Patent Document

BACKGROUND OF THE INVENTION 
     The present invention relates to a device for monitoring intraocular pressure and more particularly to an implantable pressure sensor. 
     Glaucoma, a group of eye diseases affecting the retina and optic nerve, is one of the leading causes of blindness worldwide. Glaucoma results when the intraocular pressure (IOP) increases to pressures above normal for prolonged periods of time. IOP can increase due to an imbalance of the production of aqueous humor and the drainage of the aqueous humor. Left untreated, an elevated IOP causes irreversible damage the optic nerve and retinal fibers resulting in a progressive, permanent loss of vision. 
     The eye&#39;s ciliary body epithelium constantly produces aqueous humor, the clear fluid that fills the anterior chamber of the eye (the space between the cornea and iris). The aqueous humor flows out of the anterior chamber through the uveoscleral pathways, a complex drainage system. The delicate balance between the production and drainage of aqueous humor determines the eye&#39;s IOP. 
     Open angle (also called chronic open angle or primary open angle) is the most common type of glaucoma. With this type, even though the anterior structures of the eye appear normal, aqueous fluid builds within the anterior chamber, causing the IOP to become elevated. Left untreated, this may result in permanent damage of the optic nerve and retina. Eye drops are generally prescribed to lower the eye pressure. In some cases, surgery is performed if the IOP cannot be adequately controlled with medical therapy. 
     Only about 10% of the population suffers from acute angle closure glaucoma. Acute angle closure occurs because of an abnormality of the structures in the front of the eye. In most of these cases, the space between the iris and cornea is more narrow than normal, leaving a smaller channel for the aqueous to pass through. If the flow of aqueous becomes completely blocked, the IOP rises sharply, causing a sudden angle closure attack. 
     Secondary glaucoma occurs as a result of another disease or problem within the eye such as: inflammation, trauma, previous surgery, diabetes, tumor, and certain medications. For this type, both the glaucoma and the underlying problem must be treated. 
       FIG. 1  is a diagram of the front portion of an eye that helps to explain the processes of glaucoma. In  FIG. 1 , representations of the lens  110 , cornea  120 , iris  130 , ciliary bodies  140 , trabecular meshwork  150 , and Schlemm&#39;s canal  160  are pictured. Anatomically, the anterior chamber of the eye includes the structures that cause glaucoma. Aqueous fluid is produced by the ciliary bodies  140  that lie beneath the iris  130  and adjacent to the lens  110  in the anterior chamber. This aqueous humor washes over the lens  110  and iris  130  and flows to the drainage system located in the angle of the anterior chamber. The angle of the anterior chamber, which extends circumferentially around the eye, contains structures that allow the aqueous humor to drain. The first structure, and the one most commonly implicated in glaucoma, is the trabecular meshwork  150 . The trabecular meshwork  150  extends circumferentially around the anterior chamber in the angle. The trabecular meshwork  150  seems to act as a filter, limiting the outflow of aqueous humor and providing a back pressure producing the IOP. Schlemm&#39;s canal  160  is located beyond the trabecular meshwork  150 . Schlemm&#39;s canal  160  has collector channels that allow aqueous humor to flow out of the anterior chamber. The two arrows in the anterior chamber of  FIG. 1  show the flow of aqueous humor from the ciliary bodies  140 , over the lens  110 , over the iris  130 , through the trabecular meshwork  150 , and into Schlemm&#39;s canal  160  and its collector channels. 
     In glaucoma patients, IOP can vary widely during a 24 hour period. Generally, IOP is highest in the early morning hours before medication is administered upon waking. Higher pressures damage the optic nerve and can lead to blindness. Accordingly, it would be desirable to measure IOP over time in order to assess the efficacy of various treatments. The present invention provides an IOP measuring device. 
     SUMMARY OF THE INVENTION 
     In one embodiment consistent with the principles of the present invention, the present invention is an implantable intraocular pressure sensor system that has a sealed geometric shape with an internal pressure at a first value. The sealed geometric shape has a first light permitting surface and a second flexible surface. A pair of photocells is located in the sealed geometric shape. A light shield is coupled to the second flexible surface. When the second flexible surface is deflected, a light measurement by the pair of photocells indicates an intraocular pressure condition. 
     In another embodiment consistent with the principles of the present invention, the present invention is an implantable intraocular pressure sensor system that has a sealed geometric shape with an internal pressure at a first value. The sealed geometric shape has a first light permitting surface and a second flexible surface. A pair of photocells is located in the sealed geometric shape. A light shield is coupled to the second flexible surface. When the second flexible surface is deflected, a light measurement by the pair of photocells indicates an intraocular pressure condition. The system also has a processor coupled to a power source and memory. The processor is configured to read the measured resistance and write values corresponding to intraocular pressure to the memory. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed. The following description, as well as the practice of the invention, set forth and suggest additional advantages and purposes of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a diagram of the front portion of an eye. 
         FIG. 2  is a block diagram of an IOP measuring system according to the principles of the present invention. 
         FIG. 3  is a perspective view of an IOP sensor according to the principles of the present invention. 
         FIG. 4  is a perspective view of an IOP sensor according to the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is now made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like parts. 
       FIG. 2  is a block diagram of an IOP measuring system  200  according to the principles of the present invention. In  FIG. 2 , the IOP measuring system includes power source  205 , IOP sensor  210 , processor  215 , memory  220 , data transmission module  225 , and optional speaker  230 . 
     Power source  205  is typically a rechargeable battery, such as a lithium ion or lithium polymer battery, although other types of batteries may be employed. In addition, any other type of power cell is appropriate for power source  205 . Power source  205  provides power to the system  200 , and more particularly to processor  215 . Power source can be recharged via an RFID link or other type of magnetic coupling. 
     Processor  215  is typically an integrated circuit with power, input, and output pins capable of performing logic functions. In various embodiments, processor  215  is a targeted device controller. In such a case, processor  215  performs specific control functions targeted to a specific device or component, such as a data transmission module  225 , speaker  230 , power source  205 , or memory  220 . In other embodiments, processor  215  is a microprocessor. In such a case, processor  215  is programmable so that it can function to control more than one component of the device. In other cases, processor  215  is not a programmable microprocessor, but instead is a special purpose controller configured to control different components that perform different functions. 
     Memory  220  is typically a semiconductor memory such as NAND flash memory. As the size of semiconductor memory is very small, and the memory needs of the system  200  are small, memory  220  occupies a very small footprint of system  200 . Memory  220  interfaces with processor  215 . As such, processor  215  can write to and read from memory  220 . For example, processor  215  can be configured to read data from the IOP sensor  210  and write that data to memory  220 . In this manner, a series of IOP readings can be stored in memory  220 . Processor  215  is also capable of performing other basic memory functions, such as erasing or overwriting memory  220 , detecting when memory  220  is full, and other common functions associated with managing semiconductor memory. 
     Data transmission module  225  may employ any of a number of different types of data transmission. For example, data transmission module  225  may be active device such as a radio. Data transmission module  225  may also be a passive device such as the antenna on an RFID tag. In this case, an RFID tag includes memory  220  and data transmission module  225  in the form of an antenna. An RFID reader can then be placed near the system  200  to write data to or read data from memory  220 . Since the amount of data typically stored in memory  220  is likely to be small (consisting of IOP readings over a period of time), the speed with which data is transferred is not crucial. Other types of data that can be stored in memory  220  and transmitted by data transmission module  225  include, but are not limited to, power source data (e.g. low battery, battery defect), speaker data (warning tones, voices), IOP sensor data (IOP readings, problem conditions), and the like. 
     Optional speaker  230  provides a warning tone or voice to the patient when a dangerous condition exists. For example, if IOP is at a level that is likely to lead to damage or presents a risk to the patient, speaker  230  may sound a warning tone to alert the patient to seek medical attention or to administer eye drops. Processor  215  reads IOP measurements from IOP sensor  210 . If processor  215  reads one or a series of IOP measurements that are above a threshold, then processor  215  can operate speaker  230  to sound a warning. The threshold can be set and stored in memory  220 . In this manner, an IOP threshold can be set by a doctor, and when exceeded, a warning can be sounded. 
     Alternatively, data transmission module may be activated to communicate an elevated IOP condition to a secondary device such as a PDA, cell phone, computer, wrist watch, custom device exclusively for this purpose, remote accessible data storage site (e.g. an internet server, email server, text message server), or other electronic device. In one embodiment, a personal electronic device uploads the data to the remote accessible data storage site (e.g. an internet server, email server, text message server). Information may be uploaded to a remote accessible data storage site so that it can be viewed in real time, for example, by medical personnel. In this case, the secondary device may contain the speaker  230 . For example, in a hospital setting, after a patient has undergone glaucoma surgery and had system  200  implanted, a secondary device may be located next to the patient&#39;s hospital bed. Since IOP fluctuations are common after glaucoma surgery (both on the high side and on the low side which is also a dangerous condition), processor  215  can read IOP measurements made by an implanted IOP sensor  210 . If processor  215  reads an unsafe IOP condition, data transmission module  225  can alert the patient and medical staff via speaker  230  or by transmitting the unsafe readings to a secondary device. 
     Such a system is also suitable for use outside a hospital setting. For example, if an unsafe IOP condition exists, processor  215  can operate speaker  230  to sound an audible warning. The patient is then alerted and can seek medical attention. The warning can be turned off by a medical professional in a number of ways. For example, when data transmission module  225  is an RFID tag, an RFID link can be established between an external device and system  200 . This external device can communicate with system  200  to turn off the speaker  230 . Alternatively, an optical signal may be read by system  200 . In this case, data transmission module  225  has an optical receptor that can receive a series of light pulses that represent a command—such as a command to turn off speaker  230 . 
     System  200  is preferably in a small, implantable, integrated package. As such, all of the components of system  200  can be built on a substrate, such as a semiconductor wafer, by any of a number of different processes. 
       FIG. 3  is a perspective view of an IOP sensor according to the principles of the present invention. In  FIG. 3 , IOP sensor  210  is a sealed cube with two photocells  325  &amp;  330 , atop surface  310 , a side  315 , a light shield  320  and an optional light source  305 . Top surface  310  of IOP sensor allows light to enter the cube (e.g., it is transparent or translucent—a light permitting surface). Photocells  325  and  330  detect the amount of light entering the cube. Light shield  320  at least partially blocks the light detected by photocell  330 . Light shield  320  is fixed to side  315 . Side  315  is flexible. Therefore, as side  315  moves in response to a pressure change, the amount of light blocked by light shield  320  changes and the amount of light detected by photocell  330  also changes. Side  315  may be thinner than the other sides, top  310 , and bottom of the cube so that side  315  is more flexible. The top  310 , bottom and other sides (other than side  315 ) may be rigid or flexible. An optional light source  305 , as described below, is provided. Alternatively, IOP sensor may use ambient light entering the eye. While described as a cube, IOP sensor  210  may be other geometric shapes that allow for deflection of side  315  and movement of attached shield  320 . 
     The pressure inside the cube of IOP sensor  210  is determined during the manufacturing process and can be about 0 kg/cm 2 , about 0 kPa, or about 0 psig. The cube of IOP sensor  210  can be filled with any of a number of a variety of different gases, such as nitrogen, argon, sulfur hexafluoride, or the like. When the internal pressure is 0 kg/cm 2 , 0 kPa, or 0 psig., side  315  will tend to deflect inward because the pressure inside the eye is higher than 0 kg/cm 2 , 0 kPa, or 0 psig. (as shown in  FIG. 4 ). 
     The configuration of photocells  325  &amp;  330  shown in  FIG. 3  allows for a comparison between the light detected by photocell  325  and photocell  330  to be made. Since photocell  325  is not shielded by light shield  320 , photocell  325  detects the “full amount” of light entering through top surface  310 . Since photocell  330  is shielded by light shield  320 , photocell  330  detects less than the “full amount” of light entering through top surface  310 . A comparison between the amount of light measured by photocells  325  and  330 , therefore, can be used to determine the amount of deflection experienced by side  315 . The higher the external pressure, the greater the deflection of side  315 , and the less measured by photocell  330 . Accordingly, the amount of light measured by photocell  330  indicates the amount of external pressure (IOP). This use of two photocell ( 325  &amp;  330 ) allows for the IOP sensor  210  to work under different light conditions (since ambient light conditions change). 
     For IOP measurements, calibrating the IOP sensor  210  is generally not critical. Since a change in the amount of light detected by photocell  330  can be correlated with a magnitude of IOP, a change in IOP can be easily detected. Generally, a series of light measurements taken over time corresponds to the relative magnitude of IOP over time. More precise calibration of IOP can be done in a doctor&#39;s office, for example, by measuring IOP in a traditional manner and correlating that measurement with a quantity of light measured by photocell  325  and  330 . 
     Optional light source  305  is typically an LED. Light source  305  may be mounted to or integrated with top surface  310  of IOP sensor  210 . Alternatively, IOP sensor  210  may rely on ambient light (and light source  305  is absent). In another embodiment, a light source exterior to the eye can be used. For example, a light source may be attached to a hand held pressure reader and/or charger device that interfaces with IOP sensor  210 . In this manner, an external light source (which can be calibrated) can be used to facilitate a pressure reading. 
     IOP sensor  210  can be manufactured via any of a number of different methods. For example, in a MEMS-based method, IOP sensor  210  is built in layers. In this manner, layers of a biocompatible material are deposited to build IOP sensor  210 . Other vapor deposition methods, such as those used in the semiconductor industry, may also be employed. 
       FIG. 4  is a perspective view of an IOP sensor according to the principles of the present invention. In  FIG. 4 , side  315  of IOP sensor  210  is deflected inward. Accordingly, light shield  320  is also deflected inward to partially obscure light reaching photocell  330 . In this manner, the internal pressure is less than the external pressure. The pressure difference determines how far light shield  320  moves and how much light photocell  330  detects. In other words, the distance that light shield  320  travels is dependent on the difference between the internal and external pressures. The distance that light shield  320  travels also determines the amount of light that is detected by photocell  330 . Accordingly, the amount of light detected by photocell  330  (as compared to the amount of light detected by photocell  325 ) indicates the difference between the internal and external pressures. Such a light reading can be used to determine the change in IOP. 
     In another embodiment of the present invention, an array of IOP sensors  210  (shown in  FIGS. 3 &amp; 4 ) can be used together. In this configuration, more than one IOP sensor  210  is attached to a substrate and then implanted in the eye. Using more than one IOP sensor  210  allows for redundancy and more accurate measurement of IOP. As the number of IOP sensors  210  in array increases, the statistical variance of the resulting IOP measurement decreases (and thus accuracy increases). In another embodiment, multiple photodetector pairs can be used with a single light source to achieve redundancy. 
     From the above, it may be appreciated that the present invention provides a system measuring IOP. The present invention provides an IOP sensor and associated peripherals. The present invention is illustrated herein by example, and various modifications may be made by a person of ordinary skill in the art. 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Technology Category: 1