JP2007202734A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intraocular pressure sensor to realize a higher accuracy sensor system, a simpler structure and a smaller system which is a contact pressure sensor to be used as a tonometer used for an early diagnosis of glaucoma. <P>SOLUTION: The pressure sensor, employing a structure in which the main oscillation of a piezoelectric single crystal serves as a bending oscillation, is built so as to make an oscillation figure conversion section length (L) range from 75% to 92% of a maximum output value. By using the change of resonance frequency or resonance resistance (output voltage) in accordance with the height of the aqueous humor pressure at the time when the leakage energy of a lateral oscillation is emitted into aqueous humor through a cornea, the pressure sensor senses the intraocular pressure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric vibration-type compact intraocular pressure sensor that belongs to the structure of a pressure sensor that directly contacts a cornea to detect intraocular pressure, and that enables highly accurate measurement in spite of being invasive (in vivo). .

  About 6% of people over the age of 40 are said to have “glaucoma”. The two most basic types of glaucoma are open angle glaucoma (POAG) and closed angle glaucoma (PACG), which belong to primary glaucoma (Primary galucoma) and depend on the mechanism of aqueous outflow inhibition. Things are the cause. Among them, normal-tension glaucoma (NTG) is a topic in academic societies because it is genetically very common in Japanese. On the other hand, secondary glaucoma (Secondary galucoma) is associated with primary glaucoma, and this is considered to be caused by a decrease in corner function or obstruction due to other diseases.

And although glaucoma is a disease that accounts for the top causes of blindness, about half of the patients are not aware of the illness and are generally regarded as diseases of the elderly. It is one of the diseases for which early detection and early treatment are desired because it can occur even in the layer, and it is difficult to recover vision once affected or progressed.
The following three items are essential for early detection of glaucoma: (1) Tonometry, (2) Fundus examination, and (3) Perimetry. A comprehensive diagnosis is made from the data results. This intraocular pressure sensor was developed from such a social background and necessity.
In addition, the applicant has not found any prior art documents related to the present invention by the present application other than the prior art documents specified by the prior art document information described above.

  Generally used intraocular pressure sensor devices (tonometers) are roughly classified into “contact type” and “non-contact type”. In the contact method, a constant pressure is applied to the cornea and the amount of change is measured. The press-fitting method, and the “force” or “time” required to cause a constant change in the cornea is measured. "Schetz Tonometer" and "Abrasion Tonometer" are famous. These contact-type tonometers have high measurement accuracy, but there are problems that the operation is complicated and skill is required, and the apparatus is complicated and expensive.

  On the other hand, in the “non-contact type” used for group health examinations, an air injection nozzle embedded in the center of the objective lens is brought close to the eye to be examined, and air is blown toward the center of the cornea from that position. The air pressure at the moment when the central part of the lens is deformed into a predetermined shape is detected and used as a measured value. In such a non-contact type, a large measurement error occurs unless the alignment of the air injection nozzle with respect to the eye cornea to be examined is accurate. The eye to be examined is easy to move and it is difficult to accurately align the position of the air injection nozzle, and the skill of the measurer and measurement error are inevitable. In recent years, there are some that automatically perform alignment, but the applicant does not have the accuracy evaluation data.

  In order to solve the above-described problems, the present invention introduces (propagates) bending vibration generated by the natural vibration of the vibration part serving as a structure into a vibration state conversion part constructed integrally with the vibration part, and has the same frequency. After conversion to lateral vibration, the lateral vibration is diffused into the eyeball (cornea) through the eyepiece constructed at the end of the vibration mode conversion part, and the change of vibration diffusion state due to the pressure change of aqueous humor present just under the cornea Is a pressure sensor that detects a change in frequency of natural vibration or a change in resonance resistance.

  Further, in the present invention, the connecting portion of the vibration state converting portion constructed experimentally integrated with one end in the longitudinal direction of the rod-like bending vibration portion is defined as the fixed end, and the length to the eyepiece at the tip opposite to the fixed end is set. When the vibration output value and the resonance frequency are measured while the entire eyepiece is bound and fixed while changing the length (L: the length of the vibration state conversion portion), the vibration output value and the resonance frequency value are cyclic. Therefore, paying attention to the vibration output value, the vibration output value is an arbitrary value corresponding to the range of 75% to 92% with respect to the value (maximum output value) that is the maximum output within the arbitrary one cycle. It is the pressure sensor which set the length dimension (L) of the said vibration state conversion part to length.

  The sensor structure of the present invention is constructed of a piezoelectric single crystal, and the eyepiece surface is polished with an Au thin film with a Ti thin film as a base and further subjected to hydrophobic processing. It is characterized by.

  Here, the outline of the eyeball cross section and the names of each part are shown in FIG. In a normal person, the aqueous humor that fills the space between the lens and the cornea is well-balanced in production and excretion, and the pressure (intraocular pressure) is kept constant. Its primary drainage mechanism is located at the corner of the anterior chamber, and in the normal state is responsible for 83 to 96% of the aqueous humor outflow. The secondary drainage mechanism is the secondary outflow tract and the uveal-scleral aqueous humor outflow system. However, in glaucoma, it has been found that the pressure of aqueous humor increases due to outflow inhibition mainly in the corners. Therefore, the pressure of aqueous humor is measured. Doing is a powerful clue to diagnosing glaucoma.

  Therefore, in the present invention, flexural vibration, which is the natural vibration of the piezoelectric single crystal structure, is used, converted into lateral vibration in the vibration state conversion section serving as a vibration transmission system, and brought into contact with the cornea at a constant pressure to transmit vibration energy through the cornea. Diffuse (leak) into the aqueous humor. At that time, since the permeation conditions of leak energy differ depending on the pressure of the aqueous humor, the impedance of the vibration transmission system as seen from the vibration system changes, resulting in a change in the amount of vibration restraint (resistance) relative to the main vibration. As a result, it is possible to measure intraocular pressure by detecting these values from changes in the vibration output voltage caused by changes in the natural vibration frequency and the value of the resonance resistance. As a result, it is possible to provide a low-cost, small-sized, and general-purpose tonometric sensor that has high measurement accuracy and can be easily measured because of the contact type.

  In the present invention, bending vibration energy, which is a natural vibration of the piezoelectric single crystal structure, is converted into lateral vibration in the propagation system, and the vibration energy is transmitted to the aqueous humor under the cornea via the eyepiece of the propagation system, Measures intraocular pressure from changes in the natural vibration frequency and resonance resistance value reflecting the state of vibration energy mole corresponding to the pressure of the aqueous humor. Therefore, it is possible to provide an accurate, inexpensive, small-sized, and general-purpose tonometric sensor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 shows a tuning fork type sensor element using one of the piezoelectric single crystals and a quartz material as an example for explaining the contents of the present invention. For simplicity, electrodes necessary for exciting flexural vibration, The lead portion and the like are omitted. In FIG. 2, the upper side partitioned by the lines (a)-(a ′) is the vibration part, the lower side is the vibration state conversion part, and this boundary part is the fixed end of the vibration part.

  When an AC voltage is applied from the outside to the tuning fork type sensor element, as shown in FIG. 3, a bending vibration indicated by a solid line and a dotted line with the maximum amplitude at the free end (vibrating part opposite the fixed end) is generated in the vibrating part. For this reason, the vibration state conversion unit near the fixed end of each vibration unit branch receives this main vibration and induces stretching vibration in the longitudinal direction of the vibration state conversion unit. In other words, the fixed end is not completely “fixed”, and stretching vibrations in the opposite direction are induced on the left and right of one vibration part branch, and the vibration by the two vibration part branches penetrates the front and back of the vibration state conversion part. It becomes a reciprocating vibration that rotates around a nodal point (symbolized as a black dot in Fig. 3) that occurs symmetrically. As a result, the eyepiece at the fixed end of the vibration state conversion part is a "lateral vibration" parallel to the paper surface. Will be induced.

  At this time, the distance between the fixed end of the vibration part of the sensor element and the eyepiece part, that is, the length in the longitudinal direction of the vibration state conversion part is set to (L), and the eyepiece is experimentally changed while changing this dimension. When the part is separately fixed to the base using an adhesive or the like (bound and fixed) and bending vibration is excited, the resonance frequency and output voltage of the sensor element have a certain period as shown in FIG. It was confirmed that it changed. This is because the flexural vibration, which is the main vibration shown in FIG. 4 (b), propagates in the vibration state conversion section while changing the shape, but at that time, it has a specific standing wave corresponding to the length (L). The vibration energy leaks to the fixing base through the eyepiece in the portion of the L dimension where the frequency change rate is large or the output voltage is low. On the contrary, there is no change in frequency, or in the portion of the L dimension where the output voltage is high, it means that vibration energy is confined and there is no outflow of energy to the outside.

  Normally, when designing a resonant oscillator, the vibration energy is confined by setting the L dimension so that the vibration energy of the main vibration does not flow out to the support system, or the frequency is not changed, or the output voltage is set to a high L dimension. However, in the intraocular pressure sensor of the present invention, the bending vibration energy, which is the main vibration, is converted into lateral vibration by the vibration state conversion unit, and the vibration energy is transmitted through the eyepiece. Intraocular pressure is measured from a change in resonance frequency or a change in output voltage caused by a change in vibration energy corresponding to the pressure of aqueous humor under the cornea.

  Therefore, the setting of the leakage amount of vibration energy is important, and the L dimension is set as shown in FIG. 4B so that the vibration energy is in contact with the maximum output value between 75% and 92%. Setting so as to leak (leak) to the outside (measurement site) via the eye part is a condition for minimizing vibration disturbance and maintaining high sensitivity.

  FIG. 5 is a diagram illustrating a state during measurement of intraocular pressure. The sensor element requires two electrical terminals for connection to an external oscillator circuit due to the vibration, and the nodal point described in FIG. (In terms of the shape of the vibration mode, there are two points penetrating the front and back of the vibration mode conversion unit, but if expressed on the surface of the vibration mode conversion unit, it appears at the front and back and left and right symmetrical positions, so there are four points) This is used as a sensor element support portion, and also serves as a structure for drawing out two electrical terminals. The eyepiece is polished by mechanical polishing and flattened. The surface of the eyepiece is constructed by sputtering a thin Au film based on a Ti thin film, and then subjected to sterilization washing and hydrophobic treatment immediately before measurement. It is desirable to use it. This is because tears and the like wet the side surface of the vibration state converting portion of the sensor element, and have the effect of preventing the occurrence of measurement errors due to unnecessary leakage of vibration energy.

  In intraocular pressure measurement, the eye to be examined is anesthetized, the sensor element is caused to vibrate (oscillate), the frequency or the output voltage is recorded, and then the eyepiece (the bottom of the vibration state converter) is kept at a constant pressure (eyepiece). It is possible to detect the intraocular pressure from the frequency or the difference between the output voltage and the contacted eye cornea.

It is the top view which shows the schematic of an eyeball cross section, and each part name. It is a conceptual diagram which shows the concept of the intraocular pressure sensor of this invention. It is a conceptual diagram which shows the concept of the vibration mode of the intraocular pressure sensor of this invention. (A) It is a graph which shows the relationship between the resonance frequency change and vibration output change, and the vibration mode conversion part length (L). (B) It is the graph which expanded and described the relationship between a vibration output change and a vibration state conversion part length about the arbitrary periods in the graph of (a), and demonstrated the position of the vibration state conversion part length to set. It is a state figure which shows the mode at the time of intraocular pressure measurement.

Claims (3)

The bending vibration generated by the natural vibration of the vibration part built in the structure is introduced into the vibration state conversion part integrated with the vibration part, converted into the horizontal vibration of the same frequency, and then the transverse vibration is converted into the vibration state. Diffuses in the eyeball (cornea) through the eyepiece constructed at the end of the head part, and changes in the vibration diffusion state due to changes in the aqueous humor present directly under the cornea can change the frequency of the natural vibration or change in the resonance resistance. A pressure sensor characterized by detecting as The connection part with the vibration state conversion part constructed integrally with one end in the longitudinal direction of the rod-shaped bending vibration part as a fixed end in the description of claim 1, and located at a tip opposite to the fixed end of the vibration state conversion part The maximum output value of 75 that is within an arbitrary period of the vibration output value that changes periodically when the length of the eyepiece is changed (L: the length of the vibration state conversion unit) is changed. A pressure sensor characterized by being set in a range of% to 92%. 3. The sensor structure according to claim 1 and claim 2, wherein the sensor structure is constructed of a piezoelectric single crystal, the eyepiece surface is constructed of an Au thin film after polishing and further subjected to hydrophobic processing. Features a pressure sensor.

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