ULTRASONIC TONOMETER AND ULTRASONIC ACTUATOR

An ultrasonic tonometer, which measures an intraocular pressure of a subject eye using an ultrasonic wave, has an ultrasonic actuator including an ultrasonic element that generates an ultrasonic wave and a sonotrode that propagates the ultrasonic wave generated from the ultrasonic element, and irradiating the subject eye with the ultrasonic wave. The sonotrode includes an uneven portion in which a thickness of the sonotrode varies in a sound axis direction of the ultrasonic wave.

TECHNICAL FIELD

The present disclosure relates to an ultrasonic tonometer that measures an intraocular pressure of a subject eye using an ultrasonic wave and an ultrasonic actuator that emits an ultrasonic wave.

BACKGROUND ART

As a non-contact tonometer, an air injection type tonometer is still common. The air injection type tonometer converts an air pressure in a predetermined deformed state into an intraocular pressure by detecting a deformed state of a cornea when air is injected into the cornea and an air pressure of the air injected into the cornea.

As a non-contact tonometer, an ultrasonic tonometer for measuring the intraocular pressure using an ultrasonic wave is proposed (See Patent Document 1). The ultrasonic tonometer of Patent Literature 1 converts a radiation pressure in a predetermined deformed state into an intraocular pressure by detecting a deformed state of a cornea when the cornea is irradiated with the ultrasonic wave and a radiation pressure of the ultrasonic wave radiated to the cornea.

As an ultrasonic tonometer, an apparatus that measures the intraocular pressure based on a relationship between characteristics (amplitude, phase) of a reflected wave from a cornea and the intraocular pressure is proposed (See Patent Document 2).

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF INVENTION

Problems to be Solved by Invention

However, in the ultrasonic tonometer as a related-art, the ultrasonic wave cannot be properly irradiated to a cornea of a subject eye. For example, in the tonometer of Patent Document 1, the ultrasonic wave cannot be properly irradiated to the cornea, and the cornea cannot be actually flattened or depressed. For example, in the tonometer of Patent Document 2, the ultrasonic wave cannot be properly irradiated to the cornea, and the characteristics of the reflected wave cannot be sufficiently detected.

In view of the problem of the related-art, an object of the present disclosure is to provide an ultrasonic tonometer and an ultrasonic actuator that are capable of properly irradiating a subject eye with an ultrasonic wave.

Means for Solving Problems

In order to solve the above problem, the present disclosure has the following configurations.

(1) An ultrasonic tonometer that measures an intraocular pressure of a subject eye using an ultrasonic wave, having:

an ultrasonic actuator including an ultrasonic element that generates an ultrasonic wave and a sonotrode that propagates the ultrasonic wave generated from the ultrasonic element, and irradiating the subject eye with the ultrasonic wave, in which the sonotrode includes an uneven portion in which a thickness of the sonotrode varies in a sound axis direction of the ultrasonic wave.

(2) The ultrasonic tonometer according to the above (1), in which the sonotrode further includes an opening, and the uneven portion is provided on at least one of an outer surface and an inner surface of the sonotrode.
(3) The ultrasonic tonometer according to the above (1) or (2), in which the uneven portion includes a thick portion formed alternately along the sound axis direction and a thin portion having a thinner thickness of the sonotrode than the thick portion.
(4) The ultrasonic tonometer according to the above (3), in which a length of a pair of the thick portion and the thin portion along the sound axis direction is equal to an integral multiple of a half wavelength of an ultrasonic wave generated from the ultrasonic element.
(5) The ultrasonic tonometer according to the above (3), in which a plurality of pairs of the thick portion and the thin portion are provided, in the uneven portion, at intervals of an integral multiple of a half wavelength of an ultrasonic wave generated from the ultrasonic element along the sound axis direction.
(6) The ultrasonic tonometer according to any one of the above (3) to (5), further having a curvature portion between the thick portion and the thin portion.
(7) The ultrasonic tonometer according to any one of the above (1) to (6), in which the ultrasonic actuator is Langevin type.
(8) An ultrasonic actuator that emits an ultrasonic wave, having;

an ultrasonic element generating the ultrasonic wave; and

a sonotrode propagating the ultrasonic wave generated from the ultrasonic element,

in which the sonotrode includes an uneven portion in which a thickness of the sonotrode varies in a sound axis direction of the ultrasonic wave.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment of the present disclosure will be described. An ultrasonic tonometer of the first embodiment measures an intraocular pressure of a subject eye using an ultrasonic wave. The ultrasonic tonometer includes an ultrasonic actuator (for example, an ultrasonic actuator100), for example. The ultrasonic actuator irradiates the subject eye with the ultrasonic wave. The ultrasonic actuator includes an ultrasonic element (for example, an ultrasonic element110) and a sonotrode (for example, a sonotrode131), for example. The ultrasonic element generates an ultrasonic wave. The sonotrode propagates the ultrasonic wave generated from the ultrasonic element. The sonotrode includes an uneven portion (for example, an uneven portion180). The uneven portion is configured with a portion where a thickness of the sonotrode varies in a sound axial direction of the ultrasonic wave (a traveling direction of the ultrasonic wave, a vibration direction of the ultrasonic element, a radiation direction of the ultrasonic wave, a front-back direction of the ultrasonic tonometer). Thus, since the sonotrode includes the uneven portion, the ultrasonic tonometer of the present embodiment can amplify an amplitude of the ultrasonic wave and emit the ultrasonic wave more efficiently.

The sonotrode may include an opening (for example, an opening101). The opening opens in the sound axial direction of the ultrasonic wave, for example. In this case, the uneven portion may be provided on at least one of an outer surface and an inner surface of the sonotrode. The outer surface of the sonotrode is, for example, a side surface of the sonotrode when an ultrasonic output surface (a subject eye side) of the sonotrode is a front surface. The inner surface of the sonotrode is, for example, an inner wall surface of the sonotrode inside the opening. That is, the sonotrode is formed in a hollow cylindrical shape, and the uneven portion may be provided on both an outer peripheral wall surface and an inner peripheral wall surface of the sonotrode, or may be provided on either wall surface. An optical axis of an observation optical system for observing the subject eye or an optical axis of a measurement optical system for measuring the subject eye may be disposed in the opening, for example. Therefore, observation or measurement of the subject eye may be performed through the opening. That is, the ultrasonic tonometer of the present embodiment may include an optical system in which an optical axis is disposed in the opening.

The uneven portion may include a thick portion (for example, a thick portion181) and a thin portion (for example, a thin portion182). The thin portion has a thinner thickness of the sonotrode than the thick portion. The thick portion and the thin portion are alternately formed along the sound axis direction. Therefore, unevenness is formed by a difference in thickness between the thick portion and the thin portion. A curvature portion (for example, a curvature portion183) may be provided between the thick portion and the thin portion. The curvature portion is formed by a curved surface, for example. Thus, a continuous surface is formed between the thick portion and the thin portion, and the ultrasonic wave can be efficiently propagated from the thick portion to the thin portion.

A length of a pair of the thick portion and the thin portion forming the uneven portion may be equal to an integral multiple of a half wavelength of the ultrasonic wave generated from the ultrasonic element. Accordingly, the ultrasonic actuator easily resonates, and the ultrasonic wave can propagate more efficiently.

A plurality of pairs of thick portion and thin portion forming the uneven portion may be provided at intervals of an integral multiple of a half wavelength of the ultrasonic wave. Thus, a vibration mode of the ultrasonic actuator approaches a single mode (primary vibration mode, single vibration mode), and a sound pressure is efficiently increased.

Second Embodiment

An ultrasonic tonometer of a second embodiment measures the intraocular pressure of the subject eye using the ultrasonic wave, as is the same with the first embodiment. The ultrasonic tonometer (for example, an ultrasonic tonometer1) of the second embodiment includes an ultrasonic actuator (for example, then ultrasonic actuator100), for example. The ultrasonic actuator irradiates the subject eye with the ultrasonic wave. The ultrasonic actuator includes an ultrasonic element (for example, the ultrasonic element110) and a sonotrode (for example, the sonotrode131).

The ultrasonic element generates an ultrasonic wave. The sonotrode propagates the ultrasonic wave generated from the ultrasonic element. The sonotrode includes an irradiation surface (for example, an irradiation surface184) and an opening (for example, the opening101). The irradiation surface is, for example, a surface facing the subject eye. For example, the ultrasonic wave generated from the ultrasonic element propagates through the sonotrode and is output from the irradiation surface into the air. The opening opens in the sound axial direction of the ultrasonic wave, for example. The sonotrode is formed to have a substantially same propagation distance until the ultrasonic wave generated from the ultrasonic element reaches the irradiation surface between an outer surface and an inner surface of the sonotrode. Thus, a wavefront of the ultrasonic wave on the irradiation surface is aligned, and the wavefront of the ultrasonic wave is incident parallel to the irradiation surface. Therefore, the vibration mode of the ultrasonic actuator becomes the single mode, and the ultrasonic wave output from the irradiation surface propagates efficiently in the air. The propagation distance may not exactly coincide between the outer surface and the inner surface of the sonotrode. The sonotrode may include a propagation distance adjustment portion (for example, an inner groove185, an outer groove186). The propagation distance adjustment portion is provided to reduce a difference of the propagation distance between the outer surface and the inner surface of the sonotrode. For example, the propagation distance adjustment portion is provided so that the propagation distance coincides between the outer surface and the inner surface of the sonotrode. Thus, the wavefront of the ultrasonic wave on the irradiation surface is aligned. The propagation distance adjustment portion may be provided on both the outer surface and the inner surface of the sonotrode, or may be provided only on either surface.

The propagation distance adjustment portion may be a groove having a curved surface. As the ultrasonic wave propagates along the groove, the propagation distance of the ultrasonic wave can be increased. Thus, the propagation distance of the ultrasonic wave is adjusted, and the wavefront of the ultrasonic wave on the irradiation surface is aligned.

The irradiation surface may be inclined to a side of the ultrasonic element and toward a center of the sound axis. That is, the irradiation surface may be inclined to the side of the ultrasonic element and toward a center of the opening. Thus, the ultrasonic wave can be converged toward the subject eye. The irradiation surface may have a curvature. For example, the irradiation surface may be an inclined curved surface.

The ultrasonic actuators in the first and second embodiments may be Langevin type. The Langevin type ultrasonic actuator has a shape in which an ultrasonic element is sandwiched by mass members, for example. Accordingly, the Langevin type ultrasonic actuator can obtain high output.

The ultrasonic actuators in the first and second embodiments may be used not only in the tonometer but also in other fields. For example, the ultrasonic actuator may be used in a medical equipment of dermatology or the like other than ophthalmology. The ultrasonic actuator may be used in a device utilizing a high-power ultrasonic wave.

EXAMPLE

An example according to the present disclosure will be described below. An ultrasonic tonometer of the present example measures the intraocular pressure of the subject eye in a non-contact manner using an ultrasonic wave, for example. The ultrasonic tonometer measures the intraocular pressure by optically or acoustically detecting a shape change or vibration of the subject eye, for example, when the subject eye is irradiated with the ultrasonic wave. For example, the ultrasonic tonometer continuously irradiates a cornea with a pulse wave or a burst wave, and calculates the intraocular pressure based on output information of the ultrasonic wave when the cornea is deformed into a predetermined shape. The output information is, for example, an ultrasonic sound pressure, an acoustic radiation pressure, an irradiation time (for example, an elapsed time after a trigger signal is input), or a frequency. When the cornea of the subject eye is deformed, the ultrasonic sound pressure, the acoustic radiation pressure, or an acoustic flow is used, for example.

FIG. 1shows an appearance of the ultrasonic tonometer. The ultrasonic tonometer1includes a base2, a housing3, a face support unit4, a drive unit5, and the like, for example. An ultrasonic actuator100described later, an optical unit200, and the like are arranged inside the housing3. The face support unit4supports a face of a subject. The face support unit4is installed on the base2, for example. The drive unit5moves the housing3with respect to the base2for alignment, for example.

FIG. 2is a schematic view of a main configuration inside the housing. An ultrasonic actuator100and the optical unit200are arranged inside the housing3, for example. The ultrasonic actuator100and the optical unit200will be described in order usingFIG. 2.

The ultrasonic actuator100irradiates a subject eye E with an ultrasonic wave, for example. For example, the ultrasonic actuator100irradiates a cornea with the ultrasonic wave to generate an acoustic radiation pressure on the cornea. The acoustic radiation pressure is, for example, a force acting in a direction that a sound wave travels. The ultrasonic tonometer1of the present example deforms the cornea using the acoustic radiation pressure, for example. The ultrasonic unit of the example has a cylindrical shape, and an optical axis O1of the optical unit200described later is disposed in the opening101at the center.

The ultrasonic actuator100of the present example is a so-called Langevin type vibrator. As shown inFIG. 3, the ultrasonic actuator100includes an ultrasonic element110, an electrode120, a mass member130, and a fastening member160, for example. The ultrasonic element110generates an ultrasonic wave. The ultrasonic element110may be a voltage element (for example, a piezoelectric ceramic) or a magnetostrictive element. The ultrasonic element110of the example has a ring shape. For example, the ultrasonic element110may be a laminate of a plurality of piezoelectric elements.FIG. 4is an enlarged view of a region A1inFIG. 3. In the example, as shown inFIG. 4, two laminated piezoelectric elements (for example, the piezoelectric element111and the piezoelectric element112) are used as the ultrasonic element110. For example, the electrodes120(electrode121, electrode122) are connected to the two piezoelectric elements, respectively. The electrode121and the electrode122of the example are in a ring shape, for example.

The mass member130sandwiches the ultrasonic element110, for example. Since the mass member130sandwiches the ultrasonic element110, the mass member130increases a tensile strength of the ultrasonic element110, and the ultrasonic element110can withstand a strong vibration, for example. Therefore, a high-power ultrasonic wave can be generated. The mass member130may be a metal block, for example. For example, the mass member130includes a sonotrode (which is also referred to as a horn or a front mass)131and a back mass132.

The sonotrode131is a mass member disposed in front (at a subject eye side) of the ultrasonic element110. The sonotrode131propagates and amplifies the ultrasonic wave generated from the ultrasonic element110. The sonotrode131of the example has a hollow cylindrical shape (hollow tubular shape). A female screw portion133is formed on a part of an inner circle side of the sonotrode131. The female screw portion133is screwed to a male screw portion161formed in a fastening member160described later.

The sonotrode131of the example is a hollow cylinder having an uneven thickness. For example, the sonotrode131has a shape that an outer diameter and an inner diameter vary with respect to the sound axis O1direction (longitudinal direction) of the hollow cylinder. For example, as shown inFIG. 3, the uneven portion180including the thick portion181and the thin portion182is provided.FIG. 5Ashows a cross section when the thick portion181is cut perpendicular to the sound axis direction.FIG. 5Bshows a cross section when the thin portion182is cut perpendicular to the sound axis direction. The thick portion181has an outer diameter (pa and an inner diameter φb. The thin portion182has an outer diameter (pc and an inner diameter φd. The outer diameter (pa of the thick portion181is larger than the outer diameter (pc of the thin portion182, and the inner diameter φb of the thick portion181is smaller than the inner diameter φd of the thin portion182. A cross-sectional area M1of the hollow cylinder of the thick portion181is larger than a cross-sectional area M2of the hollow cylinder of the thin portion182.

The thick portion181and the thin portion182amplify the ultrasonic wave generated from the ultrasonic element110. For example, the ultrasonic wave is amplified when the ultrasonic wave propagates from the thick portion181to the thin portion182. This is due to the horn effect. For example, when water at a constant flow rate flows from a thick pipe to a thin pipe, a flow velocity in the thin pipe increases. An amplitude gain of the example is given by the area ratio (M1/M2) of the cross-sectional area M1of the thick portion181and the cross-sectional area M2of the thin portion182.

As shown inFIG. 6, pairs of the thick portion181and the thin portion182forming the uneven portion180are provided at an integral multiple of a half wavelength of the ultrasonic wave generated from the ultrasonic element110along the sound axis direction from an end surface (the irradiation surface184or a rear surface) of the ultrasonic actuator. Accordingly, the ultrasonic actuator100easily resonates, and the ultrasonic wave can propagate more efficiently. The thick portion181and the thin portion182are arranged at an intervals of a quarter wavelength A of the ultrasonic wave, respectively. For example, as shown inFIG. 6, a length of a thick portion181ain the sound axis direction is ¼ λ. A length of a thin portion182awhich is adjacent to a thick portion181ais ¼ λ. Similarly, a length of a thick portion181b, a thin portion182b, and a thick portion181cin the sound axis direction is ¼ λ. Since the thick portion181and the thin portion182are provided at the intervals of ¼ λ, the vibration mode of the ultrasonic actuator100is likely to be the single mode. Accordingly, the entire ultrasonic actuator100vibrates efficiently, and a high sound pressure can be generated.

A plurality of the thick portions181and the thin portions182of this example are provided at intervals of ¼ wavelength. That is, the uneven portion180is provided with a plurality of pairs of the thick portion181and the thin portion182at half wavelength intervals. In this case, the ultrasonic wave generated by the ultrasonic element110propagates from the thick portion181ato the thin portion182a, and then alternately propagates the thick portion181and the thin portion182in the order of the thick portion181b, the thin portion182b, and the thick portion181c. Since the plurality of the thick portions181and the thin portions182are providing in this manner, the vibration mode approaches the single mode, and the sound pressure can be efficiently increased. Further, the ultrasonic wave is repeatedly amplified by the plurality of the thick portions181and the plurality of thin portions182, the sound pressure can be further increased.

In the plurality of the thick portions181(for example, the thick portion181a, the thick portion181b, the thick portion181c) each thick portion may have the same inner and outer diameters with the other thick portion, or may have different inner and outer diameters from the other thick portion. Similarly, in the plurality of the thin portions182(for example, the thin portion182a, the thin portion182b), each thin portion may have the same inner and outer diameters with the other thin portion, or may have different inner and outer diameters from the other thin portion.

A curvature portion183is provided at a portion where the ultrasonic wave enters from the thick portion181having the large cross-sectional area M1to the thin portion182having the small cross-sectional area M2. The curvature part183is, for example, a curved surface (a shape having a curvature). In the example ofFIG. 3, a curvature portion183aand a curvature portion183bare provided between the thick portion181aand the thin portion182a. The curvature portion183ais provided on the outer surface of the sonotrode131, and the curvature portion183bis provided on the inner surface of the sonotrode131. Similarly, a curvature portion183cand a curvature portion183dare provided between the thick portion181band the thin portion182b. The curvature part183cis provided on the outer surface of the sonotrode131, and the curvature part183dis provided on the inner surface of the sonotrode131. For example, the curvature portion183is formed by a curved surface such that a variation in diameter between the thick portion181and the thin portion182is continuous.

If there is no curvature portion183between the thick portion181and the thin portion182as shown inFIG. 7A, the ultrasonic wave transmitted in the direction of the sound axis Q1through the thick portion181are reflected by the thin portion182in a direction opposite to the traveling direction. However, as in the present example ofFIG. 7B, when the curvature portion183is provided between the thick portion181and the thin portion182, the ultrasonic wave transmitted in the direction of the sound axis Q1through the thick portion181is suppressed from being reflected by the thin portion182, and the ultrasonic wave can be more efficiently propagated to the thin portion182.

As described above, since the uneven portion such as the thick portion181and the thin portion182is provided with the sonotrode, the amplitude of the ultrasonic wave propagated from the thick portion181to the thin portion182is amplified, and the ultrasonic wave is more efficiently propagated from the irradiation surface184into the air. Thus, it is possible to irradiate the subject eye with the ultrasonic wave having an output sufficient to measure the intraocular pressure. Further, since the curvature portion183provides a curvature between the thick portion181and the thin portion182, the ultrasonic wave can be smoothly propagated from the thick portion181to the thin portion182.

The sonotrode131of the present example has a shape that converges the ultrasonic wave. For example, the irradiation surface (an end surface on the subject eye side)184of the sonotrode131is inclined to a side of the ultrasonic element110and toward the center (the sound axis Q1) of the opening101. For example, the irradiation surface184has a tapered shape. The irradiation surface184may be an inclined surface having a curvature. The irradiation surface184may have a spherical shape whose radius is a working distance of the ultrasonic actuator100. Since the irradiation surface184is inclined, the ultrasonic wave emitted from the irradiation surface184converges to a target position, and a large sound pressure is generated.

Since the irradiation surface184of the sonotrode131is inclined, a time until the ultrasonic wave from the ultrasonic element110reaches the irradiation surface184is different between the outer surface (outer peripheral side) and the inner surface (inner peripheral side) of the sonotrode131. For example, since a propagation path of the ultrasonic wave propagating through the outer surface of the sonotrode131is longer than a propagation path of the ultrasonic wave propagating through the inner surface, the ultrasonic wave propagating through the outer surface reaches the irradiation surface184later than the ultrasonic wave propagating through the inner surface. Therefore, the wavefront of the ultrasonic wave shifts between the outer side and the inner side of the irradiation surface184. In this case, since a complicated vibration mode in the irradiation surface184occurs, it is difficult for the ultrasonic wave to propagate into the air.

FIG. 8shows the wavefront of the ultrasonic wave incident on the irradiation surface184. When the wavefront of the ultrasonic wave propagates perpendicularly to the ultrasonic element110and enters the irradiation surface184as it is, the wavefront of the ultrasonic wave is obliquely incident on the irradiation surface184. In this case, since a time difference occurs between the inner surface side and the outer surface side until the same wavefront of the ultrasonic wave reaches the irradiation surface184, the displacement on the irradiation surface184by the ultrasonic wave is different according to a position in the irradiation surface184. Thus, since the irradiation surface184is not sufficiently displaced, the ultrasonic wave is not efficiently emitted.

Therefore, as shown inFIG. 9, the sonotrode131of the example includes an inner groove185and an outer groove186. The inner groove185is a groove formed inside the opening101of the sonotrode131. The outer groove186is a groove formed outside the sonotrode131. A creepage distance of the inner groove185is different from a creepage distance of the outer groove186. Here, the creepage distance is, for example, a distance in the direction of the sound axis Q1along the outer surface or the inner surface of the sonotrode131. For example, since the inner groove185is cut deeper in the thickness direction than the outer groove186, the creepage distance of the inner groove185is longer than the creepage distance of the outer groove186. The difference in the creepage distance between the inner groove185and the outer groove186is used to make the wavefront of the ultrasonic wave parallel to the irradiation surface184.

The condition in which the wavefront of the ultrasonic wave is parallel to the irradiation surface184is shown in equation (1).

That is, when an inner creepage distance Lin and an outer creepage distance Lout are equal, the wavefront of the ultrasonic wave is parallel to the irradiation surface184. In order to meet with the equation (1), for example, the depth of each groove of the inner groove185and the outer groove186are set so as to cancel the difference of the creepage distance between the inner surface and the outer surface caused by the inclination of the irradiation surface184. Accordingly, since the vibration mode of the irradiation surface184becomes a single mode, the ultrasonic wave can be efficiently propagated into the air.

As described above, since the ultrasonic tonometer1of the present example includes the inner groove185and the outer groove186having a different creepage distance from each other, the wavefront of the ultrasonic wave can be made parallel to the irradiation surface184even though the irradiation surface184is inclined. As a result, the ultrasonic wave is converged on the subject eye, and the vibration mode of the irradiation surface184becomes the single-mode. Therefore, a propagation efficiency or emission efficiency of the ultrasonic wave with respect to the air is improved, and a sound pressure (or acoustic radiation pressure) capable of sufficiently deforming the cornea can be generated.

A back mass132is a mass member disposed behind the ultrasonic element110. The back mass132sandwiches the ultrasonic element110together with the sonotrode131. As a result, the back mass132couples the ultrasonic element110and the sonotrode131. The back mass132has a cylindrical shape, for example. A female screw portion134is formed in a part of an inner circular portion of the back mass132. The female screw portion134is screwed to a male screw portion161of the fastening member160described later. The back mass132includes a flange portion135. The flange portion135is held by a mount unit400.

The fastening member160fastens the mass member130and the ultrasonic element110sandwiched by the mass member130, for example. The fastening member160is a hollow bolt, for example. The fastening member160is, for example, in a cylindrical shape and includes the male screw portion161in an outer circular portion. The male screw portion161of the fastening member160is screwed to the female screw portions133,134formed inside the sonotrode131and inside the back mass132. The sonotrode131and the back mass132are tightened in a direction of pulling each other by the fastening member160. As a result, the ultrasonic element110sandwiched between the sonotrode131and the back mass132is tightened and a pressure is applied to the ultrasonic element110.

The ultrasonic actuator100may include an insulating member170. The insulating member170prevents, for example, the electrode120or the ultrasonic element110from contacting with the fastening member160. The insulating member170is disposed between the electrode120and the fastening member160, for example. The insulating member170is, for example, in a sleeve shape.

As shown inFIG. 6, the entire structure of the ultrasonic actuator100including the thick portion181, the thin portion182, and the back mass132of the sonotrode131is provided with a length based on a half of the wavelength A of the ultrasonic wave generated from the ultrasonic element110. For example, the total length of the ultrasonic actuator100is set to an integral multiple of ½ λ. This is because the vibration of the half wavelength resonance in which a vibration amplitude is large at both ends of the ultrasonic actuator100is generated in the sound axis Q1direction. In this way, the entire ultrasonic actuator100vibrates efficiently and generates a high sound pressure by making the shape with reference to ½ λ. Thus, the ultrasonic actuator100can irradiate the subject eye with an ultrasonic wave having an output sufficient to deform a cornea into a predetermined shape.

Each length of the sonotrode131, the ultrasonic element110, and the back mass132in the direction of the sound axis Q1is considered so that the propagation path length due to the sound velocity (speed of waves transmitted through a medium of vibration) or the shape is ½ λ.

The sonotrode131and the back mass132may be formed of different materials each other. For example, the back mass132may be formed of a material stiffer than the material of the sonotrode131. For example, in the present example, titanium, which is a softer material, is used for the sonotrode131, and steel, which is stiffer than titanium, is used for the back mass132. Titanium has low acoustic losses therefore increases the overall Q value of the ultrasonic actuator100. Since different materials are used for the sonotrode131and the back mass132, the Q value of the actuator100increases, and the vibrations of each portion are easily synchronized. Therefore, the ultrasonic actuator100can output a higher sound pressure. The higher the Q value is, the more the vibration mode is closed to the single mode. Therefore, the ultrasonic wave can be propagated more efficiently.

The optical unit200performs observation or measurement of a subject eye, for example (seeFIG. 2). The optical unit200includes an objective system210, an illumination optical system240, an observation system220, a fixed target projection system230, an index projection system250, a deformation detection system260, a corneal thickness measuring system270, a Z alignment detection system280, a dichroic mirror201, a beam splitter202, a beam splitter203, and a beam splitter204, for example.

The objective system210is, for example, an optical system for taking light from the outside of the housing3into the optical unit200or emitting light from the optical unit200outside the housing3. The objective210includes an optical element, for example. The objective system210may include an optical element (objective lens, relay lens, or the like).

The illumination optical system240illuminates the subject eye. The illumination optical system240illuminates the subject eye with infrared light, for example. The illumination optical system240includes an illumination light source241, for example. The illumination light source241is disposed obliquely forward of the subject eye, for example. The illumination light source241emits infrared light, for example. The illumination optical system240may include a plurality of illumination light sources241.

The observation system220captures an observation image of the subject eye, for example. The observation system220captures an anterior ocular image of the subject eye, for example. The observation system220includes a light receiving lens221and a light receiving element222, for example. The observation system220receives light from the illumination light source241reflected by the subject eye, for example. The observation system220receives a reflected light beam from the subject eye travelling about the optical axis O1, for example. For example, the reflected light from the subject eye passes through the opening101of the ultrasonic actuator100and is received by the light receiving element222via the objective210and the light receiving lens221.

The fixed target projection system230projects a fixed target onto the subject eye, for example. The fixed target projection system230includes a target light source231, a diaphragm232, a light projection lens233, and a diaphragm234, for example. Light from the target light source231passes through the diaphragm232, the projection lens233and the diaphragm232along an optical axis O2, and is reflected by the dichroic mirror201. The dichroic mirror201makes the optical axis O2of the fixed target projection system230coaxial with the optical axis O1, for example. Light from the target light source231reflected by the dichroic mirror201passes through the objective210along the optical axis O1, and is irradiated to the subject eye. Since the target of the fixed target projection system230is fixedly seen by a subject, a line of sight of the subject is stabilized.

The index projection system250projects an index onto the subject eye, for example. The index projection system250projects an index for XY alignment on the subject eye. The index projection system250includes an index light source (for example, an infrared light source)251, a diaphragm252, and a light projecting lens253, for example. Light from the index light source251passes through the diaphragm252and the projection lens253along an optical axis O3, and is reflected by the beam splitter202. The beam splitter202makes the optical axis O3of the index projection system250coaxial with the optical axis O1, for example. The light of the index light source251reflected by the beam splitter202passes through the objective210along the optical axis O1, and is irradiated to the subject eye. The light of the index light source251irradiated to the subject eye is reflected by the subject eye, passes through the objective210and the light receiving lens221along the optical axis O1again, and is received by the light receiving element222. The index received by the light receiving element222is used for the XY alignment, for example. In this case, for example, the index projection system250and the observation system220function as XY alignment detection means.

The deformation detection system260detects a cornea shape of the subject eye, for example. The deformation detection system260detects deformation of the cornea of the subject eye, for example. The deformation detection system260includes a light receiving lens261, a diaphragm262, and a light receiving element263, for example. For example, the deformation detection system260may detect the deformation of the cornea based on corneal reflection light received by the light receiving element263. For example, the deformation detection system260may detect the deformation of the cornea by receiving light emitted from the index light source251and reflected by the cornea of the subject eye, in which the light is received by the light receiving element263. For example, the corneal reflected light passes through the objective210along the optical axis O1, and is reflected by the beam splitter202and the beam splitter203. The corneal reflected light passes through the light receiving lens261and the diaphragm262along an optical axis O4, and is received by the light receiving element263.

For example, the deformation detection system260may detect a deformed state of the cornea based on a magnitude of the light receiving signal of the light receiving element236. For example, the deformation detection system260may detect that the cornea is in an applanation state when a light receiving amount of the light receiving element236is maximized. In this case, for example, the deformation detection system260is set to maximize the light receiving amount when the cornea of the subject eye is in the applanation state.

The deformation detection system260may be an anterior ocular segment image pickup unit such as an OCT or a Scheimpproof camera. For example, the deformation detection system260may detect a deformation amount or a deformation speed of the cornea.

The corneal thickness measuring system270measures a corneal thickness of the subject eye, for example. The corneal thickness measuring system270may include 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 through the light projecting lens272and the diaphragm273along an optical axis O5, and is irradiated to the subject eye. Reflected light reflected by the subject eye is condensed by the light receiving lens274along an optical axis O6, and is received by the light receiving element275.

The Z alignment detection system280detects an alignment state in the 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, for example, by detecting reflected light from the cornea. For example, the Z alignment detection system280may receive reflected light emitted from the light source271and reflected by the cornea of the subject eye. In this case, the Z alignment detection system280may receive a bright spot generated by the light from the light source271being reflected by the cornea of the subject eye, for example. In this way, the light source271may be used as a light source for Z alignment detection. For example, light from the light source271reflected by the cornea is reflected by the beam splitter204along the optical axis O6, and is received by the light receiving element281.

A detection unit500detects an output of the ultrasonic actuator100, for example. The detection unit500is, for example, a sensor such as an ultrasonic sensor, a displacement sensor, or a pressure sensor. The ultrasonic sensor detects an ultrasonic wave generated from the ultrasonic actuator100. The displacement sensor detects a displacement of the ultrasonic actuator100. The displacement sensor may continuously detect the displacement to detect vibration occurring when the ultrasonic actuator100generates the ultrasonic wave.

As shown inFIG. 2, the detection unit500is disposed outside an irradiation path A of the ultrasonic wave. The irradiation path A is, for example, a region connecting a front surface F of the ultrasonic actuator100and an irradiation target Ti of the ultrasonic wave. The detection unit500is disposed, for example, on the lateral side or the rear side of the ultrasonic actuator100. As in the present example, in the case where the detection unit500is arranged on the lateral side, it is easy to observe the subject eye in the observation system220. In the case where an ultrasonic sensor is used as the detection unit500, the detection unit500detects ultrasonic waves leaking from the lateral side or the rear side of the ultrasonic actuator100. In the case where a displacement sensor is used as the detection unit500, the detection unit500detects the displacement of the ultrasonic actuator100from the lateral side or the rear side of the ultrasonic actuator100. The displacement sensor irradiates the ultrasonic actuator100with laser light, for example, and detects the displacement of the ultrasonic actuator100based on the reflected laser light. A detection signal detected by the detection unit500is sent to a control unit.

Next, the configuration of the control system will be described with reference toFIG. 10. A control unit70controls the entire apparatus and calculates a measurement value, for example. The control unit70is configured from a general central processing unit (CPU)71, a ROM72, and a RAM73, for example. Various programs for controlling an operation of the ultrasonic tonometer1and initial values are stored in the ROM72. The RAM73temporarily stores various information. The control unit70may be configured by one control unit or a plurality of control units (that is, a plurality of processors). The control unit70may be connected to, for example, the drive unit5, a storage unit74, a display unit75, an operation unit76, the ultrasonic actuator100, the optical unit200, and the detection unit500.

The storage unit74is a non-transitory storage medium that can retain stored contents even though power supply is cut off. For example, a hard disk drive, a flash ROM, or a removable USB memory can be used as the storage unit74.

The display unit75displays a measurement result of the subject eye, for example. The display unit75may include a touch panel function.

The operation unit76receives various operation instructions from an examiner. The operation unit76outputs an operation signal according to the input operation instruction to the control unit70. The operation unit76may be, for example, a user interface of at least one of a touch panel, a mouse, a joystick, and a keyboard. In the case where the display unit75is a touch panel, the display unit75may function as the operation unit76.

A control operation of the ultrasonic tonometer1having the above configuration will be described. At first, the control unit70performs alignment of the ultrasonic tonometer1with respect to a subject eye of a subject whose face is supported by the face support unit4. For example, the control unit70detects a bright spot by the index projection system250from an anterior ocular front image acquired by the light receiving element222, and drives the drive unit5so that a position of the bright spot becomes a predetermined position. Of course, the examiner may manually perform alignment on the subject eye using the operation unit76or the like while viewing the display unit75. When the control unit70drives the drive unit5, the control unit70determines whether the alignment is appropriate based on whether the position of the bright spot of the anterior ocular image is the predetermined position or not.

After completing the alignment on the subject eye E, the control unit70measures the corneal thickness by the corneal thickness measuring system270. For example, the control unit70calculates the corneal thickness based on the light receiving signal received by the light receiving element275. For example, the controller70may obtain the corneal thickness from a positional relationship between a peak value of reflected light on the front surface of the corneal and a peak value of reflected light on the back surface of the cornea, based on the received light signal. The control unit70stores, for example, the calculated corneal thickness in the storage unit74or the like.

Subsequently, the control unit70measures the intraocular pressure of the subject eye using the ultrasonic actuator100. For example, the control unit70applies a voltage to the ultrasonic element110and irradiates the subject eye E with the ultrasonic wave. For example, the control unit70deforms the cornea by generating an acoustic radiation pressure by the ultrasonic wave. Then, the control unit70detects the deformed state of the cornea by the deformation detection system260. For example, the control unit70detects that the cornea is deformed into a predetermined shape (applanation state or flat state) based on the light receiving signal of the light receiving element263.

For example, the control unit70calculates the intraocular pressure of the subject eye based on the acoustic radiation pressure when the cornea of the subject eye deforms into the predetermined shape. The acoustic radiation pressure applied to the subject eye correlates with an irradiation time of the ultrasonic wave, and increases as the irradiation time of the ultrasonic wave increases. Therefore, the control unit70obtains the acoustic radiation pressure at the moment that the cornea is deformed into the predetermined shape based on the irradiation time of the ultrasonic wave. The relationship between the acoustic radiation pressure at the moment that the cornea is deformed into the predetermined shape and the intraocular pressure of the subject eye is obtained in advance by experiments or the like, and the relationship is stored in the storage unit74or the like. The control unit70determines the intraocular pressure of the subject eye based on the acoustic radiation pressure at the moment that the cornea is deformed into the predetermined shape and the relationship stored in the storage unit74.

The method of calculating the intraocular pressure is not limited to the above, and various methods may be used. For example, the control unit70may obtain the intraocular pressure by obtaining the deformation amount of the cornea by the deformation detection system260and multiplying the deformation amount by a conversion factor. For example, the control unit70may correct an intraocular pressure value calculated according to the corneal thickness stored in the storage unit74.

The control unit70may measure the intraocular pressure based on the ultrasonic wave reflected by the subject eye. For example, the control unit70may measure the intraocular pressure based on a change in the characteristics of the ultrasonic wave reflected by the subject eye, or may acquire the deformation amount of the cornea from the ultrasonic wave reflected by the subject eye and measure the intraocular pressure based on the deformation amount.

DESCRIPTION OF REFERENCE NUMERALS