general-purpose CPU (Central Processing Unit) 71, a ROM 72, a RAM 73, and the like. The ROM 72 stores various programs, initial values, and the like for controlling the operation of the ultrasonic tonometer 1. The RAM 73 temporarily stores various information. Note that the control unit 70 may be constituted by one control unit or a plurality of control units (that is, a plurality of 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-transitory storage medium that can retain the stored content even when the power supply is cut off. For example, a hard disk drive, a flash ROM, a removable USB memory, or the like can be used as the storage unit 74.

[0045] The display unit 75 displays, for example, the measurement results of the eye to be examined. The display unit 75 may have a touch panel function.

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

[0047] <Control operation> The control operation when measuring intraocular pressure in the ultrasonic tonometer having the above configuration will be described based on FIG. 5.

[0048] (Step S1: Alignment) First, the control unit 70 performs alignment on the eye of the subject whose face is supported by the face support unit 4. FIG. 6 is an example of an anterior eye segment image 300 taken by the observation system 220. In the example of FIG. 6(a), the alignment is in an incomplete state. The acquired anterior eye segment image 300 includes, for example, corneal reflection bright spots 311, 312, 313, 314 due to the light of the illumination light source 241.

[0049] The cross mark 310 indicates the corneal apex position of the eye to be examined calculated from the reflection bright spots of the illumination light source 241. The cross mark 320 is the optical system center (optical axis O1) of the observation system 220. The cross mark 330 indicates the sound pressure center (sound axis L1) of the ultrasonic wave output by the irradiation unit 100.

[0050] A general alignment operation is to align the corneal apex position of the eye to be examined 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 deviation in the positions between the cross mark 320 and the cross mark 330, which is caused by the characteristic variations and assembly errors of the ultrasonic element 110 of the irradiation unit 100, and the positional relationship varies for each device. Although this deviation can be reduced by a complex adjustment mechanism or by making the characteristics of the ultrasonic element 110 uniform, it is difficult to completely eliminate the deviation amount.

[0051] Therefore, in this embodiment, the deviation amount between the optical axis O1 (cross mark 320) and the acoustic axis L1 (cross mark 330) is stored in advance. When performing intraocular pressure measurement, alignment is performed so that the corneal apex coincides with the acoustic axis L1. For example, the control unit 70 detects the bright spots 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, based on the position of the optical axis O1 and the deviation amount stored in the storage unit 74, the position of the acoustic axis L1 is obtained, and the drive unit 5 is driven so that the corneal apex position and the position of the acoustic axis L1 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 manually perform alignment by operating the operation unit 76 or the like. 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] Note that the deviation amount between the optical axis O1 and the acoustic axis L1 is experimentally obtained, for example, during calibration of the device, and stored in the storage unit 74. For example, measurement may be performed while shifting the position of the device by the drive unit 5 from a state where the corneal apex position is aligned with the optical axis O1, and the position where the light reception amount of the deformation detection system 260 is maximized is set as the position of the acoustic axis L1, and the deviation amount from the optical axis O1 at that time may be stored. Further, the position where the sound pressure is maximized may be measured by a microphone, and the deviation amount from the optical axis O1 may be obtained.

[0053] Note that when the acoustic axis L1 is aligned with the corneal apex, the optical axes O3 and O4 of the deformation detection system 260 may deviate from the corneal apex. However, even if the optical axes O3 and O4 of the deformation detection system 260 deviate from the corneal apex to some extent, if they are within the region where the cornea is deformed into a predetermined shape, the deformation of the cornea can be detected.

[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 onto the eye to be examined, and the cornea of the eye to be examined is deformed by the acoustic radiation pressure of the ultrasonic waves.

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

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

[0057] Of course, the method for 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] Note that the control unit 70 may measure the intraocular pressure based on the ultrasonic wave reflected by the eye to be examined. For example, the intraocular pressure may be measured based on the change in the characteristics of the ultrasonic wave reflected by the eye to be examined, or the amount of deformation of the cornea may be obtained from the ultrasonic wave reflected by the eye to be examined, and the intraocular pressure may be measured based on the amount of deformation.

[0059] As described above, based on the deviation amount between the optical axis O1 and the acoustic axis L1, by aligning the corneal vertex position to match the acoustic axis L1, ultrasonic waves can be appropriately irradiated onto the eye to be examined. As a result, the intraocular pressure can be measured while the eye to be examined is sufficiently deformed. In addition, it is possible to suppress an increase in the size or cost of the apparatus by providing a complicated adjustment mechanism to reduce the deviation between the optical axis O1 and the acoustic axis L1 or by making the characteristics of the ultrasonic elements uniform.

[0060] Note that the ultrasonic intraocular pressure meter 1 may be provided with a measurement optical system for measuring other eye characteristics than the intraocular pressure. For example, the ultrasonic intraocular pressure meter 1 may be provided with a measurement optical system for obtaining the corneal radius of curvature or a measurement optical system for measuring the refractive power of the eye. For example, as shown by the 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 the intraocular pressure by the measurement optical system 500, as shown in FIG. 6(c), alignment is performed so that the corneal vertex (cross mark 310) coincides with the optical axis O1 (cross mark 320), whereby the eye characteristics can be accurately measured. In this way, for intraocular pressure measurement and measurement of other eye characteristics, alignment control may be switched between alignment based on the acoustic axis L1 or alignment based on the optical axis O1.

[0061] Note that if the resonance frequency of the irradiation unit 100 changes due to a temperature change or the like, the position of the acoustic axis L1 of the irradiation unit 100 may change, and the deviation amount between the acoustic axis L1 and the optical axis O1 may change. Therefore, the control unit 70 may perform alignment based on the deviation amount between the acoustic axis L1 and the optical axis O1 corresponding to the resonance frequency. In this case, the deviation amount between the acoustic axis L1 and the optical axis O1 corresponding to the resonance frequency may be experimentally obtained in advance and stored in the storage unit 74.

[0062] <Z alignment considering focal position shift> Next, Z alignment considering the focal position shift of the irradiation unit 100 due to high sound pressure will be described. The focal position of the ultrasonic wave irradiated by the irradiation unit 100 shifts farther away as the sound pressure increases. That is, the focal length of the irradiation unit 100 increases. Therefore, the control unit 70 may perform Z alignment considering the shift of 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 appropriate Z alignment position P1 detected by the Z alignment detection system 280 is set farther away from the geometric (shape-based) focal position F1 of the irradiation unit 100 in consideration of the focal position shift due to high sound pressure. For example, the focal position F1 is the center of the radius of curvature of the end face on the subject side of the irradiation unit 100. The appropriate Z alignment position P1 is preferably set at the maximum position of the acoustic radiation pressure (the focal position after the shift) F2. 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 test eye matches the appropriate Z alignment position P1 set farther away from the focal position F1.

[0064] As described above, the ultrasonic tonometer 1 of the present embodiment aligns the test eye with the appropriate Z alignment position set farther away from the geometric focal position of the irradiation unit 100, so that even when the focal position shifts due to high sound pressure, the ultrasonic wave can be appropriately irradiated to the test eye.

[0065] Also, FIG. 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 optical axes O3, O4 (the intersection) of the light transmitting and receiving system of the deformation detection system 260 may be arranged at a position P2 farther away from the appropriate Z alignment position P1 or the maximum position F2 of the acoustic radiation pressure so that the sensitivity of the deformation detection system 260 becomes maximum when the cornea is in a predetermined deformed state (for example, flattened state).

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

[0067] In addition, in the above embodiments, the deformation detection system 260 and the Z alignment detection system 280 are arranged obliquely. However, if the alignment state or the deformed state of the cornea can be detected, a front arrangement may be used. For example, the deformation detection system 260 or the Z alignment detection system 280 may be arranged on the optical axis O1 or on an optical axis branched from the optical axis O1.

[0068] In addition, the control unit 70 may change the Z alignment appropriate 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 or application time of the voltage applied to the ultrasonic element 110, these parameters and the corresponding Z alignment appropriate positions may be stored in the storage unit 74 or the like. The control unit 70 may change the Z alignment appropriate position according to the acoustic radiation pressure by reading and setting the Z alignment appropriate position corresponding to the magnitude of the applied voltage or the application time from the storage unit 74. Of course, the examiner may be able to manually adjust the setting of the Z alignment appropriate position according to the acoustic radiation pressure.

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

[0070] In addition, as a method for detecting the operating distance, a method using an optical sensor has been shown, but other sensors such as an ultrasonic sensor may be used.

[0071] In addition, in the above embodiments, an example in which a Langevin type vibrator 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, for example, by arranging a plurality of ultrasonic elements on a spherical surface that forms a focal point on the surface of the eye to be examined.

Explanation of Reference Numerals

[0072] 1 Ultrasonic tonometer 2 Base 3 Housing 4 Face support portion 5 Driving unit 6 Support base 100 Irradiation unit 200 Optical system

Claims

1. An ultrasonic tonometer for measuring the intraocular pressure of an eye to be examined using ultrasonic waves, comprising: irradiation means for irradiating ultrasonic waves onto the eye to be examined; an imaging optical system for imaging the anterior segment of the eye to be examined, and alignment detection means for detecting the alignment state of the eye to be examined based on the anterior segment image obtained by the imaging optical system; control means for correcting the alignment information obtained by the alignment detection means based on the deviation amount between the optical axis of the imaging optical system and the sound axis of the irradiation means; characterized in that the control means corrects the alignment information based on the deviation amount corresponding to the change in the resonance frequency of the irradiation means.

2. further comprising a measurement optical system that shares the optical axis with the imaging optical system and measures eye characteristics different from intraocular pressure, wherein the control means switches whether to correct the alignment information between the measurement of eye characteristics by the measurement optical system and the measurement of intraocular pressure by the irradiation means. The ultrasonic tonometer according to Claim 1.

3. further comprising drive means for moving the irradiation means, wherein the control means controls the drive means based on the corrected alignment information to align the irradiation means with the eye to be examined. The ultrasonic tonometer according to Claim 1 or 2.

4. wherein the control means causes the corrected alignment information to be displayed on a display means. The ultrasonic tonometer according to Claim 1 or 2.

5. An ultrasonic tonometer control program used in an ultrasonic tonometer for measuring the intraocular pressure of an eye to be examined using ultrasonic waves, which, when executed by the control means of the ultrasonic tonometer, performs an alignment detection step of detecting the alignment state of the eye to be examined based on the anterior segment image obtained by an imaging optical system for imaging the anterior segment of the eye to be examined; and a correction step of correcting the alignment information obtained in the alignment detection step based on the deviation amount corresponding to the change in the resonance frequency of the irradiation means between the optical axis of the imaging optical system and the sound axis of the irradiation means for irradiating ultrasonic waves onto the eye to be examined. The ultrasonic tonometer control program is characterized in that it causes the ultrasonic tonometer to execute the above steps.

Images