Patent ID: 12207880

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment according to the present disclosure will be described. An ultrasonic tonometer (e.g., an ultrasonic tonometer1) of the first embodiment measures the eye pressure of an examinee's eye by means of an ultrasonic wave. The ultrasonic tonometer includes, for example, an ultrasonic actuator (e.g., an ultrasonic actuator100) and a current adjuster (e.g., a current adjuster83). The ultrasonic actuator has an ultrasonic element (e.g., an ultrasonic element110), and irradiates the examinee's eye with the ultrasonic wave. The current adjuster adjusts a current applied to the ultrasonic element. Thus, a sound pressure or an acoustic radiation pressure output from the ultrasonic actuator can be stabilized, and eye pressure measurement can be suitably performed. For example, the ultrasonic tonometer irradiates the examinee's eye with the stable sound pressure or acoustic radiation pressure so that a cornea can be suitably deformed (brought into an applanation state).

Note that the ultrasonic tonometer may include a controller (e.g., a controller70) and an acquirer (a detector500). The controller controls the current adjuster, for example. The acquirer acquires current information regarding the level of current flowing in the ultrasonic actuator. In this case, the controller may control the current adjuster based on the current information. For example, the controller may control the current adjuster such that a predetermined current flows in the ultrasonic actuator. With this configuration, the output of the ultrasonic actuator is stabilized.

Note that the acquirer may acquire the current information by detecting the value of current or voltage applied to the ultrasonic element or a resistance value of the ultrasonic element. In this case, a current meter, a voltage meter or the like may be used, for example. Moreover, the acquirer may acquire the current information by detecting the output of the ultrasonic actuator.

Note that the current adjuster may include a variable impedance section (e.g., a variable impedance section84). In this case, the controller may change the impedance of the variable impedance section to adjust current. For example, the impedance of the variable impedance section connected in series with the ultrasonic actuator is changed so that the current flowing in the ultrasonic actuator can be adjusted.

Second Embodiment

Hereinafter, a second embodiment according to the present disclosure will be described. An ultrasonic tonometer (e.g., an ultrasonic tonometer1) of the second embodiment measures the eye pressure of an examinee's eye by means of an ultrasonic wave. The ultrasonic tonometer includes, for example, an irradiator (e.g., an ultrasonic actuator100) and a controller (e.g., a controller70). The irradiator has an ultrasonic element (e.g., an ultrasonic element110), and irradiates the examinee's eye with the ultrasonic wave. The controller controls irradiation to correct an application frequency for the ultrasonic element. With this configuration, a sound pressure (or an acoustic radiation pressure) output to the examinee's eye can be stabilized.

Note that the controller may correct the application frequency according to a temporal change in the resonant frequency of the irradiator. For example, the controller may correct the application frequency to approach the resonant frequency of the irradiator. A voltage with the application frequency close to the resonant frequency of the irradiator is applied so that the irradiator can resonate and a sufficient sound pressure or acoustic radiation pressure for eye pressure measurement can be output. Needless to say, the controller may adjust, if possible, the application frequency for the ultrasonic element to the resonant frequency of the irradiator.

Note that the application frequency may be the frequency of the voltage applied to the ultrasonic element. For example, in a case where the waveform of the voltage to be applied is a burst wave, the application frequency may be the frequency of the burst wave.

Note that the present device may further includes a detector (e.g., a detector500) configured to detect the output of the irradiator. In this case, the controller corrects the application frequency based on a detection result of the detector. For example, the controller may correct the application frequency such that the output (the sound pressure or the acoustic radiation pressure) of the irradiator increases. The detector may detect the ultrasonic wave output from the irradiator, or may detect vibration of the irradiator. The controller may correct the application frequency based on the amplitude of, e.g., the ultrasonic wave or vibration detected by the detector.

Note that the controller may display the corrected application frequency on a display (e.g., a display75). With this configuration, a change in the application frequency can be checked.

Note that the controller may correct the resonant frequency of the irradiator. For example, the ultrasonic tonometer may further include a clamper (e.g., a back mass132, a sonotrode131, a driver600or the like) configured to clamp the ultrasonic element. In this case, the controller may adjust the clamp pressure of the clamper, and in this manner, the resonant frequency may be stabilized. With this configuration, an increase in a difference between the resonant frequency and the application frequency is suppressed so that the sound pressure of the irradiator can be stabilized.

Note that the controller may display the corrected resonant frequency on the display. With this configuration, it can be easily checked whether or not the resonant frequency is stabilized.

Third Embodiment

Hereinafter, a third embodiment according to the present disclosure will be described. An ultrasonic tonometer of the third embodiment measures the eye pressure of an examinee's eye by means of an ultrasonic wave. The ultrasonic tonometer includes, for example, an irradiator (e.g., an ultrasonic actuator100) and a controller (e.g., a controller70). The irradiator has an ultrasonic element, and irradiates the examinee's eye with the ultrasonic wave. The controller controls the irradiator. The controller controls the sound pressure or acoustic radiation pressure of the ultrasonic wave output by the irradiator to change eye pressure measurement accuracy. With this configuration, the eye pressure can be measured with suitable measurement accuracy.

Note that the controller may control the rate (speed) of increase in the sound pressure or the acoustic radiation pressure, thereby changing the eye pressure measurement accuracy. For example, in a case where the eye pressure is measured based on elapsed time when a cornea changes to a predetermined shape by the acoustic radiation pressure, the rate of increase in the sound pressure or the acoustic radiation pressure to the time may be slowed. With this configuration, time until the cornea deforms to the predetermined shape increases, and therefore, deformation of the cornea can be detected with favorable accuracy.

Note that the controller may control a voltage, current, or frequency applied to the ultrasonic element. With this configuration, the rate of increase in the sound pressure or the acoustic radiation pressure can be easily changed.

The controller may perform switching between a first measurement mode (e.g., a screening mode) for roughly measuring the eye pressure of the examinee's eye and a second measurement mode (a high-accuracy measurement mode) for measuring the eye pressure with higher accuracy (higher precision) than that of the first measurement mode.

With this configuration, the controller can perform eye pressure measurement with different levels of accuracy. For example, the ultrasonic tonometer can perform eye pressure measurement with first measurement accuracy and second measurement accuracy.

The controller may perform switching to the second measurement mode based on the eye pressure measured in the first measurement mode. For example, in a case where the eye pressure measured in the first measurement mode is lower than a predetermined value, the controller may transition to measurement in the second measurement mode. In a case where the eye pressure is higher than the predetermined value, the controller may perform no measurement in the second measurement mode. With this configuration, an increase in measurement time and a burden on an examinee for measuring a more detailed eye pressure value can be prevented.

The controller may change the measurement accuracy in the second measurement mode based on the eye pressure measured in the first measurement mode.

For example, the controller may increase the measurement accuracy in the second measurement mode as the eye pressure value measured in the first measurement mode decreases. With this configuration, the eye pressure can be measured with accuracy suitable for each examinee.

First Example

Hereinafter, a first example according to the present disclosure will be described. An ultrasonic tonometer of the first example measures, for example, the eye pressure of an examinee's eye in a non-contact manner by using an ultrasonic wave. For example, the ultrasonic tonometer measures the eye pressure by optically or acoustically detecting, e.g., a change in the shape of the examinee's eye or vibration upon irradiation of the examinee's eye with the ultrasonic wave. For example, the ultrasonic tonometer calculates the eye pressure based on, e.g., ultrasonic wave output information when a cornea is continuously irradiated with a pulse wave or a burst wave and deforms to a predetermined shape. The output information is, for example, the sound pressure, acoustic radiation pressure, irradiation time (e.g., elapsed time after a trigger signal has been input), or frequency of the ultrasonic wave. Note that in the case of deforming the cornea of the examinee's eye, the sound pressure, acoustic radiation pressure, or acoustic flow of the ultrasonic wave is used, for example.

FIG.1illustrates a device appearance. An ultrasonic tonometer1includes, for example, abase2, a housing3, a face supporter4, and a driver5. In the housing3, e.g., an ultrasonic actuator100and an optical unit200as described later are arranged. The face supporter4supports a face with examinee's eyes. The face supporter4is, for example, placed on the base2. The driver5moves the housing3relative to the base2for alignment, for example.

FIG.2is a schematic view of a main configuration in the housing. In the housing3, e.g., the ultrasonic actuator100and the optical unit200are arranged. The ultrasonic actuator100and the optical unit200will be sequentially described with reference toFIG.2.

The ultrasonic actuator100irradiates an examinee's eye E with an ultrasonic wave, for example. For example, the ultrasonic actuator100irradiates a cornea with the ultrasonic wave, thereby generating an acoustic radiation pressure on the cornea. The acoustic radiation pressure is, for example, force acting in a sound wave travel direction. The ultrasonic tonometer1of the present example deforms the cornea by utilizing this acoustic radiation pressure, for example. Note that an ultrasonic unit of the present example is in a cylindrical shape, and in a center opening101, the optical axis O1of the optical unit200described later is arranged.

FIG.3Ais a sectional view of a schematic configuration of the ultrasonic actuator100.FIG.3Billustrates, in closeup, the state of an area A1illustrated inFIG.3A. The ultrasonic actuator100of the present example is a so-called Langevin transducer. The ultrasonic actuator100includes, for example, an ultrasonic element110, an electrode120, amass member130, and a fastening member160. The ultrasonic element110generates the ultrasonic wave. The ultrasonic element110may be a voltage element (e.g., piezoelectric ceramics) or a magnetostriction element. The ultrasonic element110of the present example is in a ring shape. For example, the ultrasonic element110may be configured such that multiple piezoelectric elements are stacked on each other. In the present example, a stack of two piezoelectric elements (e.g., a piezoelectric element111and a piezoelectric element112) is used as the ultrasonic element110. For example, the electrode120(an electrode121and an electrode122) is connected to each of these two piezoelectric elements. The electrode121and the electrode122of the present example are in a ring shape, for example.

The mass member130sandwiches the ultrasonic element110, for example. The mass member130sandwiches the ultrasonic element110to increase the tensile strength of the ultrasonic element110such that high resistance to vibration is obtained, for example. Accordingly, high ultrasonic wave output can be generated. For example, the mass member130may be a metal block. For example, the mass member130includes a sonotrode (also called a horn or a front mass)131and a back mass132.

The sonotrode131is a mass member arranged in the front (an examinee's eye side) of the ultrasonic element110. The sonotrode131causes the ultrasonic wave generated by the ultrasonic element110to propagate in air. The sonotrode131of the present example is in a cylindrical shape. An internal thread portion133is formed at part of an inner circular portion of the sonotrode131. The internal thread portion133engages with an external thread portion161formed at the later-described fastening member160. Note that the sonotrode131may have a shape for converging the ultrasonic wave. For example, an examinee's-eye-side end surface of the sonotrode131may be inclined to an opening101side to have a tapered shape. The sonotrode131may be a cylinder having a non-uniform thickness. For example, the sonotrode131may have a shape of which outer and inner diameters change in a cylinder longitudinal direction.

The back mass132is a mass member arranged in the back of the ultrasonic element110. The back mass132and the sonotrode131together sandwich the ultrasonic element110. The back mass132is in a cylindrical shape, for example. An internal thread portion134is formed at part of an inner circular portion of the back mass132. The internal thread portion134engages with the external thread portion161of the later-described fastening member160. Moreover, the back mass132includes a flange portion135. The flange portion135is held by an attachment portion400.

The fastening member160fastens the mass member130and the ultrasonic element110sandwiched by the mass member130, for example. For example, the fastening member160is a hollow bolt. For example, the fastening member160is in a cylindrical shape, and at an outer circular portion thereof, includes the external thread portion161. The external thread portion161of the fastening member160engages with the internal thread portions133,134formed inside the sonotrode131and the back mass132. The sonotrode131and the back mass132are, by the fastening member160, fastened in the direction of pulling against each other. Accordingly, the ultrasonic element110sandwiched between the sonotrode131and the back mass132is fastened, and pressure is on the ultrasonic element110.

Note that the ultrasonic actuator100may include an insulating member170. The insulating member170prevents, for example, contact of the electrode120or the ultrasonic element110with the fastening member160. The insulating member170is arranged between the electrode120and the fastening member160, for example. For example, the insulating member170is in a sleeve shape.

<Optical Unit>

The optical unit200performs examinee's eye observation or measurement (seeFIG.2), for example. The optical unit200includes, for example, an objective system210, an observation system220, a fixation target projection system230, a target projection system250, a deformation detection system260, a dichroic mirror201, a beam splitter202, a beam splitter203, and a beam splitter204.

The objective system210is, for example, an optical system for taking light into the optical unit200from the outside of the housing3or for irradiating the outside of the housing3with light from the optical unit200. The objective system210includes an optical element, for example. The objective system210may include an optical element (e.g., an objective lens or a relay lens).

An illuminating optical system240illuminates the examinee's eye. For example, the illuminating optical system240illuminates the examinee's eye with infrared light. The illuminating optical system240includes an illuminating light source241, for example. The illuminating light source241is, for example, arranged diagonally in the front of the examinee's eye. The illuminating light source241emits the infrared light, for example. The illuminating optical system240may include multiple illuminating light sources241.

The observation system220captures an observation image of the examinee's eye, for example. The observation system220captures an image of an anterior segment of the examinee's eye, for example. The observation system220includes, for example, a light receiving lens221and a light receiving element222. For example, the observation system220receives light from the illuminating light source241after the light has been reflected on the examinee's eye. The observation system receives a reflected light flux about the optical axis O1from the examinee's eye, for example. For example, the reflected light from the examinee's eye passes the opening101of the ultrasonic actuator100, and is received by the light receiving element222through the objective system210and the light receiving lens221.

The fixation target projection system230projects a fixation target on the examinee's eye, for example. The fixation target projection system230includes, for example, a target light source231, a diaphragm232, a light projecting lens233, and a diaphragm234. Light from the target light source231passes, along an optical axis O2, the diaphragm232, the light projecting lens233, the diaphragm232and the like, and is reflected by the dichroic mirror201. The dichroic mirror201causes, for example, the optical axis O2of the fixation target projection system230to be coaxial with the optical axis O1. After having been reflected by the dichroic mirror201, the light from the target light source231passes the objective system210along the optical axis O1, and the examinee's eye is irradiated with such light. An examinee fixates the target provided by the fixation target projection system230, and therefore, an examinee's visual line is stabilized.

The target projection system250projects a target on the examinee's eye, for example. The target projection system250projects a target for XY-alignment on the examinee's eye. The target projection system250includes, for example, a target light source (e.g., may be an infrared light source)251, a diaphragm252, and a light projecting lens253. Light from the target light source251passes, along an optical axis O3, the diaphragm252and the light projecting lens253, and is reflected by the beam splitter202. The beam splitter202causes, for example, the optical axis O3of the target projection system250to be coaxial with the optical axis O1. After having been reflected by the beam splitter202, the light from the target light source251passes the objective system210along the optical axis O1, and the examinee's eye is irradiated with such light. After the examinee's eye has been irradiated with the light from the target light source251, such light is reflected on the examinee's eye, and passes the objective system210, the light receiving lens221and the like again along the optical axis O1. Then, the light is received by the light receiving element222. The target of which light has been received by the light receiving element is, for example, utilized for XY-alignment. In this case, the target projection system250and the observation system220function as XY-alignment detection means, for example.

The deformation detection system260detects the corneal shape of the examinee's eye, for example. For example, the deformation detection system260detects deformation of the cornea of the examinee's eye. The deformation detection system260includes, for example, a light receiving lens261, a diaphragm262, and a light receiving element263. For example, the deformation detection system260may detect deformation of the cornea based on cornea reflected light received by the light receiving element263. For example, the deformation detection system260may detect deformation of the cornea by receiving, by the light receiving element263, the light emitted from the target light source251and reflected on the cornea of the examinee's eye. For example, the cornea reflected light passes the objective system210along the optical axis O1, and is reflected by the beam splitter202and the beam splitter203. Then, the cornea reflected light passes the light receiving lens261and the diaphragm262along an optical axis O4, and is received by the light receiving element263.

The deformation detection system260may detect a cornea deformation state based on the level of a light receiving signal of the light receiving element236, for example. For example, the deformation detection system260may detect that the cornea is brought into an applanation state when the amount of light received by the light receiving element236reaches the maximum amount. In this case, the deformation detection system260is set such that the light receiving amount is maximized when the cornea of the examinee's eye is brought into the applanation state, for example.

Note that the deformation detection system260may be an anterior segment cross-sectional image capturing unit such as an OCT or a shine proof camera. For example, the deformation detection system260may detect the amount or speed of deformation of the cornea.

A corneal thickness measurement system270measures the corneal thickness of the examinee's eye, for example. The corneal thickness measurement system270may include, for example, a light source271, a light projecting lens272, a diaphragm273, a light receiving lens274, and a light receiving element275. For example, light from the light source271passes the light projecting lens272and the diaphragm273along an optical axis O5, and the examinee's eye is irradiated with such light. Then, the light reflected on the examinee's eye is condensed by the light receiving lens274along an optical axis O6, and is received by the light receiving element275.

A Z-alignment detection system280detects an alignment state in a Z-direction, for example. The Z-alignment detection system280includes a light receiving element281, for example. The Z-alignment detection system280may detect the alignment state in the Z-direction by detecting the reflected light from the cornea, for example. For example, the Z-alignment detection system may receive the reflected light generated by reflection of the light from the light source271on the cornea of the examinee's eye. In this case, the Z-alignment detection system280may receive a raster generated by reflection of the light from the light source271on the cornea of the examinee's eye. As described above, the light source271may also serve as a light source for Z-alignment detection. For example, the light emitted from the light source271and reflected on the cornea is reflected by the beam splitter204along the optical axis O6, and is received by the light receiving element281.

<Detector>

A detector500detects the output of the ultrasonic actuator100, for example. The detector500is a sensor such as an ultrasonic sensor, a displacement sensor, or a pressure sensor. The ultrasonic sensor detects the ultrasonic wave generated from the ultrasonic actuator100. The displacement sensor detects displacement of the ultrasonic actuator100. The displacement sensor may continuously detect displacement to detect vibration when the ultrasonic actuator100generates the ultrasonic wave.

As illustrated inFIG.2, the detector500is arranged outside an ultrasonic wave irradiation path A. The irradiation path A is, for example, a region connecting a front surface F of the ultrasonic actuator100and an ultrasonic wave irradiation target Ti. The detector500is, for example, arranged in the side or back of the ultrasonic actuator100. In a case where the detector500is arranged in the side of the ultrasonic actuator100as in the present example, observation of the examinee's eye by the observation system220is easily performed. In a case where the ultrasonic sensor is used as the detector500, the detector500detects the ultrasonic wave leaking from the side or back of the ultrasonic actuator100. In a case where the displacement sensor is used as the detector500, the detector500detects displacement of the ultrasonic actuator100from the side or back of the ultrasonic actuator100. For example, the displacement sensor irradiates the ultrasonic actuator100with laser light, and based on reflected laser light, detects displacement of the ultrasonic actuator100. A signal detected by the detector500is transmitted to a controller.

<Controller>

Next, the configuration of a control system will be described with reference toFIG.5. A controller70performs entire device control and arithmetic processing for a measurement value, for example. The controller70is, for example, implemented by a general central processing unit (CPU)71, a general ROM72, and a general RAM73. The ROM72stores various programs, initial values and the like for controlling operation of the ultrasonic tonometer1. The RAM73temporarily stores various types of information. Note that the controller70may include a single controller or multiple controllers (or multiple processors). The controller70may be, for example, connected to the driver5, a storage74, a display75, an operator76, the ultrasonic actuator100, the optical unit200, and the detector500.

The storage74is a non-transitory storage medium capable of holding stored contents even when a power supply is cut off. For example, a hard disk drive, a flash ROM, or a detachable USB memory can be used as the storage74.

The display75displays an examinee's eye measurement result, for example. The display75may have a touch panel function.

The operator76receives various operation instructions from an examiner. The operator76outputs, to the controller70, an operation signal corresponding to the input operation instruction. For example, at least any of user interfaces such as a touch panel, a mouse, a joy stick, and a keyboard may be used as the operator76. Note that in a case where the display75is a touch panel, the display75may function as the operator76.

<Electric Circuit>

FIG.5is a schematic diagram of an electric circuit of the present example. The ultrasonic tonometer1includes, for example, a signal generator81, a signal amplifier82, and a current adjuster83. The signal generator81generates a voltage signal applied to the ultrasonic actuator100, for example. In the present example, a voltage signal with a burst wave is generated by the signal generator81. The voltage signal generated by the signal generator81is transmitted to the signal amplifier82. The signal amplifier82amplifies the voltage signal generated by the signal generator81. The signal amplifier82is, for example, a power amplifier. The current adjuster83adjusts a current flowing in the ultrasonic actuator100, for example.

FIG.6is a diagram of the current adjuster83. The current adjuster83has a variable impedance section84, for example. The variable impedance section84is an element capable of changing an impedance. The variable impedance section84may be a variable inductor, for example. The variable inductor is, for example, an element capable of changing, by sliding a core (e.g., a magnet) to shift the positions of the core and a coil from each other, a magnetic permeability to change the impedance (e.g., an inductance). For example, the controller70moves the core by drive of a driver85(seeFIG.4) so that the impedance can be changed. The current adjuster83of the present example changes the impedance of the variable impedance section84to adjust the current flowing in the ultrasonic actuator100.

The current Iinflowing in the ultrasonic actuator100changes according to the impedance Z0of the entire circuit. For example, as the impedance Z0of the entire circuit decreases, the current is more likely to flow in the circuit, and therefore, the current Iinflowing in the ultrasonic actuator100increases. Conversely, as the impedance Z0of the entire circuit increases, the current is less likely to flow in the circuit, and therefore, the current Iinflowing in the ultrasonic actuator100decreases. In the case of present example, the variable impedance section84and the ultrasonic actuator100are connected in series. Thus, the impedance Z0of the entire circuit is represented by Formula 1, assuming that the impedance of the variable impedance section84is ZLand the impedance of the ultrasonic actuator100is Zact. Thus, the current adjuster83changes the impedance ZLof the variable impedance section84to change the impedance Z0of the entire circuit, thereby adjusting the current Iin.
Z0=ZL+Zact[Formula 1]

For example, for increasing the current Iinflowing in the ultrasonic actuator100, the impedance ZLof the variable impedance section84is decreased. Accordingly, the impedance Z0of the entire circuit decreases, and the current Iinincreases. For decreasing the current Iinflowing in the ultrasonic actuator100, the impedance ZLof the variable impedance section84is increased. Accordingly, the impedance Z0of the entire circuit increases, and the current Iindecreases.

Note that in the present example, a current value is adjusted based on the sound pressure output from the ultrasonic actuator100. For example, the sound pressure P of the ultrasonic wave output from the ultrasonic actuator100is detected and is compared with a target sound pressure P0. In a case where the sound pressure P is lower than the target sound pressure P0, it is assumed that the current Iinflowing in the ultrasonic element110has decreased. Thus, the controller70decreases the impedance ZLof the variable impedance section84to decrease the impedance Z0of the entire circuit and increase the current L flowing in the ultrasonic actuator100. Conversely, in a case where the sound pressure P of the ultrasonic wave is higher than the target sound pressure P0, it is assumed that the current Iinflowing in the ultrasonic element110has increased. Thus, the controller70increases the impedance ZLof the variable impedance section84to increase the impedance Z0of the entire circuit and decrease the current Iinflowing in the ultrasonic actuator100.

For example, it is assumed that the impedance of the variable impedance section84at time t1before current adjustment is ZL(t1) and the impedance of the variable impedance section84at time t2after current adjustment is ZL(t2). In this case, the impedance ZL(t2) can be represented by Formula 2 by means of the impedance ZL(t1).
ZL(t2)=ZL(t1)×C(t1)  [Formula 2]

The coefficient C(t1) as described herein can be represented by Formula 3 by means of the ratio of an actual sound pressure P(t1) at the time t1to the sound pressure P0and a weighting coefficient w. Note that an experimentally-obtained numerical value is used as the coefficient w, for example.

C⁡(t1)=1(P⁡(t1)/P0)×w[Formula⁢3]

The current adjuster83sequentially changes the impedance ZLof the variable impedance section84based on Formula 2 and Formula 3 so that the sound pressure P of the ultrasonic wave output from the ultrasonic actuator100can approach the target sound pressure P0. Thus, the ultrasonic actuator100can irradiate the examinee's eye with the ultrasonic wave with a stable sound pressure.

<Adjustment of Current Value>

Hereinafter, current value adjustment control in the present example will be described based onFIG.7.

(Step S1: Voltage Signal Output)

First, the controller70controls the signal generator81to output a waveform signal. The signal generator81outputs the voltage signal with the burst wave based on a command signal from the controller70.

(Step S2: Signal Amplification)

The voltage signal output from the signal generator81is input to the signal amplifier82. The signal amplifier82amplifies the input voltage signal.

(Step S3: Ultrasonic Wave Output)

The voltage signal amplified by the signal amplifier82passes the current adjuster83, and is input to the ultrasonic actuator100. When the voltage signal with the burst wave is applied to the ultrasonic element110, the ultrasonic element110outputs the ultrasonic wave. The ultrasonic wave generated by the ultrasonic element110propagates in the sonotrode131, and the examinee's eye is irradiated with such an ultrasonic wave.

(Step S4: Ultrasonic Wave Detection)

The detector500detects the output of the ultrasonic actuator100. For example, the detector500detects the sound pressure of the ultrasonic wave irradiated from the ultrasonic actuator100. Needless to say, the detector500is not limited to detection of the sound pressure, and may detect the ultrasonic wave output from, e.g., vibration of the ultrasonic actuator100.

(Step S5: Feedback)

The detector500feeds back the detected ultrasonic wave output information to the controller70. For example, the controller70calculates the impedance ZLafter change by means of the sound pressure fed back from the detector500and Calculation Formulae 2 and 3.

(Step S6: Current Value Adjustment)

The controller70adjusts the current value. For example, the controller70controls the driver85to adjust the impedance ZLof the variable impedance section84to the calculated impedance. Accordingly, a current flowing on a variable impedance section84side in the circuit changes. As a result, the current flowing in the ultrasonic actuator100changes. For example, the controller70repeats the steps S1to S6to perform such adjustment that the current flowing in the ultrasonic actuator100becomes constant.

<Measurement Operation>

Control operation of the device having the above-described configuration will be described. First, the controller70aligns the ultrasonic tonometer1with the eye of the examinee whose face is supported on the face supporter4. For example, the controller70detects a raster generated by the target projection system250from an anterior segment front image acquired by the light receiving element222. The controller70drives the driver5such that the position of the raster reaches a predetermined position. Needless to say, while viewing the display75, the examiner may manually perform alignment with the examinee's eye by means of, e.g., the operator76. After having driven the driver5, the controller70determines alignment appropriateness based on whether or not the position of the raster of the anterior segment image is at the predetermined position.

After completion of alignment with the examinee's eye E, the controller70measures the corneal thickness by the corneal thickness measurement system270. For example, the controller70calculates the corneal thickness based on the light receiving signal received by the light receiving element275. For example, the controller70may obtain, based on the light receiving signal, the corneal thickness from a position relationship between a peak value obtained by light reflected on a corneal anterior surface and a peak value obtained by light reflected on a corneal posterior surface. The controller70causes, e.g., the storage74to store the obtained corneal thickness, for example.

Subsequently, the controller70measures the eye pressure of the examinee's eye by using the ultrasonic actuator100. For example, the controller70applies a voltage to the ultrasonic element110, thereby irradiating the examinee's eye E with the ultrasonic wave. The controller70deforms the cornea by generation of the acoustic radiation pressure by the ultrasonic wave, for example. Then, the controller70detects the cornea deformation state by the deformation detection system260. For example, the controller70detects, based on the light receiving signal of the light receiving element263, that the cornea has deformed to the predetermined shape (the applanation or flat state). Note that the ultrasonic tonometer1adjusts the current by the current adjuster83so that the cornea can be suitably deformed to the predetermined shape by stable ultrasonic wave output.

The controller70calculates, for example, the eye pressure of the examinee's eye based on the acoustic radiation pressure when the cornea of the examinee's eye deforms to the predetermined shape. The acoustic radiation pressure applied to the examinee's eye is associated with the ultrasonic wave irradiation time, and increases as the ultrasonic wave irradiation time increases. Thus, the controller70obtains, based on the ultrasonic wave irradiation time, the acoustic radiation pressure when the cornea deforms to the predetermined shape. A relationship between the acoustic radiation pressure when the cornea deforms to the predetermined shape and the eye pressure of the examinee's eye is obtained in advance by, e.g., experiment, and is stored in, e.g., the storage74. The controller70determines the eye pressure of the examinee's eye based on the acoustic radiation pressure when the cornea deforms to the predetermined shape and the relationship stored in the storage74. Note that as in the first example, the current is adjusted by the current adjuster83so that the ultrasonic wave output can be stabilized. Thus, a proper correlation between the ultrasonic wave irradiation time and the acoustic radiation pressure is easily obtained.

As described above, the ultrasonic tonometer1of the present example adjusts the value of current applied to the ultrasonic element110so that the ultrasonic wave output can be stabilized and the eye pressure can be properly measured.

For example, the ultrasonic actuator100entirely resonates so that a high sound pressure or acoustic radiation pressure can be output. However, a resonant frequency fluctuates overtime. For this reason, if a resonant state is not proper, the sound pressure (or the acoustic radiation pressure) might gradually decrease. Thus, the current applied to the ultrasonic actuator100is adjusted according to a decrease in the sound pressure (or the acoustic radiation pressure), and in this manner, a stable sound pressure or acoustic radiation pressure is obtained.

Note that in the above-described example, the detector500detects the sound pressure of the ultrasonic wave to feed back the sound pressure to the controller70, but is not limited to such a configuration. For example, the detector500may measure, by, e.g., a sampling board, a current value, a voltage value, or a resistance value in the ultrasonic actuator100. In this case, e.g., current, voltage, or resistance value information detected by the detector500is fed back to the controller70. The controller70controls the current adjuster83based on the information fed back from the detector500, thereby adjusting the current. As described above, the detector500may detect not only the sound pressure or acoustic radiation pressure of the ultrasonic wave but also the information regarding the current flowing in the ultrasonic actuator100, thereby feeding the sound pressure or the acoustic radiation pressure and the information to the controller70. Moreover, the controller70may control the current adjuster83such that the current flowing in the ultrasonic actuator100reaches a predetermined value.

Note that the current adjuster83may include a constant current circuit. The constant current circuit is a circuit configured to constantly apply a current even when a resistance changes. For example, a constant current circuit using a transistor has been known. Using the constant current circuit, the current value can be adjusted by the electric circuit configuration without the need for special control by the controller70. As described above, even in the case of using the constant current circuit, the current applied to the ultrasonic actuator100can be stabilized, and the sound pressure or acoustic radiation pressure of the ultrasonic wave applied to the examinee's eye can be stabilized.

Second Example

A second example will be described. An ultrasonic tonometer of the second example performs control operation regarding correction of an application frequency as described below. A mechanical configuration is similar to that of the first example, and therefore, the same reference numerals are used and description thereof will be omitted.

<Correction of Application Frequency>

When an ultrasonic wave is generated by an ultrasonic actuator100, a controller70applies a voltage to an ultrasonic element110. For example, the controller70applies a voltage burst wave to the ultrasonic element110. In the present example, for measuring an examinee's eye of equal to or greater than 5 mmHg, a sound pressure (or an acoustic radiation pressure) of equal to or higher than 140 dB is generated. The sound pressure (or the acoustic radiation pressure) gradually increases by continuous application of a voltage burst wave B as illustrated inFIG.8. For example, for obtaining a high sound pressure (or a high acoustic radiation pressure), the burst wave B is continuously applied to the ultrasonic element110for a time of equal to or longer than 1 to 100 msec.

When the ultrasonic actuator100of the second example resonates with a resonant frequency fr, a high sound pressure or acoustic radiation pressure is output. Thus, the controller70applies, to the ultrasonic element110, a burst wave with the same frequency as the resonant frequency frof the ultrasonic actuator100, thereby resonating the ultrasonic actuator100. However, even in a case where a burst wave with a constant application frequency fbis applied, the resonant frequency frof the ultrasonic actuator100might fluctuate over time as illustrated inFIG.9. In this case, the resonant frequency frand the application frequency fbshift from each other, and a proper resonant state is not obtained. As illustrated inFIG.10, this leads to a gradual decrease in the sound pressure (or the acoustic radiation pressure). For this reason, the controller70of the second example corrects the application frequency fbin association with a change in the resonant frequency fr, and in this manner, a stable sound pressure or acoustic radiation pressure is obtained.

FIG.11is a graph of a relationship between the application frequency fband a current flowing in the ultrasonic element110. For example, when a predetermined level (an amplitude V) of burst wave B is applied, the controller70repeatedly corrects the application frequency fbsuch that the value of current flowing in the ultrasonic element110increases. In a case where the resonant state of the ultrasonic actuator100is proper, a resistance value of the ultrasonic element110decreases, and the current flowing in the ultrasonic element110increases. Thus, the controller70adjusts the application frequency fbsuch that the current value increases, and in this manner, the application frequency fbsubstantially approaches the resonant frequency fr.

For example, the controller70searches such an application frequency fbthat the current value increases. For example, the controller70corrects the application frequency in association with an increase/decrease in the current value measured upon a change in the application frequency fb. For example, inFIG.11, the controller70first applies a burst wave with an application frequency fb1to measure a current value Ib1thereupon. Next, a burst wave with an application frequency fb2lower than the application frequency fb1is applied, and a current value Ib2thereupon is measured. The current value Ib2as described herein is smaller than the current value Ib1. Thus, a burst wave with an application frequency fb3higher than the application frequency fb1is applied next, and a current value Ib3thereupon is measured. By repeating this process, the controller70corrects the application frequency fb.

As described above, in the ultrasonic tonometer of the second example, the controller70corrects the application frequency applied to the ultrasonic element110so that a proper resonant state of the ultrasonic actuator100can be maintained and a sufficient level of sound pressure (or acoustic radiation pressure) can be stably applied to the examinee's eye. Thus, eye pressure measurement using the ultrasonic wave is allowed.

Note that the controller70may correct the application frequency fbbased on a detection result from a detector500. For example, in a case where the detector500detects the ultrasonic wave output from the ultrasonic actuator100, the application frequency fbmay be corrected such that, e.g., the sound pressure or amplitude of the ultrasonic wave increases. In a case where the detector500detects displacement (vibration) of the ultrasonic actuator100, the application frequency fbmay be corrected such that the amplitude of the ultrasonic actuator100increases. As described above, the application frequency fbis corrected such that the resonant state of the ultrasonic actuator100is properly maintained, and therefore, a sufficient level of sound pressure or acoustic radiation pressure can be applied to the examinee's eye.

Note that as illustrated inFIG.12, the controller70may display the corrected application frequency fbon a display75. Thus, the degree of correction of the frequency is easily checked. Moreover, the controller70may display, e.g., the amount of correction of the application frequency fbon the display75. It may be optionally selected whether or not the application frequency fbis displayed on the display75.

Note that it may be also optionally selected whether correction of the application frequency fbas described above is automatically performed by the controller70or manually performed by an examiner. For example, the controller70may determine, based on an operation signal output by operation of an operator76by the examiner, whether or not the application frequency fbis automatically corrected.

Note that the controller70may correct the resonant frequency fr. The controller70may perform correction such that the resonant frequency frbecomes constant, thereby maintaining a proper resonant state of the ultrasonic actuator100. The method for correcting the resonant frequency includes, for example, adjustment of a clamp pressure of the ultrasonic element110. For example, as illustrated inFIG.3, a driver600configured to turn a sonotrode131relative to a back mass132is provided so that the clamp pressure of the ultrasonic element110can be controlled. In this case, the controller70controls the driver600to adjust the clamp pressure of the ultrasonic element110, and therefore, fluctuation in the resonant frequency frcan be corrected. Note that in the case of correcting the resonant frequency fr, the corrected resonant frequency frmay be displayed on the display75as illustrated inFIG.13. Thus, it can be easily checked whether or not the resonant frequency f& is stable. For correction of the resonant frequency fr, it may be, as in correction of the application frequency fb, optionally selected whether correction is automatically or manually performed.

Third Example

A third example will be described. An ultrasonic tonometer of the third example performs control operation as described below (seeFIG.14). A mechanical configuration is similar to that of the first example, and therefore, the same reference numerals are used and description thereof will be omitted.

(Step11: Alignment)

First, a controller70aligns a measurer3with an examinee's eye. The face of an examinee is supported on a face supporter4. For example, the controller70detects a raster generated by a target projector250from an anterior segment front image acquired by a light receiving element222. The controller70drives a driver5such that the position of the raster reaches a predetermined position. Needless to say, while viewing a display75, an examiner may manually perform alignment with the examinee's eye by means of, e.g., an operator76. After having driven the driver5, the controller70determines alignment appropriateness based on whether or not the position of the raster of the anterior segment image is at the predetermined position.

(Step S12: Corneal Thickness Measurement)

After completion of alignment with the examinee's eye E, the controller70measures a corneal thickness by a corneal thickness measurement system270. For example, the controller70calculates the corneal thickness based on a light receiving signal received by a light receiving element275. For example, the controller70may obtain, based on the light receiving signal, the corneal thickness from a position relationship between a peak value obtained by light reflected on a corneal anterior surface and a peak value obtained by light reflected on a corneal posterior surface. The controller70causes, e.g., a storage74to store the obtained corneal thickness, for example.

(Step S13: Screening)

The controller70measures an eye pressure in a screening mode. In the screening mode, a rough eye pressure of the examinee's eye is measured in a short period of time. For example, the controller70applies a burst wave Bmaxwith the maximum voltage Vmaxas illustrated inFIG.15Ato an ultrasonic element110of an ultrasonic actuator100. Accordingly, the ultrasonic actuator100irradiates the examinee's eye with an ultrasonic wave. The cornea of the examinee's eye is deformed by an acoustic radiation pressure generated by the ultrasonic wave. The controller70detects, based on a cornea deformation signal (a light receiving signal of a light receiving element263) obtained by a deformation detection system260, that the cornea has deformed to a predetermined shape (an applanation or flat state).

The controller70calculates, for example, the eye pressure of the examinee's eye based on the acoustic radiation pressure when the cornea of the examinee's eye deforms to the predetermined shape. The acoustic radiation pressure applied to the examinee's eye is associated with ultrasonic wave irradiation time, and increases as the ultrasonic wave irradiation time increases. Thus, the controller70obtains the acoustic radiation pressure based on the ultrasonic wave irradiation time. A relationship between the acoustic radiation pressure when the cornea deforms to the predetermined shape and the eye pressure of the examinee's eye is obtained in advance by, e.g., experiment, and is stored in, e.g., a storage74. The controller70determines an eye pressure value of the examinee's eye based on the acoustic radiation pressure when the cornea deforms to the predetermined shape and the relationship stored in the storage74.

(Step S14: High-Accuracy Measurement)

Subsequently, the controller70measures the eye pressure in a high-accuracy measurement mode. In the high-accuracy measurement mode, the eye pressure is measured with higher accuracy than that in the screening mode. The controller70controls a voltage applied to the ultrasonic element110, thereby changing the rate of increase in a sound pressure (e.g., the amount of increase per unit time) and improving measurement accuracy. For example, the controller70applies the burst wave Bmaxwith the maximum voltage Vmaxas illustrated inFIG.15Ain the screening mode, whereas applies a burst wave B1with a lower voltage Vi than the maximum voltage Vmaxas illustrated inFIG.15Bto the ultrasonic element110. The controller70decreases the voltage applied to the ultrasonic element110, thereby slowing an increase in the sound pressure. For example,FIG.16Ais a graph of a temporal change in the sound pressure when the voltage with the burst wave Bmaxis applied, andFIG.16Bis a graph of a temporal change in the sound pressure when the voltage with the burst wave B1is applied. As illustrated inFIGS.16A and16B, the rate of increase in the sound pressure to time is lower in the case of applying a lower voltage than in the case of applying a higher voltage.

For example, it is assumed that a sound pressure required for measurement for an examinee's eye with an eye pressure value Pais K1and a sound pressure required for measurement for an eye pressure value Pb(>Pa) greater than the eye pressure value Pais K2. Moreover, as illustrated inFIGS.16A and16B, it is assumed that time until the sound pressure K1after the burst wave Bmaxhas been applied is T11and time until the sound pressure K2after the burst wave Bmaxhas been applied is T12. Further, it is assumed that time until the sound pressure K1after the burst wave B1has been applied is T21and time until the sound pressure K2after the burst wave B1has been applied is T22. By decreasing the voltage, an increase in the sound pressure is slowed. Thus, an interval Δt2between the time T21and the time T22is longer than an interval Δt1between the time T11and the time T12. Thus, a temporal resolution is improved. For example,FIG.17Aillustrates a cornea deformation signal when the burst wave Bmaxis applied, andFIG.17Billustrates a cornea deformation signal when the burst wave B1is applied. Moreover, inFIGS.17A and17B, thick dashed Iines indicate cornea deformation signals when measurement is performed for the eye with the eye pressure value Pa, and solid lines indicate cornea deformation signals when measurement is performed for the eye with the eye pressure value Pb. By slowing an increase in the sound pressure, an interval between the peaks of the cornea deformation signals for each eye pressure value is expanded, and therefore, the probability of erroneous detection of a peak position is decreased. Thus, eye pressure measurement accuracy is improved.

FIG.18Aillustrates a cornea deformation signal Qawhen the burst wave Bmaxis applied, andFIG.18Billustrates a cornea deformation signal Qbwhen the burst wave B1is applied. The cornea deformation signals Qa, Qbas described herein are signals upon measurement for eyes with the same eye pressure. Detection time T2for the cornea deformation signal Qbis longer than detection time T1for the cornea deformation signal Qa, and a change in the cornea deformation signal is slow. Thus, even in a case where unexpected noise (peak noise) N has been caused, it is less likely to erroneously detect the peak of the cornea deformation signal.

The controller70applies the voltage Vi to the ultrasonic element110, thereby deforming the examinee's eye by the acoustic radiation pressure more slowly increasing as compared to the screening mode. Then, the controller70detects, by the deformation detection system260, that the cornea has deformed to the predetermined shape, and based on the level of the acoustic radiation pressure thereupon, measures the eye pressure of the examinee's eye.

As described above, the ultrasonic tonometer of the third example controls the sound pressure or acoustic radiation pressure of the ultrasonic wave so that the eye pressure measurement accuracy can be changed. Thus, the eye pressure can be simply measured in a short period of time, and can be measured with high accuracy. Consequently, measurement can be performed in association with the intended use of the device.

Note that in the above-described third example, the rate of increase in the sound pressure or the acoustic radiation pressure is controlled in such a manner that the voltage applied to the ultrasonic element110is controlled, but the present disclosure is not limited to such a configuration. For example, the rate of increase in the sound pressure or the acoustic radiation pressure may be adjusted in such a manner that a current applied to the ultrasonic element110is controlled, and accordingly, the eye pressure measurement accuracy may be changed. For example, the current flowing in the ultrasonic element110in the high-accuracy measurement mode may be decreased as compared to the screening mode, and in this manner, the rate of increase in the sound pressure may be decreased and the measurement accuracy may be increased. Alternatively, the rate of increase in the sound pressure or the acoustic radiation pressure may be adjusted in such a manner that the frequency of the voltage applied to the ultrasonic element110is controlled.

Note that the controller70may perform switching to the high-accuracy measurement mode based on the eye pressure value measured in the screening mode. For example, in the case of a great eye pressure value, if measurement in the high-accuracy measurement mode is performed, there is a probability that it takes time to complete measurement and a burden is on the examinee. For this reason, in a case where the eye pressure value measured in the screening mode is equal to or less than a predetermined value, switching to the high-accuracy measurement mode may be performed.

Alternatively, based on the eye pressure value measured in the screening mode, the sound pressure or the acoustic radiation pressure in the high-accuracy measurement mode may be controlled. For example, as the eye pressure value in the screening mode decreases, the rate of increase in the sound pressure in the high-accuracy measurement mode may decrease. With this configuration, eye pressure measurement can be performed for an examinee with a smaller eye pressure value with more favorable accuracy, and an increase in measurement time for an examinee with a great eye pressure value can be avoided.

Note that in the case of performing measurement in multiple measurement modes with different levels of accuracy, all measurement results are not necessarily displayed on the display75. For example, the measurement result obtained in any one of the measurement modes may be displayed on the display75. For example, the measurement result obtained in a higher-accuracy measurement mode of the multiple measurement modes may be displayed on the display75.

Note that the method for calculating the eye pressure is not limited to above, and various methods may be used. For example, the controller70may obtain the eye pressure in such a manner that the amount of deformation of the cornea is obtained by the deformation detection system260and is multiplied by a conversion factor. Note that the controller70may correct the calculated eye pressure value according to the corneal thickness stored in the storage74, for example.

Note that the controller70may measure the eye pressure based on the ultrasonic wave reflected on the examinee's eye. For example, the eye pressure may be measured based on a change in the characteristics of the ultrasonic wave reflected on the examinee's eye. Alternatively, the controller70may acquire the amount of deformation of the cornea from the ultrasonic wave reflected on the examinee's eye, and based on such a deformation amount, may measure the eye pressure. Alternatively, the eye pressure may be obtained based on vibration characteristics of the cornea upon irradiation with the ultrasonic wave.

LIST OF REFERENCE SIGNS

1non-contact ultrasonic tonometer2base3housing4face supporter6support base100ultrasonic actuator200optical unit400attachment portion500detector