Patent Publication Number: US-2007123767-A1

Title: Intraocular pressure sensor and method of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application for a utility patent is a continuation-in-part of a previously filed application for utility patent, now abandoned, having the application Ser. No. 10/452,109, filed Jun. 2, 2003. This application for a utility patent is also a continuation-in-part of a second previously filed application for utility patent, still pending, having application Ser. No. 11/059,571, filed Feb. 16, 2005. This application also claims the benefit of U.S. Provisional Application No. 60/384,632, filed May. 31, 2002. The previous applications are hereby incorporated by reference in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
      Not Applicable  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to medical devices for monitoring conditions in an eye of a patient, and more particularly to an intraocular pressure sensor adapted to be positioned within the eye for measuring the intraocular pressure thereof.  
      2. Description of the Prior Art  
      Implantable devices for monitoring internal physiological conditions of a patient are known in the art. One such prior art device includes an implantable pressure transducer that transmits pressure signals out of the patient by means of a wire passing through the patient&#39;s skull. These types of devices are generally unsatisfactory due to increased risk of infection and patient discomfort caused by the externally extending wire.  
      Monitoring devices that are completely implantable within a patient are also known in the art. One such prior art device includes a sensor for sensing a physiological condition of the patient and a transmitter and battery assembly for transmitting the sensor signals out of the patient&#39;s body. These types of devices are also unsatisfactory for many types of medical conditions since the batteries are bulky and must be periodically replaced, thus necessitating additional surgery.  
      The state of the art includes the following:  
      Frenkel, U.S. Pat. No. 5,005,577, teaches an implantable intraocular lens that includes a pressure sensor for measuring the pressure within an eye. A similar device is taught in Schnakenberg et al., U.S. Pat. No. 6,443,893.  
      Tremblay et al., U.S. Pat. No. 5,704,352, teaches an implantable, passive bio-sensor for monitoring internal physiological conditions of a patient. The bio-sensor includes at least one sensor or transducer for monitoring a physiological condition of the patient and a passive transponder that receives sensor signals from the sensor or sensors, digitizes the sensor signals, and transmits the digitized signals out of the patient&#39;s body when subjected to an externally generated interrogation signal. In one embodiment, the bio-sensor is incorporated into the sidewall of a shunt used for treating hydrocephalus for non-invasively monitoring the operation of the shunt.  
      Frenkel, U.S. Pat. No. 5,005,577, teaches an apparatus for monitoring intraocular pressure. The apparatus includes an implantable intraocular lens and at least one sensor apparatus responsive to intraocular pressure being affixed to the lens.  
      Jeffries et al., U.S. Pat. No. 6,193,656 B1, teaches an apparatus for monitoring intraocular pressure in an eye. The apparatus includes a miniature pressure sensor having an attachment for connecting the miniature pressure sensor to the iris of the eye or an intraocular lens. The miniature pressure sensor is preferably a Polysilicon Resonant Transducer (PRT).  
      Waters, Jr. et al., U.S. Pat. No. 4,922,913, teaches an intraocular pressure sensor that utilizes a small sensitive piezo-resistance strain gauge cell mounted in a curved semi-rigid holder which serves to position the planar pressure sensitive surface of the strain gauge cell in contact with the eyeball surface. Deformation of the strain gauge cell due to contact with the eyeball produces an output signal corresponding to the intraocular pressure. The sensor is small and can be worn in the eye like a contact lens for extended periods of time permitting the intraocular pressures to be accurately monitored under normal living conditions, including during sleep. Fine wires are led from the sensor out over the eyelid for connection to an external recording/monitoring apparatus.  
      The above-described references are hereby incorporated by reference in full.  
      The prior art teaches various sensors for monitoring physiological conditions within the body. However, the prior art does not teach an intraocular pressure sensor having the construction and benefits described herein. The present invention fulfills these needs and provides further related advantages as described in the following summary.  
     SUMMARY OF THE INVENTION  
      The present invention teaches certain benefits in construction and use which give rise to the objectives described below.  
      The present invention is a method for measuring an intraocular pressure within an eye. An intraocular pressure sensor that is adapted to be implanted intrasclerally is provided. An incision is cut through a scleral layer of the eye. The scleral layer is lifted with a grasping tool. The intraocular pressure sensor is inserted under the scleral layer, and the incision of the scleral layer is closed.  
      A primary objective of the present invention is to provide a method for measuring an intraocular pressure within an eye having advantages not taught by the prior art.  
      It is another object of the present invention to provide a method for measuring an intraocular pressure utilizing a pressure sensor adapted to be surgically implanted intrascleral for measuring the pressure within the eye.  
      It is another object of the present invention to provide a biosensor that does not require a physical connection, by wire or otherwise, to an external source.  
      It is another object of the present invention to provide a biosensor that permits non-invasive queries of conditions inside the eye of the patient.  
      Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The accompanying drawings illustrate the present invention. In such drawings:  
       FIG. 1  is an exploded perspective view of one embodiment of an intraocular pressure sensor of the present invention;  
       FIG. 2  is a block diagram of the general structure of the intraocular pressure sensor;  
       FIG. 3  is a block diagram of one particular embodiment thereof;  
       FIG. 4  is a side elevational view of a contact lens upon which the intraocular pressure sensor is operatively installed, illustrating how the intraocular pressure sensor can be positioned against an eye in one embodiment of the invention;  
       FIG. 5  is a perspective view of an intraocular lens upon which the intraocular pressure sensor has been operatively installed;  
       FIG. 6  is a side elevational view of a glaucoma drainage device upon which the intraocular pressure sensor has been operatively installed, the glaucoma drainage device being operatively installed in the eye;  
       FIG. 7  is a sectional view of the glaucoma drainage device illustrating the placement of the intraocular pressure sensor on a lumened tube of the glaucoma drainage device;  
       FIG. 8  is a block diagram of an activator/assessor device that is used in conjunction with the intraocular pressure sensor;  
       FIG. 9  is a perspective view of the activator/assessor device being used to transmit a query signal to the intraocular pressure sensor and receive a response signal in return;  
       FIG. 10  is a block diagram illustrating the activator/assessor device being used to query the intraocular pressure sensor for the purposes of calibration;  
       FIG. 11  is a block diagram illustrating the activator/assessor device being used to query the intraocular pressure sensor for purposes of ascertaining the pressure within the eye;  
       FIG. 12  is a block diagram illustrating how the activator/assessor device is adapted to work through a wireless network with a central monitoring station;  
       FIG. 13  is a chart illustrating a range of intraocular pressures, from hyper pressure, to normal pressure, and to hypo pressure;  
       FIG. 14  is a top plan view of a temporary profile device having the intraocular pressure sensor mounted therein;  
       FIG. 15  is a sectional view thereof taken along line  15 - 15  in  FIG. 14 ;  
       FIG. 16  is a perspective view of an eye, illustrating how a scleral layer is retracted for insertion of the intraocular pressure sensor;  
       FIG. 17  is a side sectional view of an eye, illustrating how a scleral layer is retracted for insertion of the intraocular pressure sensor; and  
       FIG. 18  is a side sectional view thereof, illustrating how the intraocular pressure sensor is positioned intrasclerally once the scleral layer has healed.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The above-described drawing figures illustrate the invention, an intraocular pressure sensor  10  for sensing pressure in a system such as an eye  12  of an animal. The intraocular pressure sensor  10  may be used as part of an intraocular pressure sensor system  110 , described in greater detail below.  
      Intraocular Pressure Sensor  
      As shown in  FIG. 1 , the intraocular pressure sensor  10  is manufactured using microelectromechanical systems (MEMS) manufacturing techniques, so it is small enough to be readily adapted to many methods of continuously monitoring the pressure within the eye  12 . The intraocular pressure sensor  10  may be positioned directly against the eye  12 , implanted into the eye  12 , or integrated with a medical device that is used in conjunction with monitoring or treating the eye  12 . Several possible embodiments are described in greater detail below.  
      As shown in  FIG. 2 , the intraocular pressure sensor  10  includes a pressure sensor  20  for sensing pressure within they eye  12  and for generating a sensor signal representative of the pressure; and a transponder  30  electrically coupled with the pressure sensor  20  for both powering the pressure sensor  20  and reporting via wireless communication the pressure being sensed by the pressure sensor  20 .  
      In one embodiment, as shown in  FIG. 1 , the pressure sensor  20  (shown in  FIG. 2 ) includes a sensor reed  22  and a strain gauge  24 . The sensor reed  22  is micro-machined, etched, or otherwise formed from a silicon chip body  25 . The sensor reed  22  may include any arm, lever, or similar projection which may be moved, biased, or otherwise altered in configuration in response to changes of pressure within the eye  12 . The sensor reed  22  is preferably a lever that is formed to be parallel to the surface of the silicon chip body  25 .  
      The strain gauge  24  is operably positioned to measure the flexion of the sensor reed  22 , either on the sensor reed  22  itself, or adjacent to the sensor reed  22  on the silicon chip body  25 . For purposes of this application, the term strain gauge  24  shall include any form of strain gauge, including but not limited to a single Wheatstone bridge, a plurality of Wheatstone bridges, or any other form of circuitry with an equivalent operative sensor capability, in any configuration or arrangement.  
      As shown in  FIG. 2 , the transponder  30  includes a processor  32  responsive to the pressure sensor  20  for converting the sensor signal to a pressure signal representative of the pressure, and a sensor antenna  34  adapted for receiving an interrogation signal  14  generated from outside the eye  12 . In one embodiment, the processor  32  is a microprocessor. In another embodiment, the processor  32  includes a modulator  36  for converting the pressure signal into a response signal  16 , and a power converter  38  coupled with the sensor antenna  34  for converting the interrogation signal  14  to a power signal for energizing the processor  32 . In addition to receiving the interrogation signal  14 , the sensor antenna  34  further functions to transmit the response signal  16  out of the eye  12 .  
      The sensor antenna  34  is electromagnetically coupled with an activator/assessor antenna  71  (shown in  FIGS. 8 and 9 ) for receiving an interrogation signal  14 , as described below. The power converter  38  is coupled with the sensor antenna  34  for extracting energy from the electromagnetic couple with the activator/assessor antenna  71 . The power converter  38  converts this electromagnetic energy to a current signal for powering the processor  32 . The modulator  36  is coupled with the processor  32  and the power converter  38  for receiving the digitized data from the processor  32  and for modulating the interrogation signal  14  in accordance with the digitized data stream to alter the electronic characteristics of the interrogation signal  14  to generate a response signal  16  which can be detected by the activator/assessor device  70 . The response signal  16  functions to transmit the pressure readings reported by the strain gauge  24 . The modulation technique may include load-shift keying, or similar or equivalent techniques that may be devised by those skilled in the art.  
      In one embodiment, the processor  32  is a microprocessor. In another embodiment, as shown in  FIG. 3 , the processor  32  includes a signal conditioner and amplifier  120 , an A/D converter  122 , a reference  124 , an encoder  126 , a modulator  128 , a transmitter power amplifier  132 , and an sensor oscilloscope  130 . The signal conditioner and amplifier  120  is operably connected to the strain gauge  24  and to the A/D converter  122  (which is operably connected to the reference). The A/D converter  122  is also operably attached to the encoder  126 , which is operably attached to the modulator  128 . The sensor oscilloscope  130  is operably connected to the modulator  128  for sending the signal to the sensor antenna  34  through the transmitter power amplifier  132 . The various elements are powered by the power supply  134 , which receives its power from the sensor antenna  34 .  
      In one embodiment, as shown in  FIG. 1 , the sensor reed  22  is integral with a silicon chip body  25  and etched therefrom using etching techniques known in the art. The silicon chip body  25  may be bonded to a wireless IC broadcast chip  28  that includes the various circuits described above. In an alternative embodiment, the various components could be formed on a single, or multiple chips, depending upon the specific requirements of the intraocular pressure sensor  10 . In this form, the intraocular pressure sensor  10  is adapted to be positioned adjacent to, within, or otherwise operably engaged with the eye  12  so that the sensor reed  22  is operatively responsive to the pressure in the eye  12 .  
      Activator/Assessor Device  
      As shown in  FIGS. 8-11 , intraocular pressure sensor  10  is preferably used as part of an intraocular pressure sensor system  110  that also includes an activator/assessor device  70 . The activator/assessor device  70  functions to simultaneously energize the transponder  30  and the pressure sensor  20 , and also receive and report the response signal  16 .  
      In one embodiment, as shown in  FIG. 8 , the activator/assessor device  70  may include an activator/assessor processor  72  operably attached to RAM  74 , Flash RAM  76 , and a clock  98  for running the various software programs required to utilize the activator/assessor device  70 . The activator/assessor device  70  may include a second oscilloscope  78  and a power amplifier  79  for transmitting through an activator/assessor antenna  71 , and a demodulator  96  for receiving transmissions.  
      The activator/assessor processor  72  may also be operably attached to an LCD display  80 , a serial USB port  82  or similar connection, a battery  84  or other power source, and various other elements that together enable the function if the activator/assessor device  70 . The activator/assessor processor  72  is also operably attached to a signal conditioner  86  that is operably connected to a recorder  88  or equivalent means for recording the results of the signals received. The results can be stored in the RAM  74  or other memory means and later transmitted, downloaded, printed, or otherwise outputted to the doctor or other person tending to the treatment of the eye  12 . For reporting data locally, the activator/assessor device  70  may include an LCD display  80  and audible feedback  81  such as speakers.  
      While the form of the activator/assessor device  70  can vary is size and shape depending upon the needs of the user, it is anticipated that the preferred embodiment will be a small handheld and battery  84  powered device, as shown in  FIG. 9 . In the embodiment illustrated, a keypad  90  is used to operatively control the activator/assessor device  70 . The term keypad  90  is hereby defined to include any similar control mechanisms known in the art could also be used for this purpose, including but not limited to voice recognition software, a mouse, a touch-screen, a control pad, a track ball, or other mechanism known in the art. The keypad  90  includes a power button  92  and a manual actuation button  94 ; however, the keypad  90  could include a more complicated alphanumeric keyboard, voice actuation, or other control mechanism if desired. The power button  92  is used to power up the device, or turn it off to conserve battery  84  power. The manual actuation button  94  is used to trigger a query; however, it is also contemplated that the activator/assessor device  70  could also be programmed to automatically query the intraocular pressure sensor  10  at regular intervals as prescribed by a doctor, or upon receipt of a command signal from a central monitoring station (shown in  FIG. 12 , and described below).  
      In one embodiment, the activator/assessor processor  72  converts the analog signals from the sensors to digital signals and formats the digitized signals as a binary data stream for transmission out of the patient. The activator/assessor processor  72  is also operable for coding and formatting a unique device ID number (not shown) for transmission with the digitized transducer signals for use in identifying the device. In some embodiments of the invention, the activator/assessor processor  72  may be programmed for analyzing the signals before transmitting the signals out of the patient&#39;s body. For example, if the intraocular pressure sensor  10  is provided with a pressure transducer, the activator/assessor processor  72  can be programmed to alert the patient with an audible feedback in the event that the data is unusual and should be immediately reviewed by the doctor.  
      The LCD display  80  is hereby defined to include similar mechanisms used to display data. The LCD display  80  provides a read-out of important information, such as the IOP pressure, and may also include information about temperature and other pertinent information. The LCD display  80  preferably also includes important treatment information. At the very least, the LCD display  80  could display a warning to see a doctor. In more advanced alternative embodiments, the LCD display  80  could also include specific instructions regarding taking of medication (changing frequency, dose, etc.), altering behaving such as eating habits that may affect the pressure within the eye, and other guidance prescribed by a doctor or trained nurse/technician.  
      While the various features of the invention have been described in terms of specific embodiments, it should be noted that the invention is not limited thereto, but should be construed to include equivalent embodiments that can be developed by those skilled in the art when provided the teachings of the present invention.  
      Contact Lens  
      In a first embodiment, as shown in  FIG. 4 , the intraocular pressure sensor  10  may be adapted to be operably installed in a contact lens  60  or similar eye  12  canopy that is adapted to be placed directly on the eye  12 . The intraocular pressure sensor  10  is used in conjunction with a contact lens  60  having an inner lens surface  62  and an opposing outer lens surface  64 . The inner lens surface  62  is adapted to operably contact the eye  12 . The intraocular pressure sensor  10  is operably mounted on the contact lens  60  so that the pressure sensor  20  operably contacts the eye  12  when the contact lens  60  is operably placed on the eye  12 .  
      Intraocular Lens  
      In a second embodiment, as shown in  FIG. 5 , the intraocular pressure sensor  10  is adapted to be operably installed on an intraocular lens  100  that is adapted to be surgically implanted into the eye  12 . The intraocular lens  100  may be constructed of polymethylmethacrylate (PMMA) and may be operatively installed in the eye  12  using surgical techniques well known in the art. The pressure sensor  20  is operatively positioned on the intraocular lens  100  to enable measurement of the pressure of the eye  12 .  
      Glaucoma Drainage Device  
      In a third embodiment, as shown in  FIGS. 6-7 , the intraocular pressure sensor  10  may also be adapted to be used on conjunction with a glaucoma drainage device  40 . The glaucoma drainage device  40  includes a lumened tube  42  and an explant plate  48 . The lumened tube  42  has a proximal end  44  and a distal end  46 . The explant plate  48  has an internal surface  50  and an opposing external surface  52  that together terminate in a plate perimeter  54 . The plate perimeter  54  is shaped to fit on the eye  12  and the internal surface  50  is concave to define an internal cavity  56  when the plate perimeter  54  is positioned on the eye  12 . The proximal end  44  of the lumened tube  42  can be positioned through a tube aperture  58  of the explant plate  48  that is adjacent the plate perimeter  54 . During surgery, the distal end  46  of the lumened tube  42  is positioned within the eye  12 , to relieve pressure from within the eye  12  as directed by the doctor. The intraocular pressure sensor  10  is operable positionable adjacent the proximal end  44  for sensing flow pressure through the lumened tube  42 .  
      Method of Use  
      The intraocular pressure measurement system  110  may be used to measure the pressure an a system such as the eye, or other part of an animal such as a human, or any other system that may require continuous, remote pressure monitoring. As shown in  FIG. 10 , the intraocular pressure measurement system  110  is first calibrated. A seminal voltage Vs of the activator/assessor device  70  is used to generate a transmittal frequency FH 1 . The transmittal frequency FH 1  is received by the intraocular pressure sensor  10  and used to generate a consistent core voltage Vcc, which in turn is used to generate a second transmittal frequency FH 2 . The second transmittal frequency FH 2  is received by the activator/assessor device  70  and used to generate a terminal voltage Vt 1 .  
      As shown in  FIG. 11 , the intraocular pressure measurement system  110  may be used to measure the pressure sensed by the intraocular pressure sensor  10 . The seminal voltage Vs is used to generate the transmittal frequency FH 1 , which is received by the intraocular pressure sensor  10  and used to generate the consistent core voltage Vcc. The consistent core voltage Vcc is then modified based upon the change in pressure measured by the intraocular pressure sensor  10 , to a sensor-modified voltage Vsm. The sensor-modified voltage Vsm is used to generate a third transmittal frequency FH 3 . The third transmittal frequency FH 3  is received by the activator/assessor device  70  and used to generate a second terminal voltage Vt 2 .  
      The difference between the terminal voltage Vt 1  and the second terminal voltage Vt 2  is representative of the pressure being measured by the intraocular pressure sensor  10 . Those skilled in the art can devise many equivalent ways to practice this method, and such alternatives should be considered within the scope of the claimed invention.  
      Wireless Network  
      As shown in  FIG. 12 , the intraocular pressure measurement system  110  may be incorporated into a wireless network for reporting data regarding the pressure in the eye  12 . The wireless network may include a receiver  112  such as a satellite system, a cellular transmitter/receiver, and/or any other commercial relay or system capable of handling network communications. Data from the activator/assessor device  70  is transmitted to the receiver  112  using any suitable protocol, such as 802.11 or other suitable network protocol. From the receiver  112 , the data is then communicated to a central monitoring station  114  via a global computer network, a phone system, fiber optics, another wireless network, or any other network.  
      The central monitoring station  114  may process the data is many ways, including compiling and reporting the data, or simply forwarding the data to a doctor&#39;s office  116 . The central monitoring station  114  and/or the doctor&#39;s office  116  may also actively monitor the data, alerting the user or the doctor to any spikes in pressure or other circumstances that may require medical care. For example, the central monitoring station  114  (or, of course, the doctor&#39;s office  116 ) may compile the data for later analysis by treating physicians, and store the data on the global computer network so that the user&#39;s physician may access the data at any time. If there is a dangerous and/or prolonged spike in intraocular pressure, the central monitoring station  114  may automatically page the treating physician and alert him or her to the situation, so that proper medical care may be immediately administered.  
       FIG. 13  is a chart illustrating a range of intraocular pressures, from hyper pressure, to normal pressure, and to hypo pressure. This information, following the guidelines of skilled doctors, is integrated into the software so that appropriate treatments can be immediately implemented in real-time. If a patient&#39;s intraocular pressure moves into abnormal high pressure, for example, the patient could be directed to take additional medication or take other steps to remedy the situation. If a patient&#39;s intraocular pressure moves into hyper pressure, the patient could be directed to take additional medication, take more drastic steps, or immediately consult his or her doctor.  
      Temporary Profile Device  
       FIG. 14  is a top plan view that illustrates a temporary profile device  140  having the intraocular pressure sensor  10  mounted therein. The temporary profile device  140  device is generally ring shaped, with an outer perimeter  142  and an inner perimeter  144  that defines an inner aperture  146 . The temporary profile device  140  is adapted to be worn by a user in a manner similar to a contact lens, but for a more limited time. The temporary profile device  140  does not cover the cornea, so the eye is not deprived of oxygen. Furthermore, the user&#39;s vision is not in any way obstructed, and the user does not suffer as much irritation from the temporary profile device  140 .  
      As shown in  FIGS. 14 and 15 , a top surface  148  of the temporary profile device  140  is adapted to fit comfortably under the eyelid, and a bottom surface  150  preferably is concave to house the intraocular pressure sensor  10 . The concave bottom surface  150  preferably further houses the transponder  30  described above, and may further include additional electronics, such as a battery  152 , and any other elements that may be required or desired.  
      Intrascleral Implantation of the Intraocular Pressure Sensor  
      As shown in  FIGS. 16, 17 , and  18 , in another embodiment of the invention the intraocular pressure sensor  10  is adapted to be implanted intrasclerally, in an intrascleral space  167  under a scleral layer  160  of the eye  161 . In one embodiment, an incision is made through the scleral layer  160 , and the intraocular pressure sensor  10  is inserted under the scleral layer  160 .  
      As illustrated in  FIGS. 16 and 17 , the scleral layer  160  is grasped with a grasping tool  162 , a retractor or similar tool, and lifted clear to enable the intraocular pressure sensor  10  to be inserted under the scleral layer  160 , preferably with another grasping tool  164 .  
       FIG. 18  illustrates the eye once the scleral layer  160  has healed. The cut made through the scleral layer  160  usually closes itself, or it may be closed with a fastener  166  such as a staple or a suture, or using similar surgical tools and/or methods.  
      The intraocular pressure sensor  10  may include additional elements to facilitate the above-described method. For example, the intraocular pressure sensor  10  may include an attachment point  165  that enables the intraocular pressure sensor  10  to be surgically attached to the eye, with sutures or the like, to prevent movement of the intraocular pressure sensor  10  within the intrascleral space  167 .  
      While the invention has been described with reference to at least one preferred embodiment, it is to be clearly understood by those skilled in the art that the invention is not limited thereto. Rather, the scope of the invention should also include obvious and/or equivalent alternatives to the limitations described herein.