Patent Publication Number: US-2015087953-A1

Title: Non-invasive intraocular pressure sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 102134839, filed on Sep. 26, 2013. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an intraocular pressure sensor and more particularly relates to a non-invasive intraocular pressure sensor. 
     2. Description of Related Art 
     With the development of the society, people are spending more and more time on working. The progress of technology also increases use of electronic products significantly. Long hours of work or use of electronic products at a close distance may result in overuse of the eyes and easily cause discomfort, such as eye fatigue and excessive intraocular, etc., which accelerates aging of the eye and easy causes high degree myopia. In general, people having high degree myopia, diabetes, or high blood pressure, or having a family history of glaucoma are at high risk of glaucoma, or even blindness. Therefore, it is a very important part to timely monitor intraocular pressure in order to maintain the health of the eyes. 
     Currently, the typical method for measurement of the intraocular pressure is to use an optical instrument or a piezoresistive tonometer to measure the patient&#39;s eye pressure when the patient comes to see the doctor. However, these two methods are limited by the clinic hours and are not suitable for long-term monitoring. In addition, there is another method for measuring the intraocular pressure, which is to implant a chip in the eyes of the patient so as to monitor for a long time. However, this method requires surgery. There are certain risks due to surgery, and thus the patient&#39;s acceptance is generally not high. In recent years, a resistive non-invasive intraocular pressure sensor has been developed, which includes a resistive element embedded in the contact lens and utilizes resistance variation caused by the variation of the intraocular pressure of the eyeball to measure the intraocular pressure. The advantage is that the intraocular pressure of the patient can be monitored for a long period of time without surgery. However, the resistance value has very little variation, and the frequency of variation in the intraocular pressure is 0.01 Hz or less. It can be known from the equation of noise power spectral density, namely V 2 =4 kTR (unit: V 2 /Hz, wherein k represents the Boltzmann constant, T represents the absolute temperature, and R represents the resistance value), that the noise is very large when the resistance and the frequency are both very small. Therefore, it is difficult to use this method to measure the correct values of intraocular pressure variation, and due to a large number of noise, the subsequent signal processing of the values also becomes difficult. 
     SUMMARY OF THE INVENTION 
     The invention provides a non-invasive intraocular pressure sensor that is adapted for long-term monitoring and obtaining relatively stable intraocular pressure signals without surgery. 
     A non-invasive intraocular pressure sensor of the invention is adapted to be configured on an eyeball. The non-invasive intraocular pressure sensor includes a sensing unit and a readout circuit. The sensing unit includes a plurality of electrode layers and a dielectric layer. The dielectric layer encloses the electrode layers and fills between the electrode layers. The electrode layers and the dielectric layer form a capacitor, and a variation of capacitance of the capacitor varies with the variation of the intraocular pressure of the eyeball. The readout circuit is electrically connected to the sensing unit. 
     In an embodiment of the invention, the electrode layers include a first electrode layer and a second electrode layer electrically insulated from the first electrode layer. 
     In an embodiment of the invention, a material of the dielectric layer is a polymer material. 
     In an embodiment of the invention, the electrode layers include circular main body portions that share a center axis. 
     In an embodiment of the invention, the main body portions partially overlap each other in a front view thereof. 
     In an embodiment of the invention, the main body portions do not overlap each other in the front view thereof. 
     In an embodiment of the invention, each of the electrode layers further includes a plurality of protruding portions protruding from the main body portion. 
     In an embodiment of the invention, the protruding portions all protrude outward or inward, wherein the main body portions partially overlap each other and the protruding portions partially overlap each other. 
     In an embodiment of the invention, the electrode layers include a first electrode layer and a second electrode layer electrically insulated from the first electrode layer, wherein the first electrode layer includes a first main body portion and a plurality of first protruding portions protruding from the first main body portion, and the second electrode layer includes a second main body portion and a plurality of second protruding portions protruding from the second main body portion. The first protruding portions protrude toward the second main body portion while the second protruding portions protrude toward the first main body portion, and the first protruding portions and the second protruding portions are arranged alternately. 
     In an embodiment of the invention, the readout circuit converts the variation of the capacitance to a voltage signal. 
     In an embodiment of the invention, the readout circuit converts the variation of the capacitance to a digital signal. 
     In an embodiment of the invention, the readout circuit converts the variation of the capacitance to an oscillation frequency signal. 
     In an embodiment of the invention, the readout circuit includes an inductor, wherein the sensing unit and the inductor form an oscillation circuit. 
     In an embodiment of the invention, the readout circuit includes an inductor and a resistor, wherein the sensing unit, the inductor, and the resistor form an oscillation circuit. 
     In an embodiment of the invention, the non-invasive intraocular pressure sensor further includes a soft contact lens. 
     In an embodiment of the invention, the sensing unit and the readout circuit are embedded in the soft contact lens, and the sensing unit and the soft contact lens share a center axis. 
     In an embodiment of the invention, the readout circuit is embedded in the soft contact lens while the sensing unit is disposed on an external surface of the soft contact lens and shares a center axis with the soft contact lens. 
     In an embodiment of the invention, the non-invasive intraocular pressure sensor further includes a power supply unit electrically connected to the readout circuit. 
     In an embodiment of the invention, the non-invasive intraocular pressure sensor further includes a data conversion unit electrically connected to the readout circuit and the power supply unit. 
     In an embodiment of the invention, the non-invasive intraocular pressure sensor further includes a wireless transmission unit electrically connected to the readout circuit and the power supply unit. 
     In an embodiment of the invention, the non-invasive intraocular pressure sensor further includes a data conversion unit and a wireless transmission unit, wherein the data conversion unit is electrically connected to the readout circuit and the wireless transmission unit. 
     In an embodiment of the invention, a material of the first electrode layer and the second electrode layer is a metal, an alloy, or a combination of the above. 
     In an embodiment of the invention, a material of the first electrode layer and the second electrode layer is a metal oxide. 
     Based on the above, the non-invasive intraocular pressure sensor of the invention measures the intraocular pressure by detecting the variation of capacitance resulting from the variation of the intraocular pressure of the eyeball. According to the equation of noise power spectral density, it is known that the noise is inversely proportional to the capacitance. In other words, the higher the capacitance, the lower the noise. Therefore, the non-invasive intraocular pressure sensor of the invention is able to measure values of variation of the intraocular pressure with relatively low noise and high accuracy, and the values of variation of the intraocular pressure are relatively stable and suitable for the subsequent signal processing, which is conducive to improving the analytical ability of an intraocular pressure measuring system. In addition, because the non-invasive intraocular pressure sensor of the invention is a non-implanted intraocular pressure sensor, surgery is not required. Further, the combination of the non-invasive intraocular pressure sensor and the contact lens allows the user to wear the non-invasive intraocular pressure sensor by himself/herself and use it for a long period of time, which is suitable for long-term monitoring. 
     To make the aforementioned and other features and advantages of the invention more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1A  is a schematic top view of a non-invasive intraocular pressure sensor according to the first embodiment of the invention. 
         FIG. 1B  is a schematic cross-sectional view taken along the line section A-A′ in  FIG. 1A . 
         FIG. 1C  is a schematic cross-sectional view of another non-invasive intraocular pressure sensor according to the first embodiment of the invention. 
         FIG. 2  is a diagram illustrating the relationship between a curvature of a cornea and the variation of an intraocular pressure. 
         FIG. 3A  and  FIG. 3B  are schematic top view and cross-sectional view of a non-invasive intraocular pressure sensor according to the second embodiment of the invention. 
         FIG. 4A  and  FIG. 4B  are schematic top view and cross-sectional view of a non-invasive intraocular pressure sensor according to the third embodiment of the invention. 
         FIG. 5A  and  FIG. 5B  are schematic top view and cross-sectional view of a non-invasive intraocular pressure sensor according to the fourth embodiment of the invention. 
         FIG. 6  is a diagram of a non-invasive intraocular pressure sensor according to the fifth embodiment of the invention. 
         FIG. 7  is a diagram of a non-invasive intraocular pressure sensor according to the sixth embodiment of the invention. 
         FIG. 8  is a diagram of a non-invasive intraocular pressure sensor according to the seventh embodiment of the invention. 
         FIG. 9  is a diagram of a non-invasive intraocular pressure sensor according to the eighth embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1A  is a schematic top view of a non-invasive intraocular pressure sensor according to the first embodiment of the invention.  FIG. 1B  is a schematic cross-sectional view taken along the line section A-A′ in  FIG. 1A .  FIG. 1C  is a schematic cross-sectional view of another non-invasive intraocular pressure sensor according to the first embodiment of the invention. In  FIG. 1A , a dielectric layer of a sensing unit is omitted. With reference to  FIG. 1A  and  FIG. 1B , a non-invasive intraocular pressure sensor  100  of this embodiment is adapted to be configured on an eyeball of a user for measuring an intraocular pressure of the eyeball. The non-invasive intraocular pressure sensor  100  includes a sensing unit  110  and a readout circuit  120 . The sensing unit  110  and the readout circuit  120  may be used with a flexible member. For example, the sensing unit  110  and the readout circuit  120  are disposed on or embedded in the flexible member to be worn or removed by the user easily. 
     More specifically, the non-invasive intraocular pressure sensor  100  may further include a soft contact lens  130 . In this embodiment, the sensing unit  110  is embedded in the soft contact lens  130 , for example, but the invention is not limited thereto. Moreover, the sensing unit  110  and the soft contact lens  130  share a center axis O, for example. In addition, the readout circuit  120  may be embedded in the soft contact lens  130 , disposed on the soft contact lens  130 , or connected with the soft contact lens  130  externally (that is, the readout circuit  120  is not in contact with the soft contact lens  130 ). For instance, the readout circuit  120  may be disposed on the face of the user or in other suitable positions and electrically connected with the sensing unit  110  via two wires. 
     To make it conformable to wear, the soft contact lens  130  is preferably formed using a hydrophilic material with high oxygen permeability such that the non-invasive intraocular pressure sensor  100  is adapted to be worn for a long period of time for long-term monitoring. For example, the material of the soft contact lens  130  can be hydrogel (scientific name: 2-Hydroxyethyl methacrylate, HEMA). 
     The sensing unit  110  includes a plurality of electrode layers and a dielectric layer  116 . In the following descriptions of this embodiment, a first electrode layer  112  and a second electrode layer  114  are given as an example; however, the invention should not be construed as limited thereto. In some other embodiments, the sensing unit  110  may include two electrode layers or more. In this embodiment, the first electrode layer  112  has a first main body portion  112   a  that is circular, and the second electrode layer  114  has a second main body portion  114   a  that is circular, wherein the first main body portion  112   a  and the second main body portion  114   a  share the center axis O. In addition, the first main body portion  112   a  and the second main body portion  114   a  overlap each other partially, for example; however, the invention should not be construed as limited thereto. 
     The dielectric layer  116  encloses the first electrode layer  112  and the second electrode layer  114  and fills between the first electrode layer  112  and the second electrode layer  114 , so as to electrically insulate the first electrode layer  112  and the second electrode layer  114  from each other. The dielectric layer  116  is formed using a polymer material, such as Parylene C, for example. The first electrode layer  112  and the second electrode layer  114  are formed using a metal, an alloy, or a combination thereof, for example; however, the invention should not be construed as limited thereto. In another embodiment, the first electrode layer  112  and the second electrode layer  114  are formed using a transparent conductive material, such as a metal oxide, to provide better light transmittance. The metal oxide may be indium tin oxide, indium zinc oxide, aluminum tin oxide, aluminum zinc oxide, indium germanium zinc oxide, other suitable oxides, or a stack layer including at least two of the above. 
     The first electrode layer  112 , the second electrode layer  114 , and the dielectric layer  116  disposed between the first electrode layer  112  and the second electrode layer  114  form a capacitor C, wherein a variation of capacitance of the capacitor C varies with the variation of the intraocular pressure of the eyeball. The readout circuit  120  is electrically connected to the sensing unit  110 . Depending on different design requirements, the readout circuit  120  is adapted to convert the variation of capacitance to a voltage signal, digital signal or oscillation frequency signal to be analyzed and processed by a reader and a controller that are connected externally. In the case that the variation of capacitance is converted to an oscillation frequency signal, the readout circuit  120  may further include an inductor that is not illustrated here, wherein the sensing unit  110  and the inductor form an oscillation circuit. Alternatively, the readout circuit  120  may further include the inductor and a resistor that are not illustrated here, wherein the sensing unit  110 , the inductor, and the resistor form an oscillation circuit. 
     How the variation of the intraocular pressure causes the variation of capacitance is explained below with reference to  FIG. 1B  and  FIG. 2 .  FIG. 2  is a diagram illustrating the relationship between a curvature of a cornea and the variation of the intraocular pressure. With reference to  FIG. 1B  and  FIG. 2 , when the non-invasive intraocular pressure sensor  100  is worn on the eyeball of the user, the non-invasive intraocular pressure sensor  100  is bent conform to the curvature of the cornea of the eyeball, as indicated by a curve C1 of  FIG. 2 . However, the curvature of the cornea varies with the variation of the intraocular pressure. For example, as the intraocular pressure increases, as indicated by a curve C2 of  FIG. 2 , a curvature radius R1 of the non-invasive intraocular pressure sensor  100  increases, and as a result, a projection radius R2 of the curvature radius R1 on a plane perpendicular to the center axis O decreases correspondingly. In other words, as the curvature of the cornea varies with the variation of the intraocular pressure, a degree of bending of the non-invasive intraocular pressure sensor  100  varies correspondingly. Accordingly, the first electrode layer  112  and the second electrode layer  114  may be deformed respectively. For example, the variation of the curvature of the cornea stretches the second electrode layer  114  that is disposed on an external side and compresses the first electrode layer  112  that is disposed on an internal side; or a distance D or an area between the first electrode layer  112  and the second electrode layer  114  varies with the variation of the curvature of the cornea, so that the variation of capacitance of the capacitor C varies with the variation of the intraocular pressure of the eyeball. 
     It is known from the equation of noise power spectral density, namely V 2 =kT/C (unit: V 2 /Hz, wherein k represents a Boltzmann constant, T represents an absolute temperature, and C represents the capacitance), that the higher the capacitance, the lower the noise. Therefore, in comparison with a resistive non-invasive intraocular pressure sensor, the non-invasive intraocular pressure sensor  100  of this embodiment is more suitable for measuring slight variation of the intraocular pressure. Because the non-invasive intraocular pressure sensor  100  of this embodiment is able to measure values of variation of the intraocular pressure with relatively low noise and high accuracy, the values of variation of the intraocular pressure are relatively stable and suitable for the subsequent signal processing, which is conducive to improving the analytical ability of an intraocular pressure measuring system. 
     It is worth mentioning that, as the curvature of the cornea varies with the variation of the intraocular pressure, the first electrode layer  112  and the second electrode layer  114  have the maximum deformation at an external surface of the soft contact lens  130 . Thus, in another embodiment, as illustrated in  FIG. 1C , a variation of the capacitance can be further increased by disposing the sensing unit  110  on an external surface S of the soft contact lens  130 . 
     It should be noted that the pattern design and relative configuration of the first electrode layer  112  and the second electrode layer  114  of the invention are not limited to the examples illustrated in  FIG. 1A  to  FIG. 1C . Please refer to  FIG. 3A  and  FIG. 3B ,  FIG. 4A  and  FIG. 4B , and  FIG. 5A  and  FIG. 5B  for other embodiments of the first electrode layer  112  and the second electrode layer  114 .  FIG. 3A  and  FIG. 3B  are schematic top view and cross-sectional view of a non-invasive intraocular pressure sensor according to the second embodiment of the invention. With reference to  FIG. 3A  and  FIG. 3B , a non-invasive intraocular pressure sensor  200  of this embodiment is similar to the non-invasive intraocular pressure sensor  100  of  FIG. 1A  and  FIG. 1B . Thus, identical elements are assigned with the same reference numerals. A main difference therebetween lies in that, in a front view as shown in  FIG. 3A , the first main body portion  112   a  and the second main body portion  114   a  do not overlap each other. 
       FIG. 4A  and  FIG. 4B  are schematic top view and cross-sectional view of a non-invasive intraocular pressure sensor according to the third embodiment of the invention. With reference to  FIG. 4A  and  FIG. 4B , a non-invasive intraocular pressure sensor  300  of this embodiment is similar to the non-invasive intraocular pressure sensor  100  of  FIG. 1A  and  FIG. 1B . Thus, identical elements are assigned with the same reference numerals. A main difference lies in that a first electrode layer  112 ′ of a sensing unit  110 ′ further includes a plurality of first protruding portions  112   b  connected with the first main body portion  112   a , and a second electrode layer  114 ′ further includes a plurality of second protruding portions  114   b  connected with the second main body portion  114   a . Moreover, the first main body portion  112   a  and the second main body portion  114   a  overlap each other partially while the first protruding portions  112   b  and the second protruding portions  114   b  overlap each other partially, and the first protruding portions  112   b  and the second protruding portions  114   b  all protrude outward, for example; however, the invention should not be construed as limited thereto. In another embodiment, the first protruding portions  112   b  and the second protruding portions  114   b  may all protrude inward. 
       FIG. 5A  and  FIG. 5B  are schematic top view and cross-sectional view of a non-invasive intraocular pressure sensor according to the fourth embodiment of the invention. With reference to  FIG. 5A  and  FIG. 5B , a non-invasive intraocular pressure sensor  400  of this embodiment is similar to the non-invasive intraocular pressure sensor  300  of  FIG. 4A  and  FIG. 4B . Thus, identical elements are assigned with the same reference numerals. A main difference therebetween lies in that the first protruding portions  112   b  protrude toward the second main body portion  114   a  while the second protruding portions  114   b  protrude toward the first main body portion  112   a , and the first protruding portions  112   b  and the second protruding portions  114   b  are arranged alternately without overlapping each other. It should be understood that, under the aforementioned concept, the shapes and sizes of the patterns of the first main body portion  112   a , the second main body portion  114   a , the first protruding portion  112   b , and the second protruding portion  114   b  may be varied in accordance with the design requirements, and details thereof will omitted here. 
     Hereinafter,  FIG. 6  to  FIG. 9  illustrate an intraocular pressure measuring system adapted to use the non-invasive intraocular pressure sensor  100 ,  200 ,  300 , or  400 .  FIG. 6  is a diagram of a non-invasive intraocular pressure sensor according to the fifth embodiment of the invention. With reference to  FIG. 6 , a non-invasive intraocular pressure sensor  500  of this embodiment includes a sensing unit  510  and the readout circuit  120 , wherein the sensing unit  510  may be the sensing unit  110  or  110 ′ illustrated in  FIG. 1A ,  FIG. 1B ,  FIG. 1C ,  FIG. 3A ,  FIG. 3B ,  FIG. 4A ,  FIG. 4B ,  FIG. 5A , or  FIG. 5B . 
     In addition, the non-invasive intraocular pressure sensor  500  may further include a power supply unit  140 , such as a low dropout regulator, which is electrically connected to the readout circuit  120 . Furthermore, by electrically connecting the power supply unit  140  and the readout circuit  120  to a reader  610  and electrically connecting the reader  610  to a controller  620 , the aforementioned voltage signal, digital signal, or oscillation frequency signal can be analyzed and processed. For instance, in the case that the readout circuit  120  converts the variation of capacitance to a voltage signal, the reader  610  may include an analog to digital converter (ADC); in the case that the readout circuit  120  converts the variation of capacitance to a digital signal, the reader  610  may include a digital filter; and in the case that the readout circuit  120  converts the variation of capacitance to an oscillation frequency signal, the reader  610  may include a digital frequency converter. The controller  620  is a digital signal processor or a micro processor, for example. Moreover, the controller  620  may be coupled to a storage unit or an instant monitoring system (e.g. medical station) that is not illustrated here. 
       FIG. 7  is a diagram of a non-invasive intraocular pressure sensor according to the sixth embodiment of the invention. With reference to  FIG. 7 , a non-invasive intraocular pressure sensor  600  of this embodiment is similar to the non-invasive intraocular pressure sensor  500  of  FIG. 6 . Thus, identical elements are assigned with the same reference numerals and will not be described in detail hereinafter. A main difference lies in that the non-invasive intraocular pressure sensor  600  of this embodiment further integrates a data conversion unit  150  in the non-invasive intraocular pressure sensor  600 . More specifically, the non-invasive intraocular pressure sensor  600  includes the data conversion unit  150  that is electrically connected to the readout circuit  120  and the power supply unit  140 , and the data conversion unit  150  is electrically connected with the reader  610 . 
       FIG. 8  is a diagram of a non-invasive intraocular pressure sensor according to the seventh embodiment of the invention. With reference to  FIG. 8 , a non-invasive intraocular pressure sensor  700  of this embodiment is similar to the non-invasive intraocular pressure sensor  500  of  FIG. 6 . Thus, identical elements are assigned with the same reference numerals and will not be described in detail hereinafter. A main difference lies in that the non-invasive intraocular pressure sensor  700  of this embodiment transmits a signal to the reader  610  via wireless transmission, and the reader  610  is power-supplied by the power supply unit  140  via wireless transmission. More specifically, the non-invasive intraocular pressure sensor  700  includes a wireless transmission unit  160  that is electrically connected to the readout circuit  120  and the power supply unit  140 , and the wireless transmission unit  160  is coupled to the reader  610 . The wireless transmission unit  160  may be a radio frequency identification (RFID) system. Moreover, the wireless transmission unit  160  of this embodiment may include a circular antenna, which is embedded in or disposed on the soft contact lens, for example. In addition, the circular antenna surrounds outside the sensing unit  510  and share a center axis with the sensing unit  510 , for example. 
       FIG. 9  is a diagram of a non-invasive intraocular pressure sensor according to the eighth embodiment of the invention. With reference to  FIG. 9 , a non-invasive intraocular pressure sensor  800  of this embodiment is similar to the non-invasive intraocular pressure sensor  700  of  FIG. 8 . Thus, identical elements are assigned with the same reference numerals and will not be described in detail hereinafter. A main difference lies in that the non-invasive intraocular pressure sensor  800  of this embodiment further includes the data conversion unit  150 , wherein the data conversion unit  150  is electrically connected to the readout circuit  120  and the wireless transmission unit  160 . That is, the wireless transmission unit  160  transmits signals processed by the data conversion unit  150  to the reader  610  via wireless transmission. 
     To conclude the above, the non-invasive intraocular pressure sensor of the invention measures the intraocular pressure by detecting the variation of capacitance resulting from the variation of the intraocular pressure of the eyeball. According to the equation of noise power spectral density, it is known that the noise is inversely proportional to the capacitance. In other words, the higher the capacitance, the lower the noise. Therefore, the non-invasive intraocular pressure sensor of the invention is able to measure values of variation of the intraocular pressure with relatively low noise and high accuracy, and the values of variation of the intraocular pressure are relatively stable and suitable for the subsequent signal processing, which is conducive to improving the analytical ability of the intraocular pressure measuring system. In addition, because the non-invasive intraocular pressure sensor of the invention is a non-implanted intraocular pressure sensor, surgery is not required. The combination of the non-invasive intraocular pressure sensor and the contact lens allows the user to wear the non-invasive intraocular pressure sensor by himself/herself and use it for a long period of time, which is suitable for long-term monitoring. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention covers modifications and variations of this disclosure provided that they fall within the scope of the following claims and their equivalents.