JP7639685B2 - Ultrasound tonometry - Google Patents

Description

The present disclosure relates to an ultrasonic tonometer that uses ultrasound to measure the intraocular pressure of a test eye.

Air-injection tonometers are still the most common type of non-contact tonometer. Air-injection tonometers detect the state of deformation of the cornea when air is injected onto it, and the pressure of the air injected onto the cornea, and convert the air pressure at a given state of deformation into intraocular pressure.

As a non-contact tonometer, an ultrasonic tonometer that uses ultrasound to measure intraocular pressure has been proposed (see Patent Document 1). The ultrasonic tonometer in Patent Document 1 detects the deformation state of the cornea when ultrasound is irradiated onto the cornea and the radiation pressure injected onto the cornea, and converts the radiation pressure in a specified deformation state into intraocular pressure.

Japanese Patent Application Publication No. 5-253190

However, conventional devices have not been able to properly irradiate the cornea of the subject's eye with ultrasound. For example, the device of Patent Document 1 is unable to apply to the subject's eye ultrasound that is strong enough to actually flatten or depress the cornea, and is therefore unable to properly irradiate the subject's eye with ultrasound.

In consideration of the problems inherent in the prior art, the technical objective of this disclosure is to provide an ultrasonic tonometer that can properly irradiate ultrasound to the subject's eye.

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

(1) An ultrasonic tonometer for measuring the intraocular pressure of a test eye using ultrasonic waves, comprising: an ultrasonic actuator for irradiating ultrasonic waves to the test eye; and a control means for applying an amplitude-modulated burst signal to the ultrasonic actuator, wherein the control means modulates the burst signal so that the amplitude gradually increases, thereby changing the rate of increase of the acoustic radiation pressure so that the increase in acoustic radiation pressure becomes gradual, and calculates the intraocular pressure of the test eye based on the acoustic radiation pressure when the cornea of the test eye is deformed into a predetermined shape .

FIG. 1 is an external view of an ultrasonic tonometer. FIG. 2 is a diagram showing the internal configuration of an ultrasonic tonometer. 1A and 1B are diagrams illustrating a structure of an ultrasonic actuator. 1A and 1B are diagrams illustrating a structure of an ultrasonic actuator. FIG. 2 is a diagram illustrating a control system of the ultrasonic tonometer. FIG. 4 is a diagram showing a signal applied to an ultrasonic actuator. FIG. 4 is a diagram showing a signal applied to an ultrasonic actuator. FIG. 13 is a diagram showing a time change in pressure due to ultrasonic waves. FIG. 13 is a diagram showing a time change in pressure due to ultrasonic waves. 6A and 6B are diagrams showing changes over time in the received light signal and acoustic radiation pressure of the deformation detection system.

<Embodiment>
Hereinafter, an embodiment according to the present disclosure will be described. An ultrasonic tonometer (e.g., ultrasonic tonometer 1) of this embodiment measures the intraocular pressure of a test eye using, for example, ultrasonic waves. The ultrasonic tonometer includes, for example, an ultrasonic actuator (e.g., ultrasonic actuator 100) and a control unit (e.g., control unit 70). The ultrasonic actuator irradiates, for example, ultrasonic waves to the test eye. The control unit applies, for example, an amplitude-modulated signal to the ultrasonic actuator. By including such a configuration, the ultrasonic tonometer of this embodiment can properly irradiate ultrasonic waves to the test eye. For example, the test eye can be reliably deformed by applying a gradually increasing pressure to the test eye.

The signal applied to the ultrasonic actuator may be a burst signal. By applying a burst signal, ultrasonic waves can be generated more appropriately.

The control unit may modulate the signal so that the amplitude gradually increases. This allows the increase in pressure generated by the ultrasound to be gradual. For example, the control unit may modulate the signal using a sine wave as the modulating wave.

The ultrasonic actuator may include a Langevin type transducer having an opening (e.g., opening 101). For example, the opening may be opened in a direction parallel to the sound axis of the ultrasonic waves (e.g., sound axis Q1). The opening may also be provided so that the optical axis (e.g., optical axis O1) of an observation optical system (e.g., frontal imaging system 220) for observing the subject's eye passes through it.

The ultrasonic tonometer may include a deformation detection unit (e.g., deformation detection system 260) that detects the deformation state of the cornea. In this case, the control unit may calculate the corneal hysteresis based on the deformation state of the cornea acquired by the deformation detection unit. The control unit may calculate a more accurate intraocular pressure based on the corneal hysteresis. The control unit may also correct the intraocular pressure based on the corneal hysteresis. The ultrasonic tonometer can suitably calculate the corneal hysteresis by sufficiently deforming the cornea with the ultrasonic waves of the Langevin transducer. The control unit may determine whether the cornea has been deformed into a predetermined shape based on the detection result of the deformation detection unit, and calculate the intraocular pressure of the test eye based on the output information of the ultrasonic actuator when the cornea has been deformed into the predetermined shape.

The deformation detection unit may detect the deformation state of the cornea optically or acoustically. For example, the deformation detection unit may detect the deformation state of the cornea by irradiating the cornea of the test eye with measurement light or ultrasound and detecting its reflection.

<Example>
Hereinafter, an embodiment according to the present disclosure will be described. 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. The output information is, for example, the sound pressure, acoustic radiation pressure, irradiation time (e.g., the elapsed time after the trigger signal is input), or frequency of the ultrasonic waves. In addition, 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.

As shown in FIG. 1, the ultrasonic tonometer 1 includes, for example, a base 2, a measurement unit 3, a face support unit 4, a drive unit 5, etc. Inside the measurement unit 3, an ultrasonic actuator 100, an optical unit 200, etc., which will be described later, are arranged. The face support unit 4 supports the face of the subject eye. The face support unit 4 is installed, for example, on the base 2. The drive unit 5 moves the measurement unit 3 relative to the base 2, for example, for alignment. Inside the measurement unit 3, an ultrasonic actuator 100, an optical unit 200, etc., are arranged (see FIG. 2).

<Ultrasonic actuator>
The ultrasonic actuator 100, for example, irradiates ultrasonic waves to the subject's eye E. For example, the ultrasonic actuator 100 irradiates ultrasonic waves to the cornea, generating 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 this embodiment uses, for example, this acoustic radiation pressure to deform the cornea. The ultrasonic actuator 100 of this embodiment is cylindrical, and an optical axis O1 of an optical unit 200, which will be described later, is disposed at a central opening 101.

The ultrasonic actuator 100 of this embodiment is a so-called Langevin type transducer. As shown in FIG. 3, the ultrasonic actuator 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 (e.g., piezoelectric ceramics) or a magnetostrictive element. The ultrasonic element 110 of this embodiment is ring-shaped. For example, the ultrasonic element 110 may be a stack of multiple piezoelectric elements. FIG. 4 is an enlarged view of area A1 in FIG. 3. In this embodiment, as shown in FIG. 4, the ultrasonic element 110 uses two stacked piezoelectric elements (e.g., 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.

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 front mass) 131, a back mass 132, and the like.

The sonotrode 131 is a mass member disposed in front of the ultrasonic element 110 (toward the test eye). The sonotrode 131 propagates and amplifies the ultrasonic waves generated by the ultrasonic element 110. In this embodiment, the sonotrode 131 is hollow cylindrical (hollow columnar). A female thread portion 133 is formed on a portion of the inner circle side of the sonotrode 131. The female thread portion 133 screws into a male thread portion 161 formed on the fastening member 160 described later.

The sonotrode 131 in this embodiment is a hollow cylinder having a non-uniform thickness. For example, the sonotrode 131 has a shape in which the outer diameter and inner diameter change in the direction of the sound axis O1 (longitudinal direction) of the hollow cylinder. For example, as shown in FIG. 3, the sonotrode 131 has an uneven portion 180 including a thick portion 181 and a thin portion 182.

The back mass 132 is a mass member arranged 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 the inner circular portion of the back mass 132. The female thread portion 134 screws into a male thread portion 161 of the fastening member 160 described later. The back mass 132 also has a flange portion 135. The flange portion 135 is held by the mounting portion 400.

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.

The ultrasonic actuator 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.

<Optical unit>
The optical unit 200 performs, for example, observation or measurement of the subject's eye (see FIG. 2 ). The optical unit 200 includes, for example, an objective system 210, a front imaging system 220, a fixation target projection system 230, an index projection system 250, a deformation detection system 260, a corneal thickness measurement system 270, a working distance detection system 280, a cross-sectional imaging system 290, a dichroic mirror 201, a beam splitter 202, a beam splitter 203, and a beam splitter 204.

The objective system 210 is, for example, an optical system for taking in light from outside the measurement unit 3 into the optical unit 200, or for irradiating light from the optical unit 200 to the outside of the measurement unit 3. The objective system 210 includes, for example, an optical element. The objective system 210 may include an optical element (an objective lens, a relay lens, etc.).

The illumination optical system 240 illuminates the test eye. The illumination optical system 240 illuminates the test eye with, for example, infrared light. The illumination optical system 240 includes, for example, an illumination light source 241. The illumination light source 241 is positioned, for example, diagonally in front of the test eye. The illumination light source 241 emits, for example, infrared light. The illumination optical system 240 may include multiple illumination light sources 241.

The front imaging system 220, for example, captures an observation image of the test eye. The front imaging system 220, for example, captures an image of the anterior part of the test eye. The front imaging system 220 includes, for example, a light receiving lens 221, a light receiving element 222, etc. The front imaging system 220 receives, for example, light from the illumination light source 241 reflected by the test eye. The front imaging system 220 receives, for example, a reflected light beam from the test eye centered on the optical axis O1. For example, the reflected light from the test eye passes through the opening 101 of the ultrasonic actuator 100, and is received by the light receiving element 222 via the objective system 210 and the light receiving lens 221.

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, etc. Light from the target light source 231 passes through the aperture 232, the projection lens 233, the aperture 232, etc. along the 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 to the subject's eye. The subject fixates the target of the fixation target projection system 230, thereby stabilizing the subject's line of sight.

The index projection system 250 projects an index, for example, onto the subject's eye. The index projection system 250 projects an index for XY alignment onto the subject's eye. The index projection system 250 includes, for example, an index light source (which may be, for example, an infrared light source) 251, an aperture 252, a projection lens 253, and the like. Light from the index light source 251 passes through the aperture 252 and the projection lens 253 along the optical axis O3 and is reflected by the beam splitter 202. The beam splitter 202, for example, makes the optical axis O3 of the index projection system 250 coaxial with the optical axis O1. The light from the index light source 251 reflected by the beam splitter 202 passes through the objective system 210 along the optical axis O1 and is irradiated onto the subject's eye. The light of the index light source 251 irradiated to the subject's eye is reflected by the subject's eye, passes through the objective system 210 and the light receiving lens 221 along the optical axis O1 again, and is received by the light receiving element 222. The index received by the light receiving element is used for, for example, XY alignment. In this case, for example, the index projection system 250 and the front imaging system 220 function as an XY alignment detection unit.

The deformation detection system 260 detects, for example, the deformation state of the cornea of the test eye. The deformation detection system 260 includes, for example, a light receiving lens 261, an aperture 262, a light receiving element 263, and the like. The deformation detection system 260 may detect the deformation state of the cornea, for example, based on the corneal reflected light received by the light receiving element 263. For example, the deformation detection system 260 may detect the deformation of the cornea by receiving light reflected by the cornea of the test eye from the index light source 251 with the light receiving element 263. For example, the corneal reflected light passes through the objective system 210 along the optical axis O1 and is reflected by the beam splitter 202 and the beam splitter 203. Then, the corneal reflected light passes through the light receiving lens 261 and the aperture 262 along the optical axis O4 and is received by the light receiving element 263.

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 236. For example, the deformation detection system 260 may detect that the cornea is in an applanation state when the amount of light received by the light receiving element 236 is maximized. In this case, for example, the deformation detection system 260 is set so that the amount of light received is maximized when the cornea of the test eye is in an applanation state.

The corneal thickness measurement system 270 measures, for example, the corneal thickness of the test eye. The corneal thickness measurement system 270 may include, for example, a light source 271, a light projecting lens 272, an aperture 273, a light receiving lens 274, and a light receiving element 275. Light from the light source 271 passes through the light projecting lens 272 and the aperture 273 along the optical axis O5, for example, and is irradiated onto the test eye. Then, the reflected light reflected by the test eye is collected by the light receiving lens 274 along the optical axis O6, and is received by the light receiving element 275.

The working distance detection system 280 detects, for example, the alignment state in the Z direction. The working distance detection system 280 includes, for example, a light receiving element 281. The working distance detection system 280 may detect the alignment state in the Z direction, for example, by detecting reflected light from the cornea. For example, the working distance detection system 280 may receive reflected light from the light source 271 reflected by the cornea of the test eye. In this case, the working distance detection system 280 may receive, for example, a bright spot formed by the light from the light source 271 reflected by the cornea of the test eye. In this way, the light source 271 may also be used as a light source for detecting the working distance. For example, the light from the light source 271 reflected by the cornea is reflected by the beam splitter 204 along the optical axis O6 and received by the light receiving element 281.

<Detection unit>
The detection unit 500 detects, for example, the output of the ultrasonic actuator 100. The detection unit 500 is, for example, a sensor such as an ultrasonic sensor, a displacement sensor, or a pressure sensor. The ultrasonic sensor detects ultrasonic waves generated from the ultrasonic actuator 100. The displacement sensor detects the displacement of the ultrasonic actuator 100. The displacement sensor may continuously detect the displacement to detect vibrations when the ultrasonic actuator 100 generates ultrasonic waves.

As shown in FIG. 2, the detection unit 500 is disposed outside the ultrasonic irradiation path A. The irradiation path A is, for example, an area connecting the front surface F of the ultrasonic actuator 100 and the ultrasonic irradiation target Ti. The detection unit 500 is disposed, for example, on the side or rear of the ultrasonic actuator 100. When the detection unit 500 is disposed on the side as in this embodiment, it is easy to observe the subject's eye using the front imaging system 220. When an ultrasonic sensor is used as the detection unit 500, the detection unit 500 detects ultrasonic waves leaking from the side or rear of the ultrasonic actuator 100. When a displacement sensor is used as the detection unit 500, the detection unit 500 detects the displacement of the ultrasonic actuator 100 from the side or rear of the ultrasonic actuator 100. The displacement sensor, for example, irradiates the ultrasonic actuator 100 with laser light and detects the displacement of the ultrasonic actuator 100 based on the reflected laser light. The detection signal detected by the detection unit 500 is sent to the control unit.

<Control Unit>
The configuration of the control system will be described with reference to FIG. 5. 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 and initial values for controlling the operation of the ultrasonic tonometer 1. 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 ultrasonic actuator 100, the optical unit 200, the detection unit 500, and the like.

The memory unit 74 is a non-transient storage medium that can retain its 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 memory unit 74.

The display unit 75 displays, for example, the measurement results of the test eye. The display unit 75 may have a touch panel function.

The operation unit 76 accepts 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. The operation unit 76 may use at least one user interface such as a touch panel, a mouse, a joystick, or a keyboard. When the display unit 75 is a touch panel, the display unit 75 may function as the operation unit 76.

<Measurement operation>
The control operation of the device having the above configuration will be described. First, the control unit 70 aligns the ultrasonic tonometer 1 with the subject's eye, whose face is supported by the face support unit 4. For example, the control unit 70 detects a bright spot by the index projection system 250 from the front image acquired by the light receiving element 222, and drives the drive unit 5 so that the position of the bright spot is a predetermined position. Of course, the examiner may manually perform alignment with the subject's eye using the operation unit 76 or the like while looking at the display unit 75. When the control unit 70 drives the drive unit 5, it judges whether the alignment is appropriate or not depending on whether the position of the bright spot in the anterior eye image is a predetermined position.

After completing the alignment with the subject's eye E, the control unit 70 measures the corneal thickness using the corneal thickness measurement system 270. For example, the control unit 70 calculates the corneal thickness based on the light receiving signal received by the light receiving element 275. For example, the control unit 70 may determine the corneal thickness from the positional relationship between the peak value of the reflected light from the corneal surface and the peak value of the reflected light from the corneal back surface based on the light receiving signal. The control unit 70 stores the determined corneal thickness in the memory unit 74, for example.

Next, the control unit 70 measures the intraocular pressure of the test eye using the ultrasonic actuator 100. For example, the control unit 70 applies a voltage burst signal to the ultrasonic element 110 and irradiates ultrasonic waves to the test eye E. When acoustic radiation pressure is generated on the cornea of the test eye by the ultrasonic waves irradiated from the ultrasonic actuator 100, the cornea is deformed. The control unit 70 detects the deformed state of the cornea using the deformation detection system 260. For example, the control unit 70 detects that the cornea has been deformed into a predetermined shape (applanation or flattened state) based on the light receiving signal of the light receiving element 263. The acoustic radiation pressure gradually increases, and the cornea becomes flat (applanation state). At this time, the signal of the deformation detection system 260 becomes maximum, and the control unit 70 determines that the cornea has become applanated.

When the acoustic radiation pressure becomes even stronger, the cornea collapses. At this time, the light receiving signal of the deformation detection system 260 weakens. The control unit 70 gradually weakens and stops the ultrasound irradiation. The cornea then returns from a collapsed state to an applanated state. At this time, the light receiving signal becomes maximum again. Thereafter, as the cornea returns to its original shape, the light receiving signal of the deformation detection system 260 also weakens.

The control unit 70 calculates the intraocular pressure of the test eye based on, for example, the acoustic radiation pressure when the cornea of the test eye is deformed into a predetermined shape. The acoustic radiation pressure applied to the test eye is correlated with the ultrasound irradiation time, and increases as the ultrasound irradiation time becomes longer. Therefore, the control unit 70 determines the acoustic radiation pressure when the cornea is deformed into a predetermined shape based on the ultrasound irradiation time. The relationship between the acoustic radiation pressure when the cornea is deformed into a predetermined shape and the intraocular pressure of the test eye is determined in advance by experiments, etc., and stored in the memory unit 74, etc. The control unit 70 determines the intraocular pressure of the test eye based on the acoustic radiation pressure when the cornea is deformed into a predetermined shape and the relationship stored in the memory unit 74.

<Amplitude modulation of burst signals>
The control unit 70 performs amplitude modulation on the burst signal of the voltage applied to the ultrasonic element 110. For example, FIG. 6A shows a burst signal B1 before amplitude modulation, and FIG. 6B shows a burst signal B2 after amplitude modulation. As shown in FIGS. 6A and 6B, the burst signal B1 before amplitude modulation has a constant amplitude, and the burst signal B2 after amplitude modulation has a changing amplitude. For example, the control unit 70 performs amplitude modulation so that the magnitude of the voltage gradually increases and then gradually decreases. For example, the control unit 70 may use a sine wave as the modulating wave. That is, the amplitude of the burst signal may be amplitude modulated so that the amplitude of the burst signal gradually increases along the waveform of a sine wave and then gradually decreases.

Figure 7A shows the change over time in acoustic radiation pressure when a burst signal B1 is applied to the ultrasonic actuator 100. Figure 7B shows the change over time in acoustic radiation pressure when a burst signal B2 is applied to the ultrasonic actuator 100. As shown in Figure 7, the increase in acoustic radiation pressure is more gradual when an amplitude-modulated burst signal B2 is applied compared to when a constant amplitude burst signal B1 is applied. In other words, the control unit 70 can change the rate of increase of acoustic radiation pressure (e.g., the amount of increase per unit time) by modulating the amplitude of the voltage applied to the ultrasonic element 110.

For example, the acoustic radiation pressure required to measure an eye with an intraocular pressure value J1 is K1, and the acoustic radiation pressure required to measure an intraocular pressure value J2 (>J1) greater than the intraocular pressure value J2 is K2 (see FIG. 7). In addition, the time from application of the burst signal B1 to the acoustic radiation pressure K1 is t11, and the time from application of the burst signal B1 to the acoustic radiation pressure K2 is t12 (see FIG. 7A). In addition, the time from application of the burst signal B2 to the acoustic radiation pressure K1 is t21, and the time from application of the burst signal B2 to the acoustic radiation pressure K2 is t22 (see FIG. 7B). As shown in FIG. 7A and B, the pressure rises slowly by modulating the amplitude of the voltage signal to gradually increase the voltage, so that the interval Δt2 between time t21 and time t22 is greater than the interval Δt1 between time t11 and time t12, improving the time resolution. In other words, by making the increase in acoustic radiation pressure more gradual, the interval between peaks of the corneal deformation signal for each intraocular pressure value is increased, and the possibility of erroneously detecting the peak position for each intraocular pressure value is reduced, thereby improving the accuracy of intraocular pressure measurement.

<Calculation of hysteresis>
The control unit 70 may calculate the corneal hysteresis by sufficiently deforming the cornea with ultrasonic waves from the Langevin transducer. Hysteresis is used, for example, as an index indicating the rigidity of the cornea. For example, the control unit 70 may calculate the corneal hysteresis based on the light receiving signal of the deformation detection system 260 when the cornea is deformed by ultrasonic waves. For example, in the light receiving signal Sg of the deformation detection system 260 as shown in FIG. 8, the time interval between the time t1 when the cornea changes from a normal shape to an applanation state and the signal intensity becomes maximum, and the time t2 when the cornea returns from a depressed state to an applanation state and the signal intensity becomes maximum again, is defined as time Δt. Also, the difference between the signal intensity V1 in the applanation state and the signal intensity V2 in the most deformed (depressed) state is defined as the intensity difference ΔV. The control unit 70 may obtain the corneal hysteresis based on these parameters. For example, the control unit 70 may obtain the hysteresis based on the time Δt, the intensity difference ΔV, or the like, or based on the corneal separation rate (separation rate of reflection from the cornea) obtained by ΔV/Δt. Also, for example, the control unit 70 may obtain the hysteresis based on the time Δt or the intensity difference ΔV relative to the time t1.

The method of calculating the hysteresis is not limited to the above method. For example, the control unit 70 may calculate the hysteresis of the cornea from the temporal change in the light receiving signal Sg of the deformation detection system 260. For example, the time from when the cornea starts to deform to when it returns to its original shape, the time from when the cornea starts to deform to when it is most deformed, or the time from when the cornea is most deformed to when it returns to its original shape may be calculated as the hysteresis. The control unit 70 may also calculate the slope of the signal intensity from when the cornea starts to deform to when it is most deformed, or the slope of the signal intensity from when the cornea is most deformed to when it returns to its original shape as the hysteresis. The control unit 70 may calculate the hysteresis as one of the indices indicating the temporal deformation state of the cornea.

In addition, for example, in the graph of acoustic radiation pressure P in Figure 8, the control unit 70 may determine the pressure difference ΔP between the acoustic radiation pressure P1 at time t1 and the acoustic radiation pressure P2 at time t2 as hysteresis. The control unit 70 may correct the intraocular pressure, for example, using the calculated hysteresis. For example, if the hysteresis parameter is a value when the corneal rigidity is low, the intraocular pressure may be corrected to be higher.

The method of calculating the intraocular pressure is not limited to the above-mentioned method of calculating the intraocular pressure based on the output of the ultrasonic actuator 100 when the cornea undergoes a predetermined deformation, and various methods may be used. For example, the control unit 70 may determine the amount of deformation of the cornea using the deformation detection system 260, and calculate the intraocular pressure by multiplying the amount of deformation by a conversion coefficient. The control unit 70 may also correct the calculated intraocular pressure value according to, for example, the corneal thickness of the test eye.

The control unit 70 may measure the intraocular pressure based on the ultrasound reflected by the test eye. For example, the control unit 70 may measure the intraocular pressure based on a change in the characteristics of the ultrasound reflected by the test eye, or may obtain the amount of deformation of the cornea from the ultrasound reflected by the test eye and measure the intraocular pressure based on the amount of deformation.

REFERENCE SIGNS LIST 1 Ultrasonic tonometer 2 Base 3 Measurement unit 4 Face support unit 5 Drive unit 70 Control unit 75 Display unit 76 Operation unit 100 Ultrasonic actuator 101 Opening 200 Optical unit

Claims (3)

An ultrasonic tonometer for measuring intraocular pressure of a subject's eye using ultrasound, comprising:
an ultrasonic actuator that irradiates ultrasonic waves to the subject's eye;
A control means for applying an amplitude modulated burst signal to the ultrasonic actuator ,
the control means changes a rate of increase of the acoustic radiation pressure so that the increase in the acoustic radiation pressure becomes gradual by modulating the burst signal so that the amplitude gradually increases, and calculates the intraocular pressure of the test eye based on the acoustic radiation pressure when the cornea of the test eye is deformed into a predetermined shape . 2. The ultrasonic tonometer according to claim 1 , wherein said control means modulates said burst signal using a sine wave as a modulating wave. a deformation detection means for detecting a deformation state of the cornea;
3. The ultrasonic tonometer according to claim 1 , wherein the control means calculates hysteresis of the cornea based on the deformation state of the cornea acquired by the deformation detection means.

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